JPS58172619A - Substrate for optical device - Google Patents

Abstract

PURPOSE:To obtain a substrate for a miniaturized optical device or a substrate for an optical device suitable for use in optical IC by interposing a buffer layer made of a dielectric having a lower refractive index than a light transmitting layer and small transmission loss between the light transmitting layer and an electrically conductive layer to reduce loss. CONSTITUTION:A light transmitting layer 32 made of a material having a higher refractive index than a transparent substrate 31 and an electrooptical effect is formed on the substrate 31 to manufacture an optical waveguide 30. A buffer layer 33 having a lower refractive index than the layer 32 is formed on the layer 32, and an electrically conductive layer 34 is formed on the layer 33. Since the peripheral part 331 of the layer 33 can be tapered by leaving space 42 between the surface 321 of the layer 32 and a mask 41 having an opening 411 and by carrying out vacuum deposition, sputtering or ion beam sputtering, a substrate for an optical device with no transmission loss of light waves and beams at the peripheral part of the layer 33 is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a substrate for an optical device, and particularly to a substrate for a thin film optical device for an optical IC.

Just as conductive wires are used to conduct electricity in electronic circuits, and waveguides are used in microwave circuits, various optical waveguides are used in optical signal processing systems or optical ICs.

Conventionally, miniaturized optical devices, for example, Fig. 1 (a) t (b
).

As shown in (C), it was formed using waveguides of slab type (Figure a), ridge type (Figure B) classified as rectangular type, and diffused type (Figure C). In this case, -Lvc of a slab-type substrate 1 made of, for example, quartz glass, and a thin layer 2 made of borosilicate glass are provided.

In the ridge type, a thin layer 4 made of borosilicate glass is provided on a substrate 3 made of quartz glass, for example. In addition, in the diffusion type, for example, Ti is placed on the surface of the LiNbO3 single crystal substrate 5.
A waveguide 6 made of a diffusion layer is provided.

This type of optical waveguide is used not only for light transmission, but also for various optical circuits.
For example, it is used to form optical switches or optical ICs in which these are integrated. In particular, an optical waveguide is formed using a material that has an electro-optic effect that causes a change in refractive index when an electric field is applied, and a prism-coupled type (Figure a) or waveguide as shown in Figures 2 (a) and (b) is used. A head-on type (Fig. b) optical device substrate was formed, in which a light beam is directly input from the end face of the substrate. In this in-place, prism-coupled type (Fig. a), for example, a waveguide 12 made of a T1 diffusion layer is provided on the surface of a L IN b O3 single crystal substrate 11, and a prism coupling part 13 is placed on the waveguide 12. A buffer layer 14 is provided, and a conductive layer 16 is provided on the buffer layer 14. In addition, in the heradon type (Fig. b), for example, L x N
b A waveguide 22 made of a Ti diffusion layer is provided on the surface of the Oa single-crystal substrate 21, and a buffer layer 14 of the all-mum coupling type (Fig. a) is formed on the waveguide 22 using a metal mask or a photorin graph. Therefore, it is difficult to form a smooth end surface 16 of the buffer layer 14. In particular, when forming with a metal mask, the intersection 17 of the end face 16 with the waveguide 12 is easily damaged when the metal mask is attached and removed, and it is difficult to form it smoothly, resulting in a propagation loss of the optical image beam at the end face. There are drawbacks.

Furthermore, if the substrate for an optical device is constructed in the ridge type shown in FIG. The disadvantage is that the propagation loss of the light wave beam is large.

This ridge type has the disadvantage that only a head-on type optical device substrate can be formed. However, in the head-on type, the film thickness of the propagation layer is usually only a few μm, and the flatness of the alignment end face is strictly required, making it impractical. As described above, the conventional structure has the disadvantage that there is a limit to the degree of integration when a plurality of optical devices are integrated due to the propagation loss of the light wave beam at the end face of the buffer layer.

The present invention improves the structure and formation method of these optical device substrates, as well as their constituent materials, and eliminates the drawbacks of conventional optical device substrates.

That is, an object of the present invention is to provide a structure, a method for forming an optical denosing chair substrate suitable for use in a small optical device substrate or an optical IC, and its constituent materials.

Hereinafter, the present invention will be explained in detail using the drawings.

FIGS. 3(a) and 3(b) show an optical device substrate according to an embodiment of the present invention.

As shown in the figure, the optical device substrate of this embodiment is an optical waveguide in which a light propagation layer 32 made of a material having a larger refractive index than the transparent substrate 31 and having an electro-optic effect is provided on a transparent substrate 31. 3o, a buffer layer 3 having a refractive index smaller than that of the light propagation layer 32 at least on the light propagation layer 32;
3 is provided, and furthermore, a conductive layer 34 is provided at least on the buffer layer 33.

As shown in FIGS. 3(a) and 3(b), in the optical device substrate according to the embodiment of the present invention, at the peripheral edge 331 of the buffer layer 33, the buffer layer 33 of the light wave beam propagating in the light propagation layer 32 The thickness of the peripheral end 331 of the buffer layer 33 at the position of incidence on the light propagation layer 321 covered with the light is continuously changed to provide a thickness. Further, the buffer layer 33 is formed on the surface 3 of the light propagation layer 32 as shown in FIG.
21 and a mask 41 having an opening 411.
2, and a vapor deposition means such as vacuum vapor deposition, sputter vapor deposition,
Since the buffer layer 33 having a tapered peripheral edge 331 can be formed by ion beam sputter deposition or the like, there is no propagation loss of the light wave beam at the peripheral edge of the buffer layer as seen in conventional optical device substrates. A device substrate can be realized. The space between the light propagation layer 32 and the mass flow 41 is 0.
．． I found that it is better to leave one space apart from 01 fl.

In other words, if the thickness of the buffer layer is, for example, 0.2 μm below 0.01 tll, the buffer layer and the mask will be bonded by the vapor deposited substance during the formation of the buffer layer, and as soon as the mask is removed, If it is more than 11M, the processing accuracy of the buffer layer will be more than 211I11, making it difficult to miniaturize the substrate for optical devices.In addition, in ridge-type optical waveguides, especially due to sputter deposition, When the buffer layer is formed, the buffer layer is also smoothly formed on the side surface 7 of the thin layer 4 shown in FIG. 1, and the propagation loss of the light wave beam can be eliminated. I discovered that it is possible to form

The present inventors have discovered that there is an optimal constituent material for forming this type of optical device substrate. That is, when the conductive layer 34 is mounted on the light propagation layer 32 as shown in FIG. A low propagation loss dielectric with a smaller refractive index, e.g. S 10
2 (quartz).

Soda glass, borosilicate glass + '90+α-A12
It has been confirmed that the loss can be reduced by inserting the buffer layer 32 made of at least one type of 03° spinel.

The conductive layer 34 shown in FIG. 3 is made of Au, Ag, Pt.
, Cu.

It is effective to use at least one of the following metals: Al, Cr, Ti, Mo, and W. In this case, the same effect can be obtained even if a transparent conductive film is used, for example. Furthermore, it is effective to form an electrode pattern on the conductive layer 34 by, for example, photolithography, which is used in a normal semiconductor process.

As a result of searching for the structure of the substrate for optical devices of the present invention and the possibility of its realization, it was found that, for example, LIN b Os
Using a single-crystal substrate, a light propagation layer consisting of a Ti diffusion layer was provided, and it was found that quartz Si02 glass was suitable for the buffer layer and, for example, vapor-deposited Al was suitable for the electrode.

In other words, with this kind of constituent material, by introducing thin film forming techniques such as sputtering and vacuum evaporation, it is possible to realize a substrate for an optical device having the structure according to the present invention, and it is possible to realize a light concentrating device such as an optical IC. It was confirmed that it is effective.

Next, the formation procedure and constituent material elements of the optical device substrate according to the present invention will be explained in more detail.

First, for example, on the surface of a Ti-diffused LiN b Os optical waveguide, a light propagation layer made of a Ti-diffused layer and a mask are separated by 0.1, and silica glass is deposited to a thickness of about 0.21 tm, for example by high-frequency sputtering. A buffer layer is provided except for the bonding portion. Furthermore, for example, the Ae film has a thickness of, for example, 0.2 μm.
Vacuum evaporation is performed, and a conductive layer is formed along the length using conventional photolithography. In this case, the light wave beam incident from the pre-transmission part passes through the edge of the buffer layer, and the refractive index of the light propagation layer, which applies an appropriate electric field to the conductive layer provided on the buffer layer, changes due to the electro-optic effect. , a light wave beam is propagated in a controlled manner. Specifically, the thickness of the buffer layer changes continuously over a length of about 1 inch in the case of a buffer layer of 0.2 μm, and a taper is formed at the end of the buffer layer, which causes breakage at the end of the conventional buffer layer. It can be confirmed that the propagation loss of sdB due to dirt and contamination has decreased to less than 1 dB, which is a significant improvement in the case of the above embodiment.

Although silica glass has been described as the buffer layer in the above description, the buffer layer is not limited to silica glass as long as the refractive index of light is smaller than that of the light propagation layer. An example is borosilicate glass.

In addition to soda glass, silicon nitride and other materials can also be used.

As an optical waveguide for an optical device substrate, the present inventors
The configuration shown in Figure 1(a) was used, but the configuration shown in Figure 1(b) was used.
The effects of the present invention can also be obtained by using the optical waveguides shown in ) and (C).

Furthermore, the present inventors have provided a plurality of buffer layers 33 on a light propagation layer 32 and a conductive layer 34 on the buffer layers to form an optical device substrate as shown in FIG. Since a coupling portion can be provided and there is no light propagation loss at the end of the buffer layer, it has been confirmed that it is effective for realizing optical integrated devices such as optical ICs.

As is clear from the above description, the substrate for optical devices according to the present invention has no propagation loss as seen in conventional buffer layers, so it is possible to miniaturize and integrate optical devices.
It is effective for integrated functional devices such as optical ICs.

[Brief explanation of the drawing]

Figures 1 (a), (b), and (c) are perspective views showing the structure of the thin film waveguide, and Figures 2 (a) and (b) respectively.
3-1 are respectively perspective views of conventional optical device substrates.
3(a) and (b) are respectively a perspective view and a sectional view of a substrate for an optical device, which is an embodiment of the present invention, and FIG. 4 is a diagram showing a method for forming the buffer layer of the substrate for an optical device. FIG. 5 is a perspective view of an optical device substrate according to another embodiment of the present invention. 1.3,5,11.21.31...Substrate, 1
42333 mountain...buffer': layer, 15, 24.34
. . . Conductive layer, 32 . . . Light propagation layer. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 113 Figure t (b)

Claims (6)

[Claims] (1) A light propagation layer made of a material having a refractive index larger than the transparent substrate and having an electro-optic effect is provided on a transparent substrate, and a buffer having a refractive index smaller than the light propagation layer is provided on the light propagation layer. 1. A substrate for an optical device, characterized in that a conductive layer is provided on the buffer layer. (2) The substrate for an optical device according to claim 1, wherein the thickness of the peripheral edge of the buffer layer is continuously changed so that the peripheral edge has a taper. (3) The substrate for an optical device according to claim 1, wherein the buffer layer is a buffer layer formed by vapor deposition through an opening of a mask placed floating above the light propagation layer. (4) Buffer layer is quartz, soda glass, porosilicate glass+-MgO, a A 1203. The optical device substrate according to claim 1, characterized in that the substrate is made of at least one type of spinel. (5) The conductive layer is Au, Ag, Pt, Cu, Al1. C
r, Ti. The optical device substrate according to claim 1, characterized in that the substrate is made of at least one of Mo and W. (6) The optical device substrate according to claim 1, wherein the conductive layer is patterned.