JP2936792B2 - Waveguide type optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveguide type optical device which controls light by confining light in an optical waveguide provided on a substrate, and more particularly to an improvement of a waveguide type optical device.

[0002]

2. Description of the Related Art With the practical use of optical communication systems, high-capacity, multifunctional advanced systems have been demanded, and new functions such as higher-speed generation of optical signals and switching and switching of optical transmission paths have been demanded. Addition is needed. In the current practical system, an optical signal is obtained by directly modulating the injection current of a semiconductor laser or a light-emitting diode. However, in direct modulation, high-speed modulation over several GHz is difficult due to effects such as relaxation oscillation, and wavelength fluctuation. Is disadvantageous in that it is difficult to apply to the coherent optical transmission system because of the occurrence of

As a means for solving this drawback, there is a method using an external modulator. In particular, a waveguide type optical modulator constituted by an optical waveguide formed in an electro-optic crystal substrate is small in size and high in efficiency. , High speed.

On the other hand, an optical switch is used as a means for obtaining an optical transmission line switching or network switching function. The optical switch currently in practical use is a prism,
The optical path is switched by mechanically moving a mirror, a fiber, or the like, and has disadvantages such as low speed, large shape, and unsuitability for matrix formation.

As means for solving this problem, a waveguide type optical switch using an optical waveguide has been developed, and has features such as high speed, integration of many elements, and high reliability.
In particular, a material using a ferroelectric material such as lithium niobate (LiNbO ₃ ) crystal has low light absorption, low loss, and a large electro-optic effect, and thus has high efficiency and the like. In addition, various types of light control devices such as a directional coupler type optical modulator or a light switch, a front reflection type optical switch, and a Mach-Zehnder type optical modulator have been devised.

In recent years, the research and development of high-density integration of the waveguide type optical switch has been actively, for example, Yutaka Nishimoto et al., According to the IEICE "OQE88-147", LiNbO ₃ An 8 × 8 matrix optical switch in which 64 directional coupler optical switches are integrated using a substrate has been proposed.

On the other hand, research and development of devices comprising a single optical switch, such as an external optical modulator, have been actively pursued. Such characteristic items of the optical switch device include:
There are operation stability to environment such as switching voltage (power), crosstalk, extinction ratio, loss, switching speed, temperature and humidity, and the like.

FIG. 2 is a perspective view showing an optical switch as a waveguide type optical device using a conventional directional coupler. The optical switch 11 has a substrate 12 made of LiNbO ₃ crystal, and optical waveguides 13 and 14 are formed on the substrate 12 by Ti diffusion. And the optical waveguide 1
The central portions of 3 and 14 are close to each other, and are separated by a predetermined distance (for example, 600 μm) on the light incident side and the light emitting side.

On the substrate 12, a buffer layer 15 is provided so as to cover the entire surface of the substrate 12, and the buffer layer 15 is made of silicon dioxide (SiO ₂ ) or the like. Ports 16a and 16b of optical waveguides 13 and 14 are located on the light incident side end surfaces of the substrate 12 and the buffer layer 15, respectively.
Ports 16c and 1 of the optical waveguides 13 and 14 are provided on the light exit side end face.
6d is located.

Further, on the buffer layer 16 and on the optical waveguide 13
And 14 are arranged so as to be located on the optical waveguides 13 and 14, respectively, in a portion where the control electrodes 17 are close to each other, and the control electrodes 17 are made of a metal film. A directional coupler 18 is formed by the central portion of the optical waveguides 13 and 14 close to each other and the control electrode 17. The length of the central portion close to the optical waveguides 13 and 14 is such that when the voltage is not applied to the control electrode 17, the optical power is transferred to the adjacent optical waveguide at the directional coupler 18. (Complete coupling length). Then, in order to perform polarization-independent operation, the complete coupling length is made identical in both TE and TM modes.

Next, the operation will be described.

When no voltage is applied to the control electrode 17, the light incident on the optical waveguide 13 from the port 16a is
The optical power is transferred to the adjacent optical waveguide 14 at the directional coupler 18, and exits from the port 16 d through the optical waveguide 14.

When a predetermined voltage is applied to the control electrode 17, the refractive indexes of the optical waveguides 13 and 14 change, and the optical power between the optical waveguides 13 and 14 moves at the directional coupler 18. Does not happen. Light that enters the optical waveguide 13 from the port 16a passes through the optical waveguide 13 and exits from the port 16c.

[0014]

A conventional waveguide type optical device is constructed as described above,
Makes the above-mentioned perfect coupling length coincide in both TE and TM modes in order to perform polarization-independent operation.
Even if a directional coupler is created under the condition that the complete coupling lengths of the E and TM modes match, the optical power emitted from the port 16c differs between the TE mode and the TM mode due to variations between process batches and the like. There is a problem that the output fluctuates depending on the change state of the input light, that is, a difference occurs in the complete coupling length between the TE mode and the TM mode.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a waveguide type optical device which can be adjusted so that a perfect coupling length coincides with TE and TM modes. .

[0016]

A waveguide type optical device according to the present invention comprises a plurality of optical waveguides formed on a substrate surface, a buffer layer covering the optical waveguide and the substrate surface, and an optical waveguide on the buffer layer. Compensate for the waveguide loss between the control electrode disposed at the facing position, the cutout portion of the buffer layer where the emission side of the optical waveguide is cut, and the polarization component provided in the cutout portion so as to directly contact the optical waveguide. And a metal film having a length.

[0017]

With the above construction, the power of the TM mode light is absorbed by the metal film provided in the notch so as to directly contact the optical waveguide, and the contact length between the metal film and the optical waveguide is adjusted. Thus, the optical power of the signal light at the output port is made equal in the TE and TM modes, and the optical output power does not fluctuate in the deflection state of the input light.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing an optical switch as a waveguide type optical device according to the present invention. The optical switch 11 has a substrate 12 made of a LiNbO ₃ crystal, and optical waveguides 13 and 14 having a higher refractive index than the substrate 12 are formed by forming an optical waveguide pattern on the substrate 12 and thermally diffusing Ti. Have been. And the optical waveguide 13
And 14 are close to each other at the center, and are separated by a predetermined distance (for example, 600 μm) on the light incident side and the light exit side.

A buffer layer 15 is provided on the substrate 12 so as to cover the entire surface of the substrate 12, and the buffer layer 15 is made of silicon dioxide (SiO ₂ ). Ports 16a and 16b of optical waveguides 13 and 14 are located on the light incident side end surfaces of the substrate 12 and the buffer layer 15, respectively.
Ports 16c and 1 of the optical waveguides 13 and 14 are provided on the light exit side end face.
6d is located.

Further, on the buffer layer 16 and the optical waveguide 13
The two control electrodes 17 are arranged so as to be located on the optical waveguides 13 and 14, respectively, in a portion where the control electrodes 17 and 14 are close to each other, and the control electrodes 17 are made of a metal film.
The buffer layer 15 has a function of preventing the control electrode 17 from absorbing the TM mode.

A directional coupler 18 is constituted by the central part of the optical waveguides 13 and 14 close to each other and the control electrode 17. The length of the central portion close to the optical waveguides 13 and 14 is such that when the voltage is not applied to the control electrode 17, the optical power is transferred to the adjacent optical waveguide at the directional coupler 18. (Complete coupling length). That is, the output light of the port 16d is set to have a higher power in the TM mode than in the TE mode.

The buffer layer 16 has a cutout near the port 16d of the optical waveguide 14, and the cutout 1
9 is provided with a metal film 20 having a length to compensate for the waveguide loss between the polarization components so as to directly contact the optical waveguide 14.
The metal film 20 absorbs the power of the TM mode light, and
The TM mode light is absorbed so that the power of the emitted light at 6d becomes equal in both the TE mode and the TM mode.

When the length of the metal film 20 is set, the ratio of absorption of TM mode light to the metal film 20 increases as the length of the metal film 20 increases. Initially, the length of the metal film 20 is shortened so that the power of the emitted light at the port 16d becomes equal to the TE mode light while monitoring the power of the emitted light at the port 16d of the TM mode light. I will do it. The same operation is repeated to make the power of the output light at the port 16d equal in both the TE mode and the TM mode, whereby the polarization independent operation can be performed.

Next, the operation of this embodiment will be described.

When no voltage is applied to the control electrode 17, the light incident on the optical waveguide 13 from the port 16a is
The optical power is transferred to the adjacent optical waveguide 14 at the directional coupler 18, and exits from the port 16 d through the optical waveguide 14.

At this time, the metal film 20 absorbs the power of the TM mode light, and the power of the light emitted from the port 16d is TE,
It becomes equal in both TM modes.

When a predetermined voltage is applied to the control electrode 17, the refractive index of the optical waveguides 13 and 14 changes, and the optical power between the optical waveguides 13 and 14 moves at the directional coupler 18. Does not happen. Light that enters the optical waveguide 13 from the port 16a passes through the optical waveguide 13 and exits from the port 16c.

In the above embodiment, the port 16
Although d has been described as the output of the signal light, the invention is not limited thereto, and the port 16c may be used as the output of the signal light. In this case, the metal film 20 is brought into direct contact with the optical waveguide 13.
To form

[0030]

As described above, according to the present invention, the power of the TM mode light is absorbed by the metal film provided so as to be in direct contact with the optical waveguide, and the contact length between the metal film and the optical waveguide is adjusted. Is configured so that the magnitudes of the optical powers of the TE and TM modes are equal at the output port of the signal light, so that the perfect coupling length is matched between the TE and TM modes, and the optical output power is deflected in the input light deflection state. It can be made not to fluctuate.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an optical switch as a waveguide type optical device according to the present invention.

FIG. 2 is a perspective view showing a conventional optical switch.

[Explanation of symbols]

 13, 14 Optical waveguide 15 Buffer layer 17 Control electrode 19 Notch 20 Metal plate

Claims (1)

(57) [Claims] 1. A waveguide comprising: a plurality of optical waveguides formed on a substrate surface; a buffer layer covering the optical waveguide and the substrate surface; and a control electrode disposed at a position facing the optical waveguide on the buffer layer. In the optical device, a metal film having a length that compensates for a waveguide loss between a cutout portion of the buffer layer cut out on the emission side of the optical waveguide and a polarization component provided so as to directly contact the optical waveguide in the cutout portion. A waveguide type optical device, comprising: