JPH06222403A - Directional coupling type optical waveguide - Google Patents

Abstract

PURPOSE:To provide the directional coupling type optical waveguide which facilitates mask alignment of waveguides and electrode patterns and can prevent shorting and rupturing by a strong electric field and a pyroelectric effect of the substrate by simplifying the electrode patterns (on the waveguides) of the directional coupler formed by using the optical waveguides. CONSTITUTION:The directional coupling type optical waveguide is formed out of the optical waveguide 1 installed on the ferroelectric substrate having an electro-optical effect and another optical waveguide in proximity to the optical waveguide 1. The optical waveguide part 2 subjected to polarization inversion is formed in a part of the other optical waveguide in proximity to the optical waveguide 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light control device for controlling incident light by means of an optical waveguide, and more particularly to a directional coupling type optical waveguide for controlling conversion of light in the waveguide.

[0002]

2. Description of the Related Art Conventionally, an optical control device for controlling incident light by an optical waveguide has two optical waveguides formed on a ferroelectric substrate (especially LiNbO ₃ crystal substrate) having an electro-optical effect. The optical waveguides are brought close to each other in the substrate to switch the optical paths and distribute the light intensity. At this time, the distribution intensity is controlled by changing the refractive index by applying an electric field on the waveguides to be brought close to each other. This is called a directional coupling type optical waveguide device.

Generally, a directional coupler using an optical waveguide is
By advancing and advancing the two waveguides, one of the waveguides is transferred to the other waveguide to perform light distribution (coupling mode theory).

The light distribution ratio of this optical waveguide is determined by the cross-sectional shape of the adjacent optical waveguide, the proximity parallel traveling distance (coupling length), and the refractive index of the waveguide and the substrate. Here, in manufacturing the optical waveguide, the cross-sectional shape of the optical waveguide and the proximity parallel traveling distance (coupling length) are not variable.

However, since the ferroelectric substrate having the electro-optical effect has a characteristic of changing its refractive index by an applied electric field applied in the crystal axis direction, it is possible to form an electrode on the optical waveguide and apply the applied electric field. It is possible to control the light distribution ratio by changing the refractive index.

The applied electric field for controlling the light distribution ratio is
When the Z substrate is used, it must be arranged on the waveguide (FIG. 2), and when the X substrate is used, it must be arranged so as to sandwich the waveguide (FIG. 3). Further, the direction of application of the electric field to the waveguide is changed in the directions in which the two waveguides are opposite to each other, thereby changing the respective refractive indices by + Δn and −Δn (FIGS. 2 and 3).

The problem here is the size of the optical waveguide and the distance between the adjacent optical waveguides.

Although the size of the optical waveguide depends on the wavelength of light, it is 7 to 9 μm at 1.31 μm wavelength, and the optical waveguide interval is 6 to 8 μm, which are very small in both dimensions. In order to form it, it is necessary to arrange thin and long electrodes in parallel close to each other by several μm.

[0009]

In the conventional directional coupling type optical waveguide, the use of the subdivided electrodes as described above not only makes it difficult to align the mask between the waveguide and the electrode pattern, but also causes a strong electric field. When applied, or due to the charge due to the pyroelectric effect of the substrate, a phenomenon of short-circuiting and breaking occurs.

The object of the present invention is to simplify the electrode pattern (on the waveguide) of the directional coupler using the optical waveguide, thereby facilitating the mask alignment between the waveguide and the electrode pattern, and to enhance the strong electric field and the substrate. An object of the present invention is to provide a directional coupling type optical waveguide capable of preventing short-circuit and breakage due to the pyroelectric effect.

[0011]

According to the present invention, a first optical waveguide installed on a ferroelectric substrate having an electro-optical effect and a second optical waveguide adjacent to the first optical waveguide are provided. In such a directional-coupling type optical waveguide, a directional-coupling type optical waveguide is obtained in which a part of at least one of the first and second optical waveguides is polarization-inverted.

[0012]

As described above, the polarization direction of at least one of the first and second optical waveguides causes the electric field to be applied to the two waveguides in the direction of application to the two waveguides. The directions may be the same. In this case, the directions of application of the electric field to the waveguides are such that the respective directions of the two waveguides are applied in opposite directions to the crystal axis, and the respective refractive indexes are + Δn. , -Δn can be changed, so that there is no difference in characteristics from the conventional optical control device using the directional coupler.

Further, since the electrode shape of the optical waveguide of the present invention can be made larger than that of the conventional optical waveguide, the mask alignment between the waveguide and the electrode pattern is facilitated, and the strong electric field or the focus of the substrate is increased. Short circuit and breakage due to electric effect are prevented.

[0014]

Embodiments of the present invention will be described in detail below with reference to the drawings.

As an example of the present invention, as shown in FIG. 1, a Z-cut LiNbO ₃ crystal substrate was used, and the surface (+
An optical waveguide 1 having a width of 8 μm and a depth of 6 μm was formed on the (Z plane) by Ti thermal diffusion in a directional coupling type.

Here, the proximity gap between the optical waveguide 1 and the polarization-inverted optical waveguide portion 2 was 7 μm, and the proximity coupling length was 20 mm. Further, about 0.5 μm of SiO ₂ was deposited on this branch interference type optical modulator, and one portion of the near optical waveguide was exposed as shown in FIG. 1 by photoresist patterning and SiO ₂ etching.

Next, in a WET oxygen atmosphere, 1000
After heat treatment was performed at 2 ° C. for 2 hours and after heating was completed, the mixture was naturally cooled in an electric furnace. In this way, the polarization inversion part of the optical waveguide was created.

The SiO ₂ remaining on the crystal surface was once removed with a buffer etching solution, and then a 3000 SiO ₂ film was deposited as a buffer layer on the entire optical waveguide substrate.

As shown in FIG. 4, the electrode 3 has an underlayer of Cr.
As + Au, a gold film deposited to a thickness of 1 μm was formed by lift-off to form a pattern.

An optical fiber (propagating laser light wavelength: 1.31) was added to the directional coupling type optical waveguide manufactured as described above.
Polarization maintaining fiber (μm) is connected and laser light is incident from one input port of this directional coupler,
When a voltage was applied to the electrode 3 and the output light from the crossed output port was measured, a switching curve without characteristic deterioration as compared with the conventional product was confirmed.

Although the electrode 3 is formed and installed on the optical waveguide 1 in the above embodiment, an optical device without the electrode 3 can be applied to an optical device for measuring an electric field.

By manufacturing an optical exchanger using this optical waveguide, a highly reliable optical exchanger without electrode short-circuit or breakage can be obtained.

[0023]

As described above, according to the present invention, the electrode shape can be made larger than that of the conventional optical waveguide, so that the mask alignment between the waveguide and the electrode pattern can be facilitated and the strong electric field can be increased. It is possible to prevent short circuit and breakage due to the pyroelectric effect of the substrate and the substrate.

Further, by manufacturing an optical waveguide type directional coupler using the present invention, the process can be simplified and the reliability can be improved without changing the characteristics of the conventional product.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a directional coupling type optical waveguide according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an electric field (Z substrate) in a cross section of a close gap in a directional coupler.

FIG. 3 is a schematic diagram showing an electric field (X substrate) in a cross section of a close gap in a directional coupler.

FIG. 4 is a schematic diagram showing an electric field (Z substrate) in a cross section of a near gap in a directional coupler using the present invention.

[Explanation of symbols]

 1 Optical Waveguide 2 Optical Inverted Waveguide Part 3 Electrode

Claims (2)

[Claims] 1. A directional coupler optical waveguide comprising a first optical waveguide installed on a ferroelectric substrate having an electro-optical effect, and a second optical waveguide adjacent to the first optical waveguide, wherein: A directional coupling type optical waveguide, wherein a part of at least one of the first and second optical waveguides is polarization-inverted. 2. An optical exchanger using the directional coupling type optical waveguide according to claim 1.