JPS632128A - Optical pickup - Google Patents

Abstract

PURPOSE:To attain excellent operation by providing a converging grating coupler in separating the coupler into two, for guided light output and reflected light input. CONSTITUTION:A guided diverging light 8 stimulated by a light source 7 is diffracted by the transmitted light output converging grating coupler 3 to go to an output light 9 and collected on a signal face having pits 12 on an optical disk 11. A light 10 reflected on the signal face is inputted to the reflected light inputting converging grating couplers 41, 42 of the same shape and goes to converging guided lights 81', 82' and coupled with 2 sets of 2-split photodetectors 51, 51' and 51, 52'. In operating output electric signals from the photodetectors 51, 51' and 52, 52', a reproducing signal, a focus error signal and a tracking error signal are detected. Thus, the excellent and stable operation is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup for an optical disk device, and in particular to a small and lightweight optical pickup that is efficient and capable of being integrated on a single chip with good performance. .

2. Description of the Related Art In recent years, optical disk devices such as compact disks and optical disks have attracted attention. An optical pickup that detects signals is an important component that can be said to be the heart of an optical disk device. The basic structure of a conventional optical pickup is shown in FIG. (Ura, Suhara, Nishihara.

Koyama, “Optical integrated circuitization of optical disk pickup,” IEICE Photon Quantum Electronics Study Group fee 0QE-85-
72 (1986). ) In the figure, guided light 8 excited by a semiconductor laser serving as a light source 7 is υ diffracted by a condensing grating coupler 14 to become output light 9 and focused onto the surface of an optical disk 11. The reflected light 10 from the optical disk 11 is reversely coupled by the same condensing grating coupler 14 to become the guided light 8 again, and is split into two by the condensing beam splitter 13 and focused on the photodetector ε, which outputs an electric signal. Accordingly, the reproduced signal, the 7-occas, and the tracking error signal are detected.

Problems to be Solved by the Invention In the conventional optical pickup having the structure shown in FIG. 3, the guided light passes through the condensing beam splitter 13 twice, resulting in poor light utilization efficiency. This is because the guided light 8 excited by the light source 7 enters the focused beam splitter 13 before being emitted to the outside by the focused grating coupler 14, so that about 50% of the guided light 8 enters the focused beam splitter 13. 13, the light was diffracted in an unnecessary direction and became noise light. Also, the guided light 8 reflected by the optical disk 11, reversely coupled and excited, is split into two by the condensing beam splitter 13 and becomes a signal light at about 5 degrees, and the remaining 50 degrees are left as is. The light was focused, transmitted, and returned to the light source 7.

The semiconductor laser of the light source 7 is affected by the returned light, causing multi-mode and mode hopping, making the oscillation state unstable, and causing the focused spot to become multiple and position jumps.
Good operation was not possible.

In other words, due to the double-pass type condensing beam splitter 13, the light utilization efficiency is only about 2696, which is poor.
At the same time, there was a problem in that noise light and returned light were generated, making it impossible to operate properly.

The present invention has been made in view of these points, and it is an object of the present invention to provide an optical pickup that has good light utilization efficiency, and is capable of good operation because it does not generate noise light or return light.

Means for Solving the Problems In order to solve the above problems, the present invention provides a condensing grating coupler for outputting guided light and inputting reflected light.

Effect The present invention eliminates the need for a focusing beam splitter through which the guided light passes twice by separately providing a condensing grating coupler for outputting the guided light and inputting the reflected light, and as a result, the light utilization efficiency is improved. At the same time, since no noise light or return light occurs, good operation is possible.

Embodiment FIGS. 1 and 2 are a plan view and a sectional view, respectively, showing the structure of an optical pickup according to a first embodiment of the present invention. (Second
(The figure is a cross-sectional view taken along the line A-A in FIG. 1) The optical pickup of the present invention will be explained with reference to FIGS. 1 and 2. In the same figure, a Corning 7059 glass optical waveguide 1 having a thickness of 0.96 μm is formed on a St 2 substrate having an S 102 layer 2′ having a thickness of 2 μm on the surface, a PN junction 81 photodetector 5, and a photodetector 5 having a PN junction 81 in a Si substrate 2. On the optical waveguide 1, for example, 2
Concentrating grating coupler 3 for waveguide light output of 1111 x 2 g 1 size, for example, 1 parrot each? Concentrating grating couplers 41 and 42 for inputting reflected light of the size of a parrot, for example 2
A thin film light absorbing means 6 having a thickness T 102 is formed,
A light source 7 with a wavelength of 0.79μ, for example, is provided on the end face of the optical waveguide 1.
m semiconductor lasers are provided. St as substrate 2
By using the photodetector 5, it is possible to integrate the photodetector 5 within the same substrate. Further, the reason why the 3102 layer 2 is provided is that Si 2 has a high refractive index and is difficult to function as the optical waveguide 1 as it is. The optical waveguide 1 is
It is sufficient that the refractive index is higher than that of substrate 2, and #7069 glass/
The combination does not have to be 5i02/Si. for example,
A good optical waveguide 1 using LiNbO2 as the substrate 2 can be formed by thermally diffusing metal ions such as Ti or by exchanging protons. In this case, the photodetector 6 cannot be fabricated within the substrate, but the photodetector 6 can be constructed by depositing amorphous St 2 , polycrystalline Si 2 , or the like on the optical waveguide 1 .

According to this method, the photodetector 6 can be integrated regardless of the material of the substrate.

The diverging guided light 8 excited by the light source 7 is diffracted by the guided light output condensing grating coupler 3 to become output light 9, which is focused onto a signal surface with pits 12 on the optical disk 11. The light 1o reflected on the signal surface is input to condensing grating couplers 41 and 42 for reflected light input, each having the same shape, and converged guided light 81.
, 82 and are coupled onto two sets of photodetectors 51, 61 and 62°62' divided into two. The four photodetectors 51
A reproduction signal, a focus error signal, and a tracking error signal can be detected by simple calculation of the output electric signals of degrees 5,', 6 degrees, and 52'. For example, the reproduced signal is obtained by the sum of the output signals of the four photodetectors 51, 51, 5□, and 62. The focus error signal is sent to the two outer photodetectors 51.
From the sum of the output signals of and 52', the inner two photodetectors 5
It is obtained by subtracting the sum of the output signals of 1' and 5 degrees. When the optical disc 11 is in the focal plane, the photodetectors 5 and 5
Or, the focus error signal is 0 because the focus error signal is arranged so as to be evenly coupled to 52 and 52. optical disc 1
1 is closer than the focal plane, the convergent waveguide light B1.82
The focal position of the light beam moves toward the photodetector 5, and the traveling angle of the guided light beams 8, 8 becomes more outward.
, and the value of the focus error signal becomes positive. Conversely, when the optical disk 12 moves further away from the focal plane, the focal position of the convergent guided light beams 81, 8□ moves toward the condensing grating coupler 4 for reflected light input, and the traveling angle of the guided light beams 8, 8 becomes more inward. , a large amount of light is coupled to the inner photodetector 61t52, the value of the focus error signal becomes negative and can be detected, and focus control can be performed. The tracking error signal is obtained by subtracting the sum of the output signals of photodetectors 52 and 52' from the sum of the output signals of photodetectors 61 and 61. If the incident light 9 on the optical disk 11 operates normally, the powers of the guided lights 81' and 82 coupled to the photodetectors 51 and 62 are the same, so the value of the tracking error signal is Q. . When tracking deviation occurs, the guided light beams 81' and 8 incident on the photodetectors 51 and 52
The power of the light 2' changes, the tracking error signal becomes positive or negative, and tracking control can be performed. Note that in this example, two sets of two-split photodetectors were used; however,
By arranging a large number of multi-divided parts, alignment during production becomes easier.

The condensing grating coupler 3.4, which inputs and outputs light, is formed of a curved grating whose period changes gradually. In this example, in order to improve efficiency, the cross section is tilted at an angle corresponding to the period. In the type 3 for guided light output, the depth of the groove of the grating is gradually increased along the traveling direction of the guided light 8, and in the type 4 for reflected light input, the depth of the grating grooves is gradually increased along the traveling direction of the guided light 8. The depth of the grooves in the grating was gradually reduced along the line. By changing the depth of the groove, the radiation loss coefficient of the guided light is changed, and the intensity of the output light 90 is kept almost constant regardless of the location of the condensing grating coupler 3, and the light spot on the focal plane of the optical disk 11 is The strength is also uniform, resulting in good squeezing.

Furthermore, since the condensing grating coupler is reversible, it is similarly effective even in the case of 10 inputs of reflected light, and the coupling efficiency is improved. The condensing grating coupler may have a grating with a rectangular or sinusoidal cross section, but the efficiency will be less than half that of a grating with an optimally triangular cross section. In this embodiment, the condensing grating coupler 3,
4 is formed using electron beam direct writing using, for example, electron beam resist (CMS), and the exposure amount distribution of the electron beam is given according to the cross-sectional shape of the grating.

Also, this is a resist grating coupler 3.
, 4 and fabricated into the optical waveguide 1 by ion beam etching, a highly durable one can be obtained. Furthermore, the optical waveguide 1 may be manufactured while being directly etched using a focused ion beam.

- The light absorption means 6 provided between one set of condensing grating couplers 3 and 4 is for absorbing a part of the guided light that is not outputted to the outside by the condensing grating coupler 3 for outputting the guided light. By providing this light absorption means 6, a photodetector 51, 62 of guided light that is not a signal light.
It is possible to improve the SN ratio by preventing the influence on

In this example, a T z02 film is deposited on the optical waveguide 1 to a thickness of, for example, 2 μm, and the refractive index of the T z02 film is 2.5.
Since the refractive index of the optical waveguide 1 is larger than 1.54, the guided light 8 becomes a radiation mode and is emitted into the air. Further, the deposited film used at this time may be any material as long as it has a higher refractive index than the optical waveguide 1, and metal, amorphous Si, or polycrystalline Si may be deposited. Furthermore, this may be done by etching only this part of the 8102 layer 2' to expose St 2 and setting it as a radiation mode toward the substrate side, or by cutting the optical waveguide 1 with this part.

FIG. 3 is a plan view showing the configuration of an optical pickup according to a second embodiment of the present invention. Points different from the configuration of the optical pickup of the first embodiment shown in FIGS. 1 and 2 will be explained. A collimating waveguide lens 15 is provided on the optical waveguide 1 or in the optical waveguide 1 or on the substrate 2 between the light source 7 and the condensing grating coupler 30 for outputting the guided light, and the guided light 8 is made into parallel light by the waveguide lens 15. After that, the light is made to enter the condensing grating coupler 3. With this configuration, the condensing grating coupler 3 does not have to serve as a collimating lens, so the design and manufacturing conditions are easy, and a product with good performance can be easily obtained. Any waveguide lens may be used, such as a geodesic lens or a Lunepul lens. However, if a Fresnel lens or grating lens as in this example is used, the same brainer technology used to fabricate the condensing grating coupler, such as electron beam phosphorography and thin film deposition, can be used. It can be made by a combination of methods.

In this embodiment, a grating coupler 4 for inputting reflected light is used.
Unlike the first embodiment, the reflected light 1o is input into parallel waveguide light using only one light guide, and the reflected light 1o is input into the optical waveguide 1 between the photodetector 61.5□ and the condensing grating coupler 4 for inputting the reflected light. Or the two waveguide lenses 161 and 162 provided in the optical waveguide 1 or on the substrate 2 converge the guided light 81, 82'.
The light is divided into two and focused on photodetectors 51 and 52, respectively.

Note that instead of the waveguide lenses 161 and 162, a grating type condensing beam splitter as in the conventional example may be used. The condensing beam splitter in this case is not of the type that passes through the beam twice, but only splits and condenses the guided light once, so the efficiency can be approximately 100%. Detection of the reproduction signal, focus, and tracking error signal at this time is the same as in the first embodiment.

Note that a configuration that combines the configurations of the first embodiment and this embodiment, for example, a configuration in which a collimating waveguide lens 16 is provided in the first embodiment, or a configuration without a collimating waveguide lens in this embodiment Needless to say, that's fine.

FIG. 4 is a plan view showing the configuration of an optical pickup according to a third embodiment of the present invention. 1st. The difference from the second embodiment is that there are two condensing grating couplers 41 for inputting reflected light.
．． 42 is arranged in an off-axis position tilted from the optical axis (AA' in this figure) of the condensing grating coupler 3 for outputting guided light, and is arranged to prevent guided light that does not contain signal light from entering the photodetectors 51 and 52. It becomes. In other words, the first.
This serves the same role as the light absorption means 6 in the second embodiment. It goes without saying that in the second embodiment, the same effect can be obtained even if the waveguide lenses 161 and 162 are arranged off-axis with their optical axes tilted as in the present embodiment.

What has been explained above is mainly an optical pickup using a SiO□/Si substrate, but in an embodiment using a GaAs substrate instead of SiO2/Si, the light source 1 is placed on the substrate 2 or on the optical waveguide 1. For example, by integrating it as a DFB or DBR laser, a completely monolithic optical pickup could be realized, and the same effect as an optical pickup using a Sio2/Si substrate could be confirmed.

Effects of the Invention As described above, according to the present invention, there is no need for a condensing beam splitter through which guided light passes twice, resulting in high light utilization efficiency.
Further, since no noise light or return light is generated, good and stable operation is possible.

[Brief explanation of drawings]

1 and 2 are a plan view and a sectional view showing the configuration of an optical pickup according to a first embodiment of the present invention, respectively, and FIGS. 3 and 4 are respectively a second and third embodiment of the present invention. FIG. 5 is a plan view showing the structure of an optical pickup in the prior art, and FIG. 5 is a perspective view showing the structure of a conventional optical pickup. 1... Optical waveguide, 2... Substrate, 3...
・・・Concentrating grating coupler for guided light output, 4
. . . Concentrating grating coupler for reflected light input, 5 . . . Photodetector, 6 . . . Light absorption means, 7 . . . Light source. Name of agent: Patent attorney Toshio Nakao and 1 other person f-
Circle l □ 7---Rough 5R1 8,8'---Issei Karimaru 9- Seven cutting edge fo-Pseudo ti#. Figure 5 fl
---Ninth Izuku 12---hi=/to

Claims (16)

[Claims] (1) an optical waveguide formed on a substrate, and at least one set of condensing grating couplers for outputting guided light and inputting reflected light, formed on the substrate or on the optical waveguide;
It has a light source that emits the guided light and a photodetector that detects the reflected light, and the condensing grating coupler for inputting the reflected light divides the input reflected light and focuses it on at least two positions. An optical pickup characterized in that it is configured as follows. (2) The optical pickup according to claim 1, wherein the photodetector is provided with at least two sets of photodetectors divided into two or more. (3) The optical pickup according to claim 1, characterized in that a light absorption means is provided between one set of condensing grating couplers. (4) The optical pickup according to claim 1, wherein the grating of the condensing grating coupler has a triangular cross section. (5) The optical pickup according to claim 1, characterized in that a light source is provided on the substrate or on the optical waveguide. (6) Claim 1, characterized in that an optical waveguide lens is provided on the substrate, in or on the optical waveguide between the condensing grating coupler for guided light output and the light source.
Optical pickup described in section. (7) The optical pickup according to claim 1, characterized in that one set of condensing grating couplers is arranged off-axis. (8) The optical pickup according to claim 1, wherein the depth of the groove of the grating of the condensing grating coupler for outputting guided light is gradually increased along the traveling direction of the guided light. (9) The optical pickup according to claim 1, wherein the depth of the groove of the grating of the condensing grating coupler for inputting reflected light is gradually reduced along the traveling direction of the guided light. (10) The light absorption means is a material with a higher refractive index than the optical waveguide, metal, amorphous Si, or polycrystalline Si.
4. The optical pickup according to claim 3, wherein the optical pickup comprises: deposited on the optical waveguide. (11) The optical pickup according to claim 1, wherein the substrate is SiO_2/Si. (12) The optical pickup according to claim 11, wherein the optical absorption means is obtained by omitting the SiO_2 layer. (13) The optical pickup according to claim 1, wherein the photodetector is made of amorphous Si or polycrystalline Si deposited film formed on the optical waveguide. (14) The optical pickup according to claim 6, wherein the optical waveguide lens is a Fresnel lens or a grating lens. (15) On the substrate or in or on the optical waveguide between the condensing grating coupler for reflected light input and the photodetector,
The optical pickup according to claim 1, characterized in that at least two waveguide lenses are arranged side by side or a condensing beam splitter is provided. (16) The optical pickup according to claim 15, characterized in that two waveguide lenses or a focusing beam splitter and a focusing grating coupler are arranged off-axis.