JP3575017B2 - Recording / reproducing apparatus and method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a recording / reproducing apparatus and method, and in particular, generates a first light beam of a first wavelength and a second light beam of a second wavelength,Staircase shapeThe phase of the first light beam is changed and the phase of the second light beam is not changed by the optical element in which the sawtooth-shaped unevenness having the concentric shape is formed. The present invention relates to a recording / reproducing apparatus and a method for converging a first light beam on a first recording medium and converging a second light beam on the second recording medium.
[0002]
[Prior art]
Optical disks, such as compact disks (CD) (trademark), CD-ROMs, and CD-Rs, have become widespread as recording media for recording or reproducing information using light. New recording media such as a DVD (Digital Versatile Disc) for recording data are being developed.
[0003]
When reading digital information from such an optical disc, a laser beam is focused on a recording medium, light reflected from the recording medium is detected, and the level of the reflected light is converted into binary data.
[0004]
In a high-density optical disk, a short wavelength laser beam is used (for example, when reproducing a CD, the wavelength λ is set to λ = 780 nm. When reproducing a DVD in which data is recorded at a higher density, λ is used. = 635 to 650 nm) and a large numerical aperture (NA) (for example, NA = 0.45 when playing a CD, NA = 0.6 when playing a DVD) Is used to converge the laser light to a narrower range, receive the reflected light, and reproduce the recorded information.
[0005]
If such an objective lens having a large numerical aperture (NA) is used, the amount of aberration in reflected light increases due to the inclination (skew) of the optical disk. Therefore, the substrate is designed to be thinner in DVD than in CD (CD). (1.2 mm for DVD, 0.6 mm for DVD), the amount of aberration in the reflected light is reduced.
[0006]
As described above, according to the difference between the size of the focused spot (proportional to λ / NA) defined according to the value of the NA of the objective lens and the wavelength λ of the laser beam, and the thickness of the substrate of the optical disc. Due to the difference in the amount of generated spherical aberration, it is difficult to use a conventional optical system for reading information recorded on a CD as it is for reproducing a DVD, and conversely, an optical system designed for a DVD is difficult. It is also difficult to use the CD as it is for reproduction.
[0007]
However, in the future, conventional optical disks such as CDs and high-density optical disks such as DVDs are expected to coexist. Therefore, when reproducing those optical disks, a dedicated reproducing device must be prepared for each type of optical disk. It is inconvenient if it must be done.
[0008]
Therefore, several methods have been proposed for reproducing a plurality of optical disks having different recording densities and substrate thicknesses with one apparatus.
[0009]
As one of them, a method of preparing two objective lenses for CD and DVD and switching the objective lens in accordance with the type of the optical disc to be reproduced (first method) is, for example, a technical technique TECHNICAL REPORT OF. IEICE MR95-25 (1995-08) (Mitsubishi Electric
Uta et al.).
[0010]
As a second method, for example, an aperture mechanism is provided on the optical path of laser light in a DVD optical pickup, and during CD reproduction, a portion of the laser light (reflected light) having a large aberration (a large NA) The second method is a method of reproducing a DVD and a CD by cutting only a part of the image and using only a part having a relatively small NA (for example, Japanese Patent Application Laid-Open No. Hei 6-124777, Japanese Patent Application No. Hei 8-057291). Issue.
[0011]
Further, as a third method, a method of combining an objective lens and a hologram optical element (HOE) (third method) is disclosed in, for example, JP-A-7-98431. In this method, the spherical aberration is corrected by optimizing the pitch (interval) (HOE pitch) of the unevenness of the hologram optical element, and the area of the hologram optical element where the unevenness is formed (HOE area) is reduced to reduce the NA. adjust. Further, one laser beam is split into two focal points according to the difference in the diffraction order of the hologram optical element, and the focal points are focused on optical disks having different substrate thicknesses.
[0012]
[Problems to be solved by the invention]
However, the first method requires two objective lenses and a drive mechanism for switching these objective lenses, and thus has a problem that the optical pickup becomes large and complicated.
[0013]
In the second method, the correction amount of the spherical aberration is insufficient, so that there is a possibility that the reproduction signal is deteriorated. Since the recording surface moves in the optical axis direction, the objective lens is moved in the optical axis direction by the amount obtained by dividing the difference in substrate thickness by the refractive index n (for example, n = 1.58) of the substrate (for example, 0.380 mm = 0.6 mm / 1.58 = (1.2 mm (CD) -0.6 mm (DVD)) / 1.58) and the focal point of the objective lens is moved onto the recording surface of the optical disc to be reproduced. Need to be done. Providing such a mechanism for moving the objective lens largely increases the size of the device (the two-axis actuator for the objective lens).
[0014]
In the third method, one laser beam is divided into two, and different types of optical disks are reproduced with the divided laser beams. Therefore, the third method is used for reproducing the optical disk with respect to the total amount of laser light. The problem is that the ratio of the amount of light used is small, making it difficult to effectively use the amount of laser light, and that the diffracted light of other orders other than the diffracted light used for reproduction becomes a disturbance, and the focus servo becomes unstable. Problem.
[0015]
Furthermore, in these methods, the wavelength of the laser beam used is as short as about 635 nm to about 650 nm, and the information recording layer (CD-R) is formed of a dye (dye) that absorbs light having a wavelength of about 635 nm to about 650 nm. (Recording surface) is difficult to reproduce (laser light is absorbed by a dye (dye), and sufficient reflected light cannot be obtained).
[0016]
The present invention has been made in view of such a situation, and generates laser light having a first wavelength of, for example, 780 nm or laser light having a second wavelength of, for example, 635 nm, and outputs the laser light through a hologram optical element and an objective lens. Light is focused on the first optical disk or the second optical disk. By using a long wavelength (780 nm) laser beam as the first wavelength, a CD or a CD-R can be reproduced, and a short wavelength (635 nm) laser beam is used as the second wavelength. To make the DVD playable. In addition, since the HOE is optimized so as not to generate stray light for two wavelengths, light of diffraction orders other than the diffraction light used for reproduction does not disturb, and the light amount of laser light is efficiently reproduced. It can be used for:
[0017]
[Means for Solving the Problems]
The recording / reproducing apparatus according to claim 1, wherein first generating means for generating a first light beam of a first wavelength, and second generating means for generating a second light beam of a second wavelength. Having a height that gives a phase difference to the first light beam and does not substantially give a phase difference to the second light beam.5 steps or morePhase modulation means having concentrically formed sawtooth-shaped irregularities having the staircase shape, and a first light beam having passed through the phase modulation means is condensed on a first recording medium, and a second light beam is condensed. And a light condensing means for condensing light on the second recording medium.
6. A recording / reproducing apparatus according to claim 5, wherein said first generating means generates a first light beam of a first wavelength, and said second generating means generates a second light beam of a second wavelength. A phase in which a first light beam is provided with a phase difference and a second light beam is provided with a concentric circular sawtooth-shaped unevenness having a three-step height having substantially no phase difference. And a condensing means for condensing the first light beam having passed through the phase modulating means on the first recording medium and condensing the second light beam on the second recording medium. And
[0018]
Claim9The method according to claim 1, further comprising: generating a first light beam having a first wavelength; and generating a second light beam having a second wavelength.3 steps or 5 steps or moreA step of giving a phase difference to the first light beam and substantially not giving a phase difference to the second light beam by the optical element in which the sawtooth-shaped irregularities having the step shape are formed concentrically; Converging the first light beam with the phase difference applied to the first recording medium, or condensing the second light beam without the phase difference applied to the second recording medium. It is characterized by having.
11. The recording / reproducing apparatus according to claim 10, wherein the first generating means generates a first light beam having a first wavelength, and the second generating means generates a second light beam having a second wavelength. The first light beam is provided with a phase difference, and the second light beam is formed concentrically with sawtooth-shaped irregularities having three or more steps having a height substantially not giving a phase difference. A phase modulating means for converging the first light beam having passed through the phase modulating means on the first recording medium and condensing the second light beam on the second recording medium; The modulating means substantially converts the first light beam into a first area formed to focus the first light beam on the recording surface of the first recording medium and an outer peripheral side of the first area. Has a second area formed so as to condense light outside the recording surface of the first recording medium.
[0019]
2. The recording / reproducing apparatus according to claim 1, wherein the first generating means generates a first light beam having a first wavelength, and the second generating means generates a second light beam having a second wavelength. And the phase conversion means gives a phase difference to the first light beam and a height which does not substantially give a phase difference to the second light beam.5 steps or moreThe concavo-convex shape of the saw-tooth wave having the staircase shape is formed concentrically, and the condensing means condenses the first light beam having passed through the phase modulation means on the first recording medium, and the second light beam The beam is focused on a second recording medium.
6. The recording / reproducing apparatus according to claim 5, wherein the first generating means generates a first light beam having a first wavelength, and the second generating means generates a second light beam having a second wavelength. And the phase conversion means applies a phase difference to the first light beam and a sawtooth-shaped unevenness having a three-step shape having a height substantially not giving a phase difference to the second light beam. Are concentrically formed, and the condensing means condenses the first light beam passing through the phase modulation means on the first recording medium, and condenses the second light beam on the second recording medium. I do.
[0020]
Claim9Wherein a first light beam of a first wavelength is generated, a second light beam of a second wavelength is generated,3 steps or 5 steps or moreA phase difference is given to the first light beam (substantially no phase difference is given to the second light beam) by the optical element in which the sawtooth-shaped unevenness having the staircase shape is formed concentrically. Either the first light beam having the phase difference is focused on the first recording medium, or the second light beam having no phase difference is focused on the second recording medium.
The recording / reproducing apparatus according to claim 10 generates a first light beam having a first wavelength, generates a second light beam having a second wavelength, and gives a phase difference to the first light beam; The second light beam is formed with concentric circular sawtooth-shaped irregularities having three or more steps with a height that does not substantially give a phase difference, and the first light beam that has passed through the phase modulating means is formed. Focusing on the first recording medium, focusing the second light beam on the second recording medium, and the phase modulating means condensing the first light beam on the recording surface of the first recording medium. And a second area formed so as to converge the first light beam substantially outside the recording surface of the first recording medium on the outer peripheral side of the first area. Having.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a configuration example of a first embodiment of the recording / reproducing apparatus of the present invention. In this embodiment, the optical pickup unit 1 has a predetermined one of two built-in radiation light sources (laser diodes) 21A (first generating means) and 21B (second generating means) (FIG. 2). A laser beam having a wavelength is generated, and is condensed on an optical disk 41A (for example, a CD) or an optical disk 41B (for example, a DVD) via a predetermined optical system (to be described later). (PD) 29 (FIG. 2), and outputs an output signal of each light receiving section to the arithmetic circuit 2 as a PD output signal.
[0022]
The arithmetic circuit 2 calculates a data detection signal (RF signal) for reproducing the optical disk, a focus error signal indicating a deviation of the focus of the laser light in the optical axis direction, and a radius of the optical disk from the PD output signal (signal of each light receiving unit). A tracking error signal indicating a deviation in tracking in the direction is calculated, a data detection signal is output to the reproduction circuit 3, and a focus error signal and a tracking error signal are output to the control circuit 4 (control means).
[0023]
The reproduction circuit 3 equalizes the data detection signal supplied from the arithmetic circuit 2, binarizes the data detection signal, and outputs a signal demodulated while correcting errors to a predetermined device (not shown) as a reproduction signal. It has been done.
[0024]
The control circuit 4 controls the focus servo actuator 6 according to the focus error signal supplied from the arithmetic circuit 2, and moves the objective lens 27 (light collecting means) (FIG. 2) of the optical pickup unit 1 in the optical axis direction. The optical pickup unit 1 is moved, the focus is adjusted, the tracking servo actuator 7 is controlled in accordance with the tracking error signal supplied from the arithmetic circuit 2, and the optical pickup unit 1 is moved in the radial direction of the optical disks 41A and 41B to adjust the tracking. It has been made to be.
[0025]
The control circuit 4 controls the light source switching actuator 8 to move one of the two radiation light sources 21A and 21B (FIG. 2) of the optical pickup unit 1 to a predetermined position according to the disk to be reproduced. When reproducing the optical disk 41A, a laser beam having a first wavelength λ1 is generated from the radiation light source 21A, and when reproducing the optical disk 41B, a laser beam having a second wavelength λ2 is generated from the radiation light source 21B. ing.
[0026]
Further, the control circuit 4 controls the motor 9 to rotate the optical disks 41A and 41B at a predetermined speed.
[0027]
When the control circuit 4 receives a signal corresponding to a user operation from the input device 5, the control circuit 4 controls each circuit in accordance with the signal.
[0028]
FIG. 2 shows a configuration example of the optical pickup unit 1 of FIG. The radiation light source 21A emits laser light having the first wavelength λ1 toward the grating 22A. The grating 22 </ b> A divides the laser light from the radiation light source 21 </ b> A into a substantially predetermined number (for example, three), and causes the laser light to be incident on a polarization beam splitter (PBS) 23.
[0029]
The radiation light source 21B emits the laser light having the second wavelength λ2 toward the grating 22B. When the radiation light source is switched to the radiation light source 21B, the grating 22B substantially divides the laser light from the radiation light source 21B into a predetermined number (for example, three), and divides the laser light into a polarization beam splitter ( (PBS) 23.
[0030]
Since the grating 22A or the grating 22B is provided for each radiation light source, tracking servo can be performed by a three-spot method on a plurality of optical disks having different track pitches.
[0031]
The PBS 23 transmits the laser light from the grating 22A or the grating 22B and makes the laser light incident on the collimator lens 24, reflects the laser light (reflected light from the optical disks 41A and 41B) from the collimator lens 24, and passes the multi-lens 28. The light is incident on a photodetector (PD) 29 through the light source.
[0032]
The collimator lens 24 arranges the laser light from the PBS 23 into parallel light beams and makes the parallel light beams enter the λ / 4 plate 25, and converts the parallel light beams (reflected light) incident from the λ / 4 plate 25 into convergent light and makes them enter the PBS 23. It has been done.
[0033]
The λ / 4 plate 25 converts linearly-polarized laser light incident from the collimator lens 24 into circularly-polarized light and causes the hologram optical element (HOE) 26 (phase modulation means) to enter the hologram optical element (HOE) 26.
[0034]
When the wavelength of the laser light incident from the λ / 4 plate 25 is the second wavelength λ2, the HOE 26 transmits the laser light as it is, without substantially diffracting it, and causes the laser light to enter the refraction objective lens 27. Has been done. The refraction type objective lens 27 condenses the incident laser light of the wavelength λ2 on the recording surface of the optical disc 41B via the substrate. The refractive objective lens 27 is designed such as NA and power so as to form an optimal light spot when a laser beam is condensed on the recording surface of the optical disk 41B via the substrate. .
[0035]
On the other hand, when the wavelength of the laser beam incident from the λ / 4 plate 25 is the first wavelength λ1, the HOE 26 diffracts the laser beam by a predetermined angle so that the laser beam diverges. Incident on The refraction type objective lens 27 focuses the laser light on the recording surface of the optical disc 41A via the substrate. As described above, the refractive objective lens 27 is optimized for the optical disc 41B, and if the laser beam is directly focused on the optical disc 41A having a substrate having a thickness different from that of the optical disc 41B, spherical aberration occurs. . Therefore, the HOE 26 is optimized to cancel the spherical aberration generated according to the difference in the thickness of the substrate.
[0036]
Further, when the wavelength of the laser light (reflected light) incident from the refraction type objective lens 27 is the first wavelength λ1, the HOE 26 has a predetermined angle (the thickness of the substrate of the optical disc 41A and the thickness of the optical disc 41A) so that the laser light diverges. If the wavelength of the incident laser light (reflected light) is the second wavelength λ2, the laser light is substantially diffracted by an angle that corrects the spherical aberration caused by the difference between the thickness of the substrate of the optical disk 41B and the optical disk 41B. The light is transmitted as it is without being diffracted into the λ / 4 plate 25.
[0037]
The refractive objective lens 27 converges the laser light diffracted by the HOE 26 to the recording surface (information recording layer) of the optical disk 41A to the diffraction limit. The refraction type objective lens 27 causes the laser light reflected by the optical disks 41A and 41B to enter the HOE 26.
[0038]
The multi-lens 28 gives astigmatism to the incident light beam for focus control, and causes the light beam to enter a photodetector (PD) 29. The photodetector (PD) 29 has a plurality of light receiving sections, and in each of the light receiving sections, converts the reflected light reflected by the optical disks 41A and 41B and incident via the above-described optical system into an electric signal, and converts the electric signal into an electric signal. To the arithmetic circuit 2 as a PD output signal.
[0039]
FIG. 3 is an enlarged view of the surface of the HOE 26 on the side of the refraction objective lens 27. As described above, the HOE 26 is formed concentrically with sawtooth-shaped irregularities having four-step stair-shaped slope portions each having a height d. The irregularities are formed on the recording surface of the optical disk 41A with an optimal diameter so as to obtain an optimal light spot size (that is, an optimal NA for the optical disk 41A).
[0040]
That is, the diameter of the range of the HOE 26 where the step-shaped step portion is formed is set to a predetermined value smaller than the NA of the refraction type objective lens 27, whereby the NA of the light (optical disk 41A) with the wavelength λ1 is set. Is substantially defined. The surface of the HOE 26 on the λ / 4 plate 25 side is a flat surface.
[0041]
The stepped pitch of the HOE 26 is such that when a laser beam having a wavelength λ1 is irradiated on an optical disc 41A having a substrate with a thickness of t1, spherical aberration caused by a difference in substrate thickness and axial chromatic aberration caused by a difference in wavelength are different. The value is set to a value at which a desired diffraction angle to be corrected is obtained.
[0042]
The number N of steps in the HOE 26 and the height d of each step (the height (depth) ((N−1) d) of the HOE 26 is defined by the number N and the height d) of the laser light They are set according to the values of the wavelengths λ1 and λ2. That is, the number of steps N of the step shape in the unevenness is expressed by the following equation.
N₀= Λ1 / (q × λ1-p × λ2) or
N₀= Λ1 / (p × λ2-q × λ1)
(P and q are predetermined positive integers)
N calculated by₀Is set to the value of (integer). Alternatively, the value N₀And the value when the diffraction efficiency of the zero-order light (the ratio of the light amount of the incident light to the light amount of the outgoing light) with respect to the wavelength λ1 is smaller than the diffraction efficiency of the first-order light or the minus first-order light. Is set. In short, the relationship between N and λ1, λ2 is set within a range that can achieve practically no problem of diffraction efficiency and small amount of stray light without completely optimizing.
[0043]
Further, the height d of each step is given by the following equation:
d₀= P × λ2 / (n-1)
(P is a predetermined positive integer, n is the refractive index of HOE 26)
D calculated by₀(D = d₀). Alternatively, the value d₀And the value when the diffraction efficiency of the 0th-order light (the ratio of the light quantity of the incident light to the light quantity of the output light) with respect to the wavelength λ2 is larger than the diffraction efficiency of the first-order light and the minus first-order light. Is set.
[0044]
For example, the height of one step calculated assuming that integers p and q are p = 1 and q = 1 is d.₀N₀When a laser beam (parallel ray) is incident on the HOE 26 having stepped unevenness, the HOE 26 changes the phase of the incident laser beam according to the thickness of each part of the HOE 26. When the laser light having the first wavelength λ1 is incident, as shown in FIG. 4A, the laser light passing through the area B in FIG. A phase difference of about (3/2) π radians is given, and a laser beam passing through the area C in FIG. 3 is given a phase difference of about (6/2) π radians, and a laser beam passing through the area D in FIG. Light is given a phase difference of about (9/2) π radians.
[0045]
The phase difference is equivalent to the original phase difference even if the phase is incremented or decremented by an integral multiple of 2π radians, so that the phase difference in FIG. 4A can be rewritten as shown in FIG. 4B. That is, when the laser light having the wavelength λ1 is incident on the HOE 26, the laser light passing through the area B is given a phase difference of about (（) radian with respect to the laser light passing through the area A, The laser beam passing through the region C is given a phase difference of about π radian, and the laser beam passing through the region D is given a phase difference of about (3/2) π radian. As described above, the laser beam having the wavelength λ1 is diffracted because a phase difference is given according to the incident portion of the HOE 26.
[0046]
On the other hand, when the laser light having the second wavelength λ2 is incident, as shown in FIG. 5A, the laser light passing through the area B in FIG. Is given a phase difference of about 2π radians, the laser beam passing through the region C in FIG. 3 is given a phase difference of approximately 4π radians, and the laser beam passing through the region D in FIG. A radian phase difference is given.
[0047]
As described above, the phase difference is equivalent to the original phase difference even if the phase is incremented or decremented by an integral multiple of 2π radians. Therefore, the phase difference in FIG. 5A is shown in FIG. Can be rewritten. That is, when the laser light having the wavelength λ2 is incident on the HOE 26, the phase difference between the laser light that has passed through the predetermined region among the regions A to D and the laser light that has passed through the other regions is almost zero. Therefore, the laser light having the wavelength λ2 is transmitted as it is without being substantially diffracted by the HOE 26.
[0048]
In this manner, the laser light of the first wavelength λ1 is diffracted so as to diverge (to increase the NA) by the HOE 26 as shown in FIG. The laser light of the second wavelength λ2, which is converged on the recording surface of t1), passes through the HOE 26 without being diffracted as shown in FIG. (T1> t2).
[0049]
As described above, by making the HOE 2 have power for one wavelength λ1 and not having the power for the other wavelength λ2, light of each wavelength is converged to a different position. In addition, the amount of movement of the refraction objective lens 27 (difference in the distance (working distance) between the tip of the refraction objective lens 27 and the optical disc) when reproducing different types of optical discs is reduced (for example, within 0.2 mm). be able to.
[0050]
Further, since the refraction type objective lens 27 is optimized for condensing the light of the wavelength λ2 on the optical disc 41B, no aberration occurs. Furthermore, the HOE 26 corrects the aberration with respect to the light of the wavelength λ1 generated in the refraction type objective lens 27 and the optical disk 41A. Therefore, light of any wavelength can be focused on each optical disc in a good spot shape.
[0051]
FIG. 8 shows an example of the diffraction efficiency (the ratio of the amount of incident light to the amount of output light) of the HOE 26. At the wavelength λ2, the diffraction efficiency of the 0th-order diffracted light (that is, transmitted light) shows a peak of almost 100% (peak 2 in the figure), so that the laser light of the second wavelength λ2 Pass through the HOE 26 as a zero-order diffracted light with almost no attenuation.
[0052]
As described above, since the attenuation of the light amount of the laser beam of the second wavelength λ2 when passing through the HOE 26 is almost zero, the HOE 26 is caused to travel twice (when heading toward the optical disk 41B and when reflecting off the optical disk 41B). Even if the light passes, the light amount of the laser light of the second wavelength λ2 hardly attenuates, and most of the generated light amount of the laser light can be used for reproduction or recording of the optical disk.
[0053]
On the other hand, at the wavelength λ1, the diffraction efficiency of the −1st-order diffracted light shows a peak of about 80% (peak 3 in the figure), so that the laser light of the first wavelength λ1 has a light amount of about 80%. %, And is diffracted through the HOE 26 by a predetermined diffraction angle as -1st-order diffracted light and passes therethrough.
[0054]
As described above, when passing through the HOE 26, the light amount of the laser beam of the first wavelength λ1 is attenuated to about 80%, so that the laser beam travels through the HOE 26 twice (toward the optical disk 41A and when reflected from the optical disk 41A). The light amount of the laser beam of the first wavelength λ1 after passing is about 64% (= 0.8 × 0.8 × 100%), which is sufficient for recording or reproducing data on or from the optical disk.
[0055]
Note that the wavelength band of the laser light generated by the radiation light sources 21A and 21B is sufficiently narrow, and can be considered as light having substantially a single wavelength. Therefore, when the HOE 26 obtains the zero-order light of the wavelength λ2 or obtains the first-order light of the wavelength λ1, unnecessary diffracted lights of other orders hardly occur. Therefore, it is possible to improve the use efficiency of light energy and suppress generation of stray light.
[0056]
Further, by making the surface irregularities of the HOE 26 three steps or more (N = 3) or more, the HOE 26 with good light use efficiency (diffraction efficiency) can be produced. Thus, the utilization efficiency (diffraction efficiency) of the laser light is increased. With two stages, the utilization efficiency (diffraction efficiency) of the laser light is reduced (for example, the diffraction efficiency of peak 3 in FIG. 8 is about 34%), and unnecessary first-order diffracted light is reproduced or reproduced. It is not preferable because it is generated with the same diffraction efficiency as the -1st-order diffracted light used for recording and becomes stray light.
[0057]
Further, if there are two stages, the interval between the wavelengths λ1 and λ2 becomes long, and it becomes difficult to arrange the wavelength λ1 near 780 nm and the wavelength λ2 near 635 nm. With four stages, they can be arranged near these values. In the case of five stages, the wavelengths λ1 and λ2 can be set to values closest to 780 nm or 635 nm, respectively. However, the four-stage structure of the HOE 26 can be manufactured by masking and etching the substrate twice, but the five-stage structure needs to be manufactured from a mold or the like, which increases the cost.
[0058]
In addition, a laser beam having a wavelength corresponding to the peak 2 in the drawing is generated by the radiation light source A21 (that is, the wavelength corresponding to the peak 2 in the drawing is defined as a first wavelength λ1), and the peak 1 (primary Laser light having a wavelength corresponding to the wavelength of the diffraction light) is generated by the radiation light source 21B (that is, the wavelength corresponding to the peak 1 in the drawing is defined as a second wavelength λ2), and recording and reproduction of disks having different substrate thicknesses are performed. It can also be done. Further, by appropriately changing λ1, λ2, p, and q (that is, N and d of the HOE 26), it is possible to perform recording and reproduction corresponding to various optical disks.
[0059]
As described above, the optical pickup unit 1 generates laser light having different wavelengths according to the type of optical disc (difference in substrate thickness), converges the laser light on the recording surface of the disc via the HOE 26, The reflected light is read by the PD 29 and output to the arithmetic circuit 2. When reproducing the optical disk 41A (for example, a CD), as shown in FIG. 2, a laser beam having a wavelength λ1 (for example, 780 nm) emitted from the radiation light source 21A is focused on the optical disk 41A, and the optical disk 41B (for example, a DVD). 9), as shown in FIG. 9, after switching the radiation light source to the radiation light source 21B, the laser light of the wavelength λ2 (for example, 635 nm) emitted from the radiation light source 21B is focused on the optical disk 41B.
[0060]
When reproducing the optical disk 41A by generating the laser light of the wavelength λ1 by the radiation light source 21A, the radiation light source 21B is turned off, and when reproducing the optical disk 41B by generating the laser light of the wavelength λ2 by the radiation light source 21B. Since the radiation light source 21A is turned off, disturbance (such as stray light) due to laser light having a wavelength not used for reproduction can be suppressed, and power consumption can be reduced.
[0061]
FIG. 10 shows an example of the light receiving unit of the PD 29 and an example of the operation of the arithmetic circuit 2. The PD 29 has three light receiving units 29A, 29B, and 29C. The light receiving unit 29A receives a laser beam (reflected light) used for data reading and detection of a focus error among the laser beams split by the grating 22A or the grating 22B. The light receiving units 29B and 29C receive laser light (reflected light) used for detecting a tracking error. The light receiving section 29A has four light receiving areas A to D, converts light incident on each light receiving area into an electric signal, and outputs the electric signal to the arithmetic circuit 2. The light receiving sections 29B and 29C have light receiving areas E and F, convert light incident on each light receiving area into an electric signal, and output the electric signal to the arithmetic circuit 2.
[0062]
In this embodiment, the focus servo is performed according to the astigmatism method (astigmatism method), and the arithmetic circuit 2 focuses on the four signals A to D supplied from the four light receiving areas A to D of the light receiving section 29A. An error signal ((A + C)-(B + D)) is calculated and output to the control circuit 4. The tracking servo is performed according to the three-spot method, and the arithmetic circuit 2 calculates a tracking error signal (EF) from the two signals E and F supplied from the light receiving areas E and F of the light receiving sections 29B and 29C. , To the control circuit 4. Then, the arithmetic circuit 2 calculates a data detection signal (A + B + C + D) from the four signals A to D supplied from the four light receiving areas A to D of the light receiving unit 29A, and outputs the data detection signal to the reproduction circuit 3.
[0063]
As described above, for example, when reproducing a DVD or recording data on a CD-R, the radiation light source 21B is used. When reproducing a CD or CD-R, the radiation light source 21A having the wavelength λ1 is used. To use. In this case, the thickness of the substrate is t1 = 1.2 mm and t2 = 0.6 mm, and the wavelength λ1 can be 780 nm and the wavelength λ2 can be 635 nm. Note that the PBS 23 in FIG. 2 (FIG. 9) can also be constituted by a beam splitter (BS). In this case, the λ / 4 plate 25 becomes unnecessary. However, in this case, only 1/4 of the emitted light is used.
[0064]
Next, a second embodiment of the present invention will be described. The second embodiment is different from the first embodiment in that the optical pickup unit 1 is changed so that the light source switching actuator 8 is not required. Therefore, in the second embodiment, only the optical pickup unit 1 will be described.
[0065]
FIG. 11 shows an example of the optical pickup unit 1 according to the second embodiment. In the optical pickup unit 1, a dichroic prism (DP) 31 is disposed between the grating 22A and the PBS 23, and the radiation light source 21B and the grating 22B are disposed in a direction perpendicular to the optical path from the radiation light source 21A to the PBS 23.
[0066]
The DP 31 has characteristics as shown in FIG. 12, and transmits the laser beam of the wavelength λ1 incident from the radiation light source 21A via the grating 22A to be incident on the PBS 23, and is incident from the radiation light source 21B via the grating 22B. The laser beam having the wavelength λ2 is reflected and made incident on the PBS 23. Since the film properties of DP31 need only be satisfied for either p-polarized light or s-polarized light, inexpensive ones can be used.
[0067]
The other components are the same as those of the optical pickup unit 1 in FIG. 2, and the description thereof will be omitted.
[0068]
When data is recorded or reproduced on the optical disk 41A in this embodiment, as shown in FIG. 11, the radiation light source 21A is turned on, and the laser light having the wavelength λ1 is condensed on the optical disk 41A. The reflected light is received by the PD 29. When recording or reproducing data on the optical disk 41B, as shown in FIG. 13, the radiation light source 21B is turned on, and the laser light having the wavelength λ2 is focused on the optical disk 41B, and the reflected light from the optical disk 41B is reflected. Is received by the PD 29. When recording or reproducing the optical disk 41A, the radiation light source 21B is turned off, and when recording or reproducing the optical disk 41B, the radiation light source 21A is turned off.
[0069]
As described above, by using the DP 31, the optical path of the laser light generated by the radiation light source 21A and the optical path of the laser light generated by the radiation light source 21B are combined, so that only the radiation light sources 21A and 21B are turned on / off. Since the generated laser light (wavelength) can be switched, the light source switching actuator 8 of the first embodiment becomes unnecessary, and the structure of the device can be simplified.
[0070]
Next, a third embodiment of the present invention will be described. The third embodiment shows another example of the first embodiment in which the optical pickup unit 1 is changed so that the light source switching actuator 8 becomes unnecessary. Therefore, only the optical pickup unit 1 will be described in the third embodiment.
[0071]
FIG. 14 shows an example of the optical pickup unit 1 according to the third embodiment. In the optical pickup unit 1, the laser coupler 33A is formed by integrating a light emitting unit and a light receiving unit of a laser beam, generates a laser beam having a first wavelength λ1 and causes the laser beam to enter the DP32 and to enter the DP32. The optical disc 41A receives reflected light from the optical disc 41A. The laser coupler 33B generates a laser beam of the second wavelength λ2, makes the laser beam incident on the DP 32, and receives the reflected light from the optical disk 41B incident from the DP 32.
[0072]
The DP 32 transmits or reflects the laser beam from the laser coupler 33A or 33B and makes the laser beam incident on the collimator lens 24, and transmits or reflects the reflected light from the optical disks 41A and 41B incident from the collimator lens 24, and The light is incident on the coupler 33A or the laser coupler 33B.
[0073]
Other components (the collimator lens 24, the HOE 26, and the refraction objective lens 27) are the same as those of the optical pickup unit 1 in FIG.
[0074]
When recording or reproducing data on or from the optical disc 41A in this embodiment, as shown in FIG. 14, the laser coupler 33A is turned on to focus the laser light of the wavelength λ1 on the optical disc 41A, and the reflected light from the optical disc 41A. Is received by the laser coupler 33A. When recording or reproducing data on or from the optical disk 41B, the laser coupler 33B is turned on to focus the laser light having the wavelength λ2 on the optical disk 41B, and the reflected light from the optical disk 41B is received by the laser coupler 33B. The laser coupler 33B is turned off when recording or reproducing data on the optical disk 41A, and the laser coupler 33A is turned off when recording or reproducing data on the optical disk 41B.
[0075]
As described above, by using the laser couplers 33A and 33B, the number of components can be reduced, and the entire device can be further downsized.
[0076]
The laser couplers 33A and 33B are not limited to this, and those having a similar function (for example, "Holo Laser" (trademark) of Sharp Corporation) can be used.
[0077]
Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, an optical disk 41A and a magneto-optical disk 42 on which information is recorded in the direction of magnetization using a magneto-optical film on a recording surface are reproduced. The fourth embodiment differs from the first embodiment in that the optical pickup unit 1 and the arithmetic circuit 2 are changed. Therefore, only the optical pickup unit 1 and the arithmetic circuit 2 of the fourth embodiment will be described.
[0078]
FIG. 15 shows an example of the optical pickup unit 1 of the fourth embodiment. Since the laser light incident on the recording surface of the magneto-optical disk 42 is polarized and reflected in accordance with the direction of magnetization, the direction of polarization of the reflected light (the difference between the p-polarized component and the s-polarized component) is detected and recorded. Read the information that has been written.
[0079]
The beam splitter (BS) 34 transmits the laser beam from the radiation light source 21A or the radiation light source 21B and makes the laser light incident on the collimator lens 24, and also reflects the reflected light (p-polarized component and s-polarized component Are reflected and made incident on the λ / 2 plate 35.
[0080]
The λ / 2 plate 35 rotates the polarization plane of the reflected light incident from the BS 34 by 45 degrees, and makes the reflected light incident on the PBS 38 via the multi-lens 36.
[0081]
The PBS 38 separates the incident laser light into a p-polarized component and an s-polarized component. The PD 37A has a plurality of light receiving units, receives the s-polarized light component of the laser light split by the grating 22B, and outputs an electric signal for tracking servo, focus servo, and data reproduction to the arithmetic circuit 2. It has been done.
[0082]
The PD 37B receives the p-polarized light component of the laser light split by the grating 22B, and outputs an electric signal for data reproduction to the arithmetic circuit 2.
[0083]
The magnetic coil (magnetic head) 43 applies a magnetic field corresponding to a recording signal to the magneto-optical disk 42.
[0084]
Note that the BS 34 may reflect 50% of the p-polarized component (transmit 50%) and reflect 100% of the s-polarized component (transmit 0%).
[0085]
The other components are the same as those of the optical pickup unit 1 in FIG. 2, and the description thereof will be omitted.
[0086]
FIG. 16 illustrates an example of the light receiving units of the PDs 37A and 37B and an example of the operation of the arithmetic circuit 2. The PD 37A has three light receiving units 61 to 63. The light receiving section 61 receives a laser beam (reflected light) used for reproducing data and detecting a focus error. The light receiving units 62 and 63 receive laser light (reflected light) used for detecting a tracking error. The light receiving section 61 has four light receiving areas A to D, converts light incident on each light receiving area into an electric signal, and outputs the electric signal to the arithmetic circuit 2. The light receiving units 62 and 63 have light receiving areas E and F, convert light incident on each light receiving area into an electric signal, and output the electric signal to the arithmetic circuit 2.
[0087]
The PD 37B has a light receiving area G for receiving a laser beam (reflected light) used for reproducing data (and detecting a focus error), converts incident light into an electric signal, and converts the electric signal into an arithmetic circuit 2 Output to
[0088]
In this embodiment, the focus servo is performed according to the astigma method, and the arithmetic circuit 2 calculates the focus error signal ((A + C)) from the four signals A to D supplied from the four light receiving areas A to D of the light receiving unit 61. − (B + D)) and outputs it to the control circuit 4. The tracking servo is performed according to the three-spot method, and the arithmetic circuit 2 calculates a tracking error signal (EF) from two signals E and F supplied from the light receiving areas E and F of the light receiving units 61 and 62. , To the control circuit 4.
[0089]
When reproducing the magneto-optical disk 42, the arithmetic circuit 2 detects MO data from the light receiving areas A to D of the light receiving section 61 of the PD 37A and the five signals A to D, G supplied from the light receiving area G of the PD 37B. The signal (G− (A + B + C + D)) (that is, the difference between the s-polarized component and the p-polarized component of the reflected light) is calculated and output to the reproduction circuit 3. When reading information by detecting the intensity of the reflected light from a normal optical disk (disk 41A, disk 42B, etc.), the arithmetic circuit 2 is connected to the light receiving unit 61 in the same manner as in the first to third embodiments. A data detection signal (A + B + C + D) is calculated from the four signals A to D supplied from the three light receiving regions A to D, and output to the control circuit 4. In this case, the arithmetic circuit 2 may output (A + B + C + D + G) as the data detection signal.
[0090]
As described above, the magneto-optical disk 42 can be reproduced by separating the reflected light from the magneto-optical disk 42 into each polarization component by the PBS 38 and receiving each polarization component by the PDs 37A and 37B.
[0091]
In this embodiment, when information is recorded on the magneto-optical disk 42, the laser light of the radiation light source 21B whose output has been increased from that at the time of reproduction is focused on a predetermined recording position on the recording surface of the magneto-optical disk 42. In this state, a modulation signal corresponding to the information to be recorded is supplied to the magnetic coil 43, and a magnetic field corresponding to the modulation signal is applied to the recording position where the laser light is focused, thereby recording the information. As described above, even when high-power laser light is required at the time of recording information, since the light use efficiency is good, it is not necessary to use laser light of such high output, and power consumption is suppressed. be able to.
[0092]
In the fourth embodiment, a DVD-RAM (a disc having a recording density equivalent to that of a DVD (ROM) and capable of recording information on a recording surface) that is likely to be developed in the future is used. When a magneto-optical recording system is used, recording or reproduction can be performed on the DVD-ROM and the CD, and a DVD (ROM) and a magneto-optical disk, and a DVD (ROM) and a substrate The recording and reproduction can be performed with respect to a magneto-optical disk such as HS (Hyper Storage) (trademark) having a thickness of 0.8 mm. In addition, even when the phase change method is adopted as the recording / reproduction method of the DVD-RAM, recording or reproduction can be performed in this embodiment (in this case, however, the magnetic coil 43 is not required) (phase change method). In the case of the system, a high-output laser beam is required, so this embodiment is preferable).
[0093]
The shape of the surface of the HOE 26 of each of the optical pickup units 1 of the first to fourth embodiments is changed in a region (first region) having a radius R1 from the center of the HOE 26 as shown in FIG. The slope portion has four-step sawtooth-shaped unevenness inclined in the outer circumferential direction, and in a region (second region) up to the outer radius (R1 + R2), the slope portion is inclined in the inner circumferential direction. Four steps of sawtooth-shaped unevenness. Accordingly, when a part of the laser light is shifted from the first area and is incident on the second area, the laser light incident on the second area and the light having an NA larger than the NA with respect to the optical disc 41A are the first light. The region r2 separated from the laser beam incident on the region and separated from the focal point F of the laser beam incident on the first region on the recording surface of the optical disk 41A (or the optical disk 41B) is irradiated in an out-of-focus state. .
[0094]
Of these laser lights, only the reflected light of the laser light (corresponding to the first area) focused on the focal point F on the recording surface of the optical disk 41A is detected by the photodetector or the laser coupler via the optical system. The light in the second area is hardly detected by the photodetector or the laser coupler via the optical system. With such a configuration, even when the HOE 26 and the objective lens 27 cause a field swing due to a tracking error, a good light-converged spot can be formed without generating coma aberration. Therefore, even when the incident position (optical axis) of the laser light on the HOE 26 is shifted, generation of stray light can be suppressed.
[0095]
Further, the NA for the light having the wavelength λ1 (optical disc 41A) can be accurately defined by the diameter R1 of the first region. That is, the radius R1 of the first region (specifying the NA for the optical disc 41A) is made smaller than the effective radius of the refraction objective lens 27 (specifying the NA for the optical disc 41B), so that the NA is set for each of the two optical discs. Optimization can be performed, and optimal aberration correction can be performed.
[0096]
On the other hand, as shown in FIG. 18, when irregularities are formed only in the first region on the surface of the HOE 26, the laser light incident on the second region is located near the focal point F (region r2 in FIG. 18). A part of the reflected light of the laser beam irradiated to the region r2 is also detected as stray light, and as a result, the focus servo and the tracking servo may become unstable.
[0097]
In the above embodiment, the HOE 26 is provided separately from the refraction type objective lens 27, but as shown in FIG. 19, similar to the HOE 26, a diffraction grating having a surface shape in which four steps of sawtooth-shaped irregularities are continuous. The refractive compound lens 39 can be used instead of the HOE 26 and the refractive objective lens 27 in the first to fourth embodiments. By using such a diffractive refraction compound lens 39, the eccentricity between the objective lens and the HOE can be suppressed. Further, the HOE 26 can be integrated with another optical element.
[0098]
【The invention's effect】
As described above, the recording / reproducing apparatus according to claim 1The recording / reproducing apparatus according to claim 5,And claims9According to the recording and reproducing method described in3 steps or 5 steps or moreThe phase of the first light beam is changed and condensed on the first recording medium by the sawtooth-shaped unevenness having the staircase shape, and the second recording medium is changed without changing the phase of the second light beam. Since the light is focused on the laser beam, the light of the diffraction order other than the diffracted light used for recording and reproduction does not become stray light, the amount of laser light can be efficiently used for recording and reproduction, and a stable focus servo is achieved. Can be realized. In addition, an increase in the size of the device can be suppressed. Further, CD-R can be reproduced by selecting a predetermined wavelength.
Further, according to the recording / reproducing apparatus of the tenth aspect, a first light beam of a first wavelength is generated, a second light beam of a second wavelength is generated, and the first light beam is positioned at the first light beam. The second light beam is concentrically formed with sawtooth-shaped irregularities having three or more steps at a height that does not substantially give a phase difference to the second light beam, and the second light beam passes through the phase modulation means. Is focused on the first recording medium, the second light beam is focused on the second recording medium, and the phase modulating means focuses the first light beam on the recording surface of the first recording medium. A first region formed so as to be condensed, and a first light beam formed so as to be substantially condensed outside the recording surface of the first recording medium on an outer peripheral side of the first region. Since the second region is provided, light of a diffraction order other than the diffraction light used for recording and reproduction does not become stray light, and the light amount of the laser light is efficiently recorded and reproduced. Can be utilized, it is possible to realize stable focus servo. In addition, an increase in the size of the device can be suppressed. Further, CD-R can be reproduced by selecting a predetermined wavelength.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration example of a first embodiment of a recording / reproducing apparatus according to the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration example of an optical pickup unit 1 according to the first embodiment of FIG.
FIG. 3 is an enlarged sectional view of a part of an example of the hologram optical element (HOE) 26 of FIG.
FIG. 4 is a diagram illustrating an example of a phase characteristic of a laser beam having a wavelength λ1 that has passed through the HOE 26 of FIG. 2;
FIG. 5 is a diagram illustrating an example of a phase characteristic of a laser beam having a wavelength λ2 that has passed through the HOE 26 of FIG. 2;
FIG. 6 is a diagram illustrating an example of an optical path of a laser beam having a wavelength λ1.
FIG. 7 is a diagram illustrating an example of an optical path of a laser beam having a wavelength λ2.
FIG. 8 is a diagram showing an example of diffraction efficiency of the HOE 26 with respect to laser light of each wavelength.
9 is a cross-sectional view showing a state where the radiation light source of FIG. 2 is switched to a radiation light source 21B.
10 is a block diagram illustrating a configuration example of a light receiving unit of the photodetector (PD) 29 in FIG.
FIG. 11 is a cross-sectional view illustrating a configuration example of an optical pickup unit 1 of a second embodiment of the recording / reproducing apparatus of the present invention.
FIG. 12 is a diagram illustrating characteristics of the dichroic prism of FIG. 11;
FIG. 13 is a cross-sectional view showing a state where the radiation light source of FIG. 11 is switched to the radiation light source 21B.
FIG. 14 is a sectional view showing a configuration example of an optical pickup unit 1 of a third embodiment of the recording / reproducing apparatus of the present invention.
FIG. 15 is a cross-sectional view illustrating a configuration example of an optical pickup unit 1 of a fourth embodiment of the recording / reproducing apparatus of the present invention.
16 is a block diagram illustrating a configuration example of a light receiving unit of the photodetectors (PD) 37A, 37B, and 37C in FIG.
FIG. 17 is a cross-sectional view showing another example of the surface of the HOE 26.
FIG. 18 is a sectional view showing still another example of the surface of the HOE 26.
FIG. 19 is a cross-sectional view showing an example of a diffractive refraction compound lens having continuous one-sided step-like irregularities on the surface.
[Explanation of symbols]
Reference Signs List 1 optical pickup unit, 2 arithmetic circuit, 3 reproducing circuit, 4 control circuit, 5 input circuit, 6 focus servo actuator, 7 tracking servo actuator, 8 light source switching actuator, 9 motor, 21A, 21B radiation light source, 22A, 22B grating, 23 polarizing beam splitter (PBS), 24 collimator lens, 25 λ / 4 plate, 26 hologram optical element (HOE), 27 refraction type objective lens, 29 photodetector (PD), 29A, 29B, 29C light receiving section, 31, 32 dichroic prism (DP), 33A, 33B laser coupler, 34, 36 beam splitter (BS), 37A, 37B, 37C photodetector (PD), 39 diffractive refraction compound lens, 41A 41B, an optical disk, 42 magneto-optical disk, 61 to 63 light-receiving portions

Claims (10)

A recording / reproducing apparatus that condenses one and the other of two light beams having different wavelengths on recording surfaces of a plurality of recording media having different substrate thicknesses and records or reproduces information on or from the recording medium.
First generating means for generating a first light beam of a first wavelength;
Second generating means for generating a second light beam of a second wavelength;
The first light beam is provided with a phase difference, and the second light beam is formed in a concentric shape with sawtooth-shaped irregularities having five or more steps having a height substantially giving no phase difference. Phase modulating means;
Focusing means for condensing the first light beam having passed through the phase modulation means on a first recording medium and condensing the second light beam on a second recording medium. Recording and playback device. 2. The recording / reproducing apparatus according to claim 1, wherein the phase modulation unit is a hologram optical element. The apparatus according to claim 1, further comprising a dichroic prism that combines an optical path of the first light beam incident from the first generating means and an optical path of the second light beam incident from the second generating means. Item 2. The recording / reproducing device according to Item 1. A control unit for controlling the first generation unit and the second generation unit,
The control unit controls the first generation unit and the second generation unit, and generates the first light beam only when reproducing the first recording medium. The recording / reproducing apparatus according to claim 1, wherein the second light beam is generated only when reproducing is performed. A recording / reproducing apparatus that condenses one and the other of two light beams having different wavelengths on recording surfaces of a plurality of recording media having different substrate thicknesses and records or reproduces information on the recording medium.
First generating means for generating a first light beam of a first wavelength;
Second generating means for generating a second light beam of a second wavelength;
The first light beam is provided with a phase difference, and the second light beam is formed concentrically with sawtooth-shaped irregularities having a three-step shape having a height substantially giving no phase difference. Phase modulation means;
Focusing means for focusing the first light beam having passed through the phase modulation means on a first recording medium and focusing the second light beam on a second recording medium;
A recording / reproducing apparatus comprising: The phase modulation means is a hologram optical element
The recording / reproducing apparatus according to claim 5, wherein: A dichroic prism that combines an optical path of the first light beam incident from the first generating means and an optical path of the second light beam incident from the second generating means;
The recording / reproducing apparatus according to claim 5, wherein: A control unit for controlling the first generation unit and the second generation unit,
The control unit controls the first generation unit and the second generation unit, and generates the first light beam only when reproducing the first recording medium. Generating the second light beam only when reproducing
The recording / reproducing apparatus according to claim 5, wherein: A recording / reproducing method for converging one and the other of two light beams having different wavelengths on recording surfaces of a plurality of recording media having different thicknesses of a substrate and recording or reproducing information on or from the recording medium,
Generating a first light beam of a first wavelength;
Generating a second light beam of a second wavelength;
A phase difference is given to the first light beam by an optical element in which sawtooth-shaped irregularities having three or five or more steps are formed concentrically, and the second light beam is substantially provided with a phase difference. A step of not giving a phase difference;
Converging the first light beam provided with the phase difference on a first recording medium, or condensing the second light beam not provided with a phase difference on a second recording medium And a recording / reproducing method. A recording / reproducing apparatus that condenses one and the other of two light beams having different wavelengths on recording surfaces of a plurality of recording media having different substrate thicknesses and records or reproduces information on the recording medium.
First generating means for generating a first light beam of a first wavelength;
Second generating means for generating a second light beam of a second wavelength;
The first light beam is provided with a phase difference, and the second light beam is formed concentrically with sawtooth-shaped irregularities having three or more steps having a height substantially giving no phase difference. Phase modulation means
With
Focusing means for focusing the first light beam having passed through the phase modulation means on a first recording medium, and focusing the second light beam on a second recording medium;
The phase modulation means includes: a first region formed so as to converge the first light beam on a recording surface of the first recording medium; and a first region formed on an outer peripheral side of the first region. Has a second area formed so as to converge the light beam substantially outside the recording surface of the first recording medium.
A recording / reproducing apparatus characterized by the above-mentioned.

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