JP2993391B2 - Optical pickup - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup, and more particularly to two types of optical disks having different distances from the surface of a transparent substrate to the signal surface, or from the surface of the transparent substrate to the signal surface. The present invention relates to an optical pickup used for reading recorded information from an optical disk having a two-layer structure provided with two signal surfaces having different distances from each other.

[0002]

2. Description of the Related Art With the increasing demand for recording various information signals at a high recording density, in recent years, high-density recording and reproduction of information signals using information recording media made on the basis of various construction principles and operation principles. Began to take place. For example, magnetic recording according to an information signal is performed on a ferromagnetic recording layer of an information recording medium, or recording and reproduction is performed using a magneto-optical recording medium, or, for example, an information signal is recorded on a signal surface of the information recording medium. It has already been practically used to record information signals by forming irregularities corresponding to the information signal and to reproduce the recorded information signals by optical means.

[0003] As semiconductor lasers that operate stably can be easily obtained, various types of optical recording media (hereinafter, referred to as optical discs) capable of performing high-density recording and reproduction using laser light. (May be described)
However, since it is possible to perform recording and reproduction in a non-contact state, it is resistant to scratches and dust, and has the advantage that a large storage capacity can be obtained by high-density recording.
It is also well known that research and development for practical use is currently underway, and a large amount of information signals are recorded from masters on which information signals are recorded by pits formed as geometric concave or convex parts. As copied recorded optical disks (optical disks for reproduction only), for example, compact disks are widely used, and as rewritable optical disks, for example, magneto-optical disks and other optical disks are used, for example, file memories for offices and other uses. Has been put to practical use.

Incidentally, an optical pickup (optical head) used for optically reading an information signal from the above-described optical disk includes a component for handling an optical signal of recorded information, an automatic focus control system, It is configured to include components for automatic control such as an automatic tracking control system and an automatic tilt control system. That is, the optical pickup, for example, reproducing light emitted from a semiconductor laser,
The objective lens is made incident on the objective lens via the afocal optical system or without passing through the afocal optical system, and the objective surface is placed on a signal surface provided at a predetermined distance from the surface of the transparent substrate of the optical disc. An image is formed by forming a minute light spot of the reproduction light focused by the lens, and reflected light from the minute light point of the reproduction light formed on the signal surface is formed by at least an objective lens. Through the system, for example, to a so-called quadrant photodetector,
An arithmetic circuit including an adder, a subtractor, and the like connected to the four-divided photodetector is configured to output a recording information signal, a focus error signal, a tracking error signal, and the like.

[0005] The above-mentioned optical pickup needs to have an optical system having a different configuration corresponding to the difference in the structure of the optical disk to be reproduced. That is, in the conventional CD (compact disc), which has been widely used as one of the optical discs, the signal surface is provided at a position of 1.2 mm from the surface of the transparent substrate. An operation of reading an information signal from an optical disk having a signal surface located at a position of 1.2 mm from the surface of the substrate can be favorably performed. However, recently, as an optical disk capable of performing higher-density recording than a CD, an optical disk in which a signal surface is provided at a position of 0.6 mm from the surface of a transparent substrate, or an optical disk having a signal surface at a position of 0.6 mm from the surface of a transparent substrate. In addition to the signal surface being set at a position of 6 mm, an optical disc having a laminated structure in which the signal surface is set at a position of 1.2 mm from the surface of the transparent substrate has also appeared.

As described above, the optical pickup needs to have an optical system having a different configuration in correspondence with the difference in the structure of the optical disk to be reproduced. C having a configuration in which the signal surface is provided at a position 1.2 mm from the surface of the transparent substrate.
When an optical pickup for reproducing a D (compact disc) is used, reading of an information signal from an optical disc having a configuration in which a signal surface is provided at a position of 0.6 mm from the surface of a transparent substrate is performed. Cannot be performed accurately. In order to solve the above problem, conventionally, for example, as disclosed in JP-A-6-259804,
A signal surface is provided at a position 1.2 mm from the surface of the transparent substrate using laser light emitted from one of the two semiconductor lasers using two semiconductor lasers. The reading of the information signal from the CD (compact disk) having the above-mentioned configuration is performed, and the laser beam emitted from the other one of the two semiconductor lasers is used. An optical pickup has been proposed in which an information signal is read from an optical disk having a structure in which a signal surface is provided at a position 0.6 mm from the surface of a substrate.

Another proposal which can solve the above-mentioned problem is, for example, one semiconductor in 19p-S-4 "Bifocal Optical Head (I)" of the academic lecture report of the Japan Society of Applied Physics in the fall of 1994. The laser light emitted from the laser is converted into parallel light by an optical path length adjusting lens, and then incident on an objective lens via a hologram element, so that the objective lens is 1.2 m from the surface of the transparent substrate.
An optical pickup configured to generate a minute light spot by reproduction light on both a signal surface provided at a position of m and a signal surface provided at a position of 0.6 mm from the surface of the transparent substrate. It has been disclosed.

[0008]

However, in the former solution among the above-mentioned two proposals, the former solution requires a signal plane provided at two positions at different distances from the surface of the transparent substrate of the optical disk. There is a problem that a dedicated semiconductor laser is required as a light source of the reproduction light used for reading out the information signal from one specific one, and the latter solution is one of the above two proposals. Although only one light source of reproduction light is used for reading information signals from signal surfaces provided separately at two positions at different distances from the surface of the transparent substrate of the optical disc, Since the hologram element is provided in the afocal optical system up to the objective lens, a predetermined reproduction operation cannot be performed unless the stability of the laser light source is maintained at a high level. In a problem, the emergence of no optical pick-up those issues have been determined.

[0009]

In order to solve the above-mentioned problems, the present invention provides an optical pickup having the following constitutions (1) to (3). (1) The first optical disc located at a short distance from the surface of the optical disc
An optical pickup capable of simultaneously reading each information recorded on a signal surface and a second signal surface located at a distance far from the surface of the optical disc, wherein the light source emits a single reproduction light beam; A first beam splitter that divides and outputs a single reproduction light beam radiated from a light source into two, and one of the two light beams output from the first beam splitter passes through a first light path whose optical path length is set shorter. A first optical path unit for supplying the second beam splitter, and the other of the two light beams output from the first beam splitter,
A second optical path means for supplying to the second beam splitter via a second optical path having a long optical path length, and the one and the other light fluxes output from the second beam splitter are simultaneously passed to allow the one light flux to pass therethrough; The first from the front side
An objective lens that collects the other light beam from the surface side on the second signal surface while condensing the light beam on the signal surface, and reflects the reflected light of the one light beam reflected on the first signal surface. An objective lens, a first photodetector that sequentially detects the light beam through the second beam splitter, and a reflected light of the other light beam reflected on the second signal surface through the objective lens and the second beam splitter in order. An optical pickup, comprising: a second photodetector for detecting by light. (2) The optical pickup according to claim 1, wherein the first optical path means includes an optical path length adjusting lens for adjusting the first optical path or a spherical aberration correction member of the objective lens. (3) The optical pickup according to claim 1, wherein the second optical path means includes an optical path length adjusting lens for adjusting the second optical path, a spherical aberration correction member of the objective lens, or both.

[0010]

[0011]

[0012]

[0013]

[0014]

[0015]

[0016]

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific contents of an optical pickup according to the present invention will be described in detail with reference to the accompanying drawings. 1 to 4
Is a block diagram showing a schematic configuration of an optical pickup of the present invention, and FIG. 5 is a cross-sectional view showing a configuration example of an optical disk. 1 to 4, reference numeral 1 denotes one semiconductor laser used as a light source of the reproduction light. Reference numerals 2 to 5 denote beam splitters (half prisms and half mirrors), 6 is an objective lens, 7 and 8 are total reflection mirrors, 9 is a spherical aberration correction member of the objective lens, 10 is an optical path length adjusting lens,
Reference numerals 1 and 12 denote photodetectors, 13 denotes a focusing lens, and D denotes an optical disk. In the optical pickup of the present invention illustrated in FIGS. 1 to 4, a configuration example is shown in which the spherical aberration correcting member 9 of the objective lens is provided in the optical path for adjusting the optical path or in the first optical path. As will be described later, if the difference between the distances L1 and L2 from the surface of the transparent substrate 14 to the signal surface at different positions on the optical disk D to be reproduced by the optical pickup is small, the above-mentioned objective is used. Needless to say, the spherical aberration correcting member 9 of the lens need not be used. In the optical disc D illustrated in FIG.
Is a transparent substrate, and 15 and 16 are signal surfaces. Optical disk D
The signal surfaces 15 and 16 of the (recorded optical recording medium)
A mark recording method is applied to sequential channel words formed by channel bits obtained by converting a data word to be recorded / reproduced according to a predetermined modulation method, to mark (pit) and non-mark (land). Recording information is recorded in the form described above, and a reflection surface for reproduction light is formed on the signal surface.

In FIG. 5, reference numeral 14a denotes the surface of the transparent substrate 14, and the reproduction light emitted from the objective lens 6 is incident on the optical disk D from the surface 14a of the transparent substrate 14. FIG. 5A shows a configuration example of an optical disc D in which a signal surface 15 is provided at a position (first distance) L1 from the surface 14a of the transparent substrate 14, and FIG.
(b) shows L2 from the surface 14a of the transparent substrate 14 (however, L2
FIG. 5C shows an example of the configuration of an optical disc D in which the signal surface 16 is provided at the position of the distance (second distance) of <L1). FIG. 5C shows the distance L1 from the surface 14a of the transparent substrate 14. And an optical disk D provided with a signal surface 16 at a distance of L2 (where L2 <L1) from the surface 14a of the transparent substrate 14, that is, two signal surfaces 15, 16. 2 shows a configuration example of an optical disc having a stacked configuration. For example, a compact disc (C
In D), the signal surface is 1.m from the surface 14a of the transparent substrate 14.
For example, in a digital video disk (DVD) which is arranged at a distance of 2 mm and performs higher-density recording than the above-mentioned CD, the signal surface has a distance of 0.6 mm from the surface 14a of the transparent substrate 14. The position or signal surface is 0.6 mm, 1.2 mm from the surface 14a of the transparent substrate 14.
At a distance of.

By the way, the objective lens 6 used as a constituent member of the optical pickup is used when the optical pickup performs a reproducing operation of the optical disk D of a configuration originally planned as the optical disk D to be reproduced. The optical disk D having a configuration intended to be an optical disk D to be reproduced is, for example, a transparent substrate 1 because the optical disk D has a configuration capable of favorably correcting spherical aberration.
4, the signal surface 15 is provided at the position L1 from the surface 14a of the transparent substrate 14.
When a reproducing operation is performed on an optical disk D having a configuration in which the signal surface 16 is provided at the position 2 as an optical disk to be reproduced, a minute size on the signal surface is determined based on a difference in thickness of the transparent substrate 14. Such light spots have spherical aberration.

Then, two reproduction light fluxes obtained by splitting the divergent reproduction light A radiated from one light source 1 (semiconductor laser 1) provided at a specific position of the optical pickup by the beam splitter 2 are obtained. By using the optical path length adjusting optical path and the optical path length adjusting lens 10, the optical path lengths of the two optical paths individually set for B and C have different optical path lengths. The light emitted from one objective lens 6 on which the light beams of the two reproduction light beams B and C are incident is focused on two predetermined imaging points on the optical axis. When each image is formed, two predetermined positions on the optical axis are determined by one predetermined reproduction light beam B (or C) of the two reproduction light beams B and C. Imaging point at one of In the case where an objective lens 6 having characteristics that do not cause spherical aberration is used, the predetermined one of the two reproduction light beams B and C is used as the predetermined reproduction light beam B. The reproduction light flux C (or B) other than (or C) causes spherical aberration at the image forming point at the other of the two different predetermined positions on the optical axis.

Therefore, in the optical pickup of the present invention, the spherical aberration correcting member 9 of the objective lens is provided in a predetermined optical path in order to prevent spherical aberration from occurring at the image forming point at the other position. The spherical aberration correcting member 9 of the objective lens prevents the spherical aberration from being generated. As the spherical aberration correcting member 9 of the objective lens, for example, a transparent plate having an appropriate refractive index and a predetermined thickness can be used, and as the spherical aberration correcting member 9 of the objective lens, an optical path length adjusting member is used. May be configured so that it can also be used as an optical element for optical communication. When two predetermined image points at different positions set on the optical axis are close, the close 2
By using an objective lens designed so that spherical aberration is favorably corrected when an imaging point is formed by the objective lens at an intermediate position between the two imaging points, the objective Needless to say, even if the spherical aberration correcting member 9 of the lens is not particularly used, the problematic spherical aberration can be prevented.

As described above, the divergent reproduction light A radiated from one light source 1 provided at a specific position of the optical pickup is split into two by the beam splitter 2, and the two diverged light beams are emitted from the beam splitter 2. The reproduction light beams B and C are made to pass through individually set optical paths, then enter the common objective lens 6, and are focused by the objective lens 6 at the position of the image forming point of the reproduction light beam B formed by the objective lens 6. In order for the position of the image forming point by the reproduced light beam C to be imaged to be two specific positions that are separated from each other by a predetermined distance on the optical axis, the optical path length of the optical path of the reproduction light beam B is required. And the optical path length of the optical path of the reproduction light beam C need be set to specific optical path lengths different from each other.

Therefore, in the optical pickup of the present invention, the optical path length of the optical path of the reproduction light beam B and the reproduction light beam C
The optical path length of the optical path is adjusted in order to make each of the optical path lengths a predetermined optical path length.The above-mentioned optical path length adjusting means includes an optical path length adjusting optical path and an optical path length adjusting optical path. The optical path length adjusting means such as the lens 10 is used to set the optical path length of the reproduction light flux B and the optical path length of the reproduction light flux C to predetermined optical path lengths, respectively.
In the optical pickup shown in FIGS. 1 to 4, an optical path of a bypass (detour) type with respect to a first optical path configured between the beam splitter 2 and the beam splitter 3;
That is, the optical path is configured as shown by the beam splitter 2 → the total reflection mirror 7 → the total reflection mirror 8 → the beam splitter 3, thereby functioning as an optical path for adjusting the optical path length. However, the configuration of the optical path for adjusting the optical path length is not limited to the configuration illustrated in FIGS. 1 to 4. For example, the beam splitter 2 → the total reflection mirror 7 → the total A transparent parallel plate having an appropriate refractive index and a positive lens (or a negative lens) having an appropriate curvature made of a medium having an appropriate refractive index are inserted into the optical path of the reflecting mirror 8 → beam splitter 3. To obtain the required optical path length.

In the configuration example of the optical pickup of the present invention illustrated in each of FIGS. 1 to 4, the optical disk D is driven and rotated at a predetermined rotation speed by a rotation driving mechanism (not shown). First, in the optical pickup shown in FIG. 1, one of the two reproduction light beams B and C obtained by being split into two by the above-described beam splitter 2 is used for the beam splitter 2 and the beam splitter 3. The reproduced light flux B that enters the beam splitter 3 through the first optical path formed between the beam splitter 3 and the objective lens 6 is formed between the beam splitter 3 and the objective lens 6. The light is reflected by the beam splitter 4 in the second optical path and enters the objective lens 6. The reproduction light beam B incident on the objective lens 6 generates a light spot having a small diameter on a signal surface 15 provided at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disk D.

The other reproduction light beam C of the two reproduction light beams B and C obtained by being split into two by the above-described beam splitter 2 has an optical path including total reflection mirrors 7 and 8. After passing through the optical path for length adjustment, the light enters the beam splitter 3. Spherical aberration correcting member 9
May be installed in any portion of the optical path for adjusting the optical path length configured between the beam splitter 2 and the beam splitter 3. After passing through the optical path for adjusting the optical path length, the light beam enters the beam splitter 3 and the reproduced light beam C ′ reflected by the beam splitter 3 is reflected by the beam splitter 4 in the second optical path and enters the objective lens 6. I do. Then, the reproduction light beam C ′ incident on the objective lens 6 generates a light spot having a small diameter on the signal surface 16 provided at a distance L2 from the surface 14a of the transparent substrate 14 of the optical disk D.

The optical disk D shown in FIG. 1 has a signal surface 15 provided at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disk D, and a distance L2 from the surface 14a of the transparent substrate 14. The optical disc D to be played back by the optical pickup has a configuration in which the signal surface 16 provided at the position (1) is laminated (see FIG. 5 (c)). 5A in which the signal surface 15 is provided only at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disk D, or the transparent substrate of the optical disk D described above. 14 surface 14
Of course, a configuration such as that illustrated in FIG. 5B in which the signal surface 16 is provided only at the position of the distance L2 from a may be used.

As described above, the reflected light beam B 'from the minute light spot due to the reproduced light beam B formed on the signal surface 15 of the optical disk D and the reproduced light beam C formed on the signal surface 16 of the optical disk D The reflected light flux C ′ from the minute light spot due to the above is emitted from the objective lens 6 in a state where it is focused by one common objective lens 6. Of the two reflected light beams B ′ and C ′ emitted while being focused from the objective lens 6, the reflected light beams B ′ and C ′ transmitted through the beam splitter 4 are separated by the beam splitter 5 into two beams. Divided.

The reflected light beams B 'and C' transmitted through the beam splitter 5 and the reflected light beams B 'and C' reflected by the beam splitter 5 are both imaged on the signal surface 15 of the optical disk D. The reflected light beam B ′ from the minute light spot by the reproduced light beam B
And a reflected light beam C ′ from a minute light spot due to the reproduced light beam C imaged on the signal surface 16 in FIG. One of the reflected light fluxes B ′ and C ′ transmitted through the beam splitter 5 is electrically detected by a photodetector 12 provided near an image forming position of the reflected light flux B ′. The other reflected light flux C ′ of the reflected light fluxes B ′ and C ′ converted into a signal and reflected by the beam splitter 5 is provided near the image forming position of the reflected light flux C ′. Is converted into an electric signal by the photodetector 11. It is needless to say that the reflected light to be subjected to photoelectric conversion by the photodetectors 11 and 12 may be reversed from the case described above.

The reason is that the respective photodetectors 11 and 12
, The position where the photodetectors 11 and 12 are installed is such that the two reflected light beams B ′ and C ′ that constitute the mixed light This is because one of the reflected light fluxes B ′ or C ′ is an image forming position. That is, of the two reflected light beams incident on the photodetectors 11 and 12, the reflected light beam in a state where no image is formed at the position of the photodetectors 11 and 12 has information contained in the reflected light beams. The photodetectors 11 and 12 are in a blurred state that cannot be read by the photodetectors 11 and 12.
In No. 12, information contained in the reflected light to be detected can be detected satisfactorily.

As described above, the objective lens 6 used as a constituent member of the optical pickup performs the reproducing operation of the optical disk D having the configuration originally planned as the optical disk D to be reproduced by the optical pickup. In this case, the optical pickup shown in FIG. 1 is configured such that the optical disk D having a configuration expected to be an optical disk D to be reproduced is a transparent substrate. In the case where the signal surface 15 is provided at a position (first distance) L1 from the surface 14a of the objective lens 14, the objective lens 6 is formed so that spherical aberration does not occur. In the optical pickup shown in FIG. 2, an optical disc D having a predetermined configuration as an optical disc D to be reproduced is mounted on a transparent substrate 1. The objective lens is formed so that spherical aberration does not occur when the signal surface 16 is provided at a position (a second distance) L2 from the surface 14a of the fourth surface 4a. 6 is an example in the case where 6 is used.

In the optical pickup shown in FIG.
The difference between the optical pickup shown in FIG. 1 and the optical pickup shown in FIG. An objective lens adapted to a case where the signal surface 16 is provided at a position (a second distance) L2 from the surface 14a of the transparent substrate 14. 6 is used, and accordingly, reproduction is performed on the signal surface 15 provided at a distance L1 (first distance) from the surface 14a of the transparent substrate 14 of the optical disk D. The point that the spherical aberration correcting member 9 of the objective lens is provided in the optical path (first optical path) of only the light beam B, and there is no difference between the optical pickup described with reference to FIG. ,Also, Since only the operation corresponding to the differences from the configuration described above also work only difference is, the specific detailed description thereof will be omitted.

Next, in the optical pickup shown in FIG. 3, the reproduction light beam A in the divergent light state radiated from the reproduction light source 1 is split into two by the beam splitter 2, and the two reproduction light beams B and C. One of the two reproduction light beams B and C obtained by splitting by the beam splitter 2 is one between the beam splitter 2 and the beam splitter 3, and the optical path length adjusting lens. The light passes through a first optical path provided with the light and enters the beam splitter 3. In the following description, the first
The optical path length adjusting lens 10 provided in the optical path is a collimating lens, and the reproduction light beam B incident on the beam splitter 3 from the first optical path is a parallel light beam. In the embodiment of the present invention, the above-described optical path length adjusting lens 10 is not limited to a collimating lens, and a positive (or negative) lens having a characteristic capable of performing necessary optical path length adjustment is used. May be used.

The reproduction light flux B passing through the beam splitter 3 is reflected by the beam splitter 4 in the second optical path formed between the beam splitter 3 and the objective lens 6 and enters the objective lens 6. . The reproduction light beam B incident on the objective lens 6 generates a light spot having a small diameter on the signal surface 16 provided at a distance L2 from the surface 14a of the transparent substrate 14 on the optical disk D. The signal surface 16 provided at a distance L2 from the surface 14a of the transparent substrate 14 of the optical disc D is a position of the rear focal point of the objective lens 6.

The other reproduction light beam C of the two reproduction light beams B and C obtained by being split into two by the beam splitter 2 has an optical path including total reflection mirrors 7 and 8. After passing through the optical path for length adjustment, the light enters the beam splitter 3. Spherical aberration correcting member 9
May be installed in any portion of the optical path for adjusting the optical path length configured between the beam splitter 2 and the beam splitter 3. After passing through the optical path for adjusting the optical path length, the light beam enters the beam splitter 3 and the reproduced light beam C ′ reflected by the beam splitter 3 is reflected by the beam splitter 4 in the second optical path and enters the objective lens 6. I do. Then, the reproduction light beam C ′ incident on the objective lens 6 generates a light spot with a small diameter on the signal surface 15 provided at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disc D.

The optical disk D shown in FIG. 3 has a signal surface 15 provided at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disk D, and a distance L2 from the surface 14a of the transparent substrate 14. The optical disc D to be played back by the optical pickup has a configuration in which the signal surface 16 provided at the position (1) is laminated (see FIG. 5 (c)). 5A in which the signal surface 15 is provided only at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disk D, or the transparent substrate of the optical disk D described above. 14 surface 14
Of course, a configuration having a signal surface 16 provided only at a position of a distance L2 from a as shown in FIG. 5B may be used.

As described above, the reflected light beam B 'from the minute light spot due to the reproduced light beam B formed on the signal surface 16 of the optical disk D and the reproduced light beam C formed on the signal surface 15 of the optical disk D And the reflected light beam C ′ from the minute light spot is incident on one common objective lens 6. Then, the reflected light beam B 'from the minute light spot due to the reproduced light beam B formed on the signal surface 16 of the optical disk D is emitted from the objective lens 6 as a parallel light beam B'. The reflected light beam C ′ from the minute light spot due to the reproduced light beam C imaged on the signal surface 15 at, is emitted from the objective lens 6 as a reflected light beam C ′ being converged.

As described above, of the two reflected light beams B ′ and C ′, ie, the reflected light beam B ′ in the state of a parallel light beam emitted from the objective lens 6 and the reflected light beam C ′ in the state of being converged,
The reflected light fluxes B ′ and C ′ transmitted through the beam splitter 4 are split into two by the beam splitter 5. The reflected light fluxes B 'and C' transmitted through the beam splitter 5 and the reflected light fluxes B 'and C' reflected by the beam splitter 5 are both reproduced on the signal surface 16 of the optical disk D. It is composed of a reflected light beam B ′ from a minute light spot due to the light beam B and a reflected light beam C ′ from a minute light spot due to the reproduced light beam C formed on the signal surface 15 of the optical disc D. One of the reflected light beams B ′ and C ′ reflected by the beam splitter 5 is focused by the focusing lens 13 and provided near the rear focal position of the focusing lens 13. Is converted into an electric signal by the photodetector 11
The other reflected light flux C ′ of the reflected light fluxes B ′ and C ′ transmitted through the beam splitter 5 is a photodetector 12 provided near the imaging position of the reflected light flux C ′. Is converted into an electric signal. It is needless to say that the reflected light to be subjected to photoelectric conversion by the photodetectors 11 and 12 may be reversed from the case described above, but the photoelectric conversion of the reflected light flux B ′ may be performed. It should be understood that the photodetector used in the above should be preceded by a focusing lens.

As described above, each of the photodetectors 11,
Even if the mixed light of the reflected light fluxes B ′ and C ′ is given to the light receiving unit 12, the position where the photodetectors 11 and 12 are installed is determined by the two reflected light fluxes B ′ and C forming the mixed light light. This is because one of the reflected light fluxes B ′ or C ′ is an image forming position. The reflected light beam in a state where no image is formed at the position of (1) is in such a blurred state that the information contained in the reflected light beam cannot be read by the light detectors 11 and 12, and the light detector 11 ,
In No. 12, information contained in the reflected light to be detected can be detected satisfactorily. In the optical pickup shown in FIG. 3, the optical disc D, which is originally intended as the optical disc D to be reproduced, has a signal at a position L2 (second distance) from the surface 14a of the transparent substrate 14. This is an embodiment in the case where the objective lens 6 which is made so as not to cause spherical aberration is used in the case where the configuration is such that the surface 16 is provided.

An optical disk D of a configuration originally intended as an optical disk D to be reproduced has a signal surface 15 provided at a position (first distance) L1 from the surface 14a of the transparent substrate 14. When the objective lens 6 is designed so as not to cause a spherical aberration when the configuration is as described above, the optical path length is provided in the first optical path as shown in FIG. When configuring an optical pickup having a configuration in which the adjustment lens 10 is provided, the spherical aberration correcting member 9 provided in the optical path adjustment optical path in FIG.
May be changed in the optical path on the incident light side of the optical path adjusting lens 10 provided in the first optical path provided between the beam splitter 2 and the beam splitter 3.

Next, FIG. 4 shows that the optical disk D of the configuration intended as the optical disk D to be reproduced has a signal surface 15 at a distance L1 (first distance) from the surface 14a of the transparent substrate 14. In the case of the configuration as provided, an objective lens 6 made so as not to cause spherical aberration is used, and a total reflection mirror 7 and a total reflection in an optical path for adjusting the optical path length are used. 1 shows an embodiment of an optical pickup in which a spherical aberration correcting member 9 of an objective lens and an optical path adjusting lens 10 are provided between a mirror 8 and an objective lens. In the optical pickup shown in FIG. 4, the divergent light beam A of the divergent light emitted from the light source 1 of the reproduction light is split into two by the beam splitter 2 to be two reproduction light beams B and C. One of the two reproduction light beams B and C obtained by being split into two by the beam splitter 2 described above.
Is incident on the beam splitter 3 through a first optical path formed between the beam splitter 2 and the beam splitter 3.

The reproduction light beam B that has passed through the beam splitter 3 is reflected by the beam splitter 4 in the second optical path formed between the beam splitter 3 and the objective lens 6 and enters the objective lens 6. . The reproduction light beam B incident on the objective lens 6 generates a light spot having a small diameter on a signal surface 15 provided at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disk D. The other reproduction light beam C of the two reproduction light beams B and C obtained by being split into two by the above-described beam splitter 2 is provided with total reflection mirrors 7 and 8, a spherical aberration correcting member 9 and an optical path adjusting member. The light passes through an optical path for adjusting the optical path length, which includes the lens 10, and then enters the beam splitter 3. In the following description, it is assumed that the optical path length adjusting lens 10 provided in the optical path length adjusting optical path is a collimating lens, and the reproduction light beam entering the beam splitter 3 from the optical path length adjusting optical path. C is a parallel light beam.

The optical path length adjusting lens 10 used in the embodiment of the present invention is not limited to a collimating lens, but has a positive (or positive) characteristic that can perform necessary optical path length adjustment. A negative) lens may be used. Now, the reproduction light beam C that has passed through the beam splitter 3 is reflected by the beam splitter 4 in the second optical path formed between the beam splitter 3 and the objective lens 6 and enters the objective lens 6. The reproduction light beam C incident on the objective lens 6 generates a light spot having a small diameter on the signal surface 16 provided at a distance L2 from the surface 14a of the transparent substrate 14 on the optical disk D. The signal surface 16 provided at a distance L2 from the surface 14a of the transparent substrate 14 of the optical disc D is a position of the rear focal point of the objective lens 6.

The optical disk D shown in FIG. 4 has a signal surface 15 provided at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disk D, and a distance L2 from the surface 14a of the transparent substrate 14. The optical disc D to be played back by the optical pickup has a configuration in which the signal surface 16 provided at the position (1) is laminated (see FIG. 5 (c)). 5A in which the signal surface 15 is provided only at a distance L1 from the surface 14a of the transparent substrate 14 of the optical disk D, or the transparent substrate of the optical disk D described above. 14 surface 14
Of course, a configuration having a signal surface 16 provided only at a position of a distance L2 from a as shown in FIG. 5B may be used.

As described above, the reflected light beam C 'reflected from the minute light spot by the reproduced light beam C formed on the signal surface 16 of the optical disk D and the reproduced light beam B formed on the signal surface 15 of the optical disk D are reproduced. And the reflected light flux B ′ from the minute light spot is incident on one common objective lens 6. Then, the reflected light beam C ′ from the minute light spot by the reproduced light beam C formed on the signal surface 16 of the optical disc D is emitted from the objective lens 6 as a reproduced light beam C ′ of a parallel light beam. The reflected light beam B ′ from the minute light spot due to the reproduced light beam B imaged on the signal surface 15 at, is emitted from the objective lens 6 as a reflected light beam B ′ being converged.

As described above, of the two reflected light beams C ′ and B ′ of the reflected light beam C ′ in the state of the parallel light beam emitted from the objective lens 6 and the reflected light beam B ′ of the converging state,
The reflected light fluxes C ′ and B ′ transmitted through the beam splitter 4 are split into two by the beam splitter 5. The reflected light beams C ′ and B ′ transmitted through the beam splitter 5 and the reflected light beams C ′ and B ′ reflected by the beam splitter 5 are both reproduced on the signal surface 15 of the optical disk D as described above. It comprises a reflected light beam C ′ from a minute light spot due to the light beam C and a reflected light beam B ′ from a minute light spot due to the reproduced light beam B imaged on the signal surface 16 of the optical disc D.

One of the reflected light beams C ′ and B ′ reflected by the beam splitter 5 is converged by the converging lens 13, and the rear focal position of the converging lens 13 described above. The reflected light flux C ′, which has been converted into an electric signal by the photodetector 11 provided in the vicinity and has passed through the beam splitter 5, has been described.
The other reflected light flux B ′ of B ′ is the reflected light flux B ′.
Is converted into an electric signal by the photodetector 12 provided near the image forming position. It should be noted that the above-described photodetector 11,
It is needless to say that the reflected light to be subjected to the photoelectric conversion by 12 may be reversed from the case described above, but the optical path to the photodetector used for the photoelectric conversion of the reflected light flux C ′ It goes without saying that a focusing lens should be placed in front of it.

As described above, each of the photodetectors 11,
Even if the mixed light of the reflected light fluxes C ′ and B ′ is given to the light receiving unit 12, the position where the photodetectors 11 and 12 are installed is such that the two reflected light fluxes C ′ and B constituting the mixed light light This is because one of the reflected light fluxes C ′ or B ′ is formed as an image forming position, and of the two reflected light fluxes incident on the photodetectors 11 and 12, the photodetectors 11 and 12 The reflected light beam in a state where no image is formed at the position of (1) is in such a blurred state that the information contained in the reflected light beam cannot be read by the light detectors 11 and 12, and the light detector 11 ,
In No. 12, information contained in the reflected light to be detected can be detected satisfactorily.

An optical disc D having a configuration originally intended as an optical disc D to be reproduced is provided with a signal surface 16 at a position L2 (second distance) from the surface 14a of the transparent substrate 14. When the objective lens 6 is constructed so as not to cause spherical aberration in the configuration described above, the optical path length is adjusted in the optical path adjusting optical path as shown in FIG. When an optical pickup having a configuration in which the adjustment lens 10 is provided is configured, the spherical aberration correction member 9 provided in the optical path adjustment optical path in FIG. 4 is connected to the beam splitter 2 and the beam splitter 3. The configuration may be changed so as to be provided in the first optical path configured between them.

[0049]

As is clear from the above, the optical pickup of the present invention has the following (1) to (5).
All three types of optical discs of the structure (3) can be reproduced. That is, (1) it is possible to reproduce an optical disk having a single layer structure (shown in FIG. 5A) in which the distance from the surface of the transparent substrate on which the reproduction light is incident to the signal surface is long (distance L1). Also, (2) the distance from the surface of the transparent substrate on which the reproduction light is incident to the signal surface is short (distance L
2) Reproduction of an optical disk having a single-layer structure (shown in FIG. 5B) can be performed. Further, (3) reproduction of an optical disk having a two-layer structure (shown in FIG. 5C) having different distances (distances L1 and L2) from the surface of the transparent substrate on which the reproduction light is incident to the two signal surfaces is performed. Both can be performed simultaneously.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an optical pickup of the present invention.

FIG. 2 is a block diagram illustrating a schematic configuration of an optical pickup of the present invention.

FIG. 3 is a block diagram showing a schematic configuration of an optical pickup of the present invention.

FIG. 4 is a block diagram showing a schematic configuration of an optical pickup of the present invention.

FIG. 5 is a cross-sectional view illustrating a configuration example of an optical disc.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source of reproduction light (semiconductor laser), 2-5 ... Beam splitter (half prism, half mirror), 6 ... Objective lens, 7, 8 ... Total reflection mirror, 9 ... Spherical aberration correction member of objective lens, 10 ... Lens for adjusting optical path length, 11, 12 ... Photodetector, 13 ... Focusing lens, 14 ... Transparent substrate, 14a ...
The surface of the transparent substrate 14, 15, 16, ... signal surface,

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-266429 (JP, A) JP-A-4-178931 (JP, A) JP-A-5-242551 (JP, A) JP-A-6-64551 282866 (JP, A) JP-A-6-215406 (JP, A) JP-A-7-65407 (JP, A) JP-A 8-249708 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/12-7/22

Claims (3)

(57) [Claims] An optical pickup capable of simultaneously reading information recorded on a first signal surface located at a short distance from a surface of an optical disk and a second signal surface located at a distance from a surface of the optical disk. A light source that emits a single reproduction light beam, a first beam splitter that splits and outputs a single reproduction light beam emitted from the light source, and two light beams that are output from the first beam splitter. One of the light beams passes through the first optical path whose optical path length is set short, and then passes through the second optical path.
A first optical path means for supplying to the beam splitter; and a second optical path means for supplying the other of the two light beams output from the first beam splitter to the second beam splitter via a second optical path having a longer optical path length. An optical path means, and simultaneously passing the one and the other light beams output from the second beam splitter, condensing the one light beam from the front surface side onto the first signal surface, and transmitting the other light beam. An objective lens for converging on the second signal surface from the front surface side; and a reflected light of the one light beam reflected on the first signal surface is sequentially detected via the objective lens and the second beam splitter. A first photodetector; and a second photodetector that detects reflected light of the other light beam reflected on the second signal surface via the objective lens and the second beam splitter in order. An optical pickup that features. 2. The optical pickup according to claim 1, wherein the first optical path means includes an optical path length adjusting lens for adjusting the first optical path or a spherical aberration correction member of the objective lens. 3. The optical pickup according to claim 1, wherein the second optical path means includes an optical path length adjusting lens for adjusting the second optical path, a spherical aberration correction member of the objective lens, or both. .