JPH0448440A - Optical information recording and reproducing device - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information recording/reproducing device equipped with a waveguide layer.

2. Description of the Related Art Conventional optical information recording and reproducing apparatuses include, for example, one having a configuration as shown in FIG. A waveguide layer 3 is laminated on a substrate l with a buffer layer 2 interposed therebetween. Light emitted from the laser light source 4 provided at the end of the substrate 1 is coupled to the end surface of the substrate 1 and guided into the waveguide layer 3 . The guided wave light passes through the grating 5, is diffracted by the condensing grating jig coupler 6, and propagates in the air. It is guided to the disk 7, and information is recorded thereon.

Further, the reflected light from the magneto-optical disk 7 enters the condensing grating coupler 6 again and becomes a waveguide light,
It is diffracted by the grating 5 and split into two beams a and b. These two divided light beams a and b are detected by two photodetectors 8a, 8b, and 9a arranged on the left and right sides, respectively.
, 9b, and thereby the reproduction signal S, focus error signal Fo, and track error signal Tr can be detected.

In this case, the values of the various signals detected by the photodetectors Sa, Sb, Sc, and Sd are as follows: Fo= (Sc+5d)−(Sb+5c)Tr=(S
c + 5d) - (Sa + 5b) S = Sa + Sb + Sc +
It can be determined by Sd.

Problem to be Solved by the Invention In the optical integrated pickup as described above, the luminous flux a
is located between the photodetector 8a and the photodetector 8b, and the light beam is located between the photodetector 9a and the photodetector 9b. Usually, the spacing Ga, Gb between these photodetectors is set to about 5 to 10 μm, and the spacing Ga
, Gb cannot be made very small due to crosstalk between photodetectors. In this case, in detecting the focus error signal, the light beams a and b are condensed at the intermediate position between the distances Ga and Gb during focusing. For this reason, if the spots of the light beams a and b are smaller than the spacing Ga and Gb, it is not possible to accurately detect the focus error signal even if defocus occurs before and after the in-focus point. A phenomenon of "no sensitivity to the focus error signal" occurs. Considering these two points, it is possible to eliminate such a phenomenon of lack of sensitivity by making the spot diameter of the luminous flux comparable to the spacing Ga and Gb between the photodetectors, but it is possible to eliminate the phenomenon of lack of sensitivity from the time of focusing. The amount of change in the focus error signal when the focus is off is small.

Therefore, in order to obtain a focus error signal with high detection sensitivity, the grating 5 and the photodetector 8a are used.

It is necessary to increase the distance from the photodetectors 8b, 9a, and 9b, or to narrow the distances Ga and Gb between these photodetectors.

In the case of the former method, the configuration of the optical pickup becomes large, making it impossible to obtain a compact optically integrated device. Furthermore, in the case of the latter method, as described above, the amount of change in the focus error signal is small, and the gaps Ga and Gb cannot be unnecessarily narrowed.

In order to solve these problems, the light emitted from the laser light source is guided through a waveguide formed on the substrate, and the guided light is diffracted by an optical grating coupler. At the same time, the reflected light from the optical information recording medium is focused by the condensing grating coupler and guided into the waveguide again. In an optical information recording and reproducing device that reproduces information, focus error signals, and track error signals by detecting wave light with a photodetector, the shape of the opening of the photodetector is set in the direction of the optical axis of the guided light. At least two photodetectors each having a non-uniform shape were provided.

Effect By using a photodetector having a shape that is not uniform in the optical axis direction of the guided light, it becomes possible to detect a focus error signal without the presence of a dead area as in the conventional method.
By providing a plurality of such photodetectors, it is possible to increase the detection sensitivity of the focus error signal and reproduction signal.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 and 2. Note that explanations of the same parts as in the prior art (see FIG. 8) will be omitted.

As shown in FIG. 1, a low impurity concentration layer 1 is formed on a substrate 10.
1. A buffer layer 12 and a waveguide layer 13 are sequentially laminated. A recess is formed in the waveguide layer 13 and the buffer layer 12, and the first conductive layer 14a, 1 is located under the thin region of the recess of the buffer layer 12.
4b is provided. second first conductive layer 14a,
A channel stopper 15 is provided on the surface of the low impurity concentration layer 11 in the same plane as the channel stopper 14b. The substrate 10 here also serves as a second conductive layer.

The regions surrounded by broken lines including the waveguide layer 13 and the first conductive layers 14a and 14b formed in the recessed portions constitute light receiving elements 16a and 16b as photodetectors. In this case, the light receiving elements 16a, 16b
As shown in FIG. 1, the shape of the opening is non-uniform with respect to the length of the guided light 17 in the optical axis direction, and two openings are provided here.

In the configuration shown in 2, light emitted from a laser light source (not shown) is coupled to the end face of the substrate 10, guided to the waveguide layer 13, and travels through the waveguide layer 13 as a guided light 17 until it reaches the light receiving element. 16a.

16b. Since the light-receiving elements 15a and 16b are formed in concave portions so that the buffer layer 12 is thin, photoelectric conversion is performed by being absorbed by the first conductive layers 14a and 14b below.

At this time, by making the shapes of the light receiving elements 16a and 16b non-uniform with respect to the optical axis of the guided light, it is possible to detect an electrical signal that depends on the incident position of the guided light 17. At that time, if the Hayabusa is to extract an output that depends on the incident position of the guided light 17, only one light receiving element 16a is required, but with such a structure of only one,
Depending on the incident position, the amount of light that is absorbed is only a part of the total amount of incident light, and the other part escapes to the rear, making it impossible to use the amount of incident light effectively; The light is transmitted to the light receiving elements 16a, l
There is also a risk that the light will be scattered by the 6b and become stray light. Therefore, by configuring the light receiving elements 16a and 16b as a pair as in this embodiment, it is possible to effectively utilize the total amount of light and obtain an output that depends on the incident position of the guided light. Therefore, by configuring the incident position of the guided light to correspond to the detection of the focus error signal, the value of the difference signal between the outputs of these two light receiving elements 16a and 16b can be made to correspond to the focus error signal. two light receiving elements 16a
, 1.6b can be made to correspond to the reproduced signal.

As described above, by providing the light receiving elements 16a and 16b with non-uniform shapes in the optical axis direction of the guided light, it is possible to detect a focus error signal without a dead zone area, and by providing a plurality of light receiving elements, the focus error signal can be detected. It becomes possible to obtain larger error signals and reproduced signals.

Next, a modification of the present invention will be explained based on FIG. 3. In the embodiment described above, there are two light receiving elements 16a.

16b was separated only by the first conductive layers 14a, 14b, but here, these light receiving elements 16a, ], 6b
A buffer layer 12 having a convex portion A is formed between the buffer layers 12 and a channel stopper is provided directly below the buffer layer 12. As a result, two light receiving elements 16a
, 16b can be made with a large spatial distance, so
It is possible to reduce crosstalk between these light receiving elements.

Note that if the loss of light amount does not occur due to opening and closing, it is also possible to provide only a channel stopper instead of forming such a convex portion.

Next, a design example of the photodetector (light receiving elements 16a, 16b) will be explained based on FIGS. 4 and 5.

Although the photodetector in the present invention is constructed using a plurality of photodetectors, the input/output characteristics when one photodetector is manufactured will be described here.

First, in FIG. 4, the photodetector has y=Q and y=f
It is formed in the area surrounded by (x).

The guided light, which is the incident light beam, has a width D, an intensity ■○, and x=x
When the light is incident on a position from o to xo+D, the amount of light absorption can be set as follows, and equation (1) at this time becomes as follows.

By appropriately selecting the value of C, it can be expressed as: Note that α is an absorption coefficient (energy) indicating the degree to which guided light is absorbed by silicon through the buffer layer 12, which is thinned at the photodetector portion.

Now, assuming that the output of the photodetector is linear with respect to the absorbed energy, the amount of absorption described above has a linear relationship with the output of the photodetector. To make the output of the photodetector have a linear relationship with the position (xO) of the guided light, f(x) = C--Qog
(kx) −(2) α However, k and x are constants, and the amount of absorption can be changed from almost O to nearly 100%. Now, if we take the maximum value of the optical axis deflection width (the range that requires linear output) and correspond to this range, we get the following.

As a specific numerical example, for example, if α=6X10−” = 50 μm D=10 μm and the value of C is chosen as 3/α (=500 μm), k
= o, 31.8 μm-, and at this time, X○ = (
The amount of absorption can be varied in the range of 8% to 87% in the range of 3, 14, 53, 14) μm. If a photodetector is designed based on this calculation, the result will be as shown in FIG. When a sensor of this shape is used for the light receiving element 16a on one side of FIG. 2, the other light receiving element 16b is
It can be created as a shape such as (x)=-Qog (kx) 10Co-(6)α.

In this case, f (x) + g (x) = C + Co, so Co is selected so that the second value is large enough for the absorption of the guided light, but in reality it depends on the response of the photodetector. It can be made larger without sacrificing speed. By setting such a shape, the outputs of the two light receiving elements can both be made linear with respect to the deflection of the incident beam.

Further, the shapes of the light receiving elements 16a and 16b can be set to various shapes as shown in FIGS. 6(a) to 6(e). As shown in (a), by extending the longest part of the guided light along the incident optical axis, even when the optical axis of the guided light changes significantly, the light receiving elements 16a, 16b
This is convenient because light can be incident on the space, and it can also be used as a space for forming contact holes for wiring. Furthermore, when linearity of output is not required, a linear pattern as shown in (b) may be used, or a broken line pattern as shown in (c) may be used.
Integrating light receiving elements divided into three or more parts as shown in (d), creating patterns that are not complementary to each other as shown in (e), and creating various shapes by combining these. It can be used depending on the purpose of use.

Next, let us consider the output when the two light receiving elements 16a, 16b are formed in the two complementary shapes as described above, and the output is linear with respect to the deflection of the incident beam. In addition, here, FIG. 6(a)
Assume that there are extended sections on both sides as shown in .

Now, if the focus position is at the point where the outputs of the two light receiving elements 16a and 16b match, the output will have a waveform as shown in Figure 7 (note that the deflection of the guided light is due to the focus error. (The zero position corresponds to the in-focus position.) In this case, the focus error signal may be the output of the light-receiving element 16a or the light-receiving element 16b, but it is possible to obtain an even larger signal by using the difference signal between these (indicated by the dotted line in FIG. 7). Become. Furthermore, even if the focal position deviates from the origin in Fig. 7, it only destroys the symmetry of the signal, and there is no problem as long as there is no major deviation. can.

Effects of the invention Light emitted from a laser light source is guided through a waveguide formed on a substrate, and the guided light is diffracted by an optical grating coupler and irradiated onto an optical information recording medium to record information. At the same time, the reflected light from the optical information recording medium is collected by the condensing grating coupler and guided into the waveguide again, and the guided light is detected by a photodetector, thereby reproducing information and eliminating focus errors. In an optical information recording and reproducing device that reproduces signals and track error signals, the shape of the aperture of the photodetector is formed in a non-uniform state with respect to the length in the optical axis direction of the guided light, and the non-uniform shape is Since at least two photodetectors are provided, the photodetectors have shapes that are not uniform in the optical axis direction of the guided light, thereby eliminating the focus error signal that does not have a dead area as in the conventional method. Detection becomes possible, and by providing a plurality of such photodetectors, it becomes possible to further increase the detection sensitivity of refocus error signals and reproduced signals.

]　Silicon

[Brief explanation of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention, FIG. 2 is a sectional view taken along the line A-A, FIG. 3 is a vertical sectional side view showing a modification of the present invention, and FIGS. 4 and 5 are optical FIG. 6 is an explanatory diagram showing a design example of a detector; FIG. 6 is an explanatory diagram showing a modified example of the shape of a photodetector; FIG.
The figure is a waveform diagram showing how the output of the photodetector becomes linear with respect to the deflection of the guided light, and FIG. 8 is a configuration diagram showing a conventional example. 10...Substrate, 16a, 16b-photodetector, ■7...
・Waveguide light

Claims (1)

[Claims] Light emitted from a laser light source is guided through a waveguide formed on a substrate, and the guided light is diffracted by an optical grating coupler and irradiated onto an optical information recording medium to record information, etc. The reflected light from the optical information recording medium is collected by the condensing grating coupler and guided into the waveguide again, and the guided light is detected by a photodetector, thereby reproducing information, focusing error signals, and tracking. In an optical information recording and reproducing device that reproduces an error signal, the shape of the aperture of the photodetector is formed in a non-uniform state with respect to the length in the optical axis direction of the guided light, and the shape of the aperture of the photodetector is made non-uniform. An optical information recording and reproducing apparatus characterized in that at least two of the photodetectors are provided.