JPH04157635A - Optical head and optical disk device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical head capable of recording, reproducing, or erasing information signals, and an optical disk device using the optical head.

2. Description of the Related Art In recent years, in addition to read-only optical disk devices such as CD (compact disc) players, optical disk devices capable of recording and reproducing signals have been actively developed.

Generally, recording and reproduction of optical discs is performed by focusing a radiation beam from a semiconductor laser or the like onto the recording layer of the optical disc using a lens. Here, the recording layer refers to a layer that is deformed, optical constants changed, or magnetic domains formed by a focused laser beam in a recordable optical disk. In order to increase the recording density of the optical disk, it is necessary to reduce the spot diameter of this focused beam, and D has the following relationship with the numerical aperture NA of the lens and the wavelength λ of the laser beam.

λ D engineering (1) NA The above equation (1) indicates that the larger the NA, the smaller the radius, and the higher density recording is possible.

However, when a high NA lens is used, the aberration of the spot increases due to an error in the inclination of the disk called tilt. In order to suppress this, it is effective to reduce the thickness of the disk substrate of the optical disk, and for optical disks capable of high-density recording, it is preferable that the thickness of the disk substrate is thinner than that of conventional optical disks.

FIG. 6 is a schematic diagram showing how light is collected by corresponding high NA and low NA objective lenses. In FIG. 6, the optical disk (a) is a conventional CD or one having a recording density equivalent to that of a conventional CD, and where the thickness of the disk substrate is dl, for example, d+=1.degree. 2 mm. In addition, the optical disc in (b) is an optical disc that can record at a higher density than that, and if the thickness of the disc substrate is d2, d2 is designed to be smaller than d+, for example, dp = 0.3
Let it be mm.

Therefore, while a conventional CD has a disk substrate thickness of 1.2 mm, the substrate thickness of a high-density recording optical disk is, for example, 0.3 mm, and an optical head that can record or reproduce signals on such an optical disk has been developed. is considered.

On the other hand, recently, an optical head using an optical waveguide has been proposed (for example, Ura, Suhara, and Koyama, "Optical Memory Symposium' 85J, 1985. 12)."

This optical head includes an optical waveguide, a light source that inputs light into the optical waveguide, a waveguide lens that converts the guided light propagating in the optical waveguide into parallel light, and a waveguide lens formed on the surface of the guided light. A condensing grating coupler that emits the light out of the waveguide and focuses it onto the optical disk, and a photodetector that detects the return light that is reflected by the optical disk and returns into the optical waveguide via the condensing grating coupler. Therefore, compared to conventional optical heads, it can be expected to be smaller and lighter and easier to manufacture.

Therefore, as an optical head using an optical waveguide, an optical head capable of high-density recording can be considered, similar to an optical head consisting of a conventional lens optical system. In such an optical head, the condensing grating coupler is designed to correct aberrations in accordance with the thin disk substrate mentioned above, so that spherical aberration etc. do not occur when the laser beam passes through the disk substrate.

The problem that the invention aims to solve is that if an optical head using a condensing grating coupler compatible with such a thin disk substrate
Even if an attempt is made to record or reproduce a signal on an optical disc that has a 1.2 mm thick disc substrate, such as the above, the difference in the thickness of the disc substrate causes aberrations in the beam spot, making it impossible to focus the beam and recording. , making it difficult to reproduce or erase.

In other words, it is impossible to use the same head to record, play back, or erase two types of optical disks with different disk substrate thicknesses, and optical disks with thick substrates that have been produced in large quantities are not compatible with high-density recording. The problem was that recording, playback, or erasing could not be performed using the head.

In view of this, an object of the present invention is to provide an optical head capable of recording, reproducing, or erasing signals on optical disks having different disk substrate thicknesses, and an optical disk device using the same.

Means for Solving the Problems To achieve this object, the optical head and optical disk device of the present invention have a configuration including a plurality of condensing grating couplers that emit guided light out of the waveguide and condense it. ing.

Effects According to the present invention, with the above-described configuration, laser light can be focused without aberration by using different condensing grating couplers corresponding to a plurality of optical disks having different substrate thicknesses.

Embodiment In this embodiment, the thickness of the disk substrate will be explained below as two types.

FIG. 1 is a schematic perspective view showing the structure of an optical head in a first embodiment of the present invention.

In the figure, reference numeral 101 denotes the first or second optical disk, and as mentioned in the description of the conventional example, the first optical disk has a thick disk substrate (for example, 1.
In the case of the 2 mmL second optical disc, the thickness of the disc substrate is thin (for example, 0.3 mm). 102
is an information track formed on the optical disc 101. Reference numeral 1 denotes a substrate made of LtNbOa or the like, and is attached to the head base via a focusing actuator and a tracking actuator. Note that since conventionally known focusing actuators, tracking actuators, and head bases can be used, detailed explanations and illustrations will be omitted. 2 is an optical waveguide formed on a substrate 1 by TI diffusion, 3 is a first semiconductor laser coupled to the end face of this optical waveguide 2, and 4 is a first semiconductor laser 3.
This is a first waveguide lens installed on the optical path of the guided light incident on the optical waveguide 1 from the optical waveguide 1, and is, for example, a Fresnel lens manufactured by electron beam lithography. 5 is a first condensing grating coupler formed on the optical path of the parallel guided light, which emits the guided light to the outside of the optical waveguide 2;
The light is focused on the optical disc 101.

The first condensing grating coupler 5 is a curved grating having a chirp (unequal period) produced on a waveguide by electron beam direct writing or the like. 6 is a first waveguide lens 4 and a first condensing grating coupler 5
A first beam splitter 7 is provided between the optical disk 101 and separates the guided light that returns into the optical waveguide via the first condensing grating coupler 5 after being reflected by the optical disk 101. A first waveguide focusing lens 8 is placed in the optical path of the returned light separated by the optical waveguide 2 and focuses the returned light.
This is a first photodetector that detects the returned light focused by the waveguide condensing lens 7.

Similarly, 9 is a second semiconductor laser coupled to the end face of the optical waveguide 2, and 10 is a second semiconductor laser installed on the optical path of the guided light input from the second semiconductor laser 9 to the optical waveguide 1. The waveguide lens 11 is a second condensing grating coupler formed on the optical path of the parallel guided light, which emits the guided light out of the optical waveguide 2 and focuses it onto the optical disk 101 . 12 is provided between the second waveguide lens 10 and the second condensing grating coupler 11, and is connected to the optical disk 101.
A second beam splitter separates the guided light reflected by and returned to the optical waveguide via the condensing grating coupler 11 of the rear barrel 2, and 13 is in the optical path of the returned light separated by the second beam splitter 12. A second waveguide condenser lens 14 is coupled to the side surface of the optical waveguide 2 to focus the returned light, and a second waveguide condenser lens 14 is coupled to the side surface of the optical waveguide 2 to detect the return light condensed by the second waveguide condenser lens 13. This is the second photodetector.

Here, for example, the first condensing grating force, the plastic 5
is N for a wavelength of 780 nm of radiation light from a semiconductor laser.
With A=0.45, the output light can be narrowed down to the diffraction limit, and 1.
The curved chirped grating is designed to correct the aberration due to the 2 mm disk substrate, and the second condensing grating compra 11 has a NA of 0.7 to 0.8, for example.
Furthermore, it is assumed that the lens is designed to correct aberrations caused by a disk substrate having a thickness of 0.3 mm.

Further, the first beam splitter 6 and the second beam splitter 12 are installed such that their respective reflected lights become stray light and enter the other beam.

Regarding such optical waveguides and waveguide elements,
For example, "Optical Integrated Circuits" co-authored by Nishihara, Haruna, and Suhara, Ohmsha (
1985), and in the present invention, any of these known optical waveguides and waveguide elements can be used for the optical waveguide 2 and the like.

The operation of the optical head in this embodiment configured as described above will be described below.

When the optical disc 101 is a first optical disc, a driving current is passed through the first semiconductor laser 3, and the first semiconductor laser 3 receives laser light from one end surface of the optical waveguide 2, and this laser light is converted into a guided light. and shite propagation. This guided light is the first
The light is made into parallel light by the waveguide lens 4, and after passing through the first beam splitter e, it enters the first condensing grating coupler 5. The first condensing grating coupler 5 extracts the light from the optical waveguide 2 and focuses the light onto an information track 102 on the first optical disk 101 . The reflected light from the disk surface enters the optical waveguide 2 again via the first grating coupler 5 and propagates in the opposite direction as return guided light. The light is then reflected at the first beam splitter 6 toward the first waveguide condenser lens 7 .

The first waveguide condenser lens 7 focuses the returned light onto a first photodetector 8, and the first photodetector 8 records the returned light on the first optical disc 101 based on the strength and intensity distribution of the returned light. Detects servo signals such as information signals, focus error signals, and tracking error signals that have been detected and outputs them to the outside. Further, by modulating the intensity of the laser light outputted by the first semiconductor laser 3, an information signal is recorded on or erased from the first optical disc 101.

On the other hand, if the optical disc 101 is the second optical disc,
Second semiconductor laser9. Second waveguide lens 10. Second
a condensing grating coupler 11, a second beam splinter 12. Second waveguide condenser lens 13. The second photodetector 14 performs the same operation as the first optical disc described above.

Further, the substrate 1 is supported from the head base by a focusing actuator and a tracking actuator, and the position of the substrate 1 itself is controlled by the aforementioned servo signal so that the information tracks of the disk are correctly irradiated with laser light.

As described above, according to this embodiment, the thickness of the first condensing grating coupler 5 and the disk substrate of the second optical disk formed in the optical waveguide B2 corresponds to the thickness of the disk substrate of the first optical disk. By providing the second condensing grating coupler 11 compatible with the above, it can be used for each disc, so it is possible to correct the aberration of the condensed spot according to the thickness of the disc substrate and record and reproduce signals well. Or it can be deleted.

Furthermore, since an optical waveguide element including a condensing grating coupler is employed, the optical head can be made smaller and lighter.

In this embodiment, the thickness of the disk substrate is two types, but it is of course applicable to three or more types. In that case, the number of components on the substrate l may be increased accordingly.

FIG. 2 is a schematic perspective view showing the structure of an optical head in a second embodiment of the invention.

In the same figure, except for the third beam splitter 15 and the waveguide mirror 16, it has the same configuration as the optical head of the first embodiment shown in FIG. 1, and the same components are denoted by the same symbols. It is attached. That is, in the optical head of this embodiment, the optical head of the first embodiment shown in FIG. A third beam splitter 15 is installed on the optical path of the third beam splitter 15.
The first beam splitter 6 splits the guided light into two parts.
A waveguide mirror 16 is formed in the direction of the waveguide divided in a direction different from that of the waveguide and at a position where the reflected guided light passes through the second beam splitter 12.

The operation of the optical head in this embodiment configured as described above will be described below.

A drive current is passed through the first semiconductor laser 3, and the first semiconductor laser 3 receives laser light from one end face of the optical waveguide 2, and this laser light propagates as guided light. This guided light is made into parallel light by the first waveguide lens 4, and the third
The beam splitter 15 splits the transmitted light into two parts, the transmitted light and the reflected light.
The reflected light is directed by a waveguide mirror 16 to a condensing grating coupler 5, and then sent to a second beam splitter 1.
2 and enters the second condensing grating coupler 11. The subsequent operation is similar to that of the optical head in the first embodiment of the present invention.

As described above, according to this embodiment, in addition to the effects of the first embodiment described above, the guided light from one semiconductor laser is split into two by the third beam splitter 15, and each condensing grating 7 The number of semiconductor lasers used can be reduced by guiding the laser beam to the gucanoplast.

Although the present embodiment has been described assuming that the disk substrate has two types of thickness, the present invention can also be applied to three or more types of thickness. If there are N types, it is sufficient to have a configuration including N condensing grating couplers and N-1 beam splitters that split the guided light from the semiconductor laser. Here, in order to equalize the amount of laser light focused on the disk, the light amount division ratio of each beam splitter is set as follows.
It is preferable to design as follows: 1:N-1 1:N-2 1:N-3 1;1.

FIG. 3 is a schematic perspective view showing the structure of an optical head in a third embodiment of the present invention.

In the figure, a first or second optical disc 101,
The information controller 102, the substrate 1, the optical waveguide 2, the first semiconductor laser 3, and the first waveguide lens 4 are basically the same as the components in the previous embodiments, so the details will be explained below. Further explanation will be omitted. 17 is a 5AW (surf.
ce acoustic WaVe: surface acoustic unive) transducer,
It is composed of interdigital electrodes made of piezoelectric elements such as ZnO. 18 is a surface acoustic wave generated by the 5AW) runste user 17. 5 is a first condensing grating coupler formed on the optical path of the guided light diffracted by the surface acoustic wave 18 and propagated in the first direction; 11 is a second condensing grating coupler;
A second condensing grating coupler is formed on the optical path of the guided light propagating in the direction, respectively, to emit the guided light out of the optical waveguide 2 and condense it onto the optical disk 101.

19 is provided between the first waveguide lens 4 and the path of the surface acoustic wave 18, and after being reflected by the optical disk 101, the first or second condensing grating, the blur 5.
A fourth beam splitter 20 is placed in the optical path of the return light reflected by the fourth beam splitter 19, and a fourth beam splitter 20 is placed in the optical path of the return light reflected by the fourth beam splitter 19 to focus the return light. The third waveguide condenser lens 21 is a third photodetector that is coupled to the side surface of the optical waveguide 2 and detects the returned light condensed by the third waveguide condenser lens 20.

Furthermore, regarding this kind of SAW transducer,
A detailed description can be found in the above-mentioned "Optical integrated circuit", and it goes without saying that any of these known optical waveguides and waveguide elements can be used.

The operation of the optical head in this embodiment configured as described above will be described below.

The first semiconductor laser 3 receives laser light from one end face of the optical waveguide 2, and this laser light propagates as guided light. This waveguide light is made into parallel light by the first waveguide lens 4, and after passing through the fourth beam splitter 19, the SA
Surface acoustic wave 18 generated from W transducer 17
cross. At this time, the parallel guided light is this surface acoustic wave 18
The direction of propagation can be changed by acousto-optic interaction with

Since this deflection angle changes depending on the frequency of the surface acoustic wave 18, the guided light is directed to the first condensing grating coupler 5 depending on the frequency of the high frequency voltage externally applied to the SAW transducer 17. It is also possible to propagate in both directions of the second condensing grating coupler 11 (here, the frequency of the high-frequency voltage is set to f
, and f2. ). Therefore, in the case of the first optical disc, a high frequency voltage of frequency f1 is externally applied to the SAW transducer 17, and the parallel guided light is made to enter the first condensing grating coupler 5. The first condensing grating coupler 5 extends the grating to the outside of the optical waveguide 2 and focuses the light onto an information track 102 on the first optical disk 101 . The reflected light from the disk surface enters the optical waveguide 2 again via the first grating coupler 5 and propagates in the opposite direction as return guided light. After being changed in direction by the surface acoustic wave 18, it is reflected by the fourth beam splitter 19 toward the third waveguide condenser lens 20. The third waveguide condensing lens 20 condenses the returned light onto the third photodetector 21.
1 is the first optical disc 1 based on the strength and intensity distribution of the returned light.
The information signal recorded in 01, the focus error signal, the tracking error signal, and other servo signals are detected and output to the outside. Also, by modulating the intensity of the laser light output from the first semiconductor laser 3, an information signal can be recorded on the first optical disc 101. pass away

On the other hand, in the case of the second optical disc, a high frequency voltage of frequency f2 is externally applied to the transducer 17 (5 AW), and the parallel waveguide light is made incident on the second condensing grating coupler 11. The subsequent operation is similar to that of the first optical disc described above.

Further, the substrate 1 is supported from the head base by a maker actuator and a tracking actuator (not shown), and the position of the substrate 1 itself is controlled by the aforementioned servo signal so that the laser beam is ejected correctly onto the information trunk of the disk. .

As described above, according to this embodiment, in addition to the effects of the first embodiment described above, only one semiconductor laser is used, and each condensing grating coupler emits laser light at the same time. Therefore, the output power of the semiconductor laser can be efficiently extracted from the condensing grating coupler, and it is possible to provide light with better transmission efficiency than in the second embodiment described above.

Furthermore, the waveguide lens 4 and the SAW transducer 17
By installing the fourth beam splinter 19 between them, one photodetector can detect the return light from the two condensing grating couplers.

In this embodiment, the thickness of the disk substrate is set to two types, but it is of course applicable to three or more types. In that case, the number of condensing grating couplers may be increased accordingly, and the optical path may be switched using the 5AW) transducer 17 accordingly.

Next, an optical disc device equipped with the optical head of the third embodiment of the present invention described above will be explained.

FIG. 4 is a block diagram showing the configuration of an optical disc device in a fourth embodiment, and FIG. 5 is a perspective view of an optical disc cartridge used therein.

In these two figures, 101 is the first or second optical disk as in the previous embodiments, and 22 is a cartridge that stores and protects the disk, and is made of a material of any rigidity such as plastic or resin. has been done. Reference numeral 23 designates the optical head of the third embodiment of the present invention described above, which is composed of a waveguide substrate, a focus song actuator, a trunking actuator, and a head base.

24 is installed on the bottom surface of the optical disk 101, and the optical head 2
3 in the radial direction of the disk while maintaining a constant distance from the disk surface. Also, 25
is an identification hole installed on the surface of the cartridge 22.

Here, the cartridge 22 will be explained according to FIG. 5. When the stored optical disc 101 is the first optical disc, the identification hole 25 is closed, and when it is the second optical disc, it is opened. There is. Further, in the same figure, reference numeral 41 denotes a slide/jar, which is closed to prevent dust when the main body of the cartridge 22 is removed from the optical disc device.

Reference numeral 26 indicates an LED l located above the identification hole 25 when the cartridge 22 is installed in the optical disc device of this embodiment.
These are photodiodes installed at opposing positions across 22, and output detection signals to a controller 30, which will be described later. Reference numeral 28 denotes a servo circuit, which supplies driving current to the focusing actuator and tracking actuator of the optical nozzle 23 in response to the servo signal output from the optical nozzle 23, and also supplies driving current to the linear motor 24 and the spindle motor to be described later. A control signal is output to 29. 29 is a spindle motor that rotates the optical disk 101; 30 is a controller that outputs a control signal to a high frequency drive circuit 31 (described later) and controls the operation of the servo circuit 28 using the output of the photodiode 27; 31 is a controller that outputs a control signal to the controller 30; Accordingly, a high frequency drive circuit that applies a high frequency voltage to the 5AW) transducer of the optical henode 23,
32 is a signal processing circuit to which a reproduction signal reproduced by the optical head 23 is input, or a recording signal is output to the optical head 23.

The operation of the optical disc device of this embodiment configured as described above will be described below.

First, when the curl ridge 22 is installed in the optical disc device of this embodiment, the LED 26 emits light, and the photodiode 27 detects the presence or absence of transmitted light passing through the identification hole 25. If transmitted light is detected, the controller 30 determines that it is the contents of the attached cartridge 22 or the second light beam, outputs a control signal to the high frequency drive circuit 31, and outputs a high frequency voltage of frequency f2 to the light beam. 5AW) of the head 23 is applied to the transducer. Therefore, to the light, de 23
Then, laser light is irradiated from the second condensing grating coupler and condensed onto the information track of the second optical disk without aberration. At the same time, the optical nozzle 23 obtains a claw error signal and a tracking error signal from the reflected light from the disk and outputs them to the servo circuit 28. Furthermore, the information signal on the disk is reproduced and output as a reproduction signal to the signal processing circuit 32, and information is recorded on the disk according to the recording signal input from the signal processing circuit 32.

Further, the servo circuit 28 controls the spindle controller 29 to control the optical disc 101 at CLV: Con5tant.
Linear Velocity (Constantly addicted), CAV: Con5tant
Rotate with Angular Velocity (constant angular tongue/tee), etc. Also,
The servo circuit 28 focuses the laser beam on the optical disk 101 by controlling the drive currents of the focusing actuator, tiger actuator, and king actuator in accordance with servo signals such as the focus error signal and the tracking error signal output by the optical head 23. . Furthermore, the servo circuit 28 side-chains the linear motor 24 according to a command from the controller 30, and moves the optical head 23 toward the inner circumference or outer circumference of the disk.

On the other hand, when the photodiode 26 does not detect transmitted light, the controller 30 determines that the content of the cartridge 22 is the aforementioned first optical disk, and the high-frequency drive circuit 3
1 to apply a high frequency voltage of frequency f1 to the 5AW) transducer of the optical head 23. Therefore, in the optical head 23, a laser beam is irradiated from the first condensing grating coupler, and the beam is condensed onto the information track of the first optical disk without aberration. Other operations are the same as those for the second optical disc described above.

As described above, according to this embodiment, the identification hole 25 provided on the cartridge 22 and the LED 2 for detecting the opening/closing of the identification hole 25 are provided.
6 and a photodiode 27, and an optical head 23 in which two condensing grating couplers are formed on the substrate, it is possible to automatically discriminate between a plurality of optical disks with different substrate thicknesses, and to determine the substrate thickness. It is possible to focus light accordingly, and to record, reproduce, or erase signals satisfactorily.

Note that although the optical disk device of this embodiment uses the optical head of the third embodiment of the present invention as the optical head 23, the optical head of the first embodiment of the present invention is used instead. Even if the optical head in the second embodiment is used, the same effect can be obtained.

Although the present embodiment has been described assuming that the disk substrate has two types of thickness, the present invention can also be applied to three or more types of thickness. In this case, for example, by increasing the number of identification holes 25, three or more types of optical discs can be identified. For example, by providing n identification holes, 2 n types of optical discs can be identified.

In addition, although the identification hole 25 provided on the cartridge 22, the LED 2e, and the photodiode 27 are used as disc discrimination means, the identification hole 25 may be colored with a paint having a different reflectance, or the LED 26 and the photodiode 2 may be
A mechanical switch or the like may be used instead of 7.

Furthermore, the difference in the thickness of the disk substrate may be directly determined by the laser beam reflected from the disk while the cartridge 22 is placed in a lunar chair. For example, in a focusing optical system compatible with a thin substrate, it is usually impossible to obtain a tracking error signal from an optical disk with a thick substrate due to spherical aberration of the focused beam.

Therefore, optical discs of two thicknesses can be determined from no tracking error signal. In this case, a detector such as an LED or a photodiode is not required, which has the advantage of simplifying the apparatus.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, an optical head and an optical disk device capable of recording, reproducing, or erasing information on a plurality of optical disks having different substrate thicknesses can be realized, and the practical effects thereof are significant.

[Brief explanation of drawings]

FIG. 1 is a schematic perspective view showing the structure of an optical head in a first embodiment of the invention, FIG. 2 is a schematic perspective view showing the structure of an optical head in a second embodiment of the invention, and FIG. A schematic perspective view showing the structure of an optical head in a third embodiment of the present invention, FIG. 4 is a block diagram showing the structure of an optical disk device in a fourth embodiment of the present invention, and FIG. 5 is a cartridge for an optical disk used therein. FIG. 6 is a schematic diagram showing a cross section of an optical disk with a conventional recording density and a higher recording density, and the state of light condensing by an objective lens. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Optical waveguide, 3... First semiconductor laser, 4... First waveguide lens,
5... first condensing grating coupler, 6...
1st beam splitter, 7... 1st waveguide condensing lens, 8... 1st photodetector, 9... 2nd
semiconductor laser, 10... second waveguide lens,
11... second condensing grating coupler,
12... second beam splitter, 13... second
waveguide condenser lens, 14... second photodetector,
15... Third beam splitter, 16... Waveguide mirror, 17... SAW transducer,
18... Surface acoustic wave, 19... Fourth beam splitter, 20... Third waveguide condenser lens, 21... Third photodetector, 22... Cartridge, 23. ...Optical head, 24...Linear motor, 25...Identification hole, 26...LED
, 27... photodiode, 28...
Servo circuit, 29... spindle motor, 3
0... Controller, 31... High frequency drive circuit,
32... Signal processing circuit, 101... First or second optical disc. Agent's name: Patent attorney Akira Kokaji, 2 lawyers
Figure 6 (αn #11 / High NA Lens-

Claims (9)

[Claims] (1) An optical head that includes a plurality of condensing grating couplers that emit guided light out of the waveguide and condense it. (2) The optical head according to claim 1, further comprising a plurality of light sources that cause guided light to enter the optical waveguide. (3) The optical head according to claim 1, further comprising: a light source that makes guided light enter the optical waveguide; and branching means that divides the guided light into a plurality of branched guided lights and makes each of them enter a condensing grating coupler. (4) A light source for making guided light enter an optical waveguide; and a deflection means for changing the propagation direction of the guided light within the optical waveguide and making it enter one of a plurality of grating couplers. light head. (5) Claims 1 and 2, wherein the condensing grating coupler condenses the emitted light onto the optical disk without aberration.
, 3 or 4. (6) The optical head according to claim 5, wherein the plurality of condensing grating couplers condense light onto a plurality of optical disks each having a substrate having a different thickness without aberration. (7) An optical disc device comprising the optical head according to claim 6, wherein one of the plurality of condensing grating couplers of the optical head is selected depending on the thickness of the substrate of the optical disc. (8) The optical disc device according to claim 7, further comprising disc discrimination means for discriminating between a plurality of optical discs having different substrate thicknesses. (9) The optical disc apparatus according to claim 8, wherein the disc discrimination means comprises a cartridge for storing the optical disc, a discrimination mark installed on the cartridge, and a detection means for detecting the state of the discrimination mark.