JPH03256236A - Optical pickup - Google Patents

Abstract

PURPOSE:To enable miniaturization of this optical pickup by providing an IC substrate equipped with a grating coupler, etc., for emitting laser light, a condenser lens and a variable dioptric lens, etc. CONSTITUTION:The laser light from a semiconductor laser 1 as a light source is progagated through a waveguide 3 of the IC substrate 2 and taken out by a grating splitter 4 and the grating coupler 5 to be emitted light, which is then converged by the variable dioptric lens 7 under a feedback control in refractive index by an objective lens 5 receiving reflecting light, so as to irradiate an optical disk 8. Consequently, the occurrence of aberration of light in the converged beam based on a diffraction conditional change by a beam deflection with the grating coupler is prevented, and the optical pickup is obtained in small size and light weight constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup for recording or reproducing information on an information recording medium, and particularly to an optical pickup suitable for optical integration.

[Conventional technology]

FIG. 5 shows an example of a conventional optical pickup at a practical level. After the light emitted from the laser diode 11 is converted into a parallel beam by the collimating lens 12, the direction is changed by the prism mirror 16 and the beam is focused onto the optical disk 15 by the objective lens 14.

The light reflected on the surface of the optical disk travels back along the optical path to 1
By combining the /4 wavelength plate 16 and the polarizing beam splitter 170, the light is not returned to the laser diode 11, but is reflected and imaged onto the photodiode 19 by the condensing lens 18, thereby reading information recorded on the disk.

Since optical components such as lenses and mirrors are arranged spatially in this optical pickup, it has been difficult to make it compact and lightweight.

FIG. 6 shows an example of an integrated optical pickup that has been proposed to realize miniaturization and weight reduction (IEICE Transactions Vol. 1. J86-C, 803, '85).

In the figure, 21 is a semiconductor laser as a light source, 22 is an optical waveguide that guides the emitted light of the semiconductor laser, 23 is a grating condensing beam IJ vine provided on the optical waveguide 22,
24 is a condensing coupler provided on the optical waveguide 2, 25 is an optical disk, and 27 is two pairs of light receiving elements formed on the 81 substrate 26. In the optical pickup formed in this way, the light emitted from the semiconductor laser 21 passes through the optical waveguide 2.
2 and grating focusing beam splitter 25
incident on . The zero-order light that has not been diffracted here is focused by the condensing coupler 24 onto the optical disk 25 outside the optical waveguide 22 . The reflected light from the optical disk 25 is again focused by the focusing coupler 24, travels in the opposite direction in the waveguide 22, and the propagation direction is changed by the grating focusing beam splitter 25. The light is focused on the light receiving element 27 of.

[Problem to be solved by the invention]

In the above-mentioned integrated optical pickup, the focusing and tracking drive mechanisms are composed of movable parts that combine a drive coil and a permanent magnet, and it is necessary to move the entire integrated optical pickup board. There was a problem in that it was difficult to reduce the size, weight, and price of the optical waveguide pickup, and the characteristics of the optical waveguide pickup could not be fully utilized.

In addition, by providing a means to polarize the beam emitted from the waveguide using electro-optic effects, etc., when attempting to integrate the above-mentioned movable parts on a plane, it is possible to In an optical pickup, a grating coupler is used as an objective lens, so there is a problem in that deflecting the beam changes the diffraction conditions of the condensing grating coupler, causing aberrations to the condensed beam.

An object of the present invention is to provide a small and lightweight optical pickup that solves the problems of conventional optical pickups as described above.

[Means to solve the problem]

In order to solve the above problems, the optical pickup according to the present invention integrates an optical waveguide through which a laser beam propagates, and a grating coupler for radiating the light beam propagating through the optical waveguide into an external space as parallel light. It consists of a substrate, an objective lens that focuses the externally emitted light beam, and a variable refractive index distribution lens that finely adjusts the focal position.
In addition to being smaller and lighter, it is mounted on a slider bearing similar to a magnetic disk head, and the variable refractive index distribution lens enables rough adjustment of the focusing of incident light on the disk surface by air levitation effect when the disk is running. This allows for fine focusing adjustment.

[Effect]

The present invention aims at miniaturization by forming an optical waveguide, a grating beam splitter, a grating coupler, and a photodetector on the same substrate, and also by mounting an optical pickup head on a slider bearing similar to a magnetic disk head. This creates an air levitation effect when the disc is running, and prevents out-of-focus caused by waviness and warping of the disc.
In addition to following the disk surface, the intensity of the electric field applied to the variable refractive index distribution lens is changed by feeding back the focus error signal detected by the photodetector, making it possible to finely adjust the focus. .

〔Example〕

The details of the present invention will be explained using examples.

FIG. 1 is a schematic diagram of an integrated optical pickup according to the present invention.

The light emitted from the semiconductor laser 1 as a light source is, for example, L
It propagates in an optical waveguide 6 formed by uniformly diffusing Ti from the surface of a substrate 20 made of iNbO5, passes through a grating beam splitter 4, is diffracted by a grating coupler 5, is taken out of the waveguide, and is transmitted to the outside. The light is focused onto an optical disk 8 by a condensing lens 6 and a variable refractive index distribution lens 7 . In addition, the light reflected on the surface of the optical disk 80 returns through the variable refractive index distribution lens 7 and the condensing lens 6.
The light beam propagates through the optical waveguide 5 toward the light source again by the grating coupler 5 and enters the grating beam splitter 4 . The grating beam splitter is a Bragg-type diffraction grating, and diffracts the first-order diffracted light in the direction of the two pairs of photodetectors 9. These two pairs of photodetectors make it possible to read out recording signals, obtain focus error signals, tracking error signals, and the like. The focus error signal obtained from the photodetector 9 is converted into a voltage applied to the variable index distribution lens through an external circuit (not shown). In this way, the focus error signal can be fed back to change the refractive index distribution of the variable refractive index distribution lens so that the focal point can follow the recording surface of the optical disk without shifting.

FIG. 2 shows a cross-sectional view of a variable index distribution lens made of a semiconductor multilayer heterostructure according to an embodiment of the present invention. In figure (a), 71 is a substrate, 72 is a multiple quantum well layer, 73 is a cap layer 74 is an insulating region, 75 is an upper electrode, 76 is a lower electrode, and 77 is a layer for applying voltage to the electrodes 75 and 76. It is an external circuit. In the example shown in FIG. 2(b), a part of the substrate is removed by etching, but it is also possible to selectively remove the entire substrate. FIG. 5 shows a plane view of the upper electrode 75. In FIG. 3(a), the electrode patterns form concentric circles, and it is possible to provide a concentric electric field distribution. On the other hand, in FIG. 3(b), the concentric electrode pattern is further divided radially to enable application of an elliptical electric field, for example.

Next, an example of a method for manufacturing a variable index distribution lens according to the present invention will be explained using FIG. 2.

amm on the GaAs plate 71 by the molecular beam epitaxy method.
A multiple quantum well layer 72 is formed by alternately stacking a GaAs layer and a 10 nm Ato, 5Ga0.7As layer 80 times, and a 11o, s Gao, 7As cap layer 11 is formed.
Grow 00n.

After that, an upper electrode 75 and a lower electrode 76 are formed. As the electrode, a transparent electrode such as indium oxide or a partially transparent electrode using Gr, Au, etc. may be used. Next, the upper electrode 75 is formed using a photoresist process.
is patterned as shown in FIG. 3(a) or (b).

After that, by ion implantation of chromium, oxygen, etc., the regularity of the multi-quantum well layer located between the electrode patterns is changed, and At(1,5G) on the multi-quantum well layer is
ao, 7 The As layer is selectively etched away to provide insulation between elements. Through the above steps, a variable index distribution lens having the structure shown in FIG. 2(a) is formed. Helmet, Figure 2 (b)
In order to create a variable index distribution lens having the structure shown in FIG. 1, the lower electrode 76 may be patterned using a photoresist process, and then the substrate may be partially etched away. In this example, Atg, 5 Ga Q, 7 where there is no upper electrode
Although the As cap layer 73 was removed by etching and the regularity of the multiple quantum well layer 72 was disturbed by ion implantation, this is not the case if each of the above layers has a sufficiently high resistance.

FIG. 5(o) shows the in-plane refractive index distribution when a Gaussian distribution type electric field with a high center portion is applied using the electrode of FIG. 3(a). The center is high and a symmetrical refractive index distribution can be obtained within the plane. In addition, the refractive index distribution when the center part is high and the Y direction is higher than the X direction is applied using the electrode shown in FIG. 6(b) in the third [d (d).

It can be seen from this that an elliptical gradient index lens is formed.

FIG. 4 shows another embodiment of the invention.

In the figure, 72 to 76 are the same as in FIG. The method for manufacturing this lens is to form a semiconductor multilayer heterostructure including a multiple quantum well layer in the same manner as the method for manufacturing the lens of the example shown in FIG. The objective lens portion 78 is formed by molding into a lens shape by chemical processing. Thereafter, a lower electrode is formed to obtain a variable refractive index distribution lens with an integrated objective lens.

In the above example, the semiconductor multilayer heterostructure, which is the main component of the variable index distribution lens, is made of GaAs and klGaAs.
Although an example was shown in which the semiconductor multilayer heterostructure was formed using I
nP, InAs, Garb, InGaAs
, InGaAsP.

InGaAAP, InGaAtAs, AtQa
Sb, InAtAs, GaN, AAN.

ZnS, Zn5e, ZnSSe, Si,
By being composed of at least two materials of Ge, it is possible to obtain
It is possible to create a variable refractive index distribution lens that corresponds to a wide range of wavelengths from 0.4 μm to 6 μm. A multilayer structure using the above materials can be formed using a molecular beam epitaxy method, an organometallic vapor phase epitaxy method, or a gas source molecular beam epitaxy method. Below, as an example, Q, 6
A method of manufacturing a variable index distribution lens that is effective for light in the μm band will be described with reference to FIG.

11 on the GaAs substrate 71 by the molecular beam epitaxy method.
00n (Ato, 5s Ga0.6s) o, 5I
Form Ino, 49P'' y-layer 78, then 8nm Gap, 51inn, 49P layer and 10nm
(ALO,55Gao,as)o,511no,4
A multiple quantum well layer 72 is formed by stacking 9P layers alternately for 80 cycles, and further (ALa, 55Gao, 6s)o, 5
11no, 49P cap layer 1100n is formed.

After that, an upper electrode 75 and a lower electrode 76 are formed. As the electrode, a transparent electrode such as indium tin oxide, or a partially transparent electrode using Or, Au, etc. may be used. Next, the upper electrode 75 is patterned as shown in FIG. 5(a) or U(b) using a photoresist process.

After that, by ion implantation of chromium, oxygen, etc., the regularity of the multiple quantum well layer located between the electrode patterns is changed and the regularity of the multiple quantum well layer (AAo, ss
Ga 0165 ) o, s+ In O, 49F The cap layer is selectively etched away to provide insulation between elements. Next, after patterning the lower electrode 76 using a photoresist process, the GaAs of the substrate is removed by etching to form a variable index distribution lens. In this example, the GaAs substrate does not transmit light in the 06 μm band, so GaAs was removed by etching. However, when using a substrate that transmits light in the 6 μm band, the refractive index distribution can be changed as shown in Figure 2 (a). It is possible to create lenses. In addition, in this example, (Ato, ss Gao,
65) o, 5+ Ino, 49P cap layer 73 is
Although the regularity of the multiple quantum well layer 72 was disturbed by etching and ion implantation, this is not the case if each of the above layers has a sufficiently high resistance.

In this example, a method for manufacturing a variable refractive index distribution lens has been described. However, when forming a variable refractive index distribution lens with an integrated objective lens as shown in FIG. In this case, the substrate can be processed into a lens shape as in the previous embodiment, but in the embodiment shown in FIG. 7, since GaAs does not transmit light in the 0.6 μm band,
aa, 115)o, 511no, 49P The thickness of the gloss layer 78 is 50 μm, and after the GaAs substrate 71 is removed by etching, the buffer layer 78 is formed into a lens shape by etching to form an objective lens portion.

Thereafter, a lower electrode is formed to obtain a variable refractive index distribution lens with an integrated objective lens.

Other embodiments of the invention are shown below. An optical disk device using the optical pickup of the present invention has a stack structure using a large number of disks 8 as shown in FIG. 8 in order to increase the capacity of processing information.

For miniaturization, it is desirable to make the distance between the disks as narrow as possible, but in this embodiment, it is set to [10] in consideration of the space available for moving the optical pickup. The flying distance of the optical pickup 9 according to the present invention mounted on the slider bearing is:
This can be changed by selecting the size of the bearing, but considering minute protrusions on the disk surface, we decided to levitate at least 0.1 μm, and taking into consideration the fact that the disk spacing in the stack structure was set at 10 degrees, we decided to The maximum value of the distance was set to 1 gourd.

By taking the following measures, the optical pickup can be levitated to roughly follow the disk surface, and the focal position can be moved by a maximum of 20 μm using a variable refractive index distribution lens to prevent waviness or warping of the disk. Because there is
Light can always be focused on the disk surface.

〔Effect of the invention〕

As is clear from the above description, the present invention employs a variable refractive index distribution lens whose refractive index changes depending on the applied voltage, so a focusing drive mechanism that combines a drive coil and a permanent magnet is used. It is possible to provide a small and lightweight optical pickup without the need to employ a conventional optical pickup.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a schematic configuration of an optical pickup according to the present invention, FIGS. 2(a) and (b) are sectional views showing a cross section of a variable refractive index distribution lens, and FIGS. 5(a) and ( b
) is a plan view showing the upper electrode pattern of the variable refractive index distribution lens, Fig. 3 (0) and (d) are diagrams showing the relationship between the electric field strength applied to the variable refractive index distribution lens and the refractive index distribution, and Fig. 4 5 is a cross-sectional view showing another embodiment of the variable index distribution lens according to the present invention, FIG. 5 is a diagram showing a schematic configuration of a conventional optical pickup, FIG. 6 is a perspective view showing a conventional integrated optical pickup, and FIG. FIG. 7 is a sectional view showing another embodiment of the variable index distribution lens according to the present invention, and FIG. 8 is a configuration diagram showing a method of using the optical pickup according to the present invention. 1... Semiconductor laser 2... Substrate 5... Waveguide 4... Grating beam splitter 5... Grating coupler 6... Objective lens 7... Variable refractive index distribution lens 71... Substrate 72...Multiple quantum well layer 73...Cap layer 74...Ion implantation layer 75.76...Electrode.

Claims (1)

[Claims] 1. A light source, an optical waveguide for propagating the emitted light from the light source, a substrate on which a grating coupler is formed for extracting the emitted light from the waveguide, and the light emitted to the outside. What is claimed is: 1. An optical pickup comprising: an objective lens for condensing light onto an information recording medium; and a variable refractive index distribution lens for controlling a condensing position. 2. The variable refractive index distribution lens is made of at least one of a semiconductor multilayer heterostructure, a liquid crystal, and a material having an electro-optic effect.
Optical pickup as described. 3. The optical pickup according to claim 1 or 2, wherein the variable refractive index distribution lens has a concentric refractive index distribution in response to an electric field applied concentrically. 4. Claim 1, further comprising a variable refractive index distribution lens having an elliptical refractive index distribution in response to an applied electric field.
Or the optical pickup described in 2. 5. The optical pickup according to claim 1 or 2, wherein the objective lens and the variable refractive index distribution lens are integrated. 6. The semiconductor heterostructure is GaAs, AlGaAs,
InP, InAs, GaSb, InGaAs, InGa
AsP, InGaAlP, InGaAlAs, AlGa
Sb, InAlAs, GaN, AlN, ZnS, ZnS
3. The optical pickup according to claim 2, wherein the optical pickup is made of at least two of E, ZnSSe, Si, and Ge. 7. The objective lens and the variable refractive index distribution lens,
GaAs, AlGaAs, InP, InAs, GaSb
, InGaAs, InGaAs, InGaAlP, In
GaAlAs, AlGaSb, InAlAs, GaN,
6. The optical pickup according to claim 5, wherein the optical pickup is made of at least two of AlN, ZnS, ZnSe, ZnSSe, Si, and Ge. 8. The optical pickup according to claim 1, wherein the flying distance from the surface of the traveling disk is 0.1 μm to 1 mm.