JPH0677327B2 - Information recording or reproducing device - Google Patents

Description

The present invention relates to an information recording or reproducing device.

2. Description of the Related Art In recent years, with the progress of the information society, information recording or reproducing devices such as optical disk devices and magneto-optical disk devices, which focus light on a recording medium surface and record or reproduce information, have been attracting attention. In such an information recording or reproducing apparatus, focus adjustment and position adjustment of focused light on the recording medium surface are indispensable. Conventionally, a mechanical deflecting means such as a galvanometer mirror has been used for the position adjustment, but it has a drawback that the scanning speed is slow. Therefore, it is conceivable to use an optical deflector utilizing diffraction proposed in JP-A-56-107217 or the like, instead of the mechanical deflecting means. The information recording or reproducing apparatus using such an optical deflector has an excellent characteristic that it is possible to adjust the position of the focused light at a high speed, but a problem occurs in signal detection for focus adjustment. This example will be described with reference to FIGS. 1 (A) and 1 (B).

In FIG. 1 (A), 1 is an optical deflector utilizing the diffraction of light by a surface acoustic wave, 2 is a beam splitter, 3 is an objective lens driving means, 4 is an objective lens, 5 is a condenser lens, and 6
Is a photodetector, and 7 is a recording medium. Here, the optical deflector 1
Is configured as shown in FIG. 1 (B), for example. substrate
A waveguide layer 12 having a higher refractive index than that of the substrate 11 is formed on the substrate 11, and incident light 15 is transmitted through the prism coupler 14 to the waveguide layer 12.
Be guided inside. Then, a part of the incident light propagating in the waveguide is diffracted into the deflected light 16 by the surface acoustic wave 18 generated from the comb-shaped electrode 13. This polarized light 16 and surface acoustic wave 18
The 0th-order diffracted light 17 that is not deflected by is emitted to the outside of the waveguide through the prism coupler 19.

In FIG. 1A, the deflected light 8 emitted from the optical deflector 1 passes through the beam splitter 2 and is focused on the recording medium 7 by the objective lens 3. The deflected light reflected by the recording medium is detected by the beam splitter 2 into a photodetector 6
And is imaged on the surface of the photodetector 6 by the condenser lens 5. The objective lens driving device 3 is driven according to the signal detected by the photodetector 6, and the objective lens 4 is moved so that the focal point of the deflected light matches the recording medium surface.

However, in the information recording or reproducing apparatus as described above, since the recording medium 7 surface and the photodetector 6 surface have a conjugate relationship with the deflected light 8, the focus adjusting signal light 9 is generated by the optical deflector 1. With the scanning of the polarized light, it has a drawback that it moves on the surface of the photodetector 6 and precise focus control is difficult.

It is an object of the present invention to focus information on a recording medium, and when recording or reproducing information, position adjustment of the light on the surface of the recording medium is high speed and information recording or focus adjustment can be accurately performed. It is to provide a reproducing apparatus.

The above object of the present invention is to provide an optical deflector utilizing the diffraction of light,
Condensing means for condensing the deflected light and the 0th-order diffracted light from the optical deflector onto the recording medium surface, and the 0th-order diffracted light which is provided between the optical deflector and the recording medium surface and reflected on the recording medium surface. A beam splitter that separates the light from the light irradiated onto the surface of the recording medium, a detection unit that detects the reflected light separated by the beam splitter to obtain a focus detection signal, and drives the light collection unit according to the focus detection signal. And means for adjusting the focus by scanning the deflected light with the optical deflector,
This is achieved by an information recording or reproducing device that records or reproduces information by the deflected light while adjusting the position of the deflected light on the surface of the recording medium.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a schematic diagram showing a first embodiment of the information recording or reproducing apparatus of the present invention. In the figure, 21 is an optical deflector using surface acoustic waves, 22 is a beam splitter, 23 is an objective lens driving device, 24 is an objective lens, and 25 is a light condensing unit, similar to that shown in FIG. 1 (B). A lens, 26 is a two-divided photodetector, 27 is a recording medium, and 28 is a light shielding plate. In the case of such an optical deflector using a surface acoustic wave, the recording light and the reproducing light are +1.
Although the diffracted light of the 1st order or the diffracted light of the -1st order is used, since the diffraction efficiency by the surface acoustic wave is usually 100% or less, the diffracted light of the 0th order is generated. The present invention positively utilizes the 0th-order diffracted light to perform focus adjustment. That is, as shown in FIG. 2, the 0th-order diffracted light 29 emitted from the optical deflector 21
And the polarized light 30 pass through the beam splitter 22, and the objective lens
Both images are formed on the recording medium 27 by 24.

The polarized light 30 is modulated according to the recording signal and records information on the recording medium. On the other hand, at the time of reproducing information, the deflected light 30 is incident on the recording medium, and reflected light from the recording medium is received by a detector (not shown) to reproduce the information recorded on the recording medium. The reflected light of the 0th-order diffracted light 29 is reflected by the beam splitter 22.
It is guided toward the two-part photodetector 26.

Also in the case of the first embodiment, as in the conventional example, the photodetector surface and the recording medium surface have a conjugate relationship with the deflected light 30,
Since the 0th-order diffracted light is used for focus detection, no matter how the deflected light is deflected, the focus adjustment signal light (the 0th-order diffracted light reflected by the recording medium) does not fluctuate on the detector surface. . In this way, the signal obtained by the two-division photodetector is fed back to the objective lens driving device, and the focus of the zero-order diffracted light 29 is returned.
31 is aligned with the surface of the recording medium 27. In the above system, as shown in FIG. 2, if the focus 31 of the 0th order diffracted light 29 by the objective lens 24 matches the recording medium surface, the focus 32 of the deflected light 30 by the condenser lens 24 also coincides with the recording medium surface. It is premised that they match, but when the image plane position of the deflected light 30 is different from that of the 0th-order diffracted light 29, such positional displacement may be corrected and the objective lens driving device 23 may be driven.

Next, the focusing signal detection method of the above embodiment is shown in FIG.
An explanation will be given using (B) and (C). Such a focus signal detection method has been proposed in, for example, Japanese Patent Laid-Open No. 54-155832, and the present invention is not limited to this method. Third
Figures (A), (B) and (C) show how the 0th order diffracted light is reflected from the recording medium surface due to the position difference between the objective lens 24 and the recording medium surface, and 33 is the 0th order diffracted light. Of the objective lens 24, the medium surface when there is a recording medium in front of the focus position of the objective lens 24, 34 is the medium surface when the recording medium is at the focus position of the 0th order diffracted light, and 35 is the focus of the 0th order diffracted light. It shows the medium surface when there is a recording medium behind the position. As shown in FIG. 3A, when the surface of the recording medium is on the front side of the focus position of the 0th-order diffracted light by the objective lens, the reflected light 38 from the medium becomes a divergent light flux from the objective lens 24, and the beam splitter 22 Incident on. The divergent light beam is deflected to the photodetector side by the beam splitter 22, and half of the divergent light beam is blocked by the light shielding plate 28, and as a result, the remaining light beam.
39 is attached to one side 37 of the two-division photodetector by the condenser lens 25.

On the other hand, as shown in FIG. 3B, when the surface of the recording medium coincides with the focal position of the 0th-order diffracted light by the objective lens 24,
The reflected light 40 from the medium is collimated by the objective lens 24 and enters the beam splitter 22. The parallel light flux by the beam splitter 22 is deflected to the detector side,
Half of the parallel light flux is shielded by the light shielding plate 28, so that the remaining light flux 41 is imaged by the condenser lens 25 in the middle of the two-divided photodetectors 36 and 37. On the other hand, as shown in FIG. 3C, the recording medium surface is formed by the objective lens 24.
When the focus position of the 0th-order diffracted light is on the rear side, the reflected light 42 from the medium becomes a convergent light beam by the objective lens 24, and one side of the two-division photodetector is operated by the same principle as described above.
I'm at 36.

Therefore, the objective lens driving device 23 is designed so that the difference between the signals obtained from both the two-divided photodetectors 36 and 37 is always zero.
When is driven, the focus of the 0-th order diffracted light by the condenser lens 24 matches the recording medium surface.

Next, a second embodiment of the information recording or reproducing apparatus of the present invention will be described with reference to FIG. Reference numeral 51 is an optical deflector using surface acoustic waves, 63 is a half-wave plate, 64 and 65 are polarization beam splitters, 52 is a beam splitter, 66 is a photodetector, 53 is an objective lens driving device, and 54 is an objective. A lens, 55 is a condenser lens, 56 is a two-division photodetector, and 60 is a light shielding plate. Optical deflector
As described with reference to FIG. 1B, 51 has a planar optical waveguide structure, and the polarization state of the light emitted from the optical deflector is linear polarization. Now, assuming that the mode of the guided light is the TE mode, the vibration directions of the electric fields of the 0th-order diffracted light 61 and the deflected light 62 emitted from the optical deflector are within the plane of FIG. The polarized light 62 enters the polarization beam splitter 64 while maintaining the above polarization state, while the 0th-order diffracted light 61 is reflected by the 1/2 wavelength plate 63.
The polarized light is converted into linearly polarized light orthogonal to the polarized light and is incident on the polarized beam splitter 64.

The deflected light 62 that has entered the polarization beam splitter 64 is totally reflected by a surface 67 inside the polarization beam splitter, and the 0th-order diffracted light 61 and the deflected light 62 are combined. Combined light of 0th-order diffracted light 61 and deflected light 62
The beam 68 passes through the beam splitter 52 and is focused on the recording medium 57 by the focusing lens 54. In the second embodiment, the 0th-order diffracted light can be focused very close to the position where the deflected light is focused, and the focused position of the deflected light can be more accurately matched on the recording medium. The combined light 68 is reflected from the recording medium 57 and is polarized by the beam splitter 52.
Incident on 65. The reproduction light 69, which is the reflected light of the polarized light, is detected by the photodetector 66 by the polarization beam splitter 65 and reproduces the information recorded in the recording medium 57. Further, the reflected light of the 0th-order diffracted light is transmitted through the polarization beam splitter 65, and a part thereof is blocked by the light shielding plate 60 as in the first embodiment, and enters the two-divided photodetector 56 to generate a focus detection signal. Become.

In the above example, the case where the information recorded on the recording medium is optically read and reproduced is shown. However, by using the same configuration, the deflected light is modulated according to the information signal and the information is recorded on the recording medium. It can also be a device.

Next, a third embodiment of the information recording or reproducing apparatus of the present invention will be described with reference to FIG. 72 is a prism coupler,
74 is a surface acoustic wave, 77 is an optical waveguide, 78 is a thin film lens made of a substance having an electro-optical effect, and an electrode for applying an electric field to the thin film lens. By adjusting the voltage applied to the electrode, electro-optical A variable focus thin film lens that changes the focal length using the effect, 80 is an optical recording tape,
Reference numeral 81 is a pad for pressing the recording tape against the waveguide end face 84, 82 and 83 are two-divided photodetectors, 86 is a light shielding plate, and 87 is a comb-shaped electrode for generating surface acoustic waves. The collimated laser light 71 is guided into the waveguide 78 by the prism coupler 72. The guided light 73 is a first-order diffracted light 75 and a zero-order diffracted light 76 due to the surface acoustic wave 74 generated from the comb tooth-shaped electrode 87.
To separate. Both the first-order diffracted light 75 and the 0th-order diffracted light 76 are incident on the variable-focus thin film lens 78, and the first-order diffracted light 75 is
The recording light 79 is condensed on the end face 84 of the waveguide and recorded on the recording tape 81. On the other hand, the 0th-order diffracted light 76 is emitted from the varifocal thin-film lens 78, part of which is cut off by the light shielding plate 86, becomes guided light 85, and enters the two-divided photodetectors 82 and 83. Temporarily, the focus by the variable focus thin film lens 78 is
When it is inside the waveguide end face 84, the guided light 85 is incident on the 83 side of the two-division photodetector, while the focus by the variable focus thin film lens 78 is outside the waveguide end face 84. The guided light 85 is incident on the side of the two-divided photodetector 82.
Therefore, if a voltage is applied to the electrodes of the variable-focus thin film lens so that the difference between the signals obtained from both the two-divided photodetectors 82 and 83 will always be zero, the recording guided light 79 will generate the recording guided light 79. Focus on 54.

The third embodiment has an effect that the variable focus thin film lens having no mechanical moving part and the optical deflector are provided on the same waveguide so that miniaturization can be achieved. Further, also in the present embodiment, the information reproducing apparatus can be configured by providing means for detecting the light from the optical recording tape 80.

FIG. 6 shows a fourth embodiment of the information recording / reproducing apparatus of the present invention. In FIG. 6, 91 is an optical deflector using a surface acoustic wave, 93 is an objective lens driving device, 94 is an objective lens, 95 is a condenser lens, 96 is a two-division photodetector, 97 is a recording medium, and 100 is A light blocking plate, a half-wave plate 103, a polarizing beam splitter 104, and a photodetector 105. Further, here, 108 and 109 are half mirror surfaces. Also in the fourth embodiment, the 0th-order diffracted light 101 and the deflected light 102 are combined on the surface 106 in the polarization beam splitter 104 according to the same principle as the second embodiment. This synthetic light 107
Is condensed on the recording medium 97 by the condenser lens 94. The reflected light of the combined light returns to the polarization beam splitter 104, and the 0th-order light component is transmitted by the surface 106, while the polarized light component is reflected by the surface 106. The 0th-order light component passes through the half mirror surface 108 and enters the two-division photodetector to become a focus detection signal, while the deflected light component passes through the half mirror surface 109 and enters the photodetector 105. , Becomes the playback signal.

In the above example, the case where the information recorded on the recording medium is optically read and reproduced is shown. However, by using the same configuration, the deflected light is modulated according to the information signal and the information is recorded on the recording medium. It can also be a device.

Similar to the second embodiment, the fourth embodiment has an effect that high-precision focus adjustment is possible and the optical system is simpler than that of the second embodiment.

Next, a fifth embodiment of the information recording or reproducing apparatus of the present invention will be described with reference to FIG. While the first embodiment described above uses the acousto-optic effect for the optical deflector,
In the fifth embodiment, the electro-optical effect is used for the optical deflector. Reference numeral 111 denotes an optical waveguide formed in the same manner as in the example of FIG. 1 (B), and by applying a voltage to the tooth-shaped electrode 65 of the comb, the refractive index of the optical waveguide is periodically changed.
The incident light is deflected by diffraction. The subsequent operation is exactly the same as that of the first embodiment, and the 0th-order diffracted light 121 and the deflected light 1
22 passes through the beam splitter 112, is focused on the surface of the recording medium 117 by the objective lens 114, and information is recorded or reproduced by the deflected light. The recording medium 1 for the 0th-order diffracted light 121
A part of the light reflected by 17 is blocked by the light shielding plate 110 and is detected by the two-division photodetector 116 through the condenser lens 115, whereby a focus detection signal is obtained according to the same principle as that described with reference to FIG. Objective lens drive device according to this focus detection signal
By driving 113, the deflected light 122 is correctly focused on the surface of the recording medium 117.

The deflection angle 2θ in the optical deflector is given by the following formula by the tooth-shaped electrode pitch Λ of the comb and the wavelength λ of the incident light.

The pitch of the grating created this time was 8.8 μm, the number of logarithms was 350, and the cross width was 3 mm. Further, in order to make the deflection angle multi, as shown in FIG. 8, it is sufficient to form the tooth-shaped electrodes of combs having different pitches with inclinations corresponding to the respective Bragg angles. In FIG. 8, 126, 127, and 128 are comb-shaped electrodes having different pitches, 129 is deflected light by the electrode of 126, 130 is deflected light by the electrode of 127, and 131 is deflected light by the electrode of 128. is there.

In the fifth embodiment, the electro-optical effect is used to generate the grating structure in the optical waveguide, and the light is deflected by diffraction. However, the thermo-optical effect can also be used.
In this case, the electrode formed on the optical waveguide similar to that of the fifth embodiment has a ladder structure as shown in FIG. 9, and a heater material may be used as the electrode material. The relationship between the deflection angle and the electrode pitch is the same as when the electro-optic effect is used.

The present invention is not limited to the above-mentioned embodiment, and various modifications can be made. For example, the optical deflector may be any one as long as it deflects light using diffraction. Further, the applicable range of the present invention is not limited to optical discs and magneto-optical discs, but may also be applied to image forming devices such as laser beam printers, display devices, etc. that record image information on a paper surface, a display surface, etc. by scanning focused light. It can be applied.

As described above, according to the present invention, in the information recording or reproducing apparatus including the optical deflector using diffraction, the focus control is performed by using the 0th order diffracted light, so that the recording or reproducing light is deflected. , It became possible to always perform accurate focus control.

[Brief description of drawings]

1 (A) and 1 (B) are schematic views showing an example of a conventional information recording / reproducing apparatus and an optical deflector using the acousto-optic effect used therein, and FIG. 2 is a schematic view of the information recording / reproducing apparatus of the present invention. Schematic showing the first embodiment, FIG. 3 (A) (B)
(C) is a diagram for explaining the principle of focus detection in the first embodiment, FIGS. 4 to 7 are diagrams showing other embodiments of the information recording or reproducing apparatus of the present invention, and FIG. 8 is an electric diagram. FIG. 9 is a schematic view showing an example in which the deflection angle of the optical deflector using the optical effect is made multiple, and FIG. 9 is a diagram showing the electrode shape of the optical deflector utilizing the thermo-optical effect. 21 ... Optical deflector, 22 ... Beam splitter, 23 ... Objective lens driving device, 24 ... Objective lens, 25 ... Condensing lens, 26 ... Two-segment photodetector, 27 ... Recording medium, 28 …… Shading plate, 29 …… 0th order diffracted light, 30 …… Deflected light, 31 …… 0th order diffracted light focus, 32 …… Deflected light focus.

Claims (1)

[Claims] 1. An optical deflector utilizing diffraction of light, a condensing means for condensing the deflected light from the optical deflector and the 0th-order diffracted light on a recording medium surface, the optical deflector and the recording medium surface. And a beam splitter which is provided between the beam splitter and separates the 0th-order diffracted light reflected by the surface of the recording medium from the light irradiated on the surface of the recording medium, and the reflected light separated by the beam splitter is detected to obtain a focus detection signal. It comprises a detecting means and a means for adjusting the focus by driving the light collecting means in accordance with the focus detection signal. The optical deflector scans the deflected light to adjust the position of the deflected light on the recording medium surface. Meanwhile, an information recording or reproducing device for recording or reproducing information by the polarized light.