JPH01312512A - Opposed counter and signal reader using same - Google Patents

Abstract

PURPOSE:To improve the utilization efficiency of light and facilitate optical axis alignment by forming light waveguide layers which vary in equivalent refractive index in the traveling direction of the light on both surfaces of a substrate which transmits light. CONSTITUTION:The waveguide layers 2 and 4 which vary in equivalent refractive index in the traveling direction of the light are formed on both sides of the substrate 3 which has light transmissivity. The 1st optical waveguide layer 2 and 2nd optical waveguide layer 4 decrease in thickness in a tapered shape toward a substrate end part 3a and called a 1st tapered coupler 2a and a 2nd tapered coupler 4a. The light is guided into the 1st optical waveguide layer 2 and propagated in the layer, but when it is propagated to the 1st tapered coupler 2a, it is emitted gradually to the side of the substrate 3 and emitted out of the substrate end part 3a. The light which enters the 2nd tapered coupler 4a from the substrate end part 3a is converted to the waveguide mode of propagation in the 2nd optical waveguide layer 4. Consequently, a high-efficiency input/output coupler is realized and the optical axis alignment is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a facing coupler, which is an optical input/output element used in optical discs, etc., and a signal reading device using the same.

[Prior art] Conventionally, a substrate is made of an optical material with high light transmittance at the wavelength used, a region with a slightly high refractive index is created on its surface, and an optical waveguide that confines light there is used to read signals from optical discs, etc. In this case, as shown in FIG. 5, a grating coupler lla with diffraction grating grooves formed on the surface of the substrate 9 is used to connect the waveguide mode in which light propagates within the waveguide layer 11 and the radiation mode in which light leaks to the outside. It was used as an optical input/output coupler.

[Problems to be Solved by the Invention] However, if the grating coupler 11a is to have a light condensing effect, it is necessary to use a chirve grating whose grating period is gradually reduced. Figure 6 shows a grating coupler. Here, silicon oxide (S L 02
) Buffer layer 8 1° 86 μm 1 Made by Corning, USA #
A grating coupler is fabricated by laminating 7059 glass waveguides 11 of 0.95 μm and silicon nitride (SiN) cladding layers 10 of 0.035 μm. in this case,
The period is 0.75 μm to 0.5 over a length of 1.0 mm.
When changing by 2 μm, light with a wavelength of 790 nm travels 2.0 m.
Focuses light on a space m away. Such fine processing requires the use of an electron beam lithography method, and furthermore, the light utilization efficiency thereof is as low as about 50%. Also, the radiation direction is from the substrate end 9a.
In principle, it is inclined to 15@ in the above example.

That is, when used as a reading device for, for example, an optical disc, it is necessary to install it at an angle of 15 degrees with respect to the optical disc.

The present invention has been made in order to solve the above-mentioned problems, and aims to provide a facing coupler with higher light utilization efficiency than conventional ones. The purpose is to provide an inexpensive signal reading device because it is easy to match and manufacture.

[Means for Solving the Problems] In order to achieve this object, the facing coupler of the present invention is provided with a light-transmitting substrate and a guide whose equipolarized refractive index changes in the direction of propagation of light. It consists of a wave layer. When used in a signal reading device for an optical disk or the like, it further includes a light source such as a semiconductor laser and a photodetector for photoelectric conversion.

[Function] In the facing coupler of the present invention having the above configuration, light propagating through the waveguide layer on one side of the substrate is emitted from the coupler toward the substrate and further emitted to the outside. On the other hand, the light incident on the coupler on the other side of the substrate is guided to the waveguide layer and propagates within the waveguide layer.

When used in a signal reading device for an optical disk, etc., light emitted from a light source such as a semiconductor laser enters the waveguide layer on one side of the facing coupler of the present invention, and is emitted to the outside in the same manner as described above, and the light is emitted from a light source such as a semiconductor laser. The light is reflected by the light beam, enters the coupler on the other side, propagates within the waveguide layer in the same manner as described above, and is guided to the photodetector.

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

FIG. 1 shows the configuration of the opposing coupler of the present invention. A first optical waveguide layer 2 is formed on one side of a substrate 3 made of an optical material having light transmittance, and a second optical waveguide layer 4 is formed on the other side,
It constitutes an opposing coupler 1. The thickness of the first optical waveguide layer 2 and the second optical waveguide layer 4 decreases in a tapered manner toward the substrate end 3a, and each of the first taper couplers 2a
It is called s second taper coupler 4a. The light passes through the first optical waveguide layer 2
The light is guided inside and propagates within the layer, but when it propagates to the first taper coupler 2a, it is gradually radiated toward the substrate 3, and further emitted to the outside from the substrate end 3a. On the other hand, the light incident from the substrate end 3a toward the second tapered coupler 4a is
It is converted into a waveguide mode that propagates within the optical waveguide layer 4. The Theba coupler will be explained below.

FIG. 2 is a perspective view showing the structure of the Taber coupler. The optical waveguide layer 2 is made of, for example, Z-cut lithium niobate (LiN
This is fabricated on a substrate 3 made of bOs) crystal. This optical waveguide layer 2 has a three-dimensional structure, has a surface refractive index of 2°204 relative to the refractive index of the substrate of 2.2, has a width of 4 μm, and has a Gaussian distribution in the depth (two-axis) direction. shows the refractive index distribution. On the other hand, the substrate 3 has a tapered shape that becomes thinner toward the substrate end 3a. The operating principle of the Taber coupler will be explained with reference to FIG. The light propagating within the leading wave layer 2 has a beam shape with an intensity distribution as shown in the figure. When this light propagates through the Taber coupler 2a, the intensity distribution gradually changes, and the energy corresponding to this change is radiated toward the substrate 3 side where the difference in refractive index is small. This Theba coupler 2a
There is a cutoff region where light cannot be confined.

Therefore, as the light travels further, all of the light energy is radiated to the substrate 3 side in this cutoff region, and an efficiency of 70% can be achieved. Due to the nature of light, this also applies when light is incident from the substrate 3 side. A method for manufacturing this Taber coupler 2a will be described below.

4μ width titanium (Ti) on Z-cut LiNbO3 crystal
Patterning is performed up to the substrate edge 3a with a thickness of 300 m1. The optical waveguide layer 2 is produced by diffusing this at 1000° C. for 5 hours. Furthermore, the length is 2 in the Y direction to the board end 3a.
Taber coupler 2 is created by polishing 00μm into a Taber shape.
a is produced.

A case in which the opposed coupler described above is applied to, for example, a reading device for an optical disk or the like will be explained with reference to the configuration diagram in FIG. 4. A semiconductor laser 5 as a light source and a photodetector 6 for performing photoelectric conversion are directly coupled to the opposing coupler 1, and the optical disk 7 is arranged so that its normal line and the normal line of the substrate end 3a coincide with each other. The light is emitted from the semiconductor laser 5, and
The light is guided to the optical waveguide layer 2. Hereinafter, as shown in the operating principle of the Taber coupler, from the substrate end 3a to the optical disk 7.
It is emitted towards. The light reflected by the optical disc 7 is
The light enters again from the substrate end 3a and propagates through the second optical waveguide layer 4 in the opposite manner to the above. Furthermore, the amount of light is detected by the photodetector 6,
For example, if information is recorded on the optical disc 7 by changes in reflectance, a modulation signal corresponding to the information will be detected.

Here, light input/output is achieved by using a tapered shape, but the shape is not limited to a tapered shape. That is, basically, the waveguide of light within the waveguide layer is described by the equivalent refractive index,
The above configuration means that the equivalent refractive index is changed in the direction in which light travels. For example, this can be achieved by creating a refractive index distribution by gradually changing the amount of titanium diffused in the direction of travel.

[Effects of the Invention] As is clear from the detailed description above, according to the present invention, a highly efficient input/output coupler can be realized simply by providing an equipolarized refractive index distribution at the tip of the leading wave layer. It becomes possible to make effective use of both sides. Furthermore, when applied to reading devices for optical discs, etc., it is easier to manufacture and cheaper than conventional devices, and optical axis alignment is facilitated by aligning the normal to the edge of the board with the normal to the optical disc. can.

[Brief explanation of the drawing]

1 to 4 show embodiments embodying the present invention; FIG. 1 is a side view showing the structure of the opposing coupler of the present invention, and FIG. 2 is a perspective view showing the structure of the tapered coupler. ,
FIG. 3 is a sectional view explaining the principle of operation, FIG. 4 is a configuration diagram in which the opposing coupler of the present invention is applied to a reading device for optical discs, etc., FIG. 5 is a perspective view explaining a conventional grating coupler, and FIG. 6 FIG. 2 is a cross-sectional view illustrating a method for manufacturing a conventional grating coupler. In the figure, 1 is an opposing coupler, 2 is a leading wave layer, 3 is a substrate, and 5
is a semiconductor laser, and 6 is a photodetector.

Claims (1)

[Scope of Claims] 1. A facing coupler comprising a substrate made of a light-transmitting optical material and optical waveguide layers provided on both sides of the substrate and having an equivalent refractive index that changes according to the direction in which light travels. 2. A signal reading device for an optical disk or the like, which comprises a light source such as a semiconductor laser, a photodetector that performs photoelectric conversion, and the opposing coupler.