JPH04249214A - Production of optical waveguide-type device - Google Patents

Abstract

PURPOSE:To prevent the reduction of the surface of an optical waveguide when an electrode is formed and to produce an optical waveguide-type device with the resistance to the damage by light enhanced by forming the electrode while shielding the optical waveguide forming part on the surface of lithium niobate (LiNbO3) single crystal provided with the waveguide. CONSTITUTION:The waveguide pattern of titanium (Ti) film is formed on the surface of the single crystal 1 of lithium niobate (LiNbO3), and then an electrode 3 is formed on the single crystal provided with an optical waveguide 2 by a titanium (Ti) diffusion method while shielding the optical waveguide forming part.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for manufacturing an optical waveguide type device, and more specifically, a method for manufacturing an optical waveguide type device that can obtain an optical waveguide type device such as an optical deflector with high resistance to optical damage. Regarding.

0002

2. Description of the Related Art In constructing various optoelectronic systems, it is often essential to change the intensity, phase, traveling direction, etc. of light waves in accordance with control signals applied from the outside. For this reason, research on optical waveguide type devices such as optical deflection devices is progressing.

Conventionally, these optical waveguide devices have been fabricated using a Ti diffusion method in which a titanium (Ti) film is formed on the surface of a lithium niobate (LiNbO3) single crystal, and then the LiNbO3 single crystal is heat-treated. Then, with the forming portion of the optical waveguide exposed, for example, photolithography is performed to remove LiNbO.
3. It was manufactured by forming an electrode made of, for example, an aluminum (Al) thin film on a single crystal.

0004

[Problems to be Solved by the Invention] However, in the optical waveguide type device manufactured by the above method,
When visible laser light is irradiated, electrons are excited from the impurity (e.g. Fe) level in the crystal to the conduction band and drift in the +z direction. On the way, the excited electrons fall into the trap level and become positively charged in the crystal. A phenomenon in which a space electric field is generated due to the formation of a negatively charged part and a negatively charged part, and the refractive index changes due to the electro-optic effect.In other words, so-called optical damage occurs, resulting in a significant deterioration of device characteristics. was there.

[0005] Therefore, the inventor of the present invention repeatedly investigated optical damage in optical waveguide type devices, and found that this optical damage is caused by the reduction of the optical waveguide surface by the electrode material when forming an electrode on the surface of the LiNbO3 single crystal. It turned out that this was caused by putting it away. The present invention has been made based on such circumstances, and an object of the present invention is to provide an optical waveguide capable of obtaining an optical waveguide type device with improved resistance to optical damage and without deterioration of desired characteristics. type device,
In particular, it is an object of the present invention to provide a method for manufacturing an optical waveguide type device, such as an optical deflector, in which an optical waveguide forming part and an electrode forming part are clearly distinguished.

[0006]

[Means for Solving the Problems] The gist of the present invention for achieving the above object is to use lithium niobate (LiNbO3).
) A waveguide pattern of titanium (Ti) film is formed on the surface of the single crystal, and then the lithium niobate (LiNbO3
) An optical waveguide is formed by a titanium (Ti) diffusion method that heat-treats a single crystal, and then the lithium niobate (Li
A method of manufacturing an optical waveguide type device in which an electrode is formed on a single crystal (NbO3), characterized in that the electrode is formed with the optical waveguide portion shielded.

FIG. 1 is a flowchart showing the manufacturing method of the present invention in order of steps. As shown in FIG. 1, in the method of manufacturing an optical waveguide type device of the present invention, first, a waveguide pattern of a Ti film is formed on the surface of a LiNbO3 single crystal. This T
The method for forming the waveguide pattern of the i-film includes, for example, Li
It is also possible to adopt a method in which a Ti film is formed on the surface of the NbO3 single crystal, a resist pattern is formed by ordinary photolithography, and then the Ti is etched to form a pattern, or an inverted pattern of resist etc. It is also possible to adopt a so-called lift-off method in which a Ti film is formed after the resist is formed, and then the resist is dissolved and removed by immersion in an organic solvent. Note that the Ti film can be formed by suitably employing, for example, a vacuum evaporation method or a sputtering method, and the thickness of the Ti film is usually about 100 to 1000 Å. Note that, for example, in the case of an optical deflector, etc., this waveguide pattern is made of LiNbO
3. The entire surface of the single crystal may be formed as a waveguide.

In the method of the present invention, after a Ti film waveguide pattern is formed on the surface of a LiNbO3 single crystal in this way, an optical waveguide is formed in the crystal by a Ti diffusion method. Here, the Ti diffusion conditions are generally as follows. That is, the diffusion temperature is set below the Curie temperature in order to maintain the polarized state of the crystal. Specifically, 9
00-1100°C. Note that when the substrate (LiNbO3 single crystal) is heated to 1000°C or higher, LiO2
In order to prevent external diffusion of the gas, it is diffused in an oxidizing atmosphere such as oxygen gas or air containing water vapor. The reason why an oxidizing atmosphere is used here is to make the waveguide to be manufactured less susceptible to optical damage. Diffusion time is usually about several hours to 10 hours. If the diffusion time exceeds 10 hours, defects may occur in the LiNbO3 single crystal and optical transmission loss may increase. Furthermore, although diffusion is normally performed within the reactor core tube, heating by laser annealing is also possible.

After forming an optical waveguide by diffusing Ti into the LiNbO3 single crystal in this way, the LiNbO3
An electrode material film is formed while shielding the optical waveguide formation portion on the O3 single crystal 1. Here, examples of the electrode material include aluminum (Al). The electrode is formed by a lift-off method using an electrode material. Specifically, a resist 20 is applied to the surface of the LiNbO3 single crystal 1, exposed and developed to form a desired electrode pattern, and then, as shown in FIG.
A shielding plate 1 is placed on the optical waveguide forming part on the surface of the bO3 single crystal 1.
0 is placed thereon, and a thin film of electrode material such as Al is formed. Thereafter, unnecessary resist and a thin film of electrode material such as Al may be removed using an organic solvent such as acetone to form an electrode. Here, the shielding plate has a shape and size that can completely cover the optical waveguide forming portion on the surface of the LiNbO3 single crystal, and a shape and size that exposes a predetermined electrode forming portion. is necessary. Such a shielding plate is made of, for example, a stainless steel plate or a PTFE plate.
A resin plate or the like can be suitably used. Further, the thin film of the electrode material can be formed by suitably employing a thin film forming method such as a vacuum evaporation method or a sputtering method. The film thickness of the electrode thus formed is, for example, about 2,000 to 3,000 Å in the case of a SAW electrode. In addition, in the method of the present invention, in order to compensate for the adhesion of the electrode to the LiNbO3 single crystal, the electrode and LiN
For example, it is preferable to form a Ti film between the bO3 single crystal and the bO3 single crystal. The thickness of this Ti film is 200 to 300 Å.
That's about it.

In the method of the present invention, in order to make the surface state of the waveguide of the optical waveguide device obtained by forming the electrode with the optical waveguide portion shielded as described above more stable, the optical waveguide portion is shielded. For example, an oxide film such as a SiO2 film or an Al2O film may be formed on the surface of the wave path type device. Such an oxide film can be formed, for example, by a method such as a sputtering method or a CVD method, and its film thickness is usually about 200 to 300 Å.

The optical waveguide type device obtained as described above has significantly improved resistance to optical damage.

0012

[Function] In the method for manufacturing an optical waveguide device of the present invention, lithium niobate (L) is
After forming an optical waveguide in the lithium niobate (LiNbO3) single crystal, the lithium niobate (LiNbO3) is
O3) Form an electrode on the single crystal. By forming an electrode while shielding the optical waveguide forming portion on the lithium niobate (LiNbO3) single crystal, it is possible to prevent the surface of the optical waveguide from being reduced by the electrode material during electrode formation. . Therefore, the optical waveguide type device manufactured by the method of the present invention has significantly improved optical damage resistance because the optical waveguide surface does not become reduced.

[0013]

[Embodiments] Hereinafter, an optical deflector using a two-dimensional waveguide will be shown as an embodiment of the present invention, and the present invention will be explained in more detail. After thoroughly cleaning a lithium niobate single crystal (y-cut LiNbO3) cut in the y direction, titanium (Ti) with a thickness of 200 Å is deposited on the entire surface of the crystal.
The film was formed by sputtering. Note that sputtering uses a magnetron type RF sputtering device, and T
The experiment was conducted under the following conditions: i target diameter 10 cm, RF power 100 W, and Ar gas pressure 2 x 10-2 Torr.

Next, T was heated at a diffusion temperature of 1,000°C and a diffusion time of 7 hours in a mixed gas atmosphere of oxygen gas and water vapor.
An optical waveguide was formed by i-diffusion. Next, this Li
A resist layer of 1 μm is applied over the entire surface of the NbO3 single crystal.
After applying the film to a thickness of 2 m and performing exposure and development to form a resist pattern, a stainless steel shielding plate is placed on the part where light is guided, and then a film thickness of 2 m is applied over the entire surface.
A 000A aluminum (Al) film was formed by vacuum evaporation. Note that at this time, due to the action of the shielding plate, no Al film was formed under the shielding plate. Further, a SAW electrode was formed by a lift-off method in which the resist and unnecessary Al film were removed using an organic solvent (acetone), and an optical waveguide type device with a guided wavelength of 40 mm was fabricated. In addition, vacuum evaporation is performed at an ultimate vacuum of 5 x 10-6 Torr and a rate of 10
The test was carried out under the conditions of Å/sec. FIG. 3 is an explanatory diagram schematically showing this optical waveguide type device. As shown in FIG. 3, in this optical waveguide type device, an optical waveguide 2 is formed in a y-cut LiNbO3 single crystal 1 with the x direction as the longitudinal direction (light waveguide direction), and an optical waveguide 2 is formed on the LiNbO3 single crystal 1. An electrode 3 is formed on the surface.

[0015] A He-Ne laser beam (TE0 mode) was guided through this optical waveguide type device, and the output power was measured after the light was guided for 5 minutes at each input power. The results are shown in Figure 4. Note that the output light is 1.
Detection was made through a 5 mmφ aperture. On the other hand, in the production of the optical waveguide type device, the electrodes were formed with the surface of the optical waveguide formation part exposed without shielding the surface of the LiNbO3 single crystal surface. A comparative sample was prepared in the same manner, and the relationship between input power and output power was determined for this comparative sample in the same manner as above. The results are shown in Figure 5.

As is clear from FIGS. 4 and 5, the comparative sample shows a decrease in output power, which suggests that optical damage has occurred.
In the optical waveguide type device manufactured by the method of the present invention, output power and input power showed a proportional relationship, and it was confirmed that no optical damage occurred.

[0017]

According to the present invention, with the above structure, an optical waveguide type device, in particular an optical waveguide forming part and an electrode forming part, can efficiently obtain an optical waveguide type device with significantly improved resistance to optical damage. For example, it is possible to provide a method for manufacturing an optical waveguide type device such as an optical deflector, in which the two are clearly distinguished.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the process flow of a method for manufacturing an optical waveguide type device of the present invention.

FIG. 2 is an explanatory diagram showing an example of electrode formation in the method for manufacturing an optical waveguide type device of the present invention.

FIG. 3 is a plan view schematically showing an optical waveguide type device manufactured in this example.

[Figure 4] H
It is a graph showing the relationship between input power and output power when e-Ne laser light is guided.

FIG. 5 is a graph showing the relationship between input power and output power when He--Ne laser light is guided in a comparative sample.

[Explanation of symbols]

1 LiNbO3 single crystal 2 Optical waveguide 3 Electrode

Claims (1)

[Claims] [Claim 1] Lithium niobate (LiNbO3)
A waveguide pattern of titanium (Ti) film is formed on the surface of the single crystal, and then the lithium niobate (LiNbO3)
An optical waveguide is formed by a titanium (Ti) diffusion method that heat-treats a single crystal, and then the lithium niobate (LiN)
bO3) A method for manufacturing an optical waveguide type device in which an electrode is formed on a single crystal, characterized in that the electrode is formed while shielding the optical waveguide forming part.