JPS5987411A - Substrate for optical circuit - Google Patents

Abstract

PURPOSE:To form a waveguide reduced at its transmission loss and to apply an electric field efficiently when the titled substrate is used as an electrooptical element by forming a coating layer on the surface of a projected part of a PLZT layer formed like a band on an insulated base body. CONSTITUTION:When the insulated base body 31 is formed as multi-layer constitution by selecting one of MgO, spinel, SrTiO3, and sapphire and a coating layer 33 is constituted by at least one of oxide, nitride and sulfide, transmission light is efficiently shut up in the projected part 321 of the PLZT layer and a substrate effective for the formation of an optical circuit is obtaind. If the difference in level between the projected part 321 and a peripheral part 325 is set up to 100nm or less, the light in the high order mode is not transmitted, and the loss of optical transmission is reduced. When the film layer 33 is constituted by 50-200nm thickness, the electric field is applied to the projected part 321 efficiently with the smal loss of optical transmission.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention Q:1 relates to a substrate for optical circuits. In particular, the present invention relates to a circuit board material and its structure.

Conventional examples 11, 17. Conventionally, as this type of optical waveguide, especially an optical waveguide using a thin film having an electro-optic effect, a ridge type waveguide and a low=1.degree. type waveguide are well known.

Next, the structure of the waveguide and its problems will be explained with reference to the drawings.

FIG. 1 shows a ridge waveguide 10. FIG. A second loaded waveguide 20 is shown. 1 and 2, 11 is a substrate, 12 is a thin film having an electro-optic effect,
13 indicates a buffer layer.

24 indicates a loaded paulownia material made of a band-shaped dielectric material.

For example, in the ridge-type waveguide 10, a convex portion is provided at i(J) 12 in order to obtain a sufficient light focusing effect.

For this reason, the scattering loss of bound wave light due to the side surface 15 of the convex portion has been a problem. In addition, when forming an electrode on a waveguide to form an element that utilizes the electro-optic effect, the electric field
A sufficient number of 1 (17) buffer and 7 fur layers (13) were used to effectively apply the voltage.

At this point, the buffer layer 13 covering the convex portion becomes abnormally l-1, which causes a problem of increased light propagation loss due to the electrode metal film provided on the buffer layer 13''.

Particularly in optical waveguide paulownia materials, which have a high dielectric constant, it was thought that an electric field could not be applied effectively even if the hesopha layer was made thin. Also, in the waveguide 20 of the load 41, when forming electrodes on the waveguide, a buffer layer was formed in order to prevent an increase in propagation loss due to the electrodes. For this reason, as in the case of the ridge type waveguide, it is advisable to apply an electric field to the material 12 and the buffer layer 13. Load(
There was a problem in that it could not be applied effectively because it passed through the charge 24.

Purpose of Investigation The purpose of the present invention is to eliminate the problems of the above-mentioned conventional example, and to provide a waveguide with small propagation loss and a method for effectively applying an electric field when using this waveguide as an electro-optical element. γ from a sacrificial film with an electro-optic effect, which
An object of the present invention is to provide a substrate for an optical circuit.

Village of excuses 6sei The −+′ investigation will be explained below using figures.

FIG. 3 shows the structure of the optical circuit board according to 1. In the same figure, the optical circuit board related to the inexcusable is a small one.
At least the insulating substrate 31 and the insulating substrate 31-1-
A PLZT layer 32 having a band-shaped convex portion and at least one
-11self P L Z 'r surface 322 of convex part 321 of layer
-C is characterized in that it is constructed from a composite layer 33 provided on the top.

Among these constituent materials, the present inventors constructed the insulating substrate 31 from MgO, spinel, SrTiO3, or sapphire (fl-*, g2o3), and formed the multilayer (1
If fJJ and WtZ materials are selected with η, it is assumed that light propagates through the convex portions of the PLZT layer 32, and thereby an optical circuit formation VC-II' effect 1J substrate can be formed. It's fli Kl.

That is, it is possible to epitaxially grow a PLZT-based thin film with low optical propagation loss on these insulating substrates 32 by, for example, sputter deposition.
The inventors had no idea that the T-based thin film would have a greater electro-optic effect than the LINbO3 single crystal.

In general, the inventor also made the coating layer 33 by using TiO2, Ta20.
5゜ZrO,, oxides such as Nb2O5, ZnO, S
Nitride such as i3N4, As2S3. If at least one selected from the group consisting of sulfides such as ZnS is configured, the propagating light is effectively confined in the PLZT layer convex portion 321, and at the same time, the propagation of higher-order modes that normally impede the use of optical circuits is prevented. The inventors have discovered that this PLZ can prevent the original generation of light and reduce the light propagation loss caused by the surface roughness of the side surface 324 of the stepped portion 323 of the convex portion 321.
By utilizing the small optical propagation loss, large electro-optic effect, and unique piezoelectric properties of T-based thin films, it is possible to realize various optical devices that cannot be realized with conventional substrates for optical circuits of this type, such as LiNbO3 single crystal substrates. Inventor Rake 6
11 (Acknowledged.

In this case, if, for example, a surface-polished single crystal plate with (0001) plane is used as the sapphire (α-alumina) used as the substrate 31, a (111) PLZT-based f,'j film can be epitaxially grown by, for example, sputter deposition. do. If one crystal of spinel (100) is used once a month, a PLZT system lv11 of (111)lII'i can be formed in the same way.In addition, in magnesia, for example, a single crystal plate of (100) plane can be formed. When the moon 1 is present, a (100) PLZT-based thin film can be formed.As in this example, the crystal orientation of the PLZT-based 1jj7 film can be changed by selecting the crystal plane of the substrate. ] Substrate iJ, for example, 1'-th electrode configuration/arrangement 111M for forming an optical device:
Another feature is that it is spacious. Note that this board is made of PLZT
The epitaxial growth of the system thin film and the PL
Because it is confined in the ZT-based thin film, its refractive index is PLZ.
It only needs to be smaller than the value of the T-based thin film (285 to 26), and is limited to sapphire, spinel, and magnesia. In addition, the substrate has 0,1 to o,5 of its surface axj layer.
It is sufficient that even the 71 m portion satisfies the above-mentioned necessary characteristics as a base.

Among the structures according to the present invention, the researchers also found that PLZT
The structure of the layer convex portion 121 was found to be very effective in controlling the mode of guided light and roughly controlling the electric field of propagating light. That is, in FIG. 3, the old convex portion 321 is completely formed by etching the 32-layer PLZT layer 2 in a band-like manner, and the propagating light is guided along the convex portion 321. in this case,
It has been demonstrated that when the height difference between the convex portion 321 and the peripheral portion 326 is set to 1100 nm or more F, higher-order mode light propagation, which causes noise in a normal optical circuit, does not occur and light propagation loss is small. J-, K [When providing poles, since light propagation loss occurs due to the loading of electrodes in ordinary optical circuits, for example, use quartz glass of 200 OA' or more] - Cover the heart wave path surface as a buffer layer to prevent light propagation loss. For this reason, PLZ
In the case of a material with anti-static properties such as the T-based 7VI film, the voltage applied to the apricot and helium layers is partially reduced, and no voltage is effectively applied to the optical waveguide. Attached to the inventors, TiO2, Ta205ZrO2, N'b205
, oxides such as ZnO, nitrides such as 513N4, and As25. It has been found that when the thickness of the coating layer 33 made of a sulfide such as ZnS is set to 200 nm to 200 nm, the optical propagation loss is small and the electric field can be applied effectively to the PLZT layer convex portion 321.

- In other words, when FK is larger than 60 nIn, the electric current L[C is mainly distributed to the waveguide, but the propagation loss becomes large due to the d-output effect of the propagating light in the waveguide to the coating layer, making it impractical. confirmed. Furthermore, when the thickness is set to 20 onm or more, the optical propagation loss can be ignored, but since the electric voltage is considerably divided into the coating layer, the electric voltage is not effectively divided into the waveguide, and the present invention is not effective. ! Also, please make sure that you have enough raw fins.
II ninja.

This means that the FFG structure of the present invention can fully utilize the characteristics of PLZT with large electro-optic IA and 17, and it is possible to easily realize low-voltage driving of optical devices. .

Hereinafter, in order to make the content of F misfire Ivj deeper <14F1), a specific example will be explained with a glance.

Example Description Surface polished (0001) with thickness 0.311111+
A PLZT thin film having a thickness of 0.4/1 m was deposited on the surface sapphire substrate 1 by high-frequency Macnetron spacing.

In this case, the composition of the sputtering target is 1. jPLZT
C2810/100), the temperature PM of the sapphire M body during sputtering was 6800G, and the sputtering power was 200W. The structure of the deposited PLZT thin film is a (111) single crystal with a refractive index of )i:e-Ne laser (0,
63/)m wavelength), which was 2.6. Next, this PL
After etching the surface of the ZT-based thin film by photoresist processing to form a convex portion, a thin film of Ta205 with a thickness of 1,501 cm was deposited on the surface of the convex portion by myofrequency macnetron sputtering.
A substrate for an optical circuit according to the present invention was formed by vapor deposition.

In the examples to the north, PL is used as the composition of the PLZT thin model.
ZT (2810/100) is shown, but by simply changing the composition of the sputtering target, a PLZT-based 7W film with the desired composition can be formed and used as a light propagation path.

Effects of Excuse In the optical circuit board according to the present invention, since all the light propagates in the PLZT thread, the PLZT system has a large electro-optic effect unique to the PLZT system, and an acousto-optic effect using piezoelectricity, such as a surface wave. σ et al. have the advantage that the optical propagation loss of these propagating lights is small and that the control of the propagating lights also requires low voltage driving.Therefore, this kind of If the substrate is used, a famous γj17 film optical IC can be realized in which various microscopic optical elements can be easily integrated, so the optical circuit substrate according to the present invention has great industrial value.

[Brief explanation of the drawing]

Fig. 1 ii 4rY: A diagram showing the structure of the conventional optical circuit board, Fig. 2 is a diagram showing another structure of the conventional optical circuit board, IIT 3 Fig. 1. It is a diagram showing the configuration of a circuit board. 31...] 1 (board, 32... PLZT layer, 3
3...Restored layer, 321...P L Z T
@Protrusion, 322...PLZT)lrf l'-'
l ffμ surface, 323...PLZT layer step portion, 32
4...PLZT layer step layer side difference part side surface 6...PL
Around the ZT layer. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2 Figure 3

Claims (1)

[Scope of Claims] (1) An insulating body, a band-shaped convex portion is provided on the insulating substrate (-1), and at least the above-mentioned PLZT layer.
1. A substrate for an optical circuit, comprising a coating layer provided on the surface of the convex portion of the T layer. An optical circuit board according to claim 1, characterized in that the optical circuit board comprises: 2. The optical circuit board according to claim 1, wherein the group (3) coating layer is made of at least one selected from oxides, nitrides, and sulfides. (4) The optical circuit board according to claim 1, wherein the height difference in the PLZT convex portion does not exceed 1001 m f:: from the peripheral portion of the second convex portion. (6) A substrate for an optical circuit according to the scope of the patent application, item 1, wherein the thickness of the coating layer is from 200 nm to 200 nm.