JPS5944004A - Substrate for thin-film optical circuit - Google Patents

Abstract

PURPOSE:To facilitate the formation of an optical control element on a substrate for a thin-film optical circuit by forming a light propagation medium layer covering an amorphous thin film formed selectively on the surface of a single- crystal substrate and the substrate surface, and making the refractive index of the light propagation medium layer locally different. CONSTITUTION:The amorphous thin film is formed in a desired shape on a part of the surface of the single-crystal substrate 22 and the light propagation medium layer 50 is formed over the surface. Consequently, crystal is grown differently on single-crystal parts 50a and 50b and an amorphous part 50c; areas on the single-crystal parts 40a and 50b have higher refractive indexes than the area on the amorphous part 50c and the areas on the single-crystal parts 50a and 50b form a light guide. The substrate 22 is made of sapphire, spinel, etc., the thin film 51 is made of quartz glass, silica glass, etc., and the layer 50 is made of one kind among PLZT, PZT, PLT, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of Industry-1- The present invention provides a substrate for a thin film optical circuit that can form and lengthen an optical waveguide having a thin film structure.Constitution of a conventional example and its problems Just as conductive wires are used to conduct electricity in electronic circuits, waveguides are also used in microwave circuits (in optical processing systems or optical ICs).

An optical waveguide is required.

BACKGROUND OF THE INVENTION Conventionally, a diffused waveguide as shown in FIG. 1 has been used as an optical waveguide for miniaturized optical devices or optical ICs. In this case, one example is Kuruku's LiNb05
A waveguide 12 made of a Ti diffusion layer is provided on the surface of a single-crystal substrate 110. This type of optical waveguide is used not only to transmit light, but also to miniaturize or integrate various optical circuits (1, for example, optical devices). Formation of functional devices or optical IC
Used in the formation of For this reason, a material with a large electro-optic effect has been used as a substrate for an optical circuit. However, in the case of the diffusion type optical waveguide using a bulk single crystal substrate, the material of the substrate is limited.

It cannot be monolithically integrated with various devices, and the degree of freedom in design is limited.

In order to eliminate such drawbacks of optical circuit boards using bulk substrates, a thin film optical circuit board for forming a thin film optical waveguide as shown in FIG. 2 has been proposed. That is,
A four-layer optical circuit board has a multilayer structure consisting of a substrate 22 whose surface is covered with a light propagation medium layer 21. Normally, the substrate 22 refracts light so that light can pass through the light propagation medium layer 21. The optical propagation medium layer 21 has a smaller coefficient than the optical propagation medium layer 21. The substrate 22 is made of sapphire, for example, and is an optical propagation medium 21 that can be formed into an optical waveguide and monolithic by forming various semiconductor elements thereon.
Various thin film optical circuit substrates have been proposed in which light is controlled by growing a single crystal on a single crystal substrate 22 and utilizing the electro-optic effect or acousto-optic effect of this single crystal thin film. The substrate has a wide range of applications.

By the way, in such a thin film optical circuit board, the waveguide 1
When forming optical elements such as reflectors and gratings, a dielectric or metal is formed on a monocrystalline thin film 31-1-, for example, as shown in FIG.
It is processed into the desired shape using Riya's photo phosphorography technique. Also, as shown in Fig. 4, grating 4
0 is formed on the surface of the substrate 11 to form a reflector, etc.
This requires etching of the H substrate.

As described above, these steps require strict control of the surface distortion, surface roughness, and individual striations of the single crystal thin film, and are difficult and result in poor yields. This invention eliminates the drawbacks of thin film optical circuit substrates and facilitates the formation of optical control elements on the thin film optical circuit substrates. The purpose is to give the structure of

Structure of the invention: 1. The thin film optical circuit substrate of the present invention includes a single crystal substrate,
an amorphous thin film selectively formed on the surface of the single crystal substrate; and a light propagation medium layer formed to cover the surface of the single crystal substrate and the surface of the amorphous thin film; The refractive index of the propagation medium layer is different from the refractive index of the light propagation medium layer on the region where the amorphous thin film is not formed.

DESCRIPTION OF EMBODIMENTS A thin film optical circuit substrate according to an embodiment of the present invention will be described below.

FIG. 6 shows the structure of a main part of a thin film optical circuit board according to an embodiment of the present invention. In other words, an amorphous thin film 61 is formed in a desired shape on a part of the surface of a single crystal substrate 220, and then on these surfaces. A light propagation medium layer 5o is formed thereon. In this case, the light propagation medium layer portion 50a is formed on at least the surface of the single crystal substrate 22 so that the light propagates through the light propagation medium layer 6°.

The refractive index of 5Qb must be greater than the refractive index of single crystal substrate 22. In this way, when the amorphous thin film 61 is selectively formed on the surface of the single crystal substrate 220 and then the light propagation medium layer 6° is formed on these surfaces, the light propagation medium layer 60 is formed in the underlying portion, that is, the single crystal portion 6Qa. , 50
1) The state of crystal growth differs between the top and the amorphous portion 50C, resulting in a difference in the refractive index of the A'-propagation medium layer 60. That is, the light propagation medium layer 60 has a single crystal portion 5Q.
a.

50b”- is the region J on the amorphous portion 60C.
: l:), the Ml refractive index increases, and the single crystal part 60
a.

The region of 6Qb l- becomes an optical waveguide.

The present inventors 1 discovered that there are optimal constituent materials for each component of this type of thin-film optical circuit board, and based on this, it was possible to realize a high-performance external optical circuit board. In other words, in the thin film optical circuit substrate for controlling jf and fli, an optimum method is adopted in which the problem of crystal matching between the substrate 22 and the optical propagation medium layer 50 and the relationship between the refractive indexes described above are simultaneously satisfied. It was discovered that the constituent materials of the single crystal substrate, the optical propagation medium layer, and the amorphous thin film 61 were the same, and it was confirmed that a thin film optical circuit substrate with excellent characteristics could be realized.

The structure of the thin film optical circuit board according to the embodiment of the present invention shown in FIG. LZT, PbTiOs.

LiNbO5, LiTaO3, and even PLT, PZ
T, Zn5e, ZnTeGd5. CdO, CdT
II-v+ compounds such as e, GaP, InP
Suitable materials include GaAlAs, GaAs, Ill-V group semiconductors, and sapphire, spinel, and MgO for the substrate 22.

tl-7/Remina 5rT10s, GaAs, Si
, Cre, etc. are suitable as the amorphous thin film 51.

It was confirmed that quartz glass, soda glass, borosilicate glass, silica glass, etc. are suitable. Thin film optical circuit substrates using these constituent materials include optical rC.

It is effective in realizing integrated optical circuits.

Below, the formation procedure and constituent material elements of a thin film optical circuit board according to an embodiment of the present invention will be explained in more detail. First, 1, for example, a single crystal plate of sapphire is used as a substrate, and 1
For example, an amorphous thin film of quartz glass with a thickness of 0.277
Form about m. At that time, the amorphous thin film 61 shown in FIG.
parallel like.

It is formed into a band shape with a width of 6 μm and an interval of about 6 μm. This can be achieved by a conventional photolithography technique. Amorphous thin films can be deposited using high-frequency sputtering, for example.
: Can be formed.

Next, a P L'Z T single crystal thin film is formed on the sapphire substrate including the amorphous thin film band formed from this quartz glass. This means, for example, that the substrate temperature is 600~s
This is achieved by epitaxially growing PLZT using a radio frequency sputtering deposition method. At this time, a single-crystal thin film of PLZT epitaxially grows on the surface of the sapphire substrate, but an amorphous thin film band forms.
It is polycrystalline or amorphous. Here, PLZT is an optical propagation medium and can guide light. That is, the single crystal portion 5Qa of the PLZT thin film.

The refractive index differs between sob and the other portion 6oc due to the difference in crystal structure. Usually, the single crystal portion has a high refractive index. Therefore, if light is guided to the PLZT single crystal portion 601), this portion becomes an optical waveguide.

The PLZT single crystal thin film is a material with a large electro-optic effect, and also has an acousto-optic effect, as well as piezoelectricity, so a variety of devices can be realized by providing various electrodes on its surface.

FIG. 6 shows a thin film optical circuit board according to another embodiment of the present invention, which has the same structure as the board shown in FIG. This structure forms a refractive index changing portion and serves as a grating for light, and this structure enables effects such as single reflection and diffraction of guided light.

FIG. 7 shows a thin film optical circuit board according to still another embodiment of the present invention, in which an amorphous thin film 70 is formed into a shape with a curved part as shown in the figure, and the light propagates through the light propagation medium 60. It is designed to act as a lens for incident light 71 that enters the amorphous thin film portion.

Fig. 7 shows a case where the refractive index of the light propagation medium on the surface of the amorphous thin film 7o is larger than that of other parts, and in this case, as shown in the figure, the incident light is converged and it operates as a convex lens. showed that.

In addition, in the description of the above-mentioned embodiment, the single-crystal No. 1 of the optical propagation medium is used.
1. The case where the refractive index of the surface portion of the plate is larger than the refractive index of the surface portion of the amorphous thin film is shown.

An amorphous thin film is formed of metal, and the light propagation medium is made of high jl.
If the metal is thermally diffused into the optical propagation medium when formed in A, the refractive index of that portion will normally be higher than that of the portion J: where the metal is not diffused. This allows the above j
It is possible to realize a light I control element that operates in the same way as in J and - cases.

Furthermore, in the second embodiment, the case where the single crystal substrate is composed of a single body has been explained, but the substrate may be any substrate on which a single crystal thin film can be formed. The substrate may have a single crystal thin film formed on its surface. Furthermore, the above explanation.

The case where the amorphous thin film is formed in one layer has been described, but of course it may be formed in two layers or multiple layers.

Effects of the Invention The thin film optical circuit board of the present invention as described in 2. can be fabricated in the shape of an amorphous thin film to realize various optical devices in a simple process, and it is possible to miniaturize and integrate optical devices. It is useful for the integration of optical RC, and the realization of various elements [1f-capable 0

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional optical circuit board, and FIG. 2 is a diagram showing a conventional optical circuit board. FIG. 3 is a diagram showing a conventional thin film optical circuit board, FIG. 4 is a diagram showing a conventional optical element, and FIGS. 6, 6, and 7 are thin film optical circuit boards according to embodiments of the present invention. FIG. 22... Single crystal substrate, 21.31.60...
...Light propagation medium layer, 61.61.70...Amorphous thin film. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 2 I Figure 4 0 Figure 5 Sθ Figure 6

Claims (1)

[Scope of Claims] (1) A single crystal substrate, an amorphous thin film selectively formed on the surface of the single crystal substrate, and a light film formed so as to cover the surface of the single crystal substrate and the surface of the amorphous thin film. a propagation medium layer, wherein the refractive index of the light propagation medium layer on the amorphous thin film is different from the refractive index of the light propagation medium layer on a region where the amorphous thin film is not formed. Circuit board. (2) The single crystal substrate is sapphire. Spinel, MgO. a-7 Lumina, 5rTiOs, GaAs,
The thin film optical circuit substrate according to claim 1, characterized in that it is made of either Ge or Si. (3) The thin film optical circuit substrate according to claim 1, wherein the amorphous thin film is made of at least one of quartz glass, silica glass, borosilicate glass, and soda glass. . (4) The optical propagation medium layer is P L Z T , PZT, P
LT, LiNbO3゜LiTaO5, PbTiOs,
The thin film optical circuit substrate according to claim 1, characterized in that the thin film optical circuit substrate is made of a dielectric thin film of at least one of BaTiO3, ZnO, Zn5e, and CdS. (6) The thin film according to claim 1, wherein the amorphous thin film is made of a metal selected from Ti, I, and U, and the metal is diffused into the light propagation medium thin film. Claim 1, wherein the optical circuit substrate 0 (6) optical propagation medium layer is composed of a semiconductor thin film of at least one of III-V group compounds such as GaP, GaInP, GaAs, and GaAjAs.
A thin film optical circuit board as described in 2. (a) The thin film optical circuit substrate according to claim 1, characterized in that the amorphous thin film is periodically arranged in a banded manner. (8) The thin film optical circuit substrate according to claim 1, wherein the amorphous thin film is formed in a shape including a curved portion.