Optical recording/reproducing apparatus for optical disks with various disk substrate thicknesses

Abstract

An optical disc apparatus for recording, reproducing or erasing an information signal by converging a light flux onto a recording layer through a transparent substrate. The apparatus includes one or a plurality of optical heads having a plurality of objective lenses whose aberrations have respectively been corrected for a plurality of disc substrates of different thicknesses, a cartridge for enclosing the optical disc, a discrimination hole which is formed on the cartridge, and a sensor for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal. In accordance with the result of the discrimination as to the thickness of the loaded optical disc, the objective lens, in which the occurrence of the aberration is smallest, is used, so that the information signal can preferably be recorded, reproduced or erased onto/from the optical discs having different substrate thicknesses. Instead of an optical head having objective lenses, an optical head having a waveguide and a plurality of converging grating couplers whose aberrations have respectively been corrected for a plurality of disc substrates of different thicknesses is provided to achieve the same object. An optical recording/reproducing apparatus for recording, reproducing or erasing an information signal onto/from an optical disc having at least a transparent substrate and an information layer by converging a light flux on the information layer through the transparent substrate. The apparatus includes optical converging devices, with different numerical apertures, focal distances or working distances, such as objective lenses or grating lenses, for performing aberration correction over a plurality of transparent substrates of different thicknesses of optical discs and a device for discriminating the type of optical disc based on the thicknesses of the transparent substrates. One of the optical converging devices that generates the least aberration is used according to a result of the discrimination of the thickness of the optical disk loaded in the apparatus to cause the information signal to be suitably recorded, reproduced or erased onto/from the optical discs having the different substrate thicknesses.

Description

In FIGS. 4A and 4B, respective focal distances FD and working distances WD are shown.
1:N−2
1:N−3
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1:1

FIG. 13 is a schematic perspective view showing a construction of an optical head of an optical disc apparatus according to the seventh embodiment of the invention. FIG. 14 is a block diagram showing a construction of the optical disc apparatus.

A construction of the optical head in FIG. 13 will be first described in detail.

In the diagram, since the optical disc 1, information track 200, substrate 61, optical waveguide 62, first semiconductor laser 63 and first waveguide lens 64 are fundamentally identical to the component elements in the seventh optical head 80 shown in FIG. 12, their detailed descriptions are omitted here. Reference numeral 91 denotes an SAW (surface acoustic wave) transducer arranged on the optical waveguide 62 so that a surface acoustic wave generated by the SAW transducer crosses the optical path of the waveguide light emitted from the first waveguide lens 64. The SAW transducer 91 is constructed by a cross finger electrode comprising a piezoelectric transducer of ZnO or the like. Reference numeral 92 indicates a surface acoustic wave generated by the SAW transducer 91; 96 a third converging grating coupler formed on the optical path of the waveguide light which has been diffracted by such a surface acoustic wave 92 and propagates in the first direction; and 97 a fourth converging grating coupler which is likewise formed on the optical path of the waveguide light propagating in the second direction. Each of the couplers 96 and 97 emits the waveguide light to a region out of the optical waveguide 62 and converges onto the optical disc 1. Reference numeral 93 denotes a fourth beam splitter which is arranged between the first waveguide lens 64 and the progressing path of the surface acoustic wave 92 and reflects the waveguide light returned into the optical waveguide 62 through the third or fourth converging grating couplers 96 and 97 after it had been reflected by the optical disc 1. Reference numeral 94 denotes a third waveguide converging lens which is arranged on the optical path of the return light reflected by the fourth beam splitter 93 and converges the return light and 95 indicates a third photo detector which is coupled to the side surface of the optical waveguide 62 and detects the return light converged by the third waveguide converging lens 94.

The above SAW transducer has also been described in detail in the foregoing “Optical Integrated Circuit” or the like and both of the well-known optical waveguide and waveguide type device described in the above literature can be also obviously used.

The operation of the optical head in the seventh embodiment with the above construction will now be described hereinbelow.

The first semiconductor laser 63 emits a laser beam from one edge surface of the optical waveguide 62. The laser beam propagates as a waveguide light. The waveguide light is converted into the parallel light by the first waveguide lens 64 and transmits through the fourth beam splitter 93. After that, the light transverses the surface acoustic wave 92 generated from the SAW transducer 91. At this time, the propagating direction of the parallel waveguide light is changed by an acoustic optical interaction with the surface acoustic wave 92. Since a deflection angle at this time changes in accordance with a frequency of the surface acoustic wave 92, the waveguide light can be propagated in any one of the directions of the third and fourth converging grating couplers 96 and 97 in accordance with frequencies of high-frequency voltages which are applied to the SAW transducer 91 from the outside (it is now assumed that the frequencies of the high-frequency frequency voltages are set to f₁ and f₂, respectively). In the case of the first optical disc, therefore, the high-frequency voltage of the frequency f₁ is applied to the SAW transducer 91 from the outside, thereby allowing the parallel waveguide light to enter the third converging grating coupler 96. The third converging grating coupler 96 extracts the parallel waveguide light to a region out of the optical waveguide 62 and converges onto the information track 200 on the first optical disc 1. The reflected light from the disc surface again enters the optical waveguide 62 through the third grating coupler 96 and propagates as a return waveguide light in the opposite direction. The progressing direction of the waveguide light is changed by the surface acoustic wave 92 and, after that, the waveguide light is reflected in the direction of the third waveguide converging lens 94 by the fourth beam splitter 93. The third waveguide converging lens 94 converges the return light to the third photo detector 95. The third photo detector 95 detects the information signal and the servo signals such as focusing error signal, tracking error signal, and the like which have been recorded on the first optical disc 1 on the basis of an intensity and an intensity distribution of the return light and generates to the outside. By modulating the driving current which is supplied to the first semiconductor laser 63, an eighth optical head 90 emits the intensity modulated laser beam, thereby recording or erasing the information signal onto/from the first optical disc 1.

On the other hand, in the case of the second optical disc, the high-frequency voltage of the frequency f₂ is applied to the SAW transducer 91 from the outside, thereby allowing the parallel waveguide light to enter the fourth converging grating coupler 97. The subsequent operations are executed in a manner similar to those in the case of the first optical disc.

The substrate 61 is supported from the head base by a focusing actuator and a tracking actuator (not shown). The position of the substrate 61 itself is controlled by the servo signals so that the laser beam is accurately irradiated onto the information track 200 on the disc.

An optical disc apparatus having the eighth optical head 90 mentioned above will now be described with reference to FIG. 14.

In the diagram, the optical disc 1, cartridge 2, first linear motor 4, discrimination hole 7, LED 8, photo diode 9, tracking control circuit 11, focusing control circuit 13, linear motor control circuit 15, spindle control circuit 17, spindle motor 18, signal processing circuit 19, LD driving circuit 20 and system controller 22 are the same as those in the optical disc apparatus in the third embodiment according to the invention. Reference numeral 90 denotes the eighth optical head which is constructed by the waveguide substrate, focusing actuator, tracking actuator, head base and the like. Reference numeral 85 denotes a constant voltage generating circuit which receives a control signal from the system controller 22 and generates a predetermined voltage V_i. Reference numeral 86 denotes a V/f converting circuit which receives the voltage V_i from the constant voltage generating circuit 85 and generates a high-frequency signal of a frequency f which is proportional to V_i. The V/f converting circuit 86 generates a high-frequency signal of the frequency f₁ when the input voltage V_i=V₁ and generates a high frequency signal of the frequency f₂ when V_i=V₂. Reference numeral 87 denotes an SAW driving circuit to apply a high-frequency voltage of the same frequency as the frequency f of the high-frequency signal supplied from the V/f converting circuit 86 to the SAW transducer 91 of the eighth optical head 90.

The operation of the optical disc apparatus in the seventh embodiment with the above construction will now be described hereinbelow.

First, if the cartridge 2 enclosing the second optical disc has been loaded into the optical disc apparatus of the seventh embodiment, the system controller 22 determines that the disc in the loaded cartridge 2 is the second optical disc by the detection signal of the photo diode 9, so that the controller 22 generates a control signal to the constant voltage generating circuit 85 so as to generate the voltage V₂. The V/f converting circuit 86 converts the input voltage V₂ into the frequency f₂, so that the SAW driving circuit 87 applies the high-frequency voltage of the frequency f₂ to the SAW transducer 91 of the eighth optical head 90. Therefore, in the eighth optical head 90, the laser beam is irradiated from the second converging grating coupler 97 and is converged without an aberration onto the information track 200 on the second optical disc having the disc substrate of the thickness d₂. At the same time, the third photo detector 95 of the eighth optical head 90 detects a focusing error signal and a tracking error signal from the reflected light from the optical disc and supplies to the tracking control circuit 11 and the focusing control circuit 13. Further, the information signal on the disc is supplied to the signal processing circuit 19 and the spindle control circuit 17.

On the other hand, in the case of the first optical disc, the system controller 22 generates a control signal to the constant voltage generating circuit 85 so as to generate the voltage V₁. The V/f converting circuit 86 converts the input voltage V₁ into the frequency f₁, so that the SAW driving circuit 87 applies the high-frequency voltage of the frequency f₁ to the SAW transducer 91 of the eighth optical head 90. Therefore, in the eighth optical head 90, a laser beam is emitted from the first converging grating coupler 96 and is converged without an aberration onto the information track 200 on the first optical disc having the disc substrate of the thickness d₁. The other operations are executed in a manner similar to those in the case of the foregoing second optical disc.

According to the embodiment as mentioned above, in addition to the effects of the above sixth embodiment, the number of semiconductor lasers which are necessary in the eighth optical head 90 is only one and each of the converging grating couplers does not simultaneously emit the laser beam, so that an emission power of the semiconductor laser can be efficiently taken out of the converging grating coupler. That is, the optical head having a transfer efficiency better than that of the seventh optical head 80 in the foregoing sixth embodiment can be provided.

Further, by arranging the fourth beam splitter 93 between the waveguide lens 64 and the SAW transducer 91, the return lights from the two converging grating couplers can be detected by one photo detector.

Although the number of thicknesses of the disc substrates has been set to two kinds of thicknesses in the embodiment, the invention can be also obviously applied to three or more kinds of thicknesses of the disc substrates. In such a case, the number of converging grating couplers is increased in accordance with the number of kinds of thicknesses and the optical paths are switched by the SAW transducer 91 in accordance with the increased number of such couplers.

An optical disc apparatus in the eighth embodiment of the invention will now be described.

FIG. 15 is a block diagram showing a construction of the optical disc apparatus in the eighth embodiment. In the diagram, reference numeral 1 denotes the first or second optical disc; 2 the cartridge; 4 the linear motor; 7 the discrimination hole; 8 the LED; 9 the photo diode; 13 the focusing control circuit; 15 the linear motor control circuit; 17 the spindle control circuit; 18 the spindle motor; 19 the signal processing circuit; 20 the LD driving circuit; 22 the system controller; 85 the constant voltage generating circuit; 86 the V/f converting circuit; and 87 the SAW driving circuit. The above component elements are the same as those in the optical disc apparatus in the seventh embodiment of FIG. 14 and their detailed descriptions are omitted here. Reference numeral 90 denotes an optical head which is substantially the same as the eighth optical head 90 mentioned above except that the optical head in the eighth embodiment does not have a tracking actuator. Therefore, the optical head in FIG. 15 is also referred to as an eighth optical head 90 hereinafter for convenience of explanation. Reference numeral 100 denotes a tracking error detecting circuit which receives a tracking error signal from the third photo detector 95 of the eighth optical head 90 and generates a tracking error voltage V_TE to an adder 101, which will be explained hereinafter. Reference numeral 101 denotes the adder. The voltage V_TE which is generated from the tracking error detecting circuit 100 and the voltage V_i which is generated from the constant voltage generating circuit 85 are supplied to the adder 101, so that the adder generates a voltage V₀ (V₀=V_TE+V_i) to the V/f converting circuit 86. The V/f converting circuit 86, SAW driving circuit 87, tracking error detecting circuit 100, and adder 101 construct a tracking control circuit 102. That is, it is the inventive point of the eighth embodiment that the tracking control is executed by using the SAW transducer 91 of the eighth optical head 90.

The principle of the tracking control of the eighth embodiment will now be described hereinbelow with reference to the drawings. FIG. 16 is an enlarged schematic perspective view of the converging grating coupler, SAW transducer, and portion where a surface acoustic wave has been formed. The waveguide light which enters the converging grating coupler is oscillated between solid lines and broken lines in accordance with a microchange of the frequency of the surface acoustic wave. Such an oscillation angle is called a deflection angle (shown by θ). Therefore, the emission light from the converging grating coupler is also oscillated and the converged spot moves. Since the deflecting angle θ changes in almost proportional to the frequency of the surface acoustic wave, by changing the frequency in accordance with the tracking error amount, the converged spot can be accurately positioned onto the information track.

The operation of the optical disc apparatus of the embodiment constructed as shown in FIG. 16 will now be described hereinbelow. First, if the disc in the loaded cartridge 2 is the second optical disc, the system controller 22 controls the constant voltage generating circuit 85 so as to set the output voltage V_i into V₂. The output voltage V_TE of the tracking error detecting circuit 100 has been initialized to “0”. The adder 101 adds the voltages V_i and V_TE and generates the voltage V₀ (=V₂) to the V/f converting circuit 86. The V/f converting circuit 86 changes a frequency f_s of an output signal in accordance with the input voltage V₀. The optical disc apparatus has been designed in a manner such that the signal of a frequency f_s(=f₁) is generated when V₀=V₁ and the signal of a frequency f_s(=f₂) is generated when V₀=V₂ and the frequency f_s changes in proportion to the input voltage V₀. Therefore, the V/f converting circuit 86 supplies a high-frequency signal of the frequency f₂ to the SAW driving circuit 87. The SAW driving circuit 87 applies a high-frequency voltage of the frequency f₂ to the SAW transducer 91 of the eighth optical head 90. In the eighth optical head 90, consequently, the laser beam is emitted from the fourth converging grating coupler 97 and is converged without an aberration onto the information track on the second optical disc. At the same time, in the eighth optical head 90, the reflected light from the disc is detected by the third photo detector 95. A tracking error signal is supplied to the tracking error detecting circuit 100. A focusing error signal is supplied to the focusing control circuit 13. The information signal is supplied to the spindle control circuit 17 and the signal processing circuit 19. The tracking error detecting circuit 100 produces the tracking error voltage V_TE in accordance with a track deviation amount of the converged spot on the information track 200 and supplies to the adder 101. The adder 101 sends the output voltage V₀=V₂+V_TE to the V/f converting circuit 86 as mentioned above. In accordance with the output voltage V₀, the output signal frequency f_s of the V/f converting circuit 86 is deviated from the frequency f₂ by a value corresponding to the tracking error (assumes d_f). As mentioned above, when the frequency of the driving voltage to the SAW transducer 91 changes, the emitting position of the light from the fourth converging grating coupler 97 changes and the position of the converged spot on the optical disc 1 changes for the track. Therefore, by setting a converting equation between V₀ and f_s of the V/f converting circuit 86 so as to allow the converged spot on the optical disc 1 to approach the track, the tracking error is eliminated. The other operations are executed in a manner similar to those of the optical disc apparatus in the seventh embodiment.

On the other hand, in the case of the first optical disc, the system controller 22 controls the constant voltage generating circuit 85, thereby setting the output voltage V_i into V₁. Thus, the V/f converting circuit 86 generates a high-frequency signal of the frequency f₁ to the SAW driving circuit 87 and the SAW driving circuit 87 applies a high-frequency voltage of the frequency f₁ to the SAW transducer 91 of the eighth optical head 90. Consequently, in the eighth optical head 90, the laser beam is emitted from the third converging grating coupler 96 and is converged without an aberration onto the information track 200 on the first optical disc. At the same time, the tracking error detecting circuit 100 supplies the tracking error voltage V_TE to the adder 101 from the input signal T₁. The input voltage of the V/f converting circuit 86 is set to V₀=V₁+V_TE and the tracking error can be eliminated in a manner similar to the case of the second optical disc.

FIG. 17 is a graph showing the principle of the tracking control of the embodiment and shows the relations among the V₀ and f_s and the deflection angle of the waveguide light in the eighth optical head 90. As shown in the graph, by varying the V₀ and f_s by only an amount which is proportional to the tracking error signal from V₁, accordingly, f₁ as a center in the case of the first optical disc or by only an amount which is proportional to the tracking error signal from V₂, accordingly, f₂ as a center in the case of the second optical disc, the oscillation angle of the waveguide light can be finely varied. Therefor, by varying the emitting positions of the light beams from the two converging grating couplers, the converged spot can be allowed to trace on the track.

According to the eight embodiment as mentioned above, in addition to the effects of the foregoing seventh embodiment, the change-over of the waveguide lights which enter the converging grating couplers and the tracking control can be executed by the SAW transducer 91. Thus, the optical head can be simplified and the number of manufacturing steps can be reduced.

Since the surface acoustic wave 92 is located between the fourth beam splitter 93 and the two converging grating couplers, the return waveguide light from the optical disc 1 is not influenced by the tracking control on the optical path after the surface acoustic wave 92. Therefore, the converging position on the third photo detector is not moved by the tracking control, so that a deterioration in photo detection signal can be prevented.

In the embodiment, although the SAW transducer has been used as both of the optical path switching means and the optical path deflecting means for tracking control, the SAW transducer can be also provided for the optical head only for the tracking control. For instance, it is also possible to form the SAW transducer for the sixth optical head 60 in the fifth embodiment or the seventh optical head 80 in the sixth embodiment and to execute the tracking control.

Claims

1. An optical recording/reproducing apparatus for recording, reproducing or erasing an information signal by converging a light flux onto/from a recording layer through a transparent disc substrate, comprising:

(a) N optical heads, N being greater than or equal to 2, each comprising:

light emitting means,

objective lenses, whose aberrations have respectively been corrected for said N disc substrates having different thicknesses, each for converging the light flux which is emitted from the light emitting means onto the optical disc, and

a plurality of photo detecting means each for detecting the reflected light from the optical disc;

(b) N optical head moving means which are arranged below the optical disc and move the N optical heads in the radial direction of the optical disc;

(c) disc discriminating means for discriminating the thickness of the disc substrate of the loaded optical disc and for generating a discrimination signal in accordance with the result of the discrimination; and

(d) control means for selecting the optical head having the objective lens in which the occurrence of the aberration due to the disc substrate is smallest in accordance with the discrimination signal,

wherein the selected optical head records, reproduces or erases the information signal onto/from the optical disc.

2. An apparatus according to claim 1, further comprising backward moving means for moving the non-selected optical heads to the outside of the optical disc for a period of time when the optical head which has been selected by the control means is recording, reproducing, or erasing the information signal.

3. An apparatus according to claim 1, wherein said disc discriminating means comprises:

a cartridge for enclosing the optical disc;

a discrimination hole which is formed on the cartridge and whose opening/closing state differs in correspondence to the thickness of the disc substrate of the optical disc; and

detecting means for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal.

4. An apparatus according to claim 2, wherein said disc discriminating means comprises:

a cartridge for enclosing the optical disc;

a discrimination hole which is formed on the cartridge and whose opening/closing state differs in correspondence to the thickness of the disc substrate of the optical disc; and

detecting means for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal.

5. An apparatus according to claim 1, wherein numerical apertures of at least two or more of said N objective lenses differ.

6. An apparatus according to claim 2, wherein numerical apertures of at least two or more of said N objective lenses differ.

7. An optical recording/reproducing apparatus for recording, reproducing or erasing an information signal by converging a light flux onto/from a recording layer through a transparent disc substrate, comprising:

(a) an optical head having N, N being greater than or equal to 2, converging optical systems each comprising:

light emitting means,

objective lenses, whose aberrations have respectively been corrected for said N disc substrates having different thicknesses, each for converging the light flux which is emitted from the light emitting means onto the optical disc, and

a plurality of photo detecting means each for detecting the reflected light from the optical disc;

(b) optical head moving means which is arranged below the optical disc and moves the optical head in the radial direction of the optical disc;

(c) disc discriminating means for discriminating the thickness of the disc substrate of the loaded optical disc and for generating a discrimination signal in accordance with the result of the discrimination; and

(d) control means for allowing the light emitting means, which belongs to the converging optical system in which the occurrence of the aberration due to the disc substrate is smallest in accordance with the discrimination signal, to emit light,

wherein the selected converging optical system records, reproduces or erases the information signal onto/from the optical disc.

8. An apparatus according to claim 7, wherein said disc discriminating means comprises:

a cartridge for enclosing the optical disc;

a discrimination hole which is formed on the cartridge and whose opening/closing state differs in correspondence to the thickness of the disc substrate of the optical disc; and

detecting means for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal.

9. An apparatus according to claim 7, wherein numerical apertures of at least two or more of said N objective lenses differ.

10. An optical recording/reproducing apparatus for recording, reproducing or erasing an information signal by converging a light flux onto/from a recording layer through a transparent disc substrate, comprising:

(a) an optical head including:

light emitting means,

light flux dividing means which are arranged in the light flux from the emitting means and divide the emitted light flux into N, N being greater than or equal to 2, light fluxes and deflect in different directions,

N objective lenses, whose aberrations have respectively been corrected for said N disc substrates having different thicknesses, for respectively converging said N light fluxes onto the optical disc,

light flux selecting means for selecting one of the N light fluxes divided by the light flux dividing means and for allowing said light flux to pass, and

photo detecting means for detecting the light fluxes reflected by the optical disc;

(b) optical head moving means which is arranged below the optical disc and moves the optical head in the radial direction of the optical disc;

(c) disc discriminating means for discriminating the thickness of the disc substrate of the loaded optical disc and for generating a discrimination signal in accordance with the result of the discrimination; and

(d) control means for generating a control signal to the light flux selecting means in accordance with the discrimination signal and for selecting the light flux which passes through the objective lens in which the occurrence of the aberration due to the disc substrate is smallest,

wherein the optical head records, reproduces or erases the information signal onto/from the optical disc by the selected light flux.

11. An apparatus according to claim 10, wherein said disc discriminating means comprises:

a cartridge for enclosing the optical disc;

a discrimination hole which is formed on the cartridge and whose opening/closing state differs in correspondence to the thickness of the disc substrate of the optical disc; and

detecting means for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal.

12. An apparatus according to claim 10, wherein numerical apertures of at least two or more of said N objective lenses differ.

13. An optical recording/reproducing apparatus for recording, reproducing or erasing an information signal by converging a light flux onto/from a recording layer through a transparent disc substrate, comprising:

(a) an optical head including:

an optical waveguide formed on a substrate,

N light emitting means each for emitting a waveguide light into said optical waveguide, N being greater than or equal to 2,

N converging grating couplers, whose aberrations have respectively been corrected for said N disc substrates having different thicknesses, each for emitting the waveguide light supplied from said N light emitting means to the outside of the optical waveguide and for allowing the reflected light from the optical disc to enter, and

N photo detecting means each for detecting reflected light and for generating an information signal;

(b) optical head moving means which is arranged below the optical disc and moves the optical head in the radial direction of the optical disc;

(c) selecting means for selecting the light emitting means to be allowed to emit the light from among the N emitting means;

(d) disc discriminating means for discriminating the thickness of the disc substrate of the loaded optical disc and for generating a discrimination signal according to the result of the discrimination; and

(e) control means for generating a control signal in accordance with the discrimination signal, for providing said control signal to said selecting means and for allowing the light emitting means for emitting the waveguide light into the converging grating coupler in which the occurrence of the aberration due to the disc substrate is smallest,

wherein the optical head records, reproduces or erases the information signal onto/from the optical disc by the light flux from the selected light emitting means.

14. An apparatus according to claim 13, wherein said disc discriminating means comprises:

a cartridge for enclosing the optical disc;

a discrimination hole which is formed on the cartridge and whose opening/closing state differs in correspondence to the thickness of the disc substrate of the optical disc; and

detecting means for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal.

15. An apparatus according to claim 13, wherein numerical apertures of at least two or more of the N converging grating couplers differ.

16. An optical recording/reproducing apparatus for recording, reproducing or erasing an information signal by converging a light flux onto/from a recording layer through a transparent disc substrate, comprising:

(a) an optical head including:

an optical waveguide formed on a substrate,

light emitting means for emitting a waveguide light into said optical waveguide,

light flux dividing means for dividing the waveguide light emitted from the light emitting means into N divided waveguide lights, N being greater than or equal to 2,

said N converging grating couplers, whose aberrations have respectively been corrected for said N disc substrates having different thicknesses, each for emitting each of said N divided waveguide lights to the outside of the optical waveguide and for allowing the reflected light from the optical disc to enter, and

N photo detecting means for respectively detecting said reflected lights from the N converging grating couplers and for generating information signals;

(b) optical head moving means which is arranged below the optical disc and moves the optical head in the radial direction of the optical disc;

(c) output switching means for selecting and outputting one of the output signals of said N photo detecting means;

(d) disc discriminating means for discriminating the thickness of the disc substrate of the loaded optical disc and for generating a discrimination signal in accordance with the result of the discrimination; and

(e) control means for generating a control signal to the output switching means in accordance with the discrimination signal and for selecting the photo detecting means into which the waveguide light enters from the converging grating coupler in which the occurrence of the aberration due to the disc substrate is smallest.

17. An apparatus according to claim 16, wherein said disc discriminating means comprises:

a cartridge for enclosing the optical disc;

a discrimination hole which is formed on the cartridge and whose opening/closing state differs in correspondence to the thickness of the disc substrate of the optical disc; and

detecting means for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal.

18. An apparatus according to claim 16, wherein numerical apertures of at least two or more of the N converging grating couplers differ.

19. An optical recording/reproducing apparatus for recording, reproducing or erasing an information signal by converging a light flux onto/from a recording layer through a transparent disc substrate, comprising:

(a) an optical head including:

an optical waveguide formed on a substrate,

light emitting means for emitting a waveguide light into said optical waveguide,

optical path switching means which is arranged on an optical path of said waveguide light and switches the propagating direction of the waveguide light in N directions in accordance with a control signal, N being greater than or equal to 2,

N converging grating couplers, whose aberrations have respectively been corrected for said N disc substrates having different thicknesses and which are respectively arranged in said N propagating directions which are switched by said optical path switching means and emit the waveguide light to the outside of the optical waveguide and allow the reflected light from the optical disc to enter, and

photo detecting means for detecting the reflected light and generating an information signal;

(b) optical head moving means which is arranged below the optical disc and moves the optical head in the radial direction of the optical disc;

(c) disc discriminating means for discriminating the thickness of the disc substrate of the loaded optical disc and for generating a discrimination signal in accordance with the result of the discrimination; and

(d) control means for generating a control signal to the optical path switching means in accordance with the discrimination signal and for switching the propagating direction of the waveguide light from the light emitting means to the direction of the converging grating coupler in which the occurrence of the aberration due to the disc substrate is smallest,

wherein the optical head records, reproduces or erases the information signal onto/from the optical disc by the light flux emitted from the selected converging grating coupler.

20. An apparatus according to claim 19, wherein said optical path switching means combines deflecting means for changing the propagating direction of the waveguide light by a deflection angle according to a input signal,

and wherein said apparatus comprises:

tracking error detecting means for detecting a tracking error amount of a converged spot which has been converged onto the optical disc and for generating a tracking error signal; and

tracking control means for changing the input signal to the deflecting means in accordance with said tracking error signal and for eliminating the tracking error of the converged spot.

21. An apparatus according to claim 19, wherein said disc discriminating means comprises:

a cartridge for enclosing the optical disc;

a discrimination hole which is formed on the cartridge and whose opening/closing state differs in correspondence to the thickness of the disc substrate of the optical disc; and

detecting means for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal.

22. An apparatus according to claim 20, wherein said disc discrimination means comprises:

a cartridge for enclosing the optical disc;

a discrimination hole which is formed on the cartridge and whose opening/closing state differs in correspondence to the thickness of the disc substrate of the optical disc; and

detecting means for detecting the opening/closing state of the discrimination hole and for generating a discrimination signal.

23. An apparatus according to claim 19, wherein numerical apertures of at least two or more of the N converging grating couplers differ.

24. An apparatus according to claim 20, wherein numerical apertures of at least two or more of the N converging grating couplers differ.

25. A method of recording/reproducing an information signal onto/from any of N types (where N≧2) of optical discs having first layers of different thicknesses, each of said optical discs having at least said first layer which is transparent and a second layer which is for storing information, said method comprising:

(a) emitting a light flux from a semiconductor laser,

(b) converging said light flux to a light spot on said second layer of one disc of said N types of optical discs by employing a converging optical system,

(c) receiving said light flux reflected from said one disc by a photo detector,

(d) generating an output signal from said photo detector in accordance with said received light flux, and

(e) discriminating the type of said one disc among said N types of optical discs by said output signal from said photo detector, and changing a diameter of said light spot in accordance with the thickness of said first layer of said one disc.

26. The method according to claim 25, wherein step (b) comprises operating said converging optical system to converge said light spot in accordance with the relation D∝λ/NA, where D is the diameter of the light spot, λ is the wavelength of the light flux generated by the semiconductor laser, and NA is the numerical aperture of the converging optical system.

27. The method according to claim 25, further comprising operating a signal processing unit to generate, responsive to one of (i) receipt of a reproduction signal, corresponding to said output signal, from said photo detector and (ii) receipt of recording data for recording on said one disk, a signal for performing one of a reproducing operation and a recording operation on said one disc; and controlling generation of the output signal of said signal processing unit.

28. A method of recording/reproducing an information signal onto/from any of N types (where N≧2) of optical discs having first layers of different thicknesses, each of said optical discs having at least said first layer which is transparent and a second layer which is for storing information, said method comprising:

(a) emitting a light flux from a semiconductor laser,

(b) operating a converging optical system to converge said light spot with a diameter D1 on said second layer of a first disc of said optical discs, said first disc having a first layer of thickness d1, and to converge said light spot with a diameter D2 on said second layer of a second disc of said optical discs, said second disc having a first layer of thickness d2 larger than said thickness d1, wherein D1 is smaller than D2,

(c) receiving said light flux reflected from said first and second discs by a photo detector,

(d) generating an output signal from said photo detector in accordance with said received light flux, and

(e) discriminating the type of said first and second discs among said N types of optical discs by said output signal from said photo detector.

29. The method according to claim 28, wherein said first disc has a higher recording density than that of said second disc.

30. The method according to claim 28, further comprising operating a signal processing unit to generate, responsive to one of (i) receipt of a reproduction signal, corresponding to said output signal, from said photo detector and (ii) receipt of recording data for recording on said one disk, a signal for performing one of a reproducing operation and a recording operation on said first and second discs; and controlling generation of the output signal of said signal processing unit.