JPH0430341A - Optical integrated circuit - Google Patents

Abstract

PURPOSE:To reduce crosstalk and to facilitate the suspension of a detection signal between photodetectors by providing an optical element to a light incidence side of lots of photodetectors formed closely to each other. CONSTITUTION:A laser beam propagates the deepest pat of photo diodes 18a,18b,20a,20b by the action of waveguide lenses 28a,28b,30a,30b. Thus, even when an optical disk 26 is displaced in a closing or parting direction to/from an optical integrated pickup, the laser beam propagates the deepest part of photo diodes 18a,18b,20a,20b by the action of waveguide lenses 28a,28b,30a,30b. Thus, crosstalk of a detection signal between the photodiodes 18a,18b and between the photodiodes 20a,20b is prevented in an excellent way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical integrated circuit, and relates to an optical integrated circuit suitable for, for example, an optical integrated pickup for writing or reading information on an optical disk. .

[Previous technology] As a conventional optical integrated circuit, for example, Japanese Patent Application Laid-Open No. 61-296
Publication No. 540, or Transactions of the Institute of Electronics and Communication Engineers, '861
5. Vol1. J69-No. 5R Optical Integrated Circuit of Optical Disc Pickup" is disclosed. This is an example of an optical integrated pickup that functions by a combination of a thin film waveguide, a thin film lens, and a light receiving element.
A+, +B) respectively show its plane and front view.

In these figures, light emitted from a laser diode 100 propagates through a thin film waveguide 106 made of glass formed on an S1 substrate 102 via a buffer layer 104 made of 5i02, and then passes through a condensing crating lens 108.
incident on . The laser beam is then focused onto the optical disk 110 by the diffraction effect of the focusing grating lens 108.

Next, the light reflected by the optical disk 110 travels in the opposite direction along the optical path, enters the condensing grating lens 108 again, and travels backward through the waveguide. The reversed light is split into two wavefronts by the beam split grating lens 112. One of the divided return laser beams is focused near the photodiode 114a114b, and the other is focused near the photodiodes 116a and 116b.

And these photodiodes 114a, 11.4
By performing sum and difference calculations on the detection signals photoelectrically converted by b116a and b116b, the optical disc 1
Ten bit signals, a focus error signal, and a tracking error signal are each detected.

[Problem to be solved by the invention] By the way, the photodiodes 114a, 114b,
The laser light incident on the laser beams 116a and 116b is incident within a certain angular range as shown in FIG. For example, if the optical disk 110 is displaced in the direction indicated by the arrow FA in FIG. 6(B), the laser beam will mainly enter the photodiode 114b as shown in FIG. 7(A). Conversely, if the optical disk 110 is displaced in the direction indicated by the arrow FB in FIG.
It becomes incident towards .

The same applies to photodiodes 116a and 116b.

In this way, when a focus error or tracking error occurs, the photodiodes 114a, 1]4b.

The angle of incidence of the laser beam with respect to 116a and 116b varies. For this reason, as shown by arrow FC in FIG.

There is a possibility that the laser beam that is obliquely directed toward the photodiode 114b passes through the photodiode 114b and reaches the adjacent photodiode 114a.

By the way, the focus error signal is transmitted from adjacent photodiodes 114a and 114b, or 116a and 11
6b is detected from the detection signal difference between the two. Therefore, separation of detection signals between adjacent photodiodes is important for detecting focus errors.

However, when crosstalk occurs in the detection signals as shown in FIG. 8, the quality of the detection signals deteriorates, making it impossible to perform good separation, and as a result, satisfactory focus control cannot be achieved. I won't be able to do that.

The present invention has been made in view of the above, and aims to provide an optical integrated circuit that can easily separate detection signals of photodiodes and obtain good detection signals.
That is the purpose.

[Means for Solving the Problems] The present invention provides an optical integrated circuit in which light to be detected enters a large number of monolithically adjacent light receiving elements from an oblique direction through a waveguide. It is characterized in that an optical element for introducing the detected light deep into the light-receiving element is formed on the incident side as necessary.

[Function] According to the present invention, the detected light incident on any of the light receiving elements is guided deep into the light receiving element by the action of the optical element. Therefore, the incidence of detected light on adjacent light receiving elements is reduced.

[Example] Hereinafter, an example of the optical integrated circuit according to the present invention will be described with reference to the attached section.

First Embodiment First, the configuration of a first embodiment of the present invention will be described with reference to FIG. In the figure, a buffer layer 12 of 5iO7 or the like is formed on a substrate 10 of Sl or the like, and a thin film waveguide 14 is further formed on this buffer layer 12. A laser diode 16 is hybridly integrated on one side of the thin film waveguide 14, and a photodiode array 1820 is integrated on the substrate IO. Further, on the other side of the thin film waveguide 14, a condensing grating lens 22 and a beam splitting grating lens 24 are integrated.

The laser beam output from the laser diode 16 is directed to the optical disc 2 by the action of the condensing grating lens 22.
6 Also, the optical disk 36
The reflected laser beam is split by a beam split grating lens 24 and sent to a photodiode array 1
8.20 respectively.

Among the above parts, the photodiode array 18 is composed of photodiodes 18a and 18b, and a waveguide lens 28 is provided on the light incident side of each photodiode.
a and 28b are formed respectively. Further, the photodiode array 20 includes photodiodes 20a and 20b, and waveguide lenses 30a and 30b are formed on the light incident side of each photodiode, respectively.

Waveguide lenses 28a, 28b, 30a.

As the lens 30b, a mode index lens such as a Luneburg lens, a Fresnel lens, a grating lens, etc. can be used (for example, see "Optical Integrated Circuits" by Ohmsha, Nishihara, Haruna, and Suhara, pp. 279-292). These waveguide lenses 28a, 28b, 30a, 30b allow the incident laser light to pass through the photodiodes 18a, 18b20.
The characteristics of each are designed so as to proceed deep into the regions a and 20b. Note that the waveguide lenses 28a and 28b
, 30a, 30b only need to act so that the laser beam enters the deep part of the photodiode, and it is not necessarily necessary to convert the laser beam into parallel beams.171+ Next, regarding the operation of the first embodiment configured as above, This will be explained with reference to FIG.

The laser light output from the laser diode 16 propagates through the thin film waveguide 14 and passes through the condensing grating lens 22.
incident on . The laser beam is then focused onto the optical disk 26 by the diffraction effect in the condensing grating lens 22.Next, the light reflected by the optical disk 26 travels in the opposite direction along the optical path and returns to the condensing grating lens 22. The light enters and travels backward through the thin film waveguide 14. The reversed laser beam passes through the beam split grating lens 2.
The wavefront is divided into two by 4. One of the divided return laser beams is focused near the light incident side of the photodiode array 18, and the other is focused near the light incident side of the photodiode array 20.

In this case, the photodiodes 18a18b, 2
Waveguide lenses 28a and 2 are provided on the light incident side of 0a and 20b.
8b, 30a, and 30b are formed, respectively. This laser beam is transmitted through waveguide lenses 28a, 28b, 30a,
Due to the action of 30b, photodiodes 18a and 18b
It will proceed to the deep parts of 20a and 20b.

For example, when the optical disk 26 is displaced in a direction away from the optical integrated pickup, the laser beam tends to travel as shown by the dotted line in FIG. 2 fA) (see FIG. 7 fA)). However, in this embodiment, due to the action of the waveguide lens 28b, the laser light travels deep into the photodiode 18b as indicated by the arrow F1. Therefore, crosstalk of pressure detection signals between the photodiodes 18a and 18b is effectively prevented.

Furthermore, when the optical disk 26 is displaced in a direction approaching the optical integrated pickup, the laser light tends to travel as shown by the dotted line in FIG. 2 FB) (see FIG. 7 FB)).
. However, in this embodiment, the laser light travels deep into the photodiode 18a as shown by the arrow F2 due to the action of the waveguide lens 28a.

Note that the same applies to the laser beams incident on each of the photodiodes 20a and 20b.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. 3 and Section 4. Note that the same reference numerals are used for components similar to or corresponding to those of the first embodiment described above. This embodiment is an example in which a geodesic lens is used as a waveguide lens on the light incident side of a photodiode.

When the above-mentioned photodiodes i8a and 18b are enlarged, it becomes as shown in FIG.

In the figure, a conductive layer 5 of a different conductivity type is shown on a substrate 0.
0 is formed. For example, if the board 10 is an N type 5
1, P type 81 is used as the conductive layer 50. A PN junction is formed at the interface between the substrate IO and the conductive layer 50, thereby forming a photodiode 18a18b, respectively.

The driving voltage is applied to the photodiodes 18a and 18b through an electrode 52 formed on the substrate 10 side and a conductive layer 50.
By the way, the laser light that has traveled through the thin film waveguide 14 reaches the substrate l in the photodiodes 18a and 18b.
It is necessary to penetrate into the junction between O and the conductive layer 50. Therefore, near the photodiodes 18a and 18b,
A tapered portion 56 is formed in the buffer layer 14. In this embodiment, a circular portion 58a is provided on the light incident side of the photodiodes 18a, 18b so as to be continuous with the tapered portion 56.
58b is formed.

According to such a second embodiment, the circular parts 58a, 58b
begins to act as a geodesic lens2. For example, laser light that is about to enter the photodiode 18b travels along a curved surface according to the Fermat principle, and its direction is directed inward as shown by arrow F3 in FIG. Start changing. Therefore, similarly to the first embodiment described above,
Laser light will be guided into the photodiode 18b. Photodiode 18a.

The same applies to 20a and 20b.

<Third Embodiment> Next, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, as shown in the figure, waveguide lenses 70a and 70b are formed on the thin film waveguide 14 on the photodiodes 18a and 18b, respectively. Any mode index or grating lens can be formed on the waveguide 14 in this way.

In this third embodiment as well, the laser light travels as shown by arrow F4 in the figure, and the same effects as in the above-described embodiment can be obtained. Note that the same applies to the photodiodes 20a and 20b.

Other Examples> Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, the present invention is applied to an optical integrated pickup, but if a large number of photodiodes are formed close to each other and light is incident on them obliquely, the present invention can be applied. is generally applicable.

In addition, as far as crossstock between the photodiodes is prevented, the inner photodiodes 18b and 2
A lens may be provided only for the photodiodes 0b and may not necessarily be provided for the outer photodiodes 18a and 20a.

In addition, the present invention is not limited to the shapes, materials, etc. shown in the above embodiments.

[Effects of the Invention] As explained above, according to the optical integrated circuit according to the present invention, by providing an optical element on the light incident side of a large number of light receiving elements formed close to each other, light is directed to the corresponding light receiving element. Since the crosstalk is made to penetrate, there is an effect that crosstalk is effectively reduced and detection signals between the light receiving elements can be easily separated.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a first embodiment of the optical integrated circuit according to the present invention, FIG. 2 is an explanatory diagram showing the operation of the first embodiment,
The third section is a perspective view of the main part showing the second embodiment of the present invention, the fourth section is an explanatory diagram showing the operation of the second embodiment, and the fifth section is an explanatory diagram showing the third embodiment of the present invention. , FIG. 6 is a block diagram showing a conventional example, and FIGS. 7 and 8 are explanatory diagrams showing the operation of the conventional example. DESCRIPTION OF SYMBOLS 10... Substrate, 12... Buffer layer, 14... Thin film waveguide, 16... Laser diode, 18.20.
...Photodiode array 18a, 18b20a,
20b...) Odogiode (light receiving element), 22...
- Concentrating grating lens, 24... Beam split grating lens, 26... Optical disk, 2
8a, 28b, 30a, 30b - waveguide lens (optical element), 50 - conductive layer, 58a, 58b - circular part (optical element), 70a70b - waveguide lens (optical element). Patent applicant: Victor Japan Co., Ltd.

Claims (1)

[Scope of Claim] In an optical integrated circuit in which light to be detected enters a large number of monolithically adjacent light receiving elements from an oblique direction through a waveguide, the light to be detected is incident on the detection target side of the light receiving element. 1. An optical integrated circuit characterized in that an optical element is formed as necessary for introducing the light into a deep part of a light-receiving element.