JPH01302325A - Optical waveguide device and its forming method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Summary] Regarding an optical waveguide device used in an optical switch, an optical modulator, etc. and a method for forming the same, the present invention aims to provide an optical waveguide device that can efficiently apply an electric field and prevent DC drift. an optical waveguide formed on a waveguide substrate, a first semiconductive film covering the waveguide substrate, and an optical waveguide formed on the first semiconductive film on the optical waveguide region. The buffer layer further includes a second semiconductive film covering the buffer layer, and an electrode formed on the buffer layer via the second semiconductive film.

[Industrial Application Field] The present invention relates to an optical waveguide device used in an optical switch, an optical modulator, etc., and a method for forming the same.

[Conventional technology]

Generally, lithium niohate (hereinafter referred to as LiNbOi) is well known as an optical waveguide material having good electro-optic effects. Conventionally, to form an optical waveguide device using LiNbO3 as a substrate, an optical waveguide is formed by thermally diffusing a patterned titanium (Ti) film on the surface of a LiNbOz crystal substrate, and then a metal electrode is placed close to the optical waveguide. is often used to form an optical waveguide device.

However, if a metal electrode is directly formed on the LiNbO5 substrate, a part of the optical energy traveling through the waveguide leaks out from the waveguide and is absorbed by the metal electrode, reducing the transmission efficiency of the transmitted wave.

Furthermore, since LiNb0i has a larger refractive index for microwaves (approximately 4.2) than the refractive index for light (approximately 2.1),
In particular, when microwaves on the order of GH2 are transmitted to electrodes, the transmission speed is slower than that of light, so it is necessary to match the speed with the light waves in order to operate efficiently.

Usually, as a countermeasure against these problems, a buffer layer is provided between the optical waveguide and the electrode.

[Problems to be Solved by the Invention] FIG. 4 is a perspective sectional view showing the configuration of an optical waveguide device according to a conventional example.

In the figure, 21 is a waveguide cut plate made of LiNb0i, and is equipped with an optical waveguide 22 formed by patterning a Ti film into a band shape on its surface and then thermally diffusing Ti into the waveguide substrate. There is.

Furthermore, the surfaces of the waveguide substrate and optical waveguide are made of insulating material,
For example, Ai! The optical waveguide is coated with a buffer layer 23 of 2,000 to 4,000 thick and made of O3 or Sin, etc., and the upper part of the optical waveguide on the surface of the buffer layer 23 is
An electrode 24 made of a metal thin film such as U is formed by means such as spreading and plating.

However, in the optical waveguide device shown in the figure,
! Since the i24 and the waveguide substrate 21 are electrically connected, the applied electric field is effectively reduced due to the voltage drop caused by the buffer layer 23, and the electric field applied to the optical waveguide 22 is effectively reduced. I cannot hope for a strong impression.

In addition, since a high voltage of several tens of volts, which is close to dielectric breakdown, is applied to the puff layer with a thickness of several thousand, drift occurs due to the movement of charges.

That is, LiNb0. Since it is a ferroelectric material, a charge is generated on the waveguide surface in response to the application of an electric field, and a charge of the opposite polarity corresponding to this charge is supplied from the outside near the bottom surface of the electrode. When charge accumulates near the bottom of the electrode, an electric field is generated in the opposite direction to the applied electric field, causing problems such as fluctuations in the operating point of the optical device, such as the interelectrode voltage required for switching in an optical switching element. .

An object of the present invention is to provide an optical waveguide device that can efficiently apply an electric field and prevent DC drift.

[Means to solve the problem]

As an embodiment of the first optical waveguide device of the present invention is shown in FIG. a membrane;
a buffer layer formed on the first semiconducting crotch on the optical waveguide region, a second semiconducting film covering the buffer layer, and a second semiconducting film. An embodiment of the method for forming an optical waveguide device of the present invention is as shown in FIG. forming a first semiconducting film; forming a buffer layer on the crotch of the first semiconducting film on the optical waveguide region; The present invention further comprises the steps of forming a covering second semiconductive film and forming an electrode on the second semiconductive film located above the buffer layer. The second optical waveguide device includes an optical waveguide formed on a waveguide substrate, a buffer layer formed on the optical waveguide, and a semiconductive film covering the buffer layer and the waveguide substrate. , ':S, tJi formed on the semiconductive crotch, and achieves the above object.

[Effect]

In the optical waveguide device of the present invention, the electrodes formed on the top of the optical waveguide are capacitively connected via the buffer layer and the semiconductive film, but the puff layer is present only on the top of the optical waveguide. A semiconductive film is formed to cover this buffer layer, and since the semiconductive film forms a path, the voltage drop between the electrode and the waveguide substrate is reduced.

In addition, it is a semi-conductor with a resistance large enough to allow charge to move between the waveguide substrate and the electrode! 1 is formed, so even if charge accumulates on the surface of the waveguide, the corresponding charge supplied to the electrode is uniformly distributed via the semiconducting film.

[Example] FIG. 1 is a perspective sectional view showing the configuration of an optical waveguide device according to an example of the present invention.

In the figure, l is a LiNb0r substrate, 2 is an optical waveguide, and 3 is a
4 is a SiO2 film as a buffer layer, 4a and 4b are Si films as semiconducting films, and 5 is an electrode made of Au.

Hereinafter, the process of forming an optical waveguide device according to an embodiment of the present invention will be explained with reference to FIG. thermally diffused into LiNb
An optical waveguide 2 having a diameter of about 7 μm and having a larger refractive index than the 0z substrate 1 is formed (FIG. 2(a)).

Next, a Si film 4a, which is a first semiconducting film covering the optical waveguide 2 and the LiNb0z substrate 1, is deposited by sputtering.
00 to 1000 people (Figure 2(b)).

Next, a layer of S with a thickness of about 2000 to 4000 layers is formed above the optical waveguide 2 and on the 5iftW4a to serve as a buffer layer.
An iO□ film 3 is formed (FIG. 2(C)).

Furthermore, a second semiconductive film 5illQ4b is formed by sputtering to cover the 5i(h film 3 (buffer layer) and the Si film 4a (first semiconductive film) (see FIG. 2). d)).

Finally, an electrode 5 made of a thin Au film having a width of several μm and a thickness of about 3 μm is formed on the Si film 4b above the optical waveguide 2 using methods such as vapor deposition and plating. An optical functional device according to an embodiment of the present invention is completed (FIG. 1).

As described above, in the optical waveguide device of the present invention, the Sing film 3 serving as a buffer layer exists only on the upper part of the optical waveguide 2, and the Si film 4b is formed to cover the 5in2 film 3. s, 145 and L i N b Os I
A path is now formed between Is 4Fil,
A small amount of current will flow. Therefore, the electrode 5 and Li
Since the voltage drop across the substrate with respect to the NbO5 substrate 1 is smaller than in the conventional case, the electric field applied to the optical waveguide 2 is effectively increased.

Furthermore, due to the presence of the Si film 4, when charges accumulate on the surface of the optical waveguide 2, the corresponding charges supplied to the electrodes 5 are uniformly distributed via the Si film 4. Local concentration of charge is prevented.

Therefore, it is possible to provide an optical waveguide device that can prevent the occurrence of DC drift and can effectively apply an electric field.

FIG. 3 shows another example. In this case, the 5itK! Although the step of forming 4a is omitted, this method can also improve voltage drop and DC drift.

〔Effect of the invention〕

According to the optical waveguide device of the present invention, the buffer layer exists only on the top of the optical waveguide, and the semiconductive film formed to cover the buffer layer forms a path between the electrode and the waveguide substrate. Reduce voltage drop. Therefore, the electric field applied to the optical waveguide becomes effectively large.

Furthermore, if charges accumulate on the surface of the waveguide due to the semiconducting film formed between the waveguide substrate and the electrode,
Correspondingly, the charges supplied to the electrodes are uniformly distributed through the semiconducting film, thereby preventing local concentration of charges.

Therefore, it becomes possible to use an optical single wavepath device that can prevent the occurrence of DC drift and can effectively apply an electric field.

[Brief explanation of the drawing]

FIG. 1 is a perspective cross-sectional view showing the configuration of an optical waveguide device according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of the formation process of an optical waveguide device according to an embodiment of the present invention, and FIG. FIG. 4 is a perspective sectional view showing the configuration of an optical waveguide device according to the conventional example. (Explanation of symbols) 1...LiNb0. Substrate, 2... Optical waveguide, 3... SiO□ film, 4 a, 4 b-5i film, 5... Electrode.

Claims (3)

[Claims] (1) An optical waveguide formed on a waveguide substrate, a first semiconducting film covering the waveguide substrate, and a first semiconducting film formed on the optical waveguide region. a second semiconductive film covering the buffer layer; and an electrode formed on the buffer layer via the second semiconductive film. Optical waveguide device. (2) forming a first semiconductive film on a waveguide substrate including an optical waveguide; and forming a buffer layer on the first semiconductive film on the optical waveguide region; forming a second semiconducting film covering the buffer layer and the first semiconducting film, and forming an electrode on the second semiconducting film located above the buffer layer. A method for forming an optical waveguide device, comprising the steps of: (3) an optical waveguide formed on a waveguide substrate; a buffer layer formed on the optical waveguide; a semiconductive film covering the buffer layer and the waveguide substrate; An optical waveguide device comprising an electrode formed on a film.