JPH03202816A - Optical control device and production thereof - Google Patents

Abstract

PURPOSE:To decrease the influence of the strain after patterning and to obtain desired branching characteristics by forming electrode film gratings and buffer layer gratings in the prescribed positions near control electrodes at the time of electrode patterning. CONSTITUTION:Optical waveguides 2, 3 are provided on a lithium niobate crystal substrate 1. A buffer layer 6 and the control electrodes 5 are formed thereon. The electrode film gratings 10 are formed of the same material as the material of the electrodes 5 at the time of the electrode formation. In addition, the buffer layer gratings 11 are formed of the same material as the material of the buffer layer 6 between the control electrodes 5 and the electrode film gratings 10 at the same width as the width of the optical waveguides 2, 3 and the same spacing as the size of a directional coupler 4 after forming of the gratings 10. The electrode films 10 are left like the gratings in such a manner, by which the concn. of the strains at the time of the formation of the electrode films is dispersed to the respective gratings. The strains on the buffer layers are dispersed by allowing the buffer layer to remain in the form of the gratings.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical control device that modulates light waves, switches optical paths, etc., and particularly relates to a waveguide type optical device that performs control using an optical waveguide formed in a substrate. This invention relates to a control device and its manufacturing method.

[Conventional technology]

As the practical use of optical communication systems progresses, advanced systems with higher capacity and multiple functions are required, and new functions such as generation of faster optical signals and switching and switching of optical transmission lines are required. is necessary. In current practical systems, optical signals are obtained by directly modulating the injection current of semiconductor lasers or light emitting diodes, but with direct modulation, high-speed modulation of several GHz or more is difficult due to effects such as relaxation oscillation, and wavelength fluctuations Since this occurs, the coherent optical transmission method has drawbacks such as difficulty in application.

One way to solve this problem is to use an external optical modulator. In particular, a waveguide type optical modulator constructed from an optical waveguide formed in a substrate has the advantage of being small, highly efficient, and fast. On the other hand, an optical switch is used as a means for switching optical transmission lines and providing network switching functions. Optical switches currently in use mechanically move prisms, mirrors, fibers, etc., and are slow, unreliable, and large in size and unsuitable for matrix formation. There are drawbacks.

What is being developed as a means to solve this problem is a waveguide type optical switch using an optical waveguide.
It has features such as high speed, ability to integrate multiple elements, and high reliability.

In particular, those using ferroelectric materials such as lithium niobate (LiNb03) crystals have features such as low light absorption and low loss, and high efficiency because they have a large electro-optic effect. Light control elements of various types, such as directional coupling type optical modulators or switches, and total reflection type optical switches, have been reported in the past (C205 Autumn National Conference of the Institute of Electronics Engineers of Japan, 1986). When such a waveguide-type optical control element is applied to an actual optical communication system, basic performance such as low loss and high speed, as well as particularly operational stability, are practically essential.

Figure 3 (a) is a plan view of a conventional directional coupling type optical switch, and Figure 3 (b) is the B in Figure 3 (a).
-B sectional view.

In FIG. 3(a), band-shaped optical waveguides 2 and 3 are formed by diffusing titanium on a lithium niobate crystal substrate 1 cut out perpendicularly to the Z axis to have a refractive index larger than that of the substrate. The optical waveguides 2 and 3 are close to each other within a few μm at the center of the substrate, and constitute a directional coupler 4. Furthermore, a control electrode 5 is formed on the optical waveguide constituting the directional coupler 4 via a buffer film 6 for preventing light absorption by the electrode.

In FIG. 3 (a), incident light 7 that has entered the optical waveguide 2
As it propagates through the directional coupler 4, the optical energy gradually transfers to the adjacent optical waveguide 3, and the directional coupler 4
After passing through, almost 100% of the energy is transferred to the optical waveguide 3 and becomes the output light 8.

On the other hand, when a voltage is applied to the control electrode 5, the refractive index of the optical waveguide under the electrode changes due to the electro-optic effect, and the optical waveguide 2
A phase velocity mismatch occurs between the waveguide modes propagating in and 3, and the coupling state between them changes.

Generally, the control electrode 5 is patterned using a mask after forming an electrode film so that the electrode is placed on the optical waveguides 2 and 3.
After that, it is formed by etching.

Here, the strain generated during the formation of the buffer film 6 and the electrode film is controlled by etching the electrode film. Remains unevenly in the vicinity. This distortion extends to the vicinity of the leading waveguide 2.3 and changes the waveguide characteristics, resulting in a change in the coupling state of the directional coupler 4.

[Problem to be solved by the invention]

In the above-mentioned conventional waveguide type optical control device, etching causes the film formation type to be unevenly localized in the vicinity of the electrode and the optical waveguide, thereby changing the waveguide characteristics and the coupling state. The amount of change not only varies from electrode film formation batch to electrode film formation batch, but also tends to vary among multiple directional couplers formed on one wafer even within the same electrode film formation batch. There was a drawback that the coupling state that existed when the waveguide was formed changed in each directional coupler after electrode etching, making it impossible to stably obtain the coupling state as designed.

[Means to solve the problem]

The optical control device of the first invention includes an optical waveguide formed on a dielectric crystal substrate having an electro-optic effect, a buffer layer formed on the optical waveguide, and an optical waveguide formed on the buffer layer and in the vicinity of the optical waveguide. 1 formed in! a pole; an electrode film lattice formed near the electrode using the same material as the electrode;
The present invention is characterized by comprising a buffer layer lattice formed between the electrode film lattice and the electrode and made of the same material as the buffer layer.

Further, in the method for manufacturing an optical control device according to the second invention, an optical waveguide is formed on a dielectric crystal substrate having an electro-optic effect, a buffer layer is formed on the optical waveguide, and the optical waveguide is formed on the buffer layer and on the optical waveguide. An electrode is formed near the electrode, a t-pole film lattice is patterned near the t-pole when the electrode is formed, and a buffer layer lattice is formed by etching in a region between the electrode and the electrode film lattice. .

[Effect]

Generally, the amount of strain during film formation can be considered to be uniform near any position on the dielectric crystal substrate.

As a result, even if the refractive indexes of the dielectric crystal substrate and the optical waveguide change before and after film formation, the difference in refractive index between the optical waveguide and the dielectric crystal substrate does not change. Therefore, since the coupling state of the directional coupler does not change before and after film formation, the coupling state when the leading waveguide is formed on the dielectric crystal substrate is preserved.

However, if the electrode film is patterned and etched only in the vicinity of the directional coupler of the optical waveguide to form the control electrode, the amount of strain that was uniformly distributed in the vicinity of the control electrode position will be reduced due to etching. Since the membrane distortion of the removed portion is unevenly concentrated in the vicinity of the control electrode position, the coupling state in each portion of the directional coupler changes. As a result, the directionality formed on the dielectric crystal substrate is such that when light enters from one optical waveguide of the directional coupler, the light passes through the directional coupler and then moves to the other leading waveguide. The characteristics of the coupler change after the control electrode is formed because they are affected by the combined changes in the coupling state in each part of the directional coupler.

In the present invention, by leaving the electrode film in a lattice shape during electrode film etching, the concentration of film formation strain that the removed electrode film had can be dispersed to each lattice. Furthermore, by leaving the buffer layer near the control electrode in a grid pattern,
Due to the amount of strain remaining in the control electrode, it is possible to disperse the strain formed on the buffer layer in the immediate vicinity of the control electrode. Grids made of electrode films cannot be controlled close to the poles because the switching start-up characteristics deteriorate as the control approaches the poles. Therefore, in the present invention, the buffer layer between the control electrode and the grid formed by the electrode film is etched in order to reduce the non-uniform strain generated in the buffer layer due to the strain concentrated on the control electrode.

〔Example〕

Next, the present invention will be explained with reference to FIGS. 1 and 2.

FIG. 1(a) is a plan view of a directional coupling type optical switch showing one embodiment of the present invention, FIG. 1(b) is a sectional view taken along line A-A in FIG. 1(a), and FIG. FIG. 4 is a diagram showing changes in branching ratio before and after electrode patterning for TE mode light in FIGS. 1 and 3; FIG.

As shown in FIG. 1, in this example, titanium is thermally diffused on a Z-cut lithium niobate crystal plate 1 at 900 to 1100°C for several hours to form an optical waveguide 2.3 with a depth of 3 to 10 μm. do. The optical waveguides 2.3 are located several μm apart from each other in the center of the substrate.
The directional coupler 4 is constructed by being close to each other. A control electrode 5 is formed thereon with a buffer layer 6 interposed therebetween. Furthermore, in the step of forming the control electrode, an electrode film grid 10 is formed simultaneously with the control electrode 5 and the same material. This t-pole film lattice 10 is formed parallel to the length direction of the control electrode 5 with the same width and spacing as the dimensions of the control electrode 5 from a position approximately 70 μm away from the control electrode 5. After forming the second electrode film grid 0, a buffer layer grid 11 is formed of the same material as the buffer layer 6. This buffer layer grid 11 has a control electrode 5 and a control electrode 5 to 1
A control electrode 5 is formed parallel to the length direction of the control electrode 5 in the region between the tVi film grating 10 and the tVi film grating 10 00 μm apart, with the same width as the width of the optical waveguide 2.3 and the same spacing as the dimension of the directional coupler 4. are doing.

In the optical control device of this example manufactured by the above process, the branching ratio PI / (P 1
It can be seen that the change in +Pz) is significantly smaller than that of the conventional example (indicated by the broken line). For example, when measuring the branching ratio change when voltage is applied to the control electrode, that is, the switching characteristic, this effect is found to be 1.
While the voltage shift amount was 0V or more, in this embodiment, the voltage shift amount is 0.5V or less.

〔Effect of the invention〕

As explained above, the present invention involves forming an electrode film lattice near the control electrode using the same material as the control electrode during electrode patterning, and then forming a buffer layer lattice between the control electrode and the electrode film lattice. As a result, the influence of distortion on the directional coupler after electrode patterning can be reduced.
This has the effect of stably obtaining the characteristics as designed.

[Brief explanation of drawings]

FIG. 1(a) is a plan view of a directional coupling type optical switch showing one embodiment of the present invention, FIG. 1(b) is a sectional view taken along line A-A in FIG. 1(a), and FIG. Figures 1 and 3 show changes in branching ratio before and after electrode patterning for TE mode light; Figure 3 (a) is a plan view of a conventional directional coupling type optical switch; Figure 3 (b) ) is shown in Figure 3(a)
It is a BB sectional view in . DESCRIPTION OF SYMBOLS 1... Lithium niobate crystal substrate, 2, 3... Optical waveguide, 4... Directional coupler, 5... Control electrode, 6...
... Buffer layer, 7... Incident light, 8.9... Outgoing light, 10... Electrode film lattice, 11... Buffer layer lattice.

Claims (2)

[Claims] (1) an optical waveguide formed on a dielectric crystal substrate having an electro-optic effect, a buffer layer formed on this optical waveguide, and an electrode formed on this buffer layer and in the vicinity of the optical waveguide; Optical control characterized by comprising an electrode film lattice formed near the electrode using the same material as the electrode, and a buffer layer lattice formed between the electrode film lattice and the electrode using the same material as the buffer layer. device. (2) Forming an optical waveguide on a dielectric crystal substrate having an electro-optic effect, forming a buffer layer on the optical waveguide, forming an electrode on the buffer layer and near the optical waveguide, and forming the electrode. 1. A method of manufacturing a light control device, comprising: patterning an electrode film lattice near the electrode, and forming a buffer layer lattice by etching in a region between the electrode and the electrode film lattice.