JP2903700B2 - Waveguide type optical device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a waveguide type optical device.

Conventional technology With the practical use of optical communication systems, higher capacity and more sophisticated systems are required, and new functions such as higher-speed generation of optical signals, switching of optical transmission lines, and switching are added. is necessary.

In the current practical system, an optical signal is obtained by directly modulating an injection current of a semiconductor laser or a light emitting diode. However, direct modulation has drawbacks such as difficulty in high-speed modulation of several GHz or more due to effects such as relaxation oscillation, and difficulty in application to coherent optical transmission systems due to wavelength fluctuation.

As a means to solve this, there is a method using an external modulator. In particular, a waveguide type optical modulator composed of an optical waveguide formed in an electro-optic crystal substrate is characterized by its small size, high efficiency, and high speed. There is.

On the other hand, an optical switch is used as a means for obtaining an optical transmission line switching function and a network conversion function. An optical switch currently in practical use switches an optical path by mechanically moving a prism, a mirror, a fiber, and the like, and has disadvantages such as a low speed and a large shape which is not suitable for matrix formation.

As a means for solving this problem, a waveguide type optical switch using an optical waveguide is being developed, and has features such as high speed, integration of many elements, and high reliability. In particular, those using ferroelectric materials such as lithium niobate (LiNbO ₃ ) crystals have features such as low light absorption and low loss, and high efficiency due to a large electro-optic effect. There are reports on various types of optical control devices such as directional coupler type modulators or optical switches, total reflection type optical switches, Mach-Zehnder type optical modulators, and the like.

Recent years, research and development of high-density integration of the waveguide type optical switch being actively, literature Nishimoto Hiroshira, according to IEICE OQE88-147, directional coupler using a LiNbO ₃ substrate An 8 × 8 matrix optical switch having 64 integrated optical switches is obtained.

On the other hand, research and development of devices including a single optical switch element such as an external optical modulator are also actively pursued. The characteristic items of such an optical switch device include switching voltage (power), crosstalk, extinction ratio, loss, switching speed, and operation stability against environment such as temperature and humidity.

FIG. 3 is a perspective view of an optical switch and a modulator comprising a directional coupler formed on a substrate surface, which are examples of a conventional waveguide type optical device.

In the figure, this is a waveguide type optical device in which optical waveguides 2A and 2B are formed by thermally diffusing Ti into a substrate 1. Electrodes 4A and 4B are formed above the optical waveguides 2A and 2B with a buffer layer 3 interposed therebetween in order to change the respective refractive indexes of the optical waveguides 2A and 2B using the electro-optic effect of the substrate 1. .

In the buffer layer 3, since the electrodes 4A and 4B are metal films, when this metal film is directly formed on the optical waveguides 2A and 2B, respectively, the TM mode of light guided through the optical waveguides 2A and 2B is used. It serves to prevent the loss of light power absorbed by the electrodes 4A and 4B from increasing.

In this example, silicon oxide (SiO ₂ ) is used as the buffer layer 3.
A membrane is used. Optical fibers are fixed to the ports a and c.

For example, when no voltage is applied to the electrode 4A, the light input from the port a is transferred to the other optical waveguide 2 adjacent to the directional coupler 6 so that the light is emitted from the port c. Then, when a certain voltage is applied to the electrode 4A, the refractive index of the optical waveguide 2A changes, and the optical power of the optical waveguides 2A and B does not move in the directional coupler 6, and light is not emitted. The light exits from port b.

For example, in the case of an optical switch used in an optical fiber break point measuring instrument, port b is a light source, port a is a measured optical fiber, and port c is a light receiving element.

This measuring instrument sends light from the light source to the optical fiber to be measured,
The return light from the measured optical fiber is measured by a light receiving element, and the break point of the measured optical fiber is checked. Port c is the output of the signal light.

In the case of the modulator, the optical output at the port c is turned on / off by switching the optical path at the directional coupler, and the signal is propagated as a signal. The light output is also turned on and off at the port b in the same manner, but here, the port c is used as the signal light output.

In this structure, since the optical waveguides 2A and 2B from the portion of the directional coupler to the output end are bent, when light is emitted to the port b, the light is emitted at the bent portions of the optical waveguides 2A and 2B,
This emitted light leaks to port c. For this reason, there is a disadvantage that the extinction ratio and crosstalk of the optical output (signal light) at the port c are deteriorated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a waveguide type optical device capable of eliminating a light emission at a bent portion of an optical waveguide and obtaining a high extinction ratio at a port to which signal light is output. It is.

According to the present invention, a substrate, a plurality of optical waveguides formed on one main surface of the substrate, and an electrode formed via a buffer layer above an optical coupling portion between the waveguides A waveguide type optical device comprising: a metal film directly above and in the vicinity of an optical waveguide immediately adjacent to an optical waveguide used for signal light propagation among the optical waveguides, without interposing the buffer layer. A waveguide type optical device characterized by being formed is obtained.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view of an embodiment of the present invention, and the same parts as those in FIG. 3 are denoted by the same reference numerals. Light input from the port a is emitted from the port c which is a signal output when no voltage is applied to the electrode, and is emitted from the port b which is a dummy output port when a voltage is applied.

The buffer layer 3 above and near the optical waveguide 2A from the directional coupler 6 to the port b, which is a dummy port, is removed to improve the extinction ratio and crosstalk of the signal light at the port c, and the metal film is formed. 5 are formed directly above and near the optical waveguide 2A.

With such a structure, the TM mode optical power of the light propagating through the optical waveguide 2A at the metal film 5 and the light radiated at the bent portion of the optical waveguide 2A is absorbed by the metal film 5 and the port c , Leakage light from the dummy port coupled to the light source is reduced.

By removing the buffer layer 3 above and near the optical waveguide 2A from which no signal light is emitted and directly forming the metal film 5, a high extinction ratio and high crosstalk of the signal light can be obtained.

For example, in the case of an optical switch used for a measuring device for measuring a break point of an optical fiber, port b is connected to a light source, port a is connected to a measured optical fiber, and port c is connected to a light receiving element.

This measuring instrument sends light from the light source to the optical fiber to be measured,
The return light from the optical fiber to be measured is measured by a light receiving element to check the break point of the optical fiber to be measured. As described above, the buffer layer 3 above and near the optical waveguide 2A where the signal light does not propagate is removed. By directly forming the metal film 5, the optical power in the TM mode is absorbed, noise to the light receiving element is reduced, and measurement with high resolution is possible.

It is apparent that this structure can be applied to other waveguide devices such as a total reflection type optical switch and a waveguide optical device using a compound semiconductor substrate such as GaAs and InP.

FIG. 2 is a perspective view of another embodiment of the present invention. This example shows a structure in which a plurality of directional couplers are integrated, that is, an example in which a plurality of directional couplers are integrated, in which two-stage optical switches are connected. 3 is removed, and the metal film 5 is directly formed.

The effect of this optical switch is the same as that of FIG. 3, in which a light source is connected to port b, a measured optical fiber is connected to port a, and a light receiving element is connected to port c.

The metal film 5 may be any material such as Al, Au, Pt, Ti, Cr, Cu, and Mo, and also includes an alloy. The metal film may be formed by any method such as a sputtering method and a vapor deposition method.

As described above, according to the present invention, by removing the buffer layer above and near the optical waveguide through which the signal light does not propagate and forming a metal film directly on the portion, the optical power of the TM mode is reduced. Is absorbed, the light emission at the bent portion of the optical waveguide is reduced, and an effect is obtained that a high extinction ratio of the port for outputting the signal light can be obtained.

[Brief description of the drawings]

1 and 2 are perspective views of each embodiment of the present invention, and FIG. 3 is a perspective view of a conventional waveguide type optical device. Description of Signs of Main Part 1 ... Substrate 2A, 2C ... Optical Waveguide 4A, 4C ... Electrode 5 ... Metal Film 6 ... Directional Coupler

Claims (1)

(57) [Claims] 1. A waveguide comprising: a substrate; a plurality of optical waveguides formed on one main surface of the substrate; and an electrode formed above a light coupling portion between the waveguides via a buffer layer. A waveguide type optical device, wherein a metal film is formed directly on and above an optical waveguide immediately adjacent to an optical waveguide used for signal light propagation of the optical waveguide without interposing the buffer layer. A waveguide type optical device.