JP2800297B2 - Light control device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical control device for modulating an optical wave, switching an optical path, and the like, and in particular, to a waveguide type optical control for controlling using an optical waveguide provided in a substrate. About the device.

[Conventional technology]

As the practical use of the optical communication system progresses, an advanced system having a larger capacity and more functions is required. It is necessary to add new functions such as generation of higher-speed optical signals, switching of optical transmission lines, and switching. In current practical systems, optical signals are obtained by directly modulating the injection current of a semiconductor laser or light-emitting diode.However, direct modulation makes it difficult to perform high-speed modulation of several GHz or more due to effects such as relaxation oscillation and wavelength fluctuation. However, the coherent optical transmission system has drawbacks such as difficulty in application. As a means for solving this, there is a method of using an external optical modulator. In particular, a waveguide type optical modulator constituted by an optical waveguide formed in a substrate has features of small size, high efficiency, and high speed. On the other hand, an optical switch is used as a means for obtaining a function of switching an optical transmission line or switching a network. Optical switches currently in practical use are those that mechanically move prisms, mirrors, fibers, and the like, and have disadvantages such as low speed, insufficient reliability, large shape, and unsuitability for matrix formation. What is being developed as a means for solving this problem is a waveguide type optical switch using an optical waveguide, which has features such as high speed, integration of many elements, and high reliability. In particular, those using a ferroelectric material such as lithium niobate (LiNbO ₃ ) have features such as low light absorption and low loss, and high efficiency due to a large electro-optic effect. Conventionally, various types of light control elements such as a directional coupling type optical modulator or a switch total reflection type optical switch have been reported. When such a waveguide-type light control element is applied to an actual optical communication system, it is essential for practical use to have basic performance such as low loss and high speed, and at the same time, particularly, operational stability and long-term reliability. .

[Problems to be solved by the invention]

However, the conventional waveguide type optical control device has not obtained sufficient characteristics with respect to stability and reliability. FIG. 2 is a plan view (FIG. 2A) and a sectional view (FIG. 2A) of a directional coupling type optical switch as an example of a conventional light control device.
FIG. In FIG. 2A, strip-shaped optical waveguides 2 and 3 are formed on a lithium niobate crystal substrate 1 cut out perpendicularly to the z-axis to diffuse titanium so as to have a refractive index larger than that of the substrate. Optical waveguides 2 and 3
Are close to each other by about several μm at the center of the substrate to form a directional coupler 4. A control electrode 5 is formed on the optical waveguide constituting the directional coupler 4 via a buffer film 6 for preventing light absorption by the electrode. FIG. 2B is a cross-sectional view of a part of the directional coupler 4 perpendicular to the optical waveguides 2 and 3.

In FIG. 2, the incident light 7 entering the optical waveguide 2 gradually transfers light energy to the adjacent optical waveguide 3 as it propagates through the directional coupler 4, and after passing through the directional coupler 4, the optical waveguide Almost 100% of the energy is transferred to 3, and the light 3 is emitted. On the other hand, when a voltage is applied to the control electrode 5, the refractive index of the optical waveguide under the electrode changes due to the electro-optic effect, and a phase velocity mismatch occurs between the waveguide modes propagating through the optical waveguides 2 and 3, The connection between them changes.

As the applied voltage increases, the amount of light energy transfer from the optical waveguides 2 to 3 decreases, and at a certain voltage value V _S , the incident light 7 passes 100% of the light energy after passing through the directional coupler 4.
Is returned to the optical waveguide 2. That is,
The incident light 7 becomes the outgoing light 9 from the optical waveguide 2 or the outgoing light 8 from the optical waveguide 3 depending on the presence or absence of the voltage applied to the control electrode 5.

However, in the conventional optical switch as shown in FIG.
When the temperature changes or when a DC voltage is applied, instability of the characteristics and deterioration of the characteristics over time occur. The instability of the characteristics is caused by the local electric field non-uniformity in the crystal induced by the pyroelectric effect when the temperature changes, and the charge in the crystal being locally applied to the interface between the crystal and the film by applying a DC voltage. It is caused by a change in the intensity of the electric field that is accumulated and acts on the light wave.
Further, the characteristic deterioration suitable for aging is caused by the fact that the electrode material electrochemically reacts with moisture in the air and is corroded.

Conventionally, as a means of simply eliminating local electric field distribution non-uniformity due to temperature change, a method has been reported in which an ITO film or a Si film is coated on the surface and a ground electrode is provided on the back surface of the substrate. In addition, there are problems that the film itself such as ITO and Si is easily affected by the surrounding environment and changes over time are likely to occur, and that the above-described electrode deterioration cannot be prevented for a long time. In addition, the above-mentioned films of ITO, Si, and the like also have a drawback in that it is difficult to control at the time of manufacturing because the resistance value greatly varies depending on film forming conditions.

An object of the present invention is to provide a light control device that has stable characteristics over a long period of time, has high reliability, and is easy to manufacture, excluding the above-mentioned drawbacks of the conventional light control device.

[Means for solving the problem]

An optical control device according to the present invention includes an optical waveguide formed on a dielectric crystal substrate having an electro-optic effect, an electrode disposed near a light-guiding waveguide, and a conductive resin film disposed on the electrode. .

[Action]

In the light control device of the present invention, a conductive resin film is coated on the electrode. According to an experiment conducted by the inventor, the conductive resin film is chemically stable and is particularly hydrophobic, so that it is possible to prevent the electrode material from being corroded for a long period of time. Further, the specific resistance of the film is usually several μm.
Even when inserted between electrodes having a length of several mm to several tens of mm at intervals of m to several tens of μm, the resistance becomes sufficiently high so that the driving circuit connected to the electrodes is not affected, and the This is a value of about 10 ⁴ to 10 ⁶ Ωcm, which makes it possible to equalize the electric charge accumulated in the memory. Further, unlike the conventional ITO film and Si film, the above-mentioned resistance value is very stable with respect to the surrounding environment such as temperature and humidity and also with time.

As described above, the light control device of the present invention is stable and highly reliable over a long period of time as compared with the related art. In addition, the conductive resin film used in the present invention is structurally stable,
There is an advantage that it can be formed very easily by spin coating, dip coating or the like.

〔Example〕

FIG. 1 shows a plan view (FIG. 1 (a)) and a cross-sectional view (FIG. 1 (b)) of a directional coupling type optical switch which is an embodiment of an optical control device according to the present invention. In the same manner as in the example of FIG.
The optical waveguides 2 and 3 having a depth of about 3 to 10 μm formed by thermal diffusion at about 0 ° C. for several hours are installed. Make up. The control electrode 5 is provided thereon via a buffer layer 6. In this embodiment, the control electrode is further coated with a conductive resin film 10 by spin coating, dip coating, or the like. The conductive resin film is, for example, a conductive material such as ITO, ZnO, InO, SiO to obtain a predetermined specific resistance on polyacrylonitrile, PMMA, acrylic, polyvinyl butyral, polystyrene polyester, epoxy resin, Si resin, or the like. , Si, and C are dispersed in appropriate amounts and can be easily obtained or manufactured by anyone.

Actually, after coating the polymer by spin coating, dip coating, etc.,
High quality by baking for about 20 minutes and
A film having a specific resistance of 10 ⁴ to 10 ⁶ Ωcm can be obtained with good reproducibility.

The basic operation of the directional coupling type optical switch of this embodiment is the same as that of the conventional example shown in FIG. 2, but in this embodiment, the electrode is coated with a conductive resin film to be stable and high in the long term. Reliability is obtained.

〔The invention's effect〕

As described above, the light control device of the present invention can provide a light control device that has stable characteristics over a long period of time, has high reliability, and is easy to manufacture, as compared with the conventional light control device.

[Brief description of the drawings]

1 (a) and 1 (b) are views showing an example of a light control device according to the present invention, and FIGS. 2 (a) and 2 (b) are views showing an example of a conventional light control device. Is a plan view,
(B) is a sectional view. In the figure, 1 is a lithium niobate crystal substrate, 2 and 3 are optical waveguides, 5 is a control electrode, 6 is a buffer film, and 10 is a conductive resin film.

Claims (1)

(57) [Claims] 1. An optical waveguide formed on a dielectric crystal substrate having an electro-optic effect, an electrode provided near the optical waveguide, and a conductive resin film provided on the electrode. Light control device.