JPH11258438A - Optical waveguide channel element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical wavegiuide channel element with a metal loaded type polarizer by which deterioration of polarizer characteristic and waveguide channel characteristic can be reduced. SOLUTION: An optical waveguide channel element 10 is so constructed that an optical waveguide channel 14 of a designated shape is formed in a LiNbO3 substrate 12, and a polarizer 16 comprising a first buffer layer 20 made by HfO2 (dielectric film) and a metal film 22 made of Al formed on the optical waveguide channel 14 and a second buffer layer 24 made of MgF2 formed between the optical waveguide channel 14 and the first buffer layer 20 is provided on the optical waveguide channel 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical waveguide device, and more particularly, to an optical waveguide device having a polarizer provided on an optical waveguide formed on a LiNbO ₃ substrate.

[0002]

2. Description of the Related Art In general, an optical waveguide has a function of confining radiation in a certain area and guiding and propagating the energy flow parallel to the axis of a path. Therefore, at present,
By changing the optical waveguide represented by an optical fiber cable to an optical waveguide, the size of an optical component is reduced.

As the optical waveguide, for example, GaAs
-Based, InP-based semiconductor waveguides, dielectric (glass) waveguides using an oxide film formed on Si, or using a glass substrate, L
There is a ferroelectric crystal waveguide made of iNbO ₃ or LiTaO ₃ crystal.

[0004] In particular, as an optical element such as an optical waveguide type modulator which carries information through an electrode on a light beam transmitted through the optical waveguide, L has excellent electro-optical characteristics.
Ti diffusion type LiNb in which Ti is diffused in iNbO ₃ crystal
An O ₃ waveguide is used.

This Ti diffusion type LiNbO ₃ waveguide is formed by forming a metal Ti film having a thickness of several hundred degrees on a substrate,
It is produced through a thermal diffusion operation at a temperature of about ℃ for 4 to 10 hours.

In the case where a polarizer is provided in the optical waveguide element, as shown in FIG.
On the LiNbO ₃ substrate 4 on which the i-diffused waveguide 2 is formed,
An oxide buffer layer (dielectric film) 6 of, for example, HfO ₂ or ZrO ₂ , for example, having a thickness of several hundred to several thousand Å, is formed by a deposition method such as evaporation or sputtering, and several hundred to several thousand ＡA
Similarly, the metal film 7 is formed using a film forming technique such as vapor deposition or sputtering. Thus, the optical waveguide element 9 provided with the metal-loaded polarizer 8 is manufactured.

However, the optical waveguide element 9 provided with the conventional polarizer 8 as described above deteriorates polarizer characteristics and waveguide characteristics due to long-term use in a high-temperature, high-humidity environment. There's a problem.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved metal-loaded polarizer that exhibits little deterioration in polarizer characteristics and waveguide characteristics when used in a high-temperature, high-humidity environment for a long period of time. It is an object to provide an optical waveguide element provided.

[0009]

In order to solve the above-mentioned problems, an optical waveguide device according to the present invention comprises an optical waveguide having a metal-loaded polarizer provided on an optical waveguide formed on a LiNbO ₃ substrate. In the device, the metal-loaded polarizer is formed by stacking a metal film, a first buffer layer made of an oxide film, and a second buffer layer in this order from an upper layer, and the first buffer layer and the LiNbO ₃ are stacked. the second buffer layer formed between the substrate, the first buffer layer and the LiNbO ₃ lower the LiNbO ₃ than the reaction with the substrate
It is characterized by having reactivity with a substrate. Here, as the optical waveguide, a Ti diffusion type LiNbO ₃ waveguide formed by diffusing Ti on a LiNbO ₃ substrate is used, and the metal film is preferably an Al film, but is not limited to this. .

Thus, it is possible to obtain an optical waveguide element provided with a metal-loaded polarizer, which causes less deterioration of polarizer characteristics and waveguide characteristics when used in a high-temperature, high-humidity environment for a long period of time. .

In this case, the material of the second buffer layer is a metal fluoride, and the thickness of the second buffer layer is not less than 5 ° and is 1% of the thickness of the first buffer layer.
By setting the ratio to / 10 or less, an optical waveguide element in which diffusion of oxygen from the substrate to the polarizer is further reduced can be manufactured at a low cost by reducing the thickness of the second buffer layer.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical waveguide device according to the present invention will be described below with reference to FIGS.

An optical waveguide device 10 according to a first example of the present embodiment shown in FIG. 1 has an optical waveguide 14 formed by diffusing Ti on a LiNbO ₃ substrate 12. , A polarizer 16 and a phase modulator 18 are provided.

LiNbO _{3 of the} manufactured optical waveguide element 10
The size of the substrate 12 is about 3 m in width (Z direction in FIG. 1).
m, the length in the optical waveguide 14 direction (Y direction in FIG. 1) is about 3
0 mm, and the size of the polarizer 16 is approximately 1 m at a portion corresponding to the length direction of the optical waveguide 14 (Y direction in FIG. 1).
m, a portion corresponding to the width direction of the optical waveguide 14 (the Z direction in FIG. 1) is about 2 mm.

As shown in FIG. 2, the optical waveguide device 10 comprises:
An optical waveguide 14 having a predetermined shape is formed on a LiNbO ₃ substrate 12, and a first buffer layer 20 made of HfO ₂ (dielectric film) and an Al metal film 22 are formed on the optical waveguide 14. A polarizer 16 having a second buffer layer 24 made of MgF ₂ is provided between the optical waveguide 14 and the first buffer layer 20. Here, the thickness (X direction in FIG. 1) of the LiNbO ₃ substrate 12 is about 1 mm, and the width (Z direction in FIG. 1) and depth (X direction in FIG. 1) of the optical waveguide 14 are both It is several μm. The thickness of each film of the polarizer 16 laminated on the optical waveguide 14 is 780 ° for the first buffer layer 20, 3000 ° for the metal film 22, and 40 ° for the second buffer layer 24.

The optical waveguide device according to the second example of the present embodiment has basically the same structure as the optical waveguide device 10 according to the first example of the present embodiment, The material and thickness of each film constituting the element are different from those of the optical waveguide device 10 according to the first example. Hereinafter, the same components as those of the first example are denoted by the same reference numerals, and detailed description thereof will be omitted.

That is, a second buffer layer 24 of AlF _{3 having} a thickness of 30 ° and SiO ₂ is formed on the optical waveguide 14.
First buffer layer 20 of 350 °
The polarizer 16 is formed by laminating in order the metal film 22 made of.

A method for manufacturing the optical waveguide device 10 according to the present embodiment will be described below.

First, the LiNbO ₃ substrate 12 and the LiNbO ₃
An optical waveguide 14 of the Ti diffusion type formed on the NbO ₃ substrate 12 is manufactured by a common method.

Next, the LiN on which the optical waveguide 14 is formed is formed.
After the bO ₃ substrate 12 has been washed, a second deposition is performed on the optical waveguide 14 by electron beam evaporation using an evaporation apparatus for an oxide film.
Is formed. Subsequently, the second buffer layer 2 is formed by electron beam evaporation using the above evaporation apparatus.
4, a first buffer layer 20 is formed. Furthermore, the polarizer 16 is completed by forming the metal film 22 on the first buffer layer 20 using a metal film deposition apparatus. Further, the phase modulator 18 is provided, and the optical waveguide device 10 shown in FIG. 1 is completed.

The deterioration of the optical waveguide device according to the second example of the present embodiment was determined. In addition, as a comparative example,
3000Å thick Al metal film and 800Å thick HfO
_The deterioration of the optical waveguide element provided with the polarizer formed from the buffer film of No. ₂ was also determined.

Here, the judgment of the deterioration of the optical waveguide element is made by Y
After performing a reliability test in which an optical waveguide element having a shape branch is held for a long time under high temperature and high humidity, it refers to the result of measuring the loss characteristics of the optical waveguide and the polarization extinction ratio characteristics of the polarizer to determine the deterioration. . Specifically, the temperature of the optical waveguide device is set to 75 ° C.
Before and after a reliability test in which the optical waveguide was placed in a test apparatus set at a humidity of 93% and held for 500 hours, the loss increase of the optical waveguide and the polarization extinction ratio deterioration were evaluated.

FIG. 3 shows the loss characteristics of the optical waveguide. FIG.
In the graph, the horizontal axis represents the test time, and the vertical axis represents the loss. In the comparative example, the loss of the optical waveguide was 4.0 dB at the start of the test, but is 5.3 dB after 1000 hours, which is an increase of 1.3 dB. On the other hand, in the second example of the present embodiment, the increase is only 0.5 dB from 4.0 dB to 4.5 dB. Therefore, it can be seen that the loss characteristics of the optical waveguide are greatly improved.

FIG. 4 shows the polarization extinction ratio characteristics of the polarizer.
In FIG. 4, the horizontal axis indicates the test time, and the vertical axis indicates the polarization extinction ratio. In the comparative example, the polarization extinction ratio of the polarizer was 32.0 dB at the start of the test, but becomes 29.0 dB after 1000 hours, degrading by 3.0 dB.
On the other hand, in the second example of the present embodiment, 31.5d
B changes within a range of 32.0 dB. This change is within the range of the measurement error, and therefore, it can be seen that the polarization extinction ratio characteristic of the polarizer is greatly improved.

[0025]

As described above, the Li according to the present invention is used.
An optical waveguide element in which a metal-loaded polarizer is provided on an optical waveguide formed on an NbO ₃ substrate, wherein the metal-loaded polarizer is a first buffer layer composed of a metal film and an oxide film from an upper layer; The second buffer layer is formed by laminating in order of the second buffer layer, and the second buffer layer formed between the first buffer layer and the LiNbO ₃ substrate is composed of the first buffer layer and the LiNbO ₃ substrate. LiNbO having a lower reactivity than
Has reactivity with ₃ substrates.

As a result, it is possible to obtain an optical waveguide device provided with a metal-loaded polarizer, which causes little deterioration in polarizer characteristics and waveguide characteristics even when used in a high-temperature, high-humidity environment for a long period of time. Is achieved.

Further, the material of the second buffer layer is metal fluoride, and the thickness of the second buffer layer is not less than 5 ° and not more than 1/10 of the thickness of the first buffer layer. This achieves an effect that an optical waveguide element in which diffusion of oxygen from the LiNbO ₃ substrate to the polarizer is further reduced can be manufactured at low cost by reducing the thickness of the second buffer layer.

[Brief description of the drawings]

FIG. 1 is a plan view of an optical waveguide device according to a first example of the present embodiment.

FIG. 2 is a schematic cross-sectional view of the optical waveguide device of FIG. 1 taken along the line II-II.

FIG. 3 is a diagram illustrating loss characteristics of an optical waveguide.

FIG. 4 is a diagram showing a polarization extinction ratio characteristic of a polarizer.

FIG. 5 is a schematic sectional view of a conventional optical waveguide device.

[Explanation of symbols]

10: Optical waveguide element 12: LiNbO
₃ substrate 14 optical waveguide 16 polarizer 18 phase modulator 20 first buffer layer 22 metal film 24 second buffer layer

Claims (3)

[Claims] 1. An optical waveguide device in which a metal-loaded polarizer is provided on an optical waveguide formed on a LiNbO ₃ substrate, wherein the metal-loaded polarizer is composed of an upper layer, a metal film, and an oxide film. A first buffer layer, a second buffer layer, and a second buffer layer. The second buffer layer formed between the first buffer layer and the LiNbO ₃ substrate is the first buffer layer. LiN having a lower reactivity than the LiNbO ₃ substrate
An optical waveguide device having reactivity with a bO ₃ substrate. 2. The optical waveguide device according to claim 1, wherein the material of said second buffer layer is a metal fluoride. 3. The optical waveguide device according to claim 1, wherein a thickness of said second buffer layer is not less than 5 ° and not more than 1/10 of a thickness of said first buffer layer. An optical waveguide element.