JPH0578016B2 - - Google Patents

Description

[Detailed Description of the Invention] [Summary] The present invention provides a waveguide that changes the refractive index by applying an electric field, which is provided with a film body between electrodes, and this film body changes the refractive index by polarization generated in the substrate. It can supply an opposite charge in response to a charge, has a resistance value that prevents substantial conduction between electrodes, and has a pyroelectric effect.
By uniformly distributing the charge induced in the electrode when the spontaneous polarization of LiNbO ₃ changes with temperature, the electric field changes with temperature change. To provide a waveguide optical device in which characteristic fluctuations are prevented by preventing such fluctuations.

[Industrial application field]

The present invention relates to a waveguide formed in a ferroelectric material having a pyroelectric effect, and more particularly to a waveguide optical device used in an optical switching element or the like.

[Conventional technology]

Waveguide type optical devices are capable of low driving voltage, high speed operation, and are promising for compact integration. However, in a waveguide constructed by using a crystal such as lithium niobate (LiNbO ₃ ) that has a pyroelectric effect, that is, spontaneous polarization, as a substrate and forming a diffusion layer of titanium (Ti) on the substrate, Charges based on the pyroelectric effect are generated on the surface due to temperature changes, and the charge distribution is not uniform, causing fluctuations in, for example, switching characteristics of the waveguide type optical device. FIG. 5a shows a cross-sectional view of a conventional waveguide, in which a Ti diffusion layer 2 is formed on a substrate 1 made of a Z plate LiNbO ₃ to form a waveguide, and a SiO ₂ layer is formed on the top surface of the waveguide.
A buffer layer 3 is formed, and a plurality of electrodes 4 made of aluminum, for example, are formed on the upper surface of the buffer layer 3. When the temperature is increased in this optical waveguide, Fig. 5b
As shown in , the polarization state of the substrate 1 made of Z-plate LiNbO ₃ changes due to the pyroelectric effect, so that − charges corresponding to the + charges generated on the surface of the substrate 1 are supplied from the outside to the bottom surface of the electrode 4. will be done.
Therefore, an electric field 5 as shown in the figure is generated within the substrate 1 from between the electrodes without the electrode 4 toward the electrode 4. The waveguide optical device is capable of performing, for example, a switch operation by changing the refractive index of the waveguide made of the Ti diffusion layer 2 by applying an electric field between the electrodes. When the electric field 5 is generated as described above, it has a great effect on the operating point, such as the switching characteristics, of the waveguide optical device.

Therefore, conventionally, in order to prevent this characteristic variation, the structure of the waveguide, the structure of the electrodes, etc. are often made insensitive to temperature changes.

[Problem that the invention seeks to solve]

However, the above-mentioned conventional configuration has the problem that not only the element structure is limited, but also characteristic fluctuations of the waveguide optical device due to the temperature increase effect cannot be sufficiently prevented. Therefore, it is an object of the present invention to provide a waveguide optical device that has a simple configuration and can sufficiently prevent charges generated by the pyroelectric effect from affecting the characteristics of the waveguide optical device. .

[Means for solving problems]

According to the present invention, a waveguide is formed on a substrate made of a crystal having a pyroelectrode effect, and the refractive index of the waveguide is controlled by controlling an electric field provided on the substrate near the waveguide. a plurality of electrodes for changing, and a film body between the electrodes so as to be in contact with the electrodes at least in a portion of the substrate where the electrodes are not provided between the electrodes, the film body being The present invention provides a waveguide optical device that is capable of supplying an opposite charge in response to the charge caused by polarization generated in a substrate and has a resistance value that prevents substantial conduction between electrodes.

[Effect]

By forming a slightly conductive material between the electrodes, the electric field applied to the waveguide changes as the temperature rises, by preventing charges generated by the pyroelectric effect from staying in the electrodes. This is to prevent the characteristics of the waveguide optical device from changing.

〔Example〕

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

Figure 2 shows a perspective view of a waveguide optical device, in which a substrate 1 made of a Z-plate LiNbO ₃ crystal is
Waveguides made of Ti diffused layers are formed so as to cross each other, for example, and at least two electrodes 4 are arranged across the intersections, and by changing the electric field applied to these electrodes, the waveguide can be refracted. It is possible to perform optical path switching operations by changing the ratio.

FIGS. 1a and 1b show cross-sectional views of one embodiment of the waveguide optical device of the present invention, and the same parts as those in FIGS. 5a and 5b are given the same numbers and the explanation will be omitted. A waveguide is formed on the substrate 1 by a Ti diffusion layer 2, and a 2000 Å SiO ₂ film is formed as a buffer layer 3 on the top surface of the waveguide. Next, at least two electrodes 4 made of 3000 Å aluminum are formed, and the buffer layer 3 and the electrodes are formed. A transparent film body 6 made of ITO with a thickness of 1000 Å is coated on the upper surface of 4 by sputtering. As a result, we were able to reduce the interelectrode resistance with a gap of 5 μm and a length of 10 mm from the conventional 10 ¹³ Ω or more to 10 to 10 ¹⁰ Ω. As a result, even if the temperature rises, negative charges are uniformly induced in the electrode 4 and the ITO film 6 in response to the positive charges due to polarization generated in the substrate 1 due to the pyroelectric effect, as shown in Figure 1b. . Therefore, since the charge distribution is uniform, no electric field is generated from between the electrodes toward the electrodes. Therefore, even if the temperature rises, the electric field applied from the electrode 4 to the waveguide does not change, so that fluctuations in the characteristics of the waveguide optical device due to temperature rise can be prevented. Note that if the resistance of the membrane body 6 is too low, when an electric field is applied to the waveguide from the electrodes 4, a large current will flow between the electrodes 4 through the membrane body 6, resulting in destruction of the device. Therefore, the resistance value of the membrane body 6 is selected in consideration of this fact.

FIG. 3 shows another embodiment of the waveguide optical device of the present invention. After uniformly coating the ITO film body 7 on the upper surface of the buffer layer 3, the ITO film body 7 is
A plurality of electrodes 4 are formed on the upper surface. In this case as well, effects similar to those of the embodiment shown in FIGS. 1a and 1b are produced.

Figure 4 shows a comparison of operating point fluctuations due to temperature changes between the embodiment according to the present invention and the conventional example. In the case where the temperature change was not present, the operating point varied greatly depending on the temperature change. On the other hand, as shown in characteristic B in the figure, after applying the ITO film to the chip surface based on the embodiment of the present invention, there is almost no change in the operating point even if the temperature changes. I couldn't help it.

In the above embodiment, ITO was used as the film body 6 or 7, but if it is a substance that induces electric charges, SnO ₂
Alternatively, the same effect can be obtained by using Si or SiO ₂ doped with a metal. Further, an antistatic material may be applied as the film body 6.

〔Effect of the invention〕

According to the present invention, the temperature is increased and the pyroelectric effect
To provide a waveguide optical device capable of suppressing changes in characteristics due to temperature rise, since even if electric charge changes on a LiNbO ₃ substrate, the electric field of the substrate and waveguide can be prevented from changing. be able to.

[Brief explanation of drawings]

1A and 1B are sectional views of a waveguide optical device according to an embodiment of the present invention, FIG. 2 is a perspective view of the waveguide optical device, and FIG. 3 is a cross-sectional view of another waveguide optical device of the present invention. FIG. 4 is a characteristic diagram comparing the characteristics of the embodiment of the present invention and a conventional example, and FIGS. 5a and 5b are sectional views of a conventional waveguide optical device. 1...Z plate LiNbO ₃ substrate, 2...Ti diffusion layer, 3
... Buffer layer, 4 ... Electrode, 5 ... Electric field, 6,
7...Membrane body.

Claims (1)

[Scope of Claims] 1. A waveguide formed on a substrate made of a crystal having a pyroelectric effect, and a refractive index of the waveguide provided on the substrate near the waveguide by controlling an electric field. a plurality of electrodes for changing the temperature; a membrane body is provided between the electrodes so as to be in contact with the electrodes at least in a portion of the substrate where the electrodes are not provided between the electrodes, the membrane body being in contact with the electrodes; A waveguide optical device, characterized in that it can supply an opposite charge in response to the charge caused by polarization generated in the substrate, and has a resistance value that prevents substantial conduction between electrodes. 2. The waveguide optical device according to claim 1, wherein the film body is a transparent conductive film made of ITO. 3. The waveguide optical device according to claim 1, wherein the film body is made of a transparent conductive film of _SnO2 . 4. The waveguide optical device according to claim 1, wherein the film body is made of Si. 5. Claim 1, wherein the film body is made of a material in which SiO ₂ is doped with a metal.
The waveguide optical device described in . 6. The waveguide optical device according to claim 1, wherein the film body is made of an antistatic material. 7. The waveguide optical device according to any one of claims 1 to 7, wherein the substrate is made of LiNbO ₃ . 8. The film body is formed uniformly on the upper surface of the substrate on which the waveguide is formed, and the electrode is formed on the substrate via the film body. The waveguide optical device according to item 1.