JP4213645B2 - Optical head device and information recording / reproducing method using the optical head device - Google Patents

Description

The present invention relates to an information storage medium having a transparent substrate or a transparent protective layer and a single layer or a plurality of layers of a light reflection layer or a recording layer, and light is transmitted from the transparent substrate or the transparent protective layer side. The information recorded on the light reflection layer or recording layer can be reproduced using the reflected light or transmitted light of the focused light, or recorded on the information recording medium. The present invention relates to a possible optical head device, an information recording / reproducing apparatus using the optical head device, and an information recording / reproducing method.
1. Focused light distortion caused by uneven thickness of transparent substrate or transparent protective layer, that is, influence of spherical aberration, or focused light distortion caused by inter-layer movement of focused light of multiple layers of light reflecting layer / recording layer, ie spherical surface Improvement of a single spherical aberration detection method for detecting the state of aberration, or improvement of a combination of the detection method of defocus caused by the positional deviation between the light reflection layer / recording layer and the focused light and the spherical aberration detection method, And 2. The present invention relates to an improvement in a defocus correction control method and a spherical aberration correction control method for performing defocus correction and spherical aberration correction simultaneously and stably.

  Japanese Patent Application Laid-Open No. 2000-171346 has a defocus detection system that performs defocus detection by a knife edge method, detects defocus of an objective lens, and uses a single photodetector 7 to detect the amount of spherical aberration. That is, an example of detecting the thickness unevenness of the substrate of the transparent recording medium is shown.

  In the detection optical system described in the above publication, the light 2a that is half extracted from the center by the hologram 2 that divides the condensing spot into two parts including the optical axis center, and light that is far from the optical axis center. Of the light 2a close to the center of the separated optical axis on the dividing boundary lines of the two-divided detectors 7a and 7b and 7c and 7d arranged at the image forming position with respect to the magneto-optical disk 6 at the time of focusing. The condensing spot P2, and the condensing spot P2 of the light 2b far from the optical axis center are respectively detected.

As a signal detection method,
i) The difference between the detection signals of either one of the two-divided detectors forming a pair (7a and 7b or 7c and 7d) is detected as a defocus detection signal.
ii) calculating the difference between the difference values of the detection signals of the two-divided detectors (7a and 7b and 7c and 7d) forming a pair, and detecting the spherical aberration amount,
It has been shown.

  In the above-mentioned JP-A-2000-171346, as described in paragraph [0036] in the right column on page 5, using “light 2a close to the optical axis center” or “light 2b far from the optical axis center” A focus error (defocus) is detected.

  However, as described in paragraph [0093] on the left column of page 9 of the publication, “the second light beam 2b, which is the light beam at the periphery of the condensing optical system 10, is affected by spherical aberration. It is stated that there is a problem that it is easy and it is difficult to precisely adjust the focal position. Therefore, in the above-mentioned publication, the focus error is adjusted using the “light 2a closer to the optical axis”. In this case, however, there is a problem in that the detection sensitivity for detecting the focus error (defocus) is greatly reduced. is there.

  In other words, when the focus error (defocus) is detected using the “light 2a closer to the optical axis”, it is difficult to accurately control the defocus correction because the detection sensitivity is low. In other words, it is difficult for the method disclosed in Japanese Patent Laid-Open No. 2000-171346 to detect defocus (focus error) with high accuracy and stability.

  This causes a problem that it is difficult to record and reproduce information in an optical disc that can be recorded in two layers on one side, whose recording density is several times that of a DVD type optical disc.

  An object of the present invention is to provide an optical head device in which light condensed on a recording layer via an objective lens is not affected by thickness unevenness of a transparent resin layer positioned between the recording layer and the objective lens, and the optical head thereof An information recording / reproducing apparatus and an information recording / reproducing method using the apparatus are provided.

According to the present invention, a substrate-side recording layer or light reflecting layer provided on one surface of the substrate in the vicinity of the substrate and a substrate-side recording layer or light reflecting layer are laminated and transparent to light having a predetermined wavelength. Light having a space layer, a second recording layer or light reflecting layer separated from the substrate and the substrate-side recording layer or light reflecting layer, and a protective layer protecting the second recording layer or light reflecting layer In an optical head device that irradiates at least one of the second recording layer or the light reflecting layer and the substrate-side recording layer or the light reflecting layer on the recording medium with the light having the predetermined wavelength from the protective layer side,
The light having the predetermined wavelength is condensed from at least one of the second recording layer or the light reflecting layer and the substrate-side recording layer or the light reflecting layer from the protective layer side , and the collected predetermined wavelength is collected. The first lens to which the light of the first light is returned, the second lens that corrects the influence of the thickness unevenness of the protective layer in cooperation with the first lens, and the first and second lenses. Including a photodetector that is illuminated by light;
When the wavelength of the light is λ, the numerical aperture of the first lens is NA, and the lateral magnification is M, the photodetector has a distance from a condensing point by the first lens,
5.2λ (M / NA) ² > 2.1λ (M / NA) ²
It is intended to provide an optical head device characterized by being arranged at a position that falls within the range of

The present invention also provides a first recording layer or light reflecting layer provided in the vicinity of the substrate, a space layer that is laminated on the first recording layer or light reflecting layer, and is transparent to light of a predetermined wavelength, Stacked on the space layer, stacked on the second recording layer or the light reflecting layer, and on the second recording layer or the light reflecting layer provided apart from the substrate and the first recording layer or the light reflecting layer. A protective layer for protecting the second recording layer or the light reflecting layer, and at least one of the second recording layer or the light reflecting layer and the first recording layer or the light reflecting layer. In the information recording / reproducing method of recording information by irradiating light of the predetermined wavelength from the protective layer side, or reproducing already recorded information , the second recording layer or the light reflecting layer and the substrate Less recording layer or light reflecting layer In one well and the with the protective layer side to focus the light of the predetermined wavelength, a first lens which light of the predetermined wavelength condensed is returned, in cooperation with the first lens When the second lens for correcting the influence of thickness unevenness of the protective layer, the wavelength of the light is λ, the numerical aperture of the first lens is NA, and the lateral magnification is M, the first lens The distance from the focusing point by
5.2λ (M / NA) ² > 2.1λ (M / NA) ²
Using a photodetector arranged at a position that falls within the range of
Based on the first photodetection signal, the second recording layer or the light reflecting layer and the first recording layer or the light reflecting layer are identified to collect light of a predetermined wavelength,
Based on the second light detection signal, the protection is performed in a state where light of a predetermined wavelength is condensed on either the second recording layer or the light reflecting layer and the first recording layer or the light reflecting layer. Detect the effect of layer thickness unevenness,
Variation of the first I state der based on said photodetection signal first lens is focusing the light of the predetermined wavelength to a predetermined recording layer or the light reflecting layer, a second light detection signal If There larger than a predetermined size, and defocus of the first lens is condensed state is the first lens to the predetermined recording layer or the light reflecting layer that condenses the light of a predetermined wavelength it is determined that is accompanied by different variations, there is provided the information recording and reproducing method characterized the that to change the position of the second lens for changing the condensed state by the first lens .

  According to the optical head device of the optical disk apparatus of the present invention, the thickness unevenness of the transparent resin layer positioned on the objective lens side of the optical disk can be accurately detected. However, it is possible to provide convergent light capable of recording information with a high recording density by removing the influence of the distortion of the convergent light, that is, the spherical aberration.

  In addition, according to the present invention, even when the thickness of the transparent resin layer located on the objective lens side of the optical disc is uneven, the distortion of the focused light, that is, the influence of spherical aberration is removed, and the recording density is high. Can record information.

  Furthermore, according to this invention, the thickness unevenness of the transparent resin layer located on the objective lens side of the optical disc is detected, and the influence of the blur of the objective lens is removed while removing the influence of the thickness unevenness of the transparent resin layer, An information recording / reproducing apparatus capable of reproducing information recorded on the recording layer of the recording medium or recording information on the recording medium can be obtained.

  Furthermore, the thickness unevenness detection system attenuates the amount of light within a range satisfying r ≦ 0.88 or changes the phase characteristics of light when the spot cross-sectional radius of light to be detected is 1. Or, it includes an optical element that attenuates the amount of light and changes its phase, so it can detect uneven thickness of the transparent resin layer of the recording medium with high detection sensitivity, thereby recording information at a high recording density. Is possible.

  Furthermore, since the response frequency (cut-off frequency) of the thickness unevenness correction mechanism is set lower than the response frequency (cut-off frequency) of the defocus correction control system that removes the influence of the defocus of the objective lens, the defocus detection system And stable thickness unevenness detection without being affected by the crosstalk (interference) generated between the thickness unevenness detection system and the thickness unevenness detection system.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram for explaining the basic structure of an optical head device of the present invention and an information recording / reproducing device in which the optical head device is incorporated.

  As shown in FIG. 1, an optical head device of the present invention and an information recording / reproducing apparatus 1 in which the optical head device is incorporated include a laser element 2 that emits laser light of a predetermined wavelength, and a laser beam emitted from the laser element 2. Are recorded on an information recording medium, for example, two recording layers on one side and focused on an arbitrary recording layer of the optical disc 3 capable of high-density recording, and an arbitrary recording layer of the optical disc 3 and the objective lens 4. And a defocus correction coil 5 that changes the position of the objective lens 4 so that the distance between the lens and the lens coincides with the focal length inherent to the objective lens 4.

  A thickness unevenness (spherical aberration) correction mechanism 101 that corrects the influence of the thickness unevenness (spherical aberration) of the surface cover layer 3a provided on the side on which the laser beam of the optical disk 3 is incident between the laser element 2 and the objective lens 4. Is provided.

The thickness unevenness (spherical aberration) correction mechanism 101 is provided between the optical disk 3 and the laser element 2 and separates the laser light directed from the laser element 2 toward the optical disk 3 and the laser light reflected by an arbitrary recording layer of the optical disk 3. Included in the defocus component detected by the defocus detection system 102 that detects defocus, which is the displacement of the position of the objective lens 4, from the laser light reflected by an arbitrary recording surface of the optical disk 3 separated by the beam splitter 6. Based on the thickness unevenness component detected by the thickness unevenness (spherical aberration) detection system 103 that extracts the thickness unevenness (spherical aberration) component of the cover layer 3a of the optical disc 3 to be recorded, the state of the laser light incident on the objective lens 4 is determined. This is close to the state without thickness unevenness (spherical aberration). Note that the position of the objective lens 4 is independently controlled by the defocus correction circuit 105 corresponding to the defocus detected by the defocus detection system 102.

  As shown in FIG. 1, according to the principle of thickness unevenness detection (spherical aberration detection), a thickness unevenness detection (spherical aberration detection) signal can be obtained only in a state where defocus correction is completely performed (during focusing). This indicates that it is necessary to detect defocusing with very high accuracy, and in order to satisfy this requirement, defocusing is detected using all of the spot cross sections of the laser beam (however, the defocusing of When using the knife-edge method for detection, defocus detection is performed using half of the detection light extracted by dividing the straight line including the vicinity of the center of the optical axis where the detection accuracy is highest and stable. Even when a large amount of spherical aberration components are included, it is possible to detect defocusing very stably and with high accuracy.

  FIG. 2 is a schematic diagram for more specifically explaining an example of the configuration of the optical head apparatus shown in FIG. 1 and an information recording / reproducing apparatus (hereinafter referred to as an optical disk apparatus) having the optical head apparatus.

  As shown in FIG. 2, an optical disc apparatus 10 that records information on an information recording medium, that is, an arbitrary recording layer of the optical disc 3 and reproduces information from the optical disc 3, includes a light source on a predetermined information recording layer 3d or 3b of the optical disc 3. The laser beam 12 from the laser device 11 is irradiated, the laser beam 12 ′ reflected by the arbitrary information recording layer 3d or 3b of the optical disc 3 is received, and the information recorded on the optical disc 3 is reproduced. Further, when information is recorded on the optical disc 3, the magnitude of the laser drive current supplied to the laser device 11 is changed on an arbitrary information recording layer of the optical disc 3 based on data (information) to be recorded. Thus, the laser beam whose emission intensity (light intensity) is intermittently changed is irradiated. The recording of information on the optical disc 3 and the reproduction of information from the optical disc 3 will be described in detail later. Although not shown, it goes without saying that the information recording layers 3d and 3b of the optical disc 3 are formed with a guide groove as a guide when information is recorded or a signal mark row which is already recorded information. Nor.

  In the optical disk apparatus 10 shown in FIG. 2, the laser light 12 emitted from the laser apparatus 11 is collimated by the collimating lens 13, enters the deflecting beam splitter 14, and passes through the optical disk 3 as it is. The laser beam 12 that has passed through the deflecting beam splitter 14 passes through the λ / 4 plate 15, the thickness unevenness correcting concave lens 16, and the thickness unevenness correcting convex lens 17 in order, and is guided to the objective lens 19. The thickness unevenness correcting convex lens 17 is formed to be movable in the optical axis direction by the thickness unevenness correcting convex lens driving coil 18. Further, the objective lens 19 has a track (guide groove) (not shown) formed in advance in the optical axis direction and on the optical disc 3 by a defocus correction coil (focus coil) 20 and a track deviation correction coil (track coil) 21. It is formed to be independently movable in each direction across the signal mark row.

  The laser beam 12 guided to the objective lens 19 is given a predetermined focusing property by the objective lens 19 and is focused on a predetermined recording layer of the optical disc 3. The optical disc (information recording medium) 3 is provided on one surface of the substrate 3e in the vicinity of the substrate 3e (close to the substrate) or a light reflecting layer 3d, and a space layer 3c transparent to the wavelength of the laser beam 12. , The recording layer or light reflecting layer 3b separated from the substrate 3e, the substrate-side recording layer or the light reflecting layer 3d (close to the cover layer), and the transparent protective layer (light irradiation side cover layer) 3a are sequentially laminated.

The laser beam 12 focused on one of the arbitrary recording layers (or light reflecting layers) 3d and 3b of the optical disk 3 by the objective lens 19 changes the phase characteristics of the recording layer during information recording, and collects the light. While a recording mark (pit) is formed in the irradiated recording layer, a slightly generated reflected laser beam 12 ′ is returned to the objective lens 19. On the other hand, at the time of reproducing information, the light intensity is changed according to the state of the recording layer, and the reproduction laser beam (reflection laser beam) 12 ′ is returned to the objective lens 19. Note that each of the reproduction laser beam 12 ′ and the reflected laser beam 12 ′ is handled in substantially the same manner in the signal reproduction system described below, and hence the description will be continued as the reproduction laser beam 12 ′.

  The reproduction laser beam 12 returned to the objective lens 19 passes through the thickness unevenness correcting convex lens 17, the thickness unevenness correcting concave lens 16 and the λ / 4 plate 15, and is returned to the polarizing beam splitter 14. The laser beam 11 is separated from the laser device 11 toward the objective lens 19 (optical disk 3).

  The reproduced laser beam 12 ′ separated from the laser beam 12 by the polarization beam splitter 14 is separated by approximately half by the half prism 22.

  One of the separated reproduction laser beams 12 ′ is given a predetermined focusing property by the spherical lens 23, and then is directed with respect to a direction orthogonal to the optical axis (cross section of the laser beam 12 ′) by the cylindrical lens 24 provided subsequently. Given predetermined imaging characteristics, an image is formed on the light receiving surface of the first photodetector 25 used for detection of defocus and track deviation. The first photodetector 25 is a four-divided detector having four light receiving regions 25a, 25b, 25c, and 25d divided by two straight lines that pass through the optical axis and are orthogonal to each other. Further, in FIG. 1, in order to explain the pattern of the light receiving surface, a reference view in which the state in which the separated reproduction laser beam 12 ′ is imaged is planarly displayed is integrally displayed.

The separated reproduced laser beam 12 ′ is sequentially passed through a hologram element 26 on which a predetermined diffraction pattern is formed and a sensitizing filter 27 for facilitating detection of spherical aberration, and is predetermined by a spherical lens 28. Is focused on the light receiving surface of the second photodetector 29. The second photodetector 29 can receive 0th-order light and ± 1st- order diffracted light (hereinafter simply referred to as ± 1st-order light ) that has passed through the hologram element 26 in any one direction orthogonal to the optical axis. In addition, this is a detector in which three light receiving regions 29a, 29b and 29c are arranged in series. Further, in FIG. 1, in order to explain the pattern of the light receiving surface, a reference diagram in which the state in which the separated reproduction laser beam 12 'is imaged is planarly displayed is integrally displayed.

  Note that an optical system portion including the spherical lens 23, the cylindrical lens 24, and the first photodetector 25 corresponds to the defocus detection system 102 in FIG. 1, and includes a hologram element 26, a sensitizing filter 27 for detecting spherical aberration, and a spherical surface. The optical system portion composed of the lens 28 and the second photodetector 29 corresponds to the thickness unevenness (spherical aberration) detection system 103 shown in FIG.

  Further, the optical system portion including the thickness unevenness correcting concave lens 16, the thickness unevenness correcting convex lens 17 and the thickness unevenness correcting convex lens driving coil 18 corresponds to the thickness unevenness (spherical aberration) correcting mechanism 101 of FIG. When the current having a predetermined magnitude and polarity is supplied from the spherical aberration correction circuit 104 described in FIG. 1 to the coil 18, the thickness unevenness correcting convex lens 17 is moved and the thickness unevenness correcting convex lens 17 and the thickness unevenness are detected. The distance to the correction concave lens 16 is changed, and the influence of spherical aberration (thickness unevenness of the cover layer 3a of the optical disc 3) can be corrected.

  The reproduced laser beam 12 'imaged on the first photodetector (for detecting defocus and track deviation) 25 is irradiated with the laser beam 12' irradiated by each of the four light receiving regions 25a, 25b, 25c and 25d. Is converted into an electrical signal (current) corresponding to the light intensity of each of the preamplifiers 41 (corresponding to 25a), 42 (corresponding to 25b), 43 (corresponding to 25c) and 44 (corresponding to 25d) connected to the respective light receiving regions, Converted to voltage value.

  The outputs of the preamplifiers 41 to 44 are an adder 71 for adding the output of the preamplifier 41 and the output of 43, an adder 72 for adding the output of the preamplifier 42 and the output of 44, and the output of the preamplifier 42 and the output of 43, respectively. Are added to an adder 73 that adds the outputs of the preamplifier 41 and the output of 44, respectively.

  The output of the adder 71 and the output of the adder 72 are subtracted by a subtracter 81 to generate a defocus control signal to be supplied to the defocus correction coil 20 used for correcting defocus of the objective lens 19. Then, after being amplified (rarely attenuated) to a predetermined level by the gain / band setting circuit 82, a predetermined band is set, and after the phase is compensated by the phase compensation circuit 83, the switch 84 is used at a predetermined timing. It is output to the adder 85.

Adder 85 is supplied to the (gain and bandwidth is set, the phase compensated) signal is summed with Ru voltage supplied from the driving voltage generator 86 is amplified by the amplifier 87 to a predetermined size, It is supplied to the focus coil 20 at a timing set by the switch 84.

  The output of the adder 73 and the output of the adder 74 are subtracted by a subtracter 75 in order to generate a track shift control signal to be supplied to the track shift correction coil 21 in order to correct the track shift of the objective lens 19. The gain / band setting circuit 76 amplifies (rarely attenuates) to a predetermined level, sets a predetermined band, compensates the phase by the phase compensation circuit 77, and then has a predetermined magnitude by the amplifier 78. Is supplied to the track coil 21.

  Note that the output of the adder 73 and the output of the adder 74 are further added by an adder 91 and supplied to a reproduction signal processing circuit 92 in order to obtain a reproduction signal.

  Reproduced laser light 12 ′ imaged on the second photodetector (for detecting spherical aberration (cover layer thickness unevenness)) 29 is a light receiving region 29 a that receives zero-order light and 29 b that receives ± first-order light. , 29c are converted into electrical signals (current) corresponding to the light intensity of the irradiated laser beam 12 ', and preamplifiers 31 (corresponding to 29b), 32 (corresponding to 29a) and connected to the respective light receiving regions, and 33 (corresponding to 29c) is converted into a voltage value.

Outputs of the preamplifier 33 of the preamplifier 31 is supplied to the adder 51 for adding the respective subtractors 50, and the difference signal and the sum signal of the voltage signal obtained by the ± 1-order light is generated.

  The difference signal obtained by the subtracter 50 is amplified (rarely attenuated) to a predetermined gain by the gain / band setting circuit 52, and then a predetermined band is set. After the phase is compensated by the phase compensation circuit 53, the switch 54, the data is output to the adder 55 at a predetermined timing.

Adder 55 is supplied to the (gain and bandwidth is set, the phase-compensated) difference signal is added to the Ru voltage supplied from the driving voltage generator 56 is amplified by the amplifier 57 to a predetermined size The thickness unevenness correcting convex lens drive coil 18 is supplied at the timing set by the switch 54.

  The sum signal obtained by the adder 51 is attenuated to a predetermined level by the attenuator 58 so that the sum signal can be compared with the sum signal because the sum signal has an intensity based on ± first order light. The comparator 59 compares the zeroth-order light that has been photoelectrically converted with the signal. The output of the comparator 59 is used as a recording layer abnormal jump detection signal (described later) 60.

  Next, referring to FIG. 3, a phenomenon that occurs when the thickness of the transparent protective layer 3a changes while the laser beam 12 is focused on the recording layer 3b (close to the cover layer) of the optical disc (information recording medium) 3. Will be described.

  The objective lens 19 is designed to be most condensed (the minimum circle of confusion matches the depth of the cover layer) when the transparent protective layer (cover layer) 3a has an ideal thickness.

  When the thickness of the transparent protective layer 3a becomes thinner than ideal, spherical aberration occurs. As shown in FIG. 3, the laser beam 12 passing through the outside of the objective lens 19 is more in the optical axis direction than the laser beam 12 passing through the inside. Focus on the front side of Therefore, the position of the minimum circle of confusion (the position where the light intensity (center intensity) in the spot cross section of the laser beam 12 is the highest in the optical axis direction) moves forward by δ compared to when there is no spherical aberration. On the contrary, when the thickness of the transparent protective layer 3a becomes thicker than ideal, the position of the minimum circle of confusion moves in the direction opposite to that in FIG. 3 (the back side in the optical axis direction).

  Not only when the thickness of the transparent protective layer 3a changes, but also when moving between the recording layer 3d (near the cover layer) and the layer 3b (near the cover layer) 3b (between 3d-3b) of the objective lens 19, for example ( After correcting the position of the objective lens 19 so that the spherical aberration becomes zero in the state where the light is condensed on the recording layer 3b, the spot of the laser beam 12 is moved to the recording layer 3d (close to the substrate). Sometimes the same phenomenon occurs.

  When the amount of change in thickness of the transparent protective layer 3a is relatively small compared to the ideal time, the amount of change in thickness from the ideal time and the movement distance δ shown in FIG. 3 can be regarded as approximately proportional. .

  In the present invention, the moving distance δ and the direction of the above-mentioned minimum circle of confusion are detected, and the amount of spherical aberration generated due to the change in the thickness of the transparent protective layer 3a or the spot cross section (condensing spot) of the laser light 12 is A spherical aberration amount generated when the recording layer 3b is moved between the recording layers 3b is detected at high speed.

  That is, the present invention detects the amount of spherical aberration and the direction of spherical aberration by using the shift of the minimum circle of confusion (position where the center intensity is maximum) in the optical axis direction that occurs when spherical aberration occurs. It is characterized by. In the prior art disclosed in Japanese Patent Laid-Open No. 2000-171346 and the like, as described above in the conventional problem column, the defocus detection is performed using only a part of the detection light. Detection accuracy is lowered, and defocus detection becomes unstable.

  As shown in FIG. 2, in the present invention, all of the reproduction laser beam 12 'is received by the first photodetector 25, and all of the reproduction laser beam 12' is used for defocus detection. Even if a large amount of spherical aberration components are included in ′, it is possible to detect the defocusing stably and accurately.

  Further, as shown in FIG. 2, the hologram element 26 is used, and the position where the diffracted light in the direction along the optical axis of the reproduction laser beam 12 'is shifted by a predetermined amount so that it passes through the spherical lens 28. Thus, the reproduction laser beam 12 ′ having a predetermined focusing property is operated by the hologram element 26, so that the + 1st order diffracted light is −1st order diffracted behind the light receiving surface of the second photodetector 29. The light is collected in front of the light receiving surface of the second photodetector 29, respectively. In other words, the second photodetector 29 is a position where the zero-order light that has passed through the hologram element 26 is collected, and the ± first-order light generated by the hologram element 26 is in a direction along the optical axis. When the light is condensed, the reproducing laser beam 12 ′ is disposed at a position that is in contrast to the position where the reproduction laser light 12 ′ is collected. As a result, the 0th-order light of the reproduction laser beam 12 ′ imaged on the second photodetector 29 is a small-sized focused spot 12 a, and the + 1st-order light and the −1st-order light are from the spot 12 a by the 0th-order light. Are also formed at predetermined positions on the light receiving surface of the second photodetector 29 as the large-sized spots 12b and 12c.

  As shown in FIG. 2, zero-order light spots 12a and ± first-order light spots 12b and 12c irradiated to the respective light detection cells by the light detection cells 29a, 29b and 29c in the second light detector 29 are shown. The amount of light is detected. Further, the light detection cells 29b and 29c for detecting the ± first-order light spots 12b and 12c can detect only the central portions of the light spots 12b and 12c, respectively, and light at the centers of the respective light spots 12b and 12c. The intensity is detected. The direction in which the track direction (circumferential direction) of the information storage medium 3 is projected onto the second photodetector 29 is the vertical direction of the paper surface in FIG. 2, and the longitudinal direction of the photodetection cells 29b and 29c is tracked. By making it orthogonal to the direction, it is made difficult to be affected by the diffraction pattern included in the light reflected by the pregroove (not shown) on the information storage medium 3.

  More specifically, as a specific method for detecting the spherical aberration, the hologram element 26 is used at two different points (points A and B in FIG. 4 described below) in the direction along the optical axis of the laser beam 12. Of the central intensity of each of the two light spots (± primary light spots) 12b and 12c, which are a part of the laser beam 12 separated into two by using the above, or the luminance distribution of each of the light spots 12b and 12c. It is characterized by comparing at least one of the states or the respective spot sizes of the light spots 12b and 12c. That is, the magnitude (amount) of the spherical aberration caused by the thickness unevenness of the transparent protective layer (cover layer) 3a by comparing any of the central intensity, luminance distribution, or spot size of the ± first-order light spots 12b and 12c. And the spherical aberration direction is detected.

  FIG. 4 shows the laser beam 12 at each position corresponding to the focal position of the spherical lens 28, that is, the movement position of the minimum circle of confusion when the movement of the minimum circle of confusion occurs in the direction along the optical axis of the detection optical system. It is the schematic explaining the change of the light intensity of a light spot.

  In FIG. 4, the position of the 0th-order light detection cell 29a of the second photodetector 29 with respect to the 0th-order light with the position “0” having no spherical aberration, and the position “A” with respect to the + 1st-order light are detected. The position of the cell 29b, and “B” indicates the position of the light detection cell 29c with respect to the −1st order light.

  As is apparent from FIG. 4, in the state without spherical aberration, that is, the curve α, the central intensities of the ± first-order light coincide with each other at the positions “A” and “B”, but as indicated by the curve β. In addition, when a slight spherical aberration occurs, the central intensity at the position “B” is larger than the central intensity at the position “A”. The difference in the center intensity is obtained by the subtracter 50.

  Note that, in a state where the spherical lens 28 is focused on the recording layer 3b near the cover layer, for example, a large change occurs such that the spot of the laser beam 12 shifts to the recording layer 3d due to the influence of a disturbance or the like (for example). When the abnormal skip occurs between the recording layers), the magnitude of the spherical aberration is greatly increased as shown by the curve γ, so that the detected light amount is greatly increased at both the positions “A” and “B”. To drop.

  That is, when an abnormal skip occurs between the recording layers, the total amount of light detected by the photodetection cells 29b and 29c of the second photodetector 29 is greatly reduced, so the adder 51 shown in FIG. Output signal is greatly reduced. On the other hand, since the decrease in the light amount of the laser beam 12a applied to the photodetection cell 29a is small even if an abnormal jump occurs between the recording layers, the output signal of the attenuator 58 does not change so much. Therefore, by detecting the difference between the two by the comparator 59, the abnormal jump detection signal 60 between the recording layers 3d-3b can be obtained.

  Next, the optimum range of the movement amount (distance A0 and distance B0 in FIG. 4) in the direction along the optical axis of the ± primary light generated using the hologram element 26 will be described.

  First, a study model for studying detection characteristics will be described with reference to FIG.

  In FIG. 2, the laser beam 12 emitted from the laser device 11 passes through the collimating lens 13 and the objective lens 19 as shown on the left side of FIG. It is condensed on 3d. On the other hand, the reproduction laser beam 12 'reflected by the recording layer 3b or the recording layer 3d near the substrate of the optical disk sequentially passes through the objective lens 19 and the spherical lens 28 as shown on the right side of FIG. An imaging characteristic is given and the light is irradiated on the second photodetector 29.

When the lateral magnification of the detection system is M, the optical path of the laser light is in a parallel light state between the objective lens 19 acting on the laser light 12 directed to the recording layer and the spherical lens 28 acting on the reflected laser light 12 ′. In some cases, the lateral magnification M is given by the ratio between the focal length of the spherical lens 28 and the focal length of the objective lens 19. Further, the same optical system, the longitudinal magnification is given by M ^2.

As described above with reference to FIG. 3, when the thickness unevenness δt occurs in the transparent protective layer 3a, the position of the minimum circle of confusion of the laser light 12 focused by the objective lens 19 on the recording layer 3b or 3d of the optical disc 3 Is shifted by δ. However, the detection laser beam 12 that is reflected by the recording layer 3b or 3d and then returned to the objective lens 19 is once again affected by the thickness unevenness δt of the transparent protective layer 3a. Accordingly, the positional deviation amount ζ of the minimum circle of confusion of the laser beam 12 ′ imaged on the second photodetector 29 is multiplied by the vertical magnification twice as much as the reciprocation between the objective lens 19 and the optical disk 3. As value
ζ = 4M ² δ (1)
Indicated by

NA the numerical aperture of the objective lens 19, the refractive index n of the transparent protective layer 3a, when the defocus amount is .delta.z, defocus coefficient omega ₂₀ and the spherical aberration when the thickness irregularity occurs defocus amount .delta.z and the transparent protective layer 3a The coefficient ω ₄₀ is, as shown in equation (2) and (3):

and

Given in.

Here, if the value of δz in equation (2) is substituted into δ in (1),
ζ = 8ω ₂₀ (M / NA) ² (4)
Is obtained.

When the wavelength of the laser beam 12 is λ, the change in the spot center intensity of the laser beam 12 with respect to the value of the defocus coefficient ω ₂₀ corresponding to the defocus amount δz is H. Ando et. Al .: Jpn J. Appl. Phys. Vol. 32 (1993) Pt. 1, No. 11B p. 5272 (10) (here, expressed as (M10) for identification), and η = 0 Formula when placed,

k = 2π / λ (6)
It is represented by

Here, σ is e ⁻² with respect to the center when the cross-sectional intensity distribution of the laser light 12 incident on the objective lens 19 is assumed to be a Gaussian distribution in the light transmission system on the left side of FIG. It means the ratio between the spot diameter value of the laser beam 12 at the place and the diameter of the objective lens 19 (A / W value: A represents the size of the aperture and W represents the spot diameter).

  FIG. 6 is a graph showing the calculation result of equation (5).

As is apparent from FIG. 6, the region where the change in the center intensity with respect to the defocus coefficient ω ₂₀ corresponding to the defocus amount (defocus amount) δz is in the range of 0.2 to 0.8.

Defocus coefficient number omega ₂₀ center intensity corresponding to defocus amount δz become 0.2, when σ = 0, 0.64λ, when sigma = 0.8, a 0.65 lambda. On the other hand, the central strength defocus scan coefficient number omega ₂₀ corresponding to the defocus amount δz become 0.8, any of the hour and sigma = 0.8 of sigma = 0 becomes 0.26Ramuda.

Therefore, using the formula (4), the optimum range of the distance from the focusing point of the laser beam 12 by the objective lens 19 to the second photodetector 29 (the distance of AO and the distance of BO in FIG. 4) is
ζ ≦ 5.2λ (M / NA) ² (7)
And ζ ≧ 2.1λ (M / NA) ² (8)
Given in.

  As described above, the principle of thickness unevenness detection (spherical aberration detection) of the transparent protective layer 3a of the present invention is different from the detection optical system for detecting the thickness unevenness of the transparent protective layer 3a. 1, a spherical lens 23, a cylindrical lens 24, and a first photodetector 25) are prepared, and a thickness unevenness detection system (spherical surface) in a state in which defocus correction control is performed (at the time of focusing). A feature is that an output caused by thickness unevenness (spherical aberration) is corrected using a detection signal of an aberration detection system.

  Next, the structure and sensitization principle of the sensitizing filter for detecting the spherical aberration shown in FIG. 2 will be described.

The sensitizing filter 27 for detecting spherical aberration divides the section of the reproduction laser beam 12 'into at least two sections (dividing the area in the optical path section of the light is generally called "wavefront division") and dividing the wavefront. For some of the light,
i) transmitted light amount, or
ii) Phase characteristics
By changing either or both of these, the actual sensitivity when detecting spherical aberration is sensitized. In this way, the use of the sensitizing filter 27 to sensitize the spherical aberration detection characteristic is independent of the inventive concept described so far, and is independent of the inventive content (unique features of the present invention). Means.

  Hereinafter, the principle of sensitization will be described in detail.

  As described above with reference to FIG. 3, when spherical aberration occurs, the cross-sectional spot of the reproduction laser beam 12 ′ returned to the objective lens 19 is derived from the component at the center of the optical axis (region of a predetermined radius including the optical axis). The component passing through the outer side is condensed closer to the front side than the component passing through the inner side, that is, the region including the optical axis (in order to facilitate comparison with FIG. 7A and FIG. 7B). It is displayed again.) Using this phenomenon, as shown in FIG. 7 (b), if the light from the center of the optical axis to the radius r of the cross-sectional spot of the reproduction laser beam 12 'incident on the objective lens 19 is shielded, the position of the minimum circle of confusion Moves from δ to ε.

  The present invention detects the spherical aberration using the amount of movement (increase) from δ to ε as understood from FIGS. 7A and 7B. It enhances the characteristics.

  In order to examine the condition of r at which the spherical aberration detection is increased most by the characteristic analysis, FIG. 8 that is easy to compare with FIG. 5 described above is used for the calculation model.

  For example, in the optical disk apparatus 10 shown in FIG. 2, as shown in FIG. 5, when the thickness of the transparent protective layer 3a changes by δt, the laser beam 12 is reciprocated between the objective lens 19 and the recording layer 3d. As a result, spherical aberration corresponding to 2δt occurs.

  Thereafter, the light passes through the sensitizing filter 27 for detecting spherical aberration before entering the spherical lens 28 of the detection optical system, and the characteristics of the laser light 12 are partially changed.

  As shown in FIG. 8, the location where the spherical aberration occurs and the portion where the characteristics of the laser beam 12 are changed are concentrated on the portion immediately before the laser beam 12 is incident on the objective lens 19, and there is spherical aberration and sensitization. Consider “pseudospherical aberration generation + sensitization filter function addition element 127” that functions as a filter.

  In FIG. 8, after the laser beam 12 passes through “pseudospherical aberration generation + sensitizing filter function adding element 127”, it is assumed that the thickness of the transparent protective layer 3a is maintained in an ideal state, and the light condensing in the optical disc 3 is focused. When the spot characteristic is enlarged by a detection optical system having a lateral magnification M, the detection characteristic of the second photodetector 29 shown in FIG. 5 and the second photodetector 129 of FIG. 8 which is a calculation model for analysis are used. The detection characteristics are consistent. Note that the enlargement characteristic (magnification) of the model shown in FIG. 8 can be easily converted by the equation (1).

  FIG. 7 shows an example of the sensitizing filter that shields the laser light incident on the objective lens 19 from the center of the optical axis to the position of the radius r, but FIG. 8 shows “pseudospherical aberration generation + sensitization”. As a characteristic of the sensitizing part of the filter function adding element 127 for use, the wave front is divided into three regions concentrically with respect to the laser light incident on the objective lens 19 with the circumference of the radius b and the radius a as a boundary region. Then, the change in the position ε of the place where the center intensity is maximized when the transmitted light amount is attenuated and the phase change is applied only to the ring region surrounded by the radius b and the radius a is analyzed.

  An optical element that attenuates the transmitted light amount and changes the phase only in the ring region surrounded by the radius b and the radius a is called an apodizer in a specific field of optics. The portion functioning as a sensitizing filter for detecting spherical aberration in the “+ sensitizing filter function adding element 127” will be hereinafter referred to as an “apotizer”.

  In addition, the expressions (A-1) to (A-15) quoted in the following calculation are the same as those of H. Ando: Jpn. J. Appl. Phys. Vol. 38 (1999) Pt.1 No. 2A p. Since this is a formula quoting each formula described in Appendix A of 764, it is disclosed only in the latter part, and a detailed explanation for derivation is omitted.

The coordinates on the pupil plane of the objective lens 19 are defined as (X, Y), and the coordinates on the condensing surface on the optical disc 3 are defined as (x, y). Since the complex amplitude distribution G (x, y) of the focused spot has a Fourier transform relationship with respect to the pupil function g (X, Y) of the pupil plane of the objective lens 19, P ₀ is set on the pupil plane of the objective lens 19. When the wavelength of the laser beam 12 is represented by λ, where α is the normalization constant, f is the focal length of the objective lens 19, and NA is the numerical aperture of the objective lens 19,
G (x, y)
= ΑF {g (X, Y)} _P0 (2-1)
Can be described. The intensity distribution of the laser light incident on the objective lens 19 is approximated as a Gaussian distribution, the A / W value in the X-axis direction is σx (= (A / W) _X ), and the A / W value in the Y-axis direction is σy (= (A / W) _Y ) and the amount of deviation of the center intensity due to the lens shift of the objective lens 19 is X ₀ ,

Can be expressed as However, in the formula (2-2), X ₀ is considered to be sufficiently small to be approximated as X ₀ ² ≈0.

The above rectangular coordinate system display
r = (X ² + Y ² ) ^1/2 / (fNA) (2-3)
φ = tan ⁻¹ (Y / X) (2-4)
^{ρ = NA (x 2 + y} 2) 1/2 / λ (2-5)
ψ = tan ⁻¹ (y / x) (2-6)
When converted to the polar coordinate system using

and,

It becomes.

here,

(2-2) is

And transformed.

The pupil function of the pupil plane of the objective lens 19 when the wavefront aberration ω (r, φ) is further generated under the above-described conditions is expressed by the following equation (2-10):

k = 2π / λ (2-12)
Is formulated.

In the optical disc optical system, when wavefront aberration ω (r, φ) is expanded into a polynomial expression and the terms up to the fourth order are considered,
Spherical aberration ωs
ωs (r, φ) = ω ₄₀ (r ⁴ −Qr ² + R)
(2-13)
Defocus ωd
ωd (r, φ) = ω ₂₀ r ² (2-14)
Therefore, it is preferable to consider.

  In the above equation (2-13), Q means an optimum value at which the central strength is maximum in the movement theorem. In the equation (2-13), R is a phase term and does not affect the center intensity, but affects the blending ratio of the real part and the imaginary part in the complex amplitude distribution of the focused spot.

Henkel's transformation formula is applied to the Fourier transformation in the polar coordinate system, and for the formula (2-1),
G (ρ, ψ ) = αH {g (r, φ)} _P0
(2-15)
It is written.

(2-11)

And substituting the equation (2-16) into the equation (2-15) and the focused spot amplitude distribution Gt (ρ, ψ ),
Go (ρ, ψ ): Condensation spot amplitude distribution when no aberration occurs in the conventional optical system, and
Gw (ρ, ψ ): An aberration term affecting the focused spot amplitude distribution of the conventional optical system,
Gt (ρ, ψ )
= Go (ρ, ψ ) + Gw (ρ, ψ ) (2-17)
And

and

It becomes.

Euler's formula for e ^{−ikω (r, φ) in} equation (2-19)

Is applied, the equation (2-19) becomes

And transformed.

When the values of σ, σ ₋ and Δ _OL are smaller than 1 (1> σ, 1> σ ₋ , 1> Δ _OL ), the equations (2-18) and (2-19) Against

And when the values of σ ₋ and Δ _OL are sufficiently smaller than 1 (1> σ ₋ , 1> Δ _OL ),

It is assumed that the calculation is performed.

When the value of the wavefront aberration ω (r, φ) is sufficiently smaller than 1 (1> kω), the expression (2-19)

Apply to approximate.

  The inner radius value of the ring area of the apotizer is b (corresponding to “r” in FIG. 7B) and the outer radius value is a (corresponding to “1” in FIG. 7A). When the transmission amplitude value is represented by T, an apodizer having an arbitrary shape (type) can be obtained by changing the setting condition of the value of T.

That is,
(A): If T is T = 0, the “completely light-shielded apodizer”
(B): If T is T = −1, a “phase-type apodizer” whose phase is shifted by λ / 2 is
(C): If T is 1>T> 0, a “light-attenuating apodizer” that reduces the amount of transmitted light is
(D): If T is T = te ^iθ , “a generalizer that generates a general phase shift and light amount attenuation simultaneously”
Each is defined.

The complex amplitude distribution G _anl (ρ, ψ ) of the condensing spot on the optical disk recording surface formed by the light that has passed through the ring region of the _apodizer can be obtained by Henkel transformation similarly to the equation (2-18). The integration range on the 19 pupil planes is limited within the ring region P _anl .

That is,

Defined by

Further, according to Babinet's theorem, the complex amplitude distribution Gt (ρ, ψ ) of the condensing spot by the light that has passed through the ring-shaped apodizer is obtained from the equations (2-18) and (3-1):
Gt (ρ, ψ )
= Go (ρ, ψ ) -G _anl (ρ, ψ )
(3-2)
Indicated by.

When aberration occurs, the equation corresponding to (2-17) is
Go (ρ, ψ ) is the amplitude distribution of the focused spot when there is no aberration in the conventional optical system, and
When G _anl (ρ, ψ ) is a focused spot amplitude distribution formed by light passing through the ring region of the apodizer when there is no aberration,
Gt (ρ, ψ )
= Go (ρ, ψ ) -G _anl (ρ, ψ )
+ Gw (ρ, ψ ) -Gw _anl (ρ, ψ )
(3-3)
Can be expressed as

Peak efficiency η as an important parameter that has a large effect on the focused spot characteristics,

In other words, the expression (3-4) means the central intensity ratio of the focused spot in the presence or absence of the apotizer.

As another important parameter, the radius c of the central portion of the ring region is

Defined in

  Note that the center intensity of the focused spot when there is no aberration is normalized to “1”.

That is,
| G ₀ (0, φ) −G _anl (0, φ) | ² = 1
(3-6)
And set.

Substituting the expression (3-6) into the expression (3-4),

Is obtained.

In the formula (2-18), when the values of σ ₋ and Δ _OL are sufficiently smaller than 1 (1> σ ₋ , Δ _OL ), from the formulas (A-1) and (A-13),

Therefore, the normalization constant α is obtained from the equations (3-7) and (3-8).

Is required.

As another condition, when all of σ, σ ₋ , and Δ _OL have relatively small values, the expressions (A-5), (A-7), (A-8), and (A −13)

Is approximated by

Therefore, the expression (3-9) is

And transformed.

Substituting equation (3-11) into equation (2-18), from equation (A-13),

Is derived.

In this equation (3-12), M _mν (ρ) means an integral definition equation including a Bessel function defined by equation (A-5).

Furthermore, when the formulas (2-22), (3-11) and (A-14) are applied to the formula (3-1),

Is obtained.

  .

In the formula (3-13), when an apodizer that simultaneously generates a general phase shift and light amount attenuation is used, T takes a complex number (T = te ^iθ ).

here,
ε (c) ≡2 (ab) c (1-σ ² c ² )
(3-14)
, And applying Euler's formula to the complex number T in the same way as (2-20),

And transformed.

In particular, at the position of ρ = 0 (the focused spot center amplitude position), from the expressions (3-7), (3-15) and (A-1),

Therefore, if the equation (3-16) is substituted into the equation (3-6),

Is obtained.

As a special case, when T is a real number, from equations (3-6) and (3-16),

Is guided.

Substituting this equation (3-18) into equation (3-13) yields an approximate expression

Is obtained.

Incidentally, (3-12) and (3-19) expression, sigma _- and delta _OL is sufficiently smaller than 1 (1»σ _-, 1»Δ _OL) time,

and,

And can be transformed.

The wavefront aberration in the case where spherical aberration and defocus occur at the same time is obtained from the equations (2-13) and (2-14):
ωs (r, φ)
= Ω ₄₀ (r ⁴ −Qr ² + R) + ω ′ ₂₀ r ²
(10-1)
It becomes.

here,
ω ₂₀ = ω ′ ₂₀ −Qω ₄₀ , ω ₀₀ ≡ω ₄₀ R
(10-2)
Then, equation (10-1) becomes
ωs (r, φ)
= Ω ₄₀ r ⁴ + ω ₂₀ r ² + ω ₀₀ (10-3)
And can be transformed.

In the expression (2-10), when both σ ₋ and Δ _OL are values sufficiently smaller than 1 (1> σ ₋ , 1> Δ _OL ), the expressions (3-9) and (10-3) are By substituting into equation (2-11) and using equation (A-13),

and

Is obtained.

When an apotizer that simultaneously generates phase shift and light amount attenuation is used, the equations (2-19) to (2-21), (3-1), (3-9), (10− 3) Using the formula and the formula (A-14),

and,

Can be obtained.

In the description of the present invention, the value of “Q” shown in the equation (2-13) is calculated under the condition that ω ₄₀ and σ are relatively small values. Here, it is assumed that σ ₋ ≈0 and Δ _OL ≈0 in the pupil function shown in the equation (2-16).

  Further, as will be described in detail below, the phase term R does not affect the center intensity, so R = 0.0 is set here.

Formula (3-14) is applied to a formula that approximates Formulas (2-23), (2-24), and (3-11) to Formulas (10-4) to (10-9). Then, (10-5), (10-6), (10-8) and (10-9) are

and

Is approximated by

here,

By putting

(10-16), (3-14), (3-16), (10-4), (10-7), (10-10), Substituting each of the equations (10-13) and applying the equation (3-17),

and

Is obtained.

On the other hand, from equation (10-17), the value of ω ₂₀ when | Gt (0, φ) ² | takes the maximum value under the condition of “SA> 0” is uniquely obtained,

It becomes.

In particular, when kω ₄₀ = 0, the equation (10-21) is
_{kω 20 = -S C / 2S A} (10-22)
It becomes.

When a phase difference of an angle θ occurs in the light that has passed through the ring region of the apodizer, the central intensity of the focused spot is maximized at the position ω ₂₀ where the focal position obtained by the equation (10-22) is shifted. . Detailed consideration on this phenomenon will be described later.

When T is a real number (light-shielding type or light amount attenuation type or phase type apodizer that shifts the phase by λ / 2), sin θ≈0, so that the formula (3-18), (10 -2) Using the relationship among the equations (10-18), (10-19) and (10-21), the value of Q in the equation (2-13) is
Q = −ω ₂₀ / ω _{40 ≈S B ′} / S A _′
(10-23),

and

Can be expressed as

  From formulas (10-23) to (10-25), it can be seen that the value of Q indicating the defocus position at which the central intensity when spherical aberration occurs is maximum does not depend on the amount of spherical aberration.

  FIG. 9 shows changes in the value of Q when c and σ calculated from the equations (10-23) to (10-25) change.

  As is apparent from FIG. 9, the value of Q is substantially “1” or a value in the vicinity thereof.

As can be seen from FIG. 9, when the apotizer is used, under the condition of σ = 0.7,
At the position of c> 0.67 and 0.44> c, the value of Q is larger than that of the conventional optical system (η = 100%),
For 0.67>c> 0.44, it becomes slightly smaller.

Further, this tendency becomes more prominent as the peak efficiency η decreases. Note that under the condition of σ = 0.0,
In the range of c> 0.70 and 0.45> c, the value of Q is larger than that of the conventional optical system (η = 100%),
For 0.70>c> 0.45, it becomes slightly smaller.

Therefore, under any conditions,
c ≤ 0.44 (9)
At the position of Q, the value of Q becomes large,
0.45 ≤ c ≤ 0.67 (10)
At the position of Q, the value of Q decreases.

ω ₄₀ corresponds to the amount of spherical aberration, and ω ₂₀ represents the amount of shift δz of the center intensity maximum position in the information storage medium 3 when spherical aberration occurs, as shown in equation (2).

  Therefore, it is shown that the spherical aberration detection sensitivity increases under the condition that the value of Q is larger than the conventional value (when η = 1), and the effect of the sensitizing filter appears.

As shown in the expression (3-5), c is the radius of the central portion of the ring region, and b = 0 in some cases, so that a predetermined radius (r as shown in FIG. 7B) The necessary conditions for exhibiting the sensitizing characteristics of the sensitizing filter 127 for detecting spherical aberration having the aperture of
r ≦ 0.44 × 2 = 0.88
r ≦ 0.88 (11)
It becomes.

  In summary, in the optical disc apparatus 10 shown in FIG. 2, the specific shape of the sensitizing filter 27 used when detecting spherical aberration is such that the spot cross-sectional radius of the reproduction laser beam 12 ′ is “1”. Sometimes, the amount of the laser beam 12 'can be attenuated within the range satisfying the above expression (11), the phase characteristic of the laser beam 12' can be changed, or the amount of laser beam 12 'can be attenuated and the phase characteristic can be changed. It is a shape that can be.

  The sensitizing filter 27 for detecting spherical aberration is entirely formed of a transparent plate having a predetermined thickness made of glass or transparent plastic. As a method of changing the light quantity of the laser beam 12 ', gelatin or metal called an ND filter, A transmitted light amount attenuating film made of an inorganic material is partially formed, that is, in a range satisfying the expression (11).

As a method for changing the phase characteristics, a transparent inorganic film such as S _i O ₂ is formed in a range satisfying the expression (11) on the transparent plate to form local unevenness. It is common. According to this method, the thickness of the sensitizing filter 27 for detecting spherical aberration is locally changed, and a phase change is partially caused in the spot cross section of the transmitted laser beam 12 ′. The same result is obtained when the sensitivity to 12 'is increased.

  By the way, the optical disc apparatus shown in FIG. 2 (the optical head shown in FIG. 1 and the information recording / reproducing apparatus having the optical head) is characterized by a highly accurate and reliable defocus detection system 102 (FIG. 1). The defocus correction circuit 105 (FIG. 1) is used to operate the defocus correction stably even when spherical aberration occurs due to uneven thickness of the cover layer 3a of the optical disc 3. Thus, with the in-focus state always secured, the wavefront aberration detection system 104 (FIG. 1) causes the thickness unevenness of the cover layer (transparent protective layer) 3a of the optical disc 3 or the substrate-side recording layer 3d or the cover layer-side recording layer 3b. The spherical aberration correction mechanism 101 (FIG. 1) is driven by detecting the state of spherical aberration that occurs when the laser beam is focused on either of them to correct thickness unevenness (spherical aberration).

  However, for example, referring to FIG. 2, when the thickness unevenness correcting convex lens 17 is moved for the purpose of correcting spherical aberration, the laser beam 12 of the light transmission system passes through the thickness unevenness correcting convex lens 17 and is objective. In the state immediately before entering the lens 19, the light is changed to divergent light or convergent light with respect to the state where the light was parallel before moving the thickness unevenness correcting convex lens 17. On the other hand, since the focusing property given to the laser beam 12 by the objective lens 19 is constant, as a result, the focusing position of the laser beam 12 focused on the optical disc 3 changes.

  In the optical disc apparatus 10 shown in FIG. 2, the defocus detection / correction control circuit system 111 controls the recording layer 3d or the recording layer 3b of the optical disc 3 so that the light converging position coincides with it. The unevenness detection / correction control circuit system 114 is operated to correct the spherical aberration, and at the same time, the defocus detection / correction control circuit system 111 is affected. As described above, interference (crosstalk) occurs between the thickness unevenness detection / correction control circuit system 114 and the defocus detection / correction control circuit system 111. Therefore, the "focus blur correction control" and the "thickness unevenness correction control" are performed. Both become very unstable.

  In order to reduce this problem, in the present invention, the response speeds of defocus correction control and thickness unevenness correction control are changed to reduce interference (crosstalk) between the two.

  FIG. 10 is a graph comparing the frequency characteristics (transfer functions) of the defocus correction control circuit and the thickness unevenness correction control circuit.

As shown in FIG. 10, in the present invention, the DC gain of the defocus correction control circuit and the thickness unevenness correction control circuit is represented by the DC gain of the frequency characteristic (transfer function). The DC gain Got of the thickness unevenness correction control circuit is set to be significantly larger. Also, with regard to the cutoff frequency (cut off frequensy), which is a response frequency at a gain of 1 indicating the limit to which correction control can be applied, the cutoff frequency fcf of the defocus correction control circuit is greater than the cutoff frequency fct of the thickness unevenness correction control circuit. Is also a big state,
fcf ≧ fct (12)
Is set.

  Specifically, the setting shown in the equation (12) is easily set by the gain / band setting circuit 58 and the gain / band setting circuit 83 in the optical disc apparatus 10 shown in FIG. That is, although not shown, the gain / band setting circuit 58 and the gain / band setting circuit 83 can often adjust the gain of the linear amplifier by adjusting the resistance ratio, for example. Each value can be set independently.

  Further, the DC gain Gof is derived from the structure of the drive mechanism of the objective lens 19 (focal blur correction coil 20 and track deviation correction coil 21) and the structure of the drive mechanism of the thickness unevenness correction convex lens 17 (thickness unevenness correction coil 18). It is possible to uniquely determine the cut-off frequencies fcf and fct that are determined depending on the setting of Got and Got. Although the cutoff frequencies fcf and fct are not shown, for example, in the optical disc apparatus 10 shown in FIG. 2, the gain / band setting circuit 58 and the gain / band setting circuit 83 are provided with a low-pass filter configured by a capacitor and a resistor. And the cutoff frequencies fcf and fct may be set more positively.

  As described above, the DC gain of the frequency characteristic (transfer function) of each of the defocus correction control circuit and the thickness unevenness correction control circuit is determined by the DC gain Gof of the defocus correction control circuit. The effect obtained by setting the gain to be significantly larger than the DC gain Got will be described.

  For example, in the optical disc apparatus 10 shown in FIG. 2, when the thickness of the cover layer 3a of the optical disc 3 changes suddenly, or the recording layer in which the objective lens 19 is in focus is changed from 3b to 3d, or from 3d to 3b. When the condensing point moves, the thickness unevenness detection / correction control circuit system 114 operates to move the thickness unevenness correcting convex lens 17 in a predetermined direction by a predetermined amount (distance).

  However, since the cutoff frequency fct of the thickness unevenness correction control circuit system 114 is sufficiently lower than the cutoff frequency fcf of the defocus correction control circuit system 111, the thickness unevenness correction convex lens 17 moves slowly. On the other hand, the cut-off frequency fcf of the defocus correction control circuit 111 is several times higher than the cut-off frequency fct of the thickness unevenness correction control circuit system 114. Therefore, compared to the slow movement of the thickness unevenness correction convex lens 17, The position of the objective lens 19 is adjusted at high speed.

  Thereby, even when the thickness unevenness correcting convex lens 17 is being moved, the in-focus state of the objective lens 19 is always maintained with high accuracy.

  As a result of the confirmation experiment, in order to obtain the above-described effect, the cutoff frequency fcf of the defocus correction control circuit needs to be at least twice as high as the cutoff frequency fct of the thickness unevenness correction control circuit. In order to stabilize the correction control to some extent, 10 times or more is desirable.

In other words, as a minimum condition,
fcf ≧ 2 fct (13)
The following conditions are necessary, preferably
fcf ≧ 10 fct (14)
Then, the effect of thickness unevenness correction is further enhanced.

  FIG. 11 is a schematic diagram for explaining the characteristics of the defocus detection signal and the thickness unevenness detection signal in the optical disc apparatus 10 shown in FIG. 2 (the optical head shown in FIG. 1 and the information recording / reproducing apparatus using the optical head). FIG.

  In FIG. 11A, the horizontal axis indicates a defocus detection signal with respect to the relative position of the objective lens 19 with respect to the optical disc 3, and the vertical axis indicates, for example, the output signal of the subtracter 81 illustrated in FIG. 2. For example, as shown in FIG. 2, the optical disc 3 includes a second (substrate-side) recording layer 3d and a first (cover-layer-side) recording layer 3b that are sequentially stacked on one surface of the substrate 3e. The blur detection signal “0 crosses (the signal level passes the reference level)” at two positions, the recording layer 3d position and the recording layer 3b position.

  In FIG. 11B, the horizontal axis indicates the defocus detection signal with respect to the relative position of the objective lens 19 with respect to the optical disc 3, and the vertical axis indicates the photodetection cells 25 a, 25 b, 25 c and 25 d of the first photodetector 25. 2 shows a change in the total light amount of the reproduction laser beam 12 ′ irradiated on the laser beam, for example, an output signal of the adder 75 in FIG. The level of the sum signal output from the adder 75 takes a maximum value in the vicinity of the recording layer 3d position and in the vicinity of the recording layer 3b position. In the case where the focused laser beam is not in the focused state, the spot size of the reproduction laser beam 12 ′ imaged on the individual photodetection cells 25 a, 25 b, 25 c and 25 d of the first photodetector 25 is increased, but each light is increased. Since it largely protrudes from the detection cells 25a, 25b, 25c and 25d, it is greatly reduced.

  In FIG. 11C and FIG. 11E, the horizontal axis indicates the amount of movement of the thickness unevenness correcting convex lens 17, and the vertical axis indicates the change in the thickness unevenness detection signal with respect to the position of the thickness unevenness correcting convex lens 17. Yes. 11D and 11F, the horizontal axis indicates the amount of movement of the thickness unevenness correcting convex lens 17, and the vertical axis indicates the thickness unevenness detection cell (for example, the second cell shown in FIG. 2). This represents a change in the sum of ± primary lights irradiated to the detection areas (detection cells) 29b and 29c) of the photodetector 29. 11C and 11D show a state in which spherical aberration is corrected in the vicinity of the recording layer 3d (near the substrate) (when the focused spot of the laser beam 12 ′ is in the vicinity of the recording layer 3d). FIGS. 11 (e) and 11 (f) show a state in which the spherical aberration is corrected in the vicinity of the recording layer 3b (near the cover layer) (the focused spot of the laser beam 12 ′ is shown). The state in which the amount of spherical aberration is small when in the vicinity of the recording layer 3b) is shown.

  For example, when the laser beam 12 is condensed on the recording layer 3d (near the substrate) of the optical disc 3 or in the vicinity thereof and the spherical aberration is corrected in accordance with the in-focus state, FIG. 11C and FIG. Detection characteristics as shown in FIG. 11 (d) are obtained.

  Note that if the focus position of the laser light 12 is moved to the recording layer 3b (close to the cover layer) from the state where the detection signals as shown in FIG. 11C and FIG. The detection difference signal and the sum signal are changed as described with reference to FIGS. 11A and 11B, and then defocus detection / correction control is performed at the position of the recording layer 3b (close to the cover layer).

  In the present invention, as shown in the equations (12) to (14), the defocus correction of the objective lens 19 is 2 to 10 times the thickness unevenness correction by the thickness unevenness correcting convex lens 17. Since it is executed at a high speed, a focused state is secured at a high speed immediately after the focusing position of the laser beam 12 is moved from the recording layer 3d position to the recording layer 3b position (or from the recording layer 3b to the recording layer 3d). Is done. On the other hand, as apparent from the equations (12) to (14), the thickness unevenness correction control is delayed by 10 to 2 times compared with the defocus correction, so that the laser beam 12 is generated. Immediately after the focused position is moved from, for example, the recording layer 3d position to the recording layer 3b position, thickness unevenness correction (spherical aberration correction) is insufficient, and therefore the second light detection for detecting spherical aberration is performed. The spot size of the ± first-order light spots imaged on the detection cells 29b and 29c of the detector 29 becomes very large (decrease in luminance), and the difference signal for detecting thickness unevenness (FIG. 11 (c)) Since the signal amplitude of the signal amplitude and the sum signal (FIG. 11 (d)) is reduced, the laser beam 12 is caused by disturbance vibrations utilizing the features of the present invention shown in the equations (12) to (14). Is focused from the recording layer 3d position to the recording layer 3b position. It is possible to detect a recording layer abnormal jump that suddenly changes (or from the recording layer 3b to the recording layer 3d).

  That is, the difference signal and the sum signal for detecting defocusing have the characteristics shown in FIGS. 11A and 11B as described above. Even if the position where the light is emitted changes suddenly, the sum signal level can be maintained at a level equal to or greater than Lfc shown in FIG. 11B in the vicinity of the recording layer 3b. Even if thickness unevenness (spherical aberration) correction is performed in the vicinity of the recording layer 3d, as shown in FIG. 11D, a sum signal for thickness unevenness detection (for example, an output signal of the adder 51 in FIG. 2). ) The level is greater than or equal to Lth.

  Therefore, if the condensing position of the laser beam 12 moves to the vicinity of the recording layer 3b immediately after that, the thickness unevenness detection / correction control circuit system 114 cannot follow for the reason shown in the equations (12) to (14), The spots of the spherical aberration detection laser beams 12b and 12c greatly protrude from the spherical aberration detection cells 29b and 29c, and the level of the sum signal for detecting thickness unevenness (for example, the output signal of the adder 51 shown in FIG. 2) is Lth (FIG. 11 (d)) is much lower, so it is determined by the output of the comparator 57 shown in FIG. 2 whether the level of the sum signal for detecting thickness unevenness is equal to or higher than Lth. An abnormal skip detection signal 60 can be obtained.

  Hereinafter, an application example or a modification of the optical disc apparatus shown in FIG. 2 will be described with reference to FIGS. Note that components similar to those shown in FIG. 2 (and FIG. 1) are denoted by the same reference numerals and detailed description thereof is omitted. 2 is compared with the configuration of the optical head device shown in FIG. 1 and the configuration of the information recording / reproducing apparatus using the optical head device, the same applies to the optical disc device shown in FIG. It goes without saying that there is a relationship.

  The optical disk device 210 shown in FIG. 12 is formed by removing the hologram element 26 used in the optical disk device 10 described above with reference to FIG. 2 and connecting the spherical lens 28 and the second photodetector 29 (the optical disk device 10 in FIG. 2). A half mirror 201 is disposed between them. In addition, the use of the half mirror 201 divides the reproduction laser beam 12 ′ toward the second photodetector 229, so a third photodetector 230 is added (similar to FIG. For detectors 229 and 230, both the arrangement of the optical system and the spot imaged on the light receiving surface are shown for convenience.

  Each of the second photodetector 229 and the third photodetector 230 has a minimum confusion circle formed when the reproduction laser beam 12 ′ is focused by the focusing property provided by the spherical lens 28. It is provided at a predetermined position in the back (substantially equal position from the center of the minimum circle of confusion). Further, the distance from the center of the least circle of confusion to the second photodetector 229 and the distance to the third photodetector 230 are defined according to the equations (7) and (8) described above. .

  In the optical disk device 210 shown in FIG. 12, a photodetection cell necessary for detecting the reproduction laser beam 12 ′ imaged along the optical axis of the spherical lens 28, a preamplifier used for processing the output, and an expensive A simple hologram element can be omitted. However, similarly to the optical disc apparatus 10 shown in FIG. 2, the output of the adder 91 of the reproduction signal detection system 113 is branched and attenuated to a predetermined level by the attenuator 58 in order to be able to detect an abnormal jump between recording layers. A reproduction signal is input to the comparator 59.

  An optical disk apparatus 310 shown in FIG. 13 is an example in which the knife edge method is used for the defocus detection system of the optical disk apparatus 10 described above with reference to FIG. In the optical disk device 310 shown in FIG. 13, as is apparent from the diffraction pattern that can be applied to the knife edge method, that is, the schematic diagram in the planar direction, the light shielding unit 301 a that functions as a knife edge and the ± first-order light spot. And the diffraction pattern 301b (301c) for generating the waveform is divided by a straight line including the center of the optical axis. Further, the configuration of the optical disk device 310 shown in FIG. 13 is equivalent to a portion without a pattern of the hologram element 301 (equivalent to a state without the hologram element 301, and actually a boundary portion of the light shielding portion 301a), the spherical lens 28, The optical system defined by the two photodetector cells 329a and 329d at the center of the second photodetector 329 is the defocus detection system 111 in the optical head device shown in FIG. 1 and the information recording / reproducing apparatus having the optical head device. , The optical system defined by the diffraction pattern portion 301b (301c) of the hologram element 301, the spherical lens 28, and the remaining two light detection cells 329b and 329c of the second light detector 329 has the same thickness unevenness ( This corresponds to the (spherical aberration) detection system 114. However, although some optical components are also used, the spherical aberration detection system 114 and the defocus detection system 111 are provided independently.

  In the optical disk apparatus 310 shown in FIG. 13, by using the hologram element 301, the spherical aberration detection system 114 and the defocus detection system 111 can be combined with only the single spherical lens 28 and the single photodetector 329. Thus, the size of the optical head device is reduced and the weight is further reduced. Since the defocus detection system 111 is also used as the spherical aberration detection system 114, the other one of the reproduction laser beams 12 'divided by the half prism 22 shares only the detection of the track deviation. The first photodetector 325 can also be divided into two parts. Accordingly, the number of preamplifiers used in the signal processing circuit (track deviation detection / correction control circuit system 112) is reduced.

  Further, in the optical disk apparatus 310 shown in FIG. 13, the defocus is detected by using the half detection light 12 a extracted by dividing by a straight line including the vicinity of the optical axis center where the detection accuracy is highest and stable in the knife edge method. Therefore, not only the accuracy of defocus detection can be improved, but also the highest detection reliability is ensured.

  In the optical disc device 410 shown in FIG. 14, the knife edge method is adopted as the defocus detection method and the hologram pattern of the hologram element 401 for generating ± first-order light spots, as in the optical disc device 310 shown in FIG. Further, sensitization processing is performed using a pattern similar to the sensitizing filter for detecting spherical aberration that functions in the same manner as the sensitizing filter used in the optical disc apparatus 10 shown in FIG.

  In the optical disk device 410 shown in FIG. 14, the hologram element 401 has a structure divided into three regions 401a, 401b, and 401c, and detects spherical aberration using only the laser beam 12c that passes through the region 401c. Features. Note that the radius value r of the boundary line between the region 401b and the region 401c is set so as to satisfy the expression (11), and is thus sensitized for detecting spherical aberration. Is used to detect spherical aberration. The detection area of the corresponding photodetector 429 is also divided into 429a and 429d where the 0th-order light (center portion) is imaged and 429b and 429c where the ± first-order light (outer portion) is imaged. Has been. Note that the spot 12b defined between the central portion and the outer portion of the intermediate portion, that is, the spot formed by the laser 12, is not used in this example.

  In the optical disk apparatus 410 shown in FIG. 14, as with the optical disk apparatus 310 shown in FIG. 13, half of the detection is divided and extracted by a straight line including the vicinity of the optical axis center where the detection accuracy is highest and stable in the knife edge method. Since the defocus is detected using the light 12a, not only the accuracy of defocus detection can be improved but also the highest detection reliability is ensured.

  An optical disk apparatus 510 shown in FIG. 15 is a further improvement of the optical disk apparatus 410 shown in FIG. 14. The hologram element 501 includes first to fifth five areas, that is, areas 501a, 501b (inside), (2 501b (outside), 501c and 501d, and spherical aberration is detected by using the laser beam 12b passing through the region 501b and the laser beam 12c passing through the region 501c. Further, the radius of the boundary line between the region 501c and the region 501a satisfies the expression (11) as in the optical disc apparatus shown in FIG. 14 or 13, and can sensitize spherical aberration. . Note that the detection region of the corresponding photodetector 529 is also divided into 529a and 529d where the zero-order light (center portion) is imaged and 529b and 529c where the ± first-order light (outer portion) is imaged. Has been. In addition, a part of the spots 12a and 12d defined between the central portion and the outer portion of the spot formed by the laser 12 is not used in this example.

In addition, regarding the hologram element 501, when the detection light characteristic in the range shown in the equation (10) is changed (attenuation of light amount or / and phase change), the sensitivity when detecting spherical aberration is reduced. As described above, in the optical disk device 510 shown in FIG. 15, this characteristic is actively utilized. That is, the laser beam 12c of the detection sensitivity on the photodetector 52 9 is increased, by combining the laser light 12b that detection sensitivity conversely is decreased, the sensitivity in detecting spherical aberration, more Can be improved.

Incidentally, in the hologram elements 401 and 501 used in the optical disc apparatus 410 shown in FIG. 14 and the optical disc apparatus 510 shown in FIG. 15, the duty in the diffraction pattern is set to 50%. That is, the 0th- order light component is designed to be 0 (the light amount ratio of transmitted light that goes straight without being diffracted is 0). At the same time, the structure of the hologram elements 401 and 501 is blazed so as to function in the same manner as the blazed grating (the structure in which the diffracted portion has an inclination and is easily diffracted in a specific direction), and most of the diffracted light is + 1st order. It has been devised so that it becomes light (that is, the light amount ratio of −1st order light is almost zero). Further, the center position of the diffraction fringes is shifted so that the optical axis center of the + 1st order light is on the boundary line between the light detection cells 429b (529b) and 429c (529c) or the light detection cells 429a (529a) and 429d (529d). ), The pattern is optimized to project on the boundary line.

  As described above with reference to FIG. 7B, this is because the portion from the center of the optical axis of the laser beam 12 incident on the objective lens 19 to the radius r is shielded (or the amount of transmitted light is attenuated or phase-changed). Taking advantage of the fact that the maximum position (minimum circle of confusion) of the center intensity at the time of focusing is shifted by ε, and the position of ε is regarded as a light emitting point, the light emitted from ε is recorded on the optical disc 3. When the convergent light is incident on the detection optical system shown on the right side of FIG. 8 by utilizing the fact that it is reflected by the layer 3b or 3d and then returned to the objective lens 19 again to become convergent light, the second This shows that the focal point deviation amount ζ in the vicinity of the photodetector 29 is equal to the value obtained by replacing δ in the equation (1) with ε.

  Therefore, when this convergent light is detected by a conventional defocus detection optical system, a pseudo defocus detection signal is obtained. As described above, in the optical system model shown in FIG. 8, pseudo spherical aberration is generated by the pseudo spherical aberration generation + sensitizing filter function adding element 26, and a portion from the center of the optical axis of the laser beam 12 to the radius r is formed. When the light is blocked (or the amount of transmitted light is attenuated or the phase is changed), the central intensity becomes maximum at the position ε before the recording layer 3b or 3d of the optical disc 3 in spite of focusing (this position is a pseudo light emitting point). 8), a pseudo defocus signal is detected on the second photodetector 29 after passing through the detection optical system on the right side of FIG.

  For the above reasons, when spherical aberration occurs due to uneven thickness of the transparent protective layer (cover layer) 3a of the optical disc 3, the first detection optical system (defocus detection system) is used to accurately correct the defocus. At the same time, the second detection optical system (spherical aberration detection system) shields the light from the center of the optical axis to the radius r (or attenuates the transmitted light amount or changes the phase), and then uses the conventional existing defocus detection optical system. When the signal is detected, the spherical aberration amount can be detected in the form of a pseudo defocus detection signal. An example in which a spherical aberration detection system is configured using this phenomenon is shown in FIG.

An optical disc apparatus 610 shown in FIG. 16 uses an astigmatism method known as a general defocus detection method for detecting spherical aberration. That is, as shown in FIG. 16, the hologram element 601 is divided into two regions of the first and second regions 601b and 601c, and the center of the diffraction fringe of each region is shifted, thereby diffracting in the region 601c + 1. The optical axis center of the next diffracted light is defined so as to form an image at the center position surrounded by the fifth to eighth light detection cells 625e, 625f, 625g and 625h of the light detector 625. The two regions 601b and 601c of the hologram element 601 are blazed (diffracted portions) so as to function similarly to the blazed grating, similarly to the hologram element 501 (401) described in FIG. 15 (or FIG. 14). Is inclined and has a structure that facilitates diffraction in a specific direction), the intensity of the + 1st order diffracted light is much larger than the intensity of the -1st order diffracted light. Accordingly, the ratio of each diffracted light intensity is 1: 1: 0: 0: 0 in the order of 0th- order light intensity, + 1st- order light intensity, −1st-order light intensity, + 2nd-order light intensity, and −2nd-order light intensity. .

Note that the 0th- order light (straight forward transmitted light) that has passed through the central portion of the hologram element 601 passes through the spherical lens 23 and the cylindrical lens 24, and is irradiated onto the light detection cells 625a to 625d of the light detector 625. The amount of defocus is detected by a defocus detection method called an astigmatism method, and a current is passed through the defocus correction coil 20 by the defocus detection / correction control circuit system 111 to move the position of the objective lens 19. To correct defocus.

  Further, the radius r of the boundary line (boundary circle) between the first region 601b and the second region 601c of the hologram element 601 is set so as to satisfy the expression (11) described above. . Therefore, the + 1st order diffracted light diffracted in the region 601c of the hologram element 601 in a state where the recording layer 3b or 3d on the optical disk 3 is always focused is sensitized with spherical aberration detection sensitivity, as if the model shown in FIG. As shown in FIG. 7B, the condensing position increases from δ to ε, and the increase amount is further expanded on the detection optical system as shown in the equation (1). As described above, the laser light 12c irradiated to the photodetection cells 625e, 625f, 625g, and 625h in accordance with the difference in change from δ to ε in the position of the spherical aberration (the position of the minimum circle of confusion) is a pseudo focus. Generate blur. As a result, the pattern of the laser beam 12c projected onto the photodetector 625 is as shown in (photodetection cells 625a, 625b, 625c and 625d) as shown in FIG. 16 (photodetection cells 625e, 625f, 625g and 625h). An annular shape that retains a perfect circle (as imaged) becomes an elliptical shape.

  This pattern change is signal-processed by the thickness unevenness detection / correction control circuit system 114, then converted into a thickness unevenness (spherical aberration) amount, and a current corresponding to the thickness unevenness correcting convex lens drive coil 18 is supplied to correct the thickness unevenness. By moving the convex lens 17 in a predetermined direction by a predetermined amount, it is possible to remove the influence of spherical aberration caused by the thickness unevenness of the cover layer 3a of the optical disc 3. Further, it is needless to say that the optical disk device 610 shown in FIG. 16 has the same configuration as the optical head device shown in FIG. 1 and the information recording / reproducing apparatus using the optical head device. The spherical aberration detection system 114 and the defocus detection system 111 are combined, but the laser beam used in the spherical aberration detection system 114 and the laser beam used in the defocus detection system 111 are completely transmitted by the hologram element 601. Since they are separated, optically, they can be regarded as independent systems without crosstalk.

  In the following, equations (A-1) to (A-15) used for area division of the hologram element for wavefront division using the hologram element 26 incorporated in the optical disc apparatus 10 shown in FIG. 2 are shown.

A1) Definition of Bessel function and expansion including Bessel function

Is defined.

From the formula (A-1),

Is guided.

The Bessel function described above is

From the formula (A-3),

Is obtained.

Therefore,

Is obtained.

Substituting equation (A-1) into equation (A-5),

Is replaced.

From the formula (A-6),

and

Is obtained.

When g (r, φ) is converted to Henkel,

and

It becomes.

g (r, φ) is

(A-10) is represented by the following formula:

It becomes.

The formula (A-13) is obtained by substituting the formula (A-12) into the formula (A-11) and using the formula (A-4), so that the formula (A-13) becomes b ≦ r ≦ a and Under the condition b≈a,

and,

Is defined.

In addition,

Is used to derive the above-described equation (5).

As described above, the optical head device of the optical disk device according to the present invention includes the substrate-side recording layer or light reflecting layer provided on one surface of the substrate in the vicinity of the substrate, and the substrate-side recording layer or light reflecting. A space layer transparent to light of a predetermined wavelength, a second recording layer or light reflecting layer separated from the substrate and the substrate-side recording layer or light reflecting layer, and the second recording layer or An optical recording medium having a protective layer for protecting the light reflecting layer, and at least one of the second recording layer or the light reflecting layer and the substrate-side recording layer or the light reflecting layer, the predetermined layer from the protective layer side. In an optical head device that emits light of a wavelength,
The light having the predetermined wavelength is condensed from at least one of the second recording layer or the light reflecting layer and the substrate-side recording layer or the light reflecting layer from the protective layer side, and the collected predetermined wavelength is collected. The first lens to which the light of the first light is returned, the second lens that corrects the influence of the thickness unevenness of the protective layer in cooperation with the first lens, and the first and second lenses. Including a photodetector that is illuminated by light;
When the wavelength of the light is λ, the numerical aperture of the first lens is NA, and the lateral magnification is M, the photodetector has a distance from a condensing point by the first lens,
5.2λ (M / NA) ² > 2.1λ (M / NA) ²
To identify that it is arranged in a range position from the be characterized, even if the thickness unevenness occurs in the protective layer, it is possible to eliminate distortion Mino influence of the focused beam.

The present invention also provides a first recording layer or light reflecting layer provided in the vicinity of the substrate, a space layer that is laminated on the first recording layer or light reflecting layer, and is transparent to light of a predetermined wavelength, Stacked on the space layer, stacked on the second recording layer or the light reflecting layer, and on the second recording layer or the light reflecting layer provided apart from the substrate and the first recording layer or the light reflecting layer. A protective layer for protecting the second recording layer or the light reflecting layer, and at least one of the second recording layer or the light reflecting layer and the first recording layer or the light reflecting layer. In the information recording / reproducing method for recording information by irradiating light of the predetermined wavelength from the protective layer side, or reproducing already recorded information,
The light having the predetermined wavelength is condensed from at least one of the second recording layer or the light reflecting layer and the substrate-side recording layer or the light reflecting layer from the protective layer side, and the collected predetermined wavelength is collected. A first lens that returns the light of the first lens, a second lens that cooperates with the first lens to correct the influence of thickness unevenness of the protective layer, and a wavelength of the light is λ, When the numerical aperture of the lens is NA and the lateral magnification is M, the distance from the condensing point by the first lens is
5.2λ (M / NA) ² > 2.1λ (M / NA) ²
Using a photodetector arranged at a position that falls within the range of
Based on the first photodetection signal, the second recording layer or the light reflecting layer and the first recording layer or the light reflecting layer are identified to collect light of a predetermined wavelength,
Based on the second light detection signal, the protection is performed in a state where light of a predetermined wavelength is condensed on either the second recording layer or the light reflecting layer and the first recording layer or the light reflecting layer. Detect the effect of layer thickness unevenness,
Based on the first photodetection signal, the first lens collects the light of the predetermined wavelength on a predetermined recording layer or light reflection layer, and the second photodetection signal varies. When the first lens is larger than a predetermined size, the condensing state on the predetermined recording layer or the light reflecting layer where the first lens condenses light of a predetermined wavelength is the defocus of the first lens. Since it is judged that the variation is accompanied and the position of the second lens that changes the light collection state by the first lens is changed , the thickness of the protective layer is uneven. even, to eliminate distortion Mino influence of the focused beam, information can be recorded at a high recording density.

  The present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the scope of the invention at the stage of implementation.

  In addition, the embodiments may be implemented in appropriate combination as much as possible, and in that case, the effect of the combination can be obtained.

  Further, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of constituent elements disclosed in this application. For example, if at least one of the effects of the present invention is obtained even if one or more structural requirements are deleted from all the structural requirements shown in the embodiment, the configuration from which the structural requirements are deleted is extracted as an invention. It can be done.

Incidentally, in Japanese Patent Application Laid-Open No. 2000-171346, which is the prior art, as shown in the paragraph [0082] in the right column on page 8,
SA = (S3-S4)-(S1-S2) * K
On the other hand, as shown in paragraph [0067] in the right column of page 7,
FES = S1-S2
Obviously, a part of the spherical aberration detection system is also used in the defocus detection system. As shown in FIG. 1 of the present application, the thickness unevenness (spherical aberration) correction mechanism 101 and the defocus detection system are used. 102 is different from the feature of the present invention in that it is separated and configured independently.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic explaining the basic structure of the optical head apparatus of this invention and the information recording / reproducing apparatus in which the optical head apparatus is incorporated. FIG. 2 is a schematic diagram for more specifically explaining an example of the configuration of the optical head apparatus shown in FIG. 1 and an information recording / reproducing apparatus (hereinafter referred to as an optical disk apparatus) having the optical head apparatus. In the optical disk apparatus shown in FIG. 2, a phenomenon that occurs when the thickness of the transparent protective layer near the objective lens changes while the laser beam is focused on the recording layer near the cover layer of the optical disk (information recording medium), that is, a spherical surface. Schematic explaining generation | occurrence | production of the shift | offset | difference of the minimum circle of confusion by an aberration. In the optical disk apparatus shown in FIG. 2, the laser at each position corresponding to the focal position by the spherical lens in the direction along the optical axis of the detection optical system, that is, the movement position of the minimum circle of confusion when the movement of the minimum circle of confusion occurs. Schematic explaining the change of the light intensity of the light spot of light. FIG. 5 is a schematic diagram for explaining the movement amount in the direction along the optical axis of ± first-order light generated by the hologram element for defining the optimum range of the distance A0 and the distance B0 shown in FIG. 4 and its detection characteristics. The graph which shows the calculation result of (5) Formula. FIG. 4 is a schematic diagram for explaining the principle capable of improving detection sensitivity by increasing the generation of spherical aberration described with reference to FIG. 3. The principle capable of providing the movement amount in the direction along the optical axis of ± first-order light generated by the hologram element for defining the optimum range of the distance A0 and the distance B0 shown in FIG. Schematic to explain. The graph which shows the change of the value of Q when c and (sigma) calculated from (10-23) Formula (10-25) Formula change. The graph which compares each frequency characteristic (transfer function) of a defocus correction control circuit and a thickness nonuniformity correction control circuit. FIG. 3 is a schematic diagram for explaining the characteristics of a defocus detection signal and a thickness unevenness detection signal in the optical disc apparatus 10 shown in FIG. 2 (the optical head shown in FIG. 1 and an information recording / reproducing apparatus using the optical head). FIG. 3 is a schematic cross-sectional view for explaining another embodiment of the optical disc apparatus shown in FIG. 2. FIG. 5 is a schematic cross-sectional view for explaining still another embodiment of the optical disc apparatus shown in FIG. FIG. 4 is a schematic cross-sectional view for explaining still another embodiment of the optical disc apparatus shown in FIG. 2. FIG. 5 is a schematic cross-sectional view for explaining still another embodiment of the optical disc apparatus shown in FIG. FIG. 4 is a schematic cross-sectional view for explaining still another embodiment of the optical disc apparatus shown in FIG. 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical disk apparatus (information recording / reproducing apparatus), 2 ... Laser element (light source), 3 ... Optical disk (information recording medium), 3a ... Objective lens side cover layer (transparent resin layer), 3b ... Objective lens side recording layer or reflection Layer 3c Space layer 3d Substrate recording layer or reflective layer 3e Substrate 4 Objective lens 5 Defocus correction coil 6 Beam splitter 10 Optical disc device 11 Laser element 12 ... Laser beam, 12 '... reproduction (reflection) laser beam, 13 ... collimating lens, 14 ... deflection beam splitter, 15 ... λ / 4 plate, 16 ... concave lens for uneven thickness correction, 17 ... convex lens for uneven thickness correction, 18 ... Thickness unevenness correction convex lens drive coil 1, 19 ... objective lens, 20 ... defocus correction coil (focus coil), 21 ... track deviation correction coil (track) Coil), 22 ... half prism, 23 ... spherical lens, 24 ... cylindrical lens, 25 ... first photodetector (for defocus detection), 26 ... hologram element, 27 ... sensitizing filter, 28 ... spherical lens, DESCRIPTION OF SYMBOLS 29 ... 2nd photodetector (for thickness unevenness detection), 101 ... Thickness unevenness (spherical aberration) correction mechanism, 102 ... Defocus detection system, 103 ... Thickness unevenness (spherical aberration) detection system, 104 ... Spherical aberration correction circuit , 105: Defocus correction circuit, 111: Defocus detection / correction control circuit system, 114: Thickness unevenness detection / correction control circuit system, 127: Pseudospherical aberration generation + sensitization filter function addition element, 129: Photo detector , 201 ... half mirror, 229 ... second photodetector, 230 ... third photodetector, 325 ... second photodetector (two divisions), 401 ... (with knife edge pattern) hologram Element, 429 ... second photodetector, 501 ... (blazed grating shape) hologram element, 529 ... second photodetector, 601 ... (composite) holographic element 625 ... photodetector (composite).

Claims (2)

A substrate-side recording layer or light reflecting layer provided on one surface of the substrate in the vicinity of the substrate, and a space layer that is laminated on the substrate-side recording layer or light reflecting layer and is transparent to light of a predetermined wavelength; An optical recording medium comprising: a second recording layer or a light reflecting layer separated from the substrate and the substrate-side recording layer or the light reflecting layer; and a protective layer for protecting the second recording layer or the light reflecting layer. In the optical head device that irradiates at least one of the second recording layer or the light reflecting layer and the substrate-side recording layer or the light reflecting layer with the light having the predetermined wavelength from the protective layer side,
The light having the predetermined wavelength is condensed from at least one of the second recording layer or the light reflecting layer and the substrate-side recording layer or the light reflecting layer from the protective layer side , and the collected predetermined wavelength is collected. The first lens to which the light of the first light is returned, the second lens that corrects the influence of the thickness unevenness of the protective layer in cooperation with the first lens, and the first and second lenses. Including a photodetector that is illuminated by light;
When the wavelength of the light is λ, the numerical aperture of the first lens is NA, and the lateral magnification is M, the photodetector has a distance from a condensing point by the first lens,
5.2λ (M / NA) ² > 2.1λ (M / NA) ²
It is specified that the optical head device is disposed at a position that falls within the range . A first recording layer or a light reflecting layer provided in the vicinity of the substrate, a space layer that is laminated on the first recording layer or the light reflecting layer, transparent to light of a predetermined wavelength, and a layer that is laminated on the space layer. A second recording layer or a light reflecting layer provided apart from the substrate and the first recording layer or the light reflecting layer, and the second recording layer or the light reflecting layer. An optical recording medium having a protective layer for protecting the layer or the light reflecting layer, and at least one of the second recording layer or the light reflecting layer and the first recording layer or the light reflecting layer from the protective layer side. In the information recording / reproducing method for irradiating light of the predetermined wavelength to record information, or reproducing already recorded information,
The light having the predetermined wavelength is condensed from at least one of the second recording layer or the light reflecting layer and the substrate-side recording layer or the light reflecting layer from the protective layer side, and the collected predetermined wavelength is collected. A first lens that returns the light of the first lens , a second lens that cooperates with the first lens to correct the influence of thickness unevenness of the protective layer, and a wavelength of the light is λ, When the numerical aperture of the lens is NA and the lateral magnification is M, the distance from the condensing point by the first lens is
5.2λ (M / NA) ² > 2.1λ (M / NA) ²
Using a photodetector arranged at a position that falls within the range of
Based on the first photodetection signal, the second recording layer or the light reflecting layer and the first recording layer or the light reflecting layer are identified to collect light of a predetermined wavelength,
Based on the second light detection signal, the protection is performed in a state where light of a predetermined wavelength is condensed on either the second recording layer or the light reflecting layer and the first recording layer or the light reflecting layer. Detect the effect of layer thickness unevenness,
Variation of the first I state der based on said photodetection signal first lens is focusing the light of the predetermined wavelength to a predetermined recording layer or the light reflecting layer, a second light detection signal If There larger than a predetermined size, and defocus of the first lens is condensed state is the first lens to the predetermined recording layer or the light reflecting layer that condenses the light of a predetermined wavelength information recording and reproducing method characterized by, it is determined that with different variations, to change the position of the second lens for changing the condensed state by the first lens.

Images