JP2884945B2 - Method for manufacturing optical waveguide device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical waveguide device.

[0002]

2. Description of the Related Art An optical switch as an optical waveguide device,
The optical modulator, the optical demultiplexer, and the like can be manufactured by substantially the same method. Here, an optical waveguide switch will be described as an example.

Conventionally, an optical waveguide switch has been manufactured in the following manner. That is, lithium niobate (LiN
b ₃₎ titanium (Ti) is formed on the waveguide shape on a substrate of, the titanium is thermally diffused at a temperature of 1000 to 1200 ° C.. Next, a silicon dioxide (SiO ₂ ) film is formed on the substrate surface of lithium niobate in which titanium is diffused, and a Cr / Pt / Au film is formed thereon as an electrode. Next, the Cr / Pt / Au film is etched to leave the Cr / Pt / Au film only above the portion where titanium is diffused, thereby obtaining an optical waveguide switch.

[0004]

In the conventional optical waveguide device, when a voltage for operating the device is applied to the electrode, hydrogen ions entering during the titanium thermal diffusion step move to the electrode by ionic conduction, and polarization occurs. A phenomenon occurs in which the electric field generated by the applied voltage is canceled. For this reason, it is necessary to apply a voltage for compensating for the canceled electric field, but the increase in the voltage further increases the polarization, and as a result, the applied voltage increases with time.

An object of the present invention is to provide a method for manufacturing an optical waveguide device whose operating voltage does not fluctuate for a long period of time.

[0006]

In order to achieve the above object, a method of manufacturing an optical waveguide device according to the present invention is directed to a method of manufacturing an optical waveguide by thermally diffusing an impurity into a substrate having an electro-optic effect. a method for manufacturing, electrical
After thermal diffusion of impurities into the substrate having the optical effect,
The surface of the substrate is subjected to an ion exchange treatment with a alkali metal salt.
Than it is.

[0007]

In the thermal diffusion step, hydrogen ions enter the crystal due to water vapor in the atmosphere. For this reason, hydrogen ions become mobile ions in the crystal, and when an electric field is applied to the crystal, the mobile ions move along the electric field, causing polarization. Therefore, by performing ion exchange with an alkali metal salt, hydrogen ions, which are mobile ions, can be extracted from the crystal by an ion exchange reaction, and polarization can be suppressed.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a sectional view of a main part showing a structure of an optical waveguide device for explaining an embodiment of the present invention, and shows a case where the method of the present invention is applied to the manufacture of an optical waveguide switch. In FIG. 1, 1 is a lithium niobate substrate, 2
Is a titanium diffusion layer formed by diffusing titanium linearly on the surface of the substrate 1 and forms an optical waveguide for transmitting light. Reference numeral 3 denotes a silicon dioxide film formed on the surface of the lithium niobate substrate 1 to protect the titanium diffusion layer 2. Reference numeral 4 denotes electrodes, such as chromium (Cr), platinum (Pt),
It is made of gold (Au) and is located on the titanium diffusion layer 2.
It is formed on silicon dioxide film 3.

Hereinafter, the case of manufacturing the optical waveguide device having the above configuration will be specifically described. First, 0.8mm
The thickness of the lithium niobate substrate 1 having a thickness of about 1
Titanium is linearly formed with a thickness of 0 μm and a width of about 10 μm. Next, the titanium is thermally diffused in a steam atmosphere at about 1080 ° C. to form an optical waveguide for transmitting light. Thereafter, the lithium niobate substrate 1 is subjected to ion exchange in molten lithium nitrate, but the ion exchange is not limited to lithium nitrate, and any other alkali metal salt can be used.

Thereafter, a silicon dioxide film 3 is coated on the entire surface of the lithium niobate substrate 1 where titanium is diffused for about 800
Angstrom is formed, and an electrode film having a width of about 10 μm and a thickness of about 0.6 μm is formed on the silicon dioxide film 3 immediately above the titanium diffusion layer 2 with a thickness of 0.2 μm for chromium and 0.2 μm for platinum.
An optical waveguide device having the structure shown in FIG.

FIG. 2 shows the fluctuation of the switching voltage between the optical waveguide switch of the present invention thus manufactured and the conventional example before and after the acceleration test. Here, the horizontal axis represents the voltage (V) applied to the electrode, the vertical axis represents the optical output (mW) from the optical waveguide, and the curve 11 represents the optical waveguide switch of the present invention before the acceleration test, 7 shows characteristics of a light output with respect to a switching voltage in a conventional example. Curve 13 is obtained by performing an acceleration test by applying a voltage in a 60 ° C. atmosphere for 24 hours.
The curve 12 shows the characteristics of the switching voltage and the light output of the present invention after applying the voltage in a 60 ° C. atmosphere for 24 hours to perform an acceleration test. It was done.

As apparent from FIG. 2, in the conventional example, the voltage at which the light output becomes maximum after the acceleration test has changed by as much as 12. In contrast, in the present invention example in which ion exchange was performed on the lithium niobate substrate in molten lithium nitrate after the thermal diffusion of titanium, hydrogen ions, which are mobile ions that entered the crystal during the thermal diffusion step of titanium, were subjected to an ion exchange reaction. Since it was removed, polarization did not occur, and the fluctuation of the switching voltage was suppressed. As shown by the curve 12, the fluctuation was suppressed to about 3 V even after the acceleration test. As a result, the fluctuation of the switching voltage was significantly improved as compared with the conventional one.
In the above-described embodiment, lithium nitrate is used as the ion exchange material, but another alkali metal salt can be used. In the above embodiment, the example of the optical waveguide switch has been described, but the same applies to other optical waveguide devices.

[0013]

As described above in detail, according to the method of the present invention, titanium is thermally diffused and then ion-exchanged with an alkali metal salt, whereby hydrogen, which is a mobile ion that has entered the crystal by thermal diffusion, is obtained. Since ions are removed, polarization due to ionic conduction is suppressed, and the life and reliability can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a main part showing a structure of an optical waveguide switch for explaining an embodiment of a manufacturing method according to the present invention.

FIG. 2 is a graph showing a comparison between an optical waveguide switch obtained according to an example and a conventional example, showing optical power and switching voltage characteristics before and after an acceleration test.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Lithium niobate substrate (LiNbO ₃ ) 2 Titanium diffusion layer 3 Silicon dioxide film (SiO ₂ ) 4 Electrode (Cr / Pt / Au) 11 Optical power and switching voltage characteristics before acceleration test 12 In the present invention after acceleration test Optical power and switching voltage characteristics 13 Conventional optical power and switching voltage characteristics after accelerated test

Claims (1)

(57) [Claims] 1. A method of manufacturing an optical waveguide device in which an impurity is thermally diffused into a substrate having an electro-optic effect to produce an optical waveguide , wherein the impurity is thermally diffused into the substrate having an electro-optic effect.
Then, the surface of the substrate is subjected to ion exchange treatment with an alkali metal salt.
A method of manufacturing an optical waveguide device.