JP2903702B2 - Waveguide type optical device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a waveguide type optical device, and more particularly to a configuration of an optical waveguide.

[Conventional technology]

With the practical use of optical communication systems, higher capacity and multi-functional advanced systems are required, and it is necessary to add new functions such as faster generation of optical signals, switching of optical transmission lines, and switching. Have been.

In a 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 of relaxation oscillation and the like, and difficulty in application to a coherent optical transmission system 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 or network switching function. Optical switches currently in practical use include prisms, mirrors,
The optical path is switched by mechanically moving a fiber or the like, and has disadvantages such as low speed, large shape, and unsuitability 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 a strong derivative material such as lithium niobate (LiNbO ₃ ) crystal have features such as low light absorption, low loss, and high efficiency due to a large electro-optic effect. Various types of light control devices such as a directional coupler type optical modulator or an optical switch, a total reflection type optical switch, and a Mach-Zehnder type optical modulator have been reported.

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 the environment such as temperature and humidity.

[Problems to be solved by the invention]

FIG. 4 is a perspective view of an optical switch and modulator comprising a directional coupler formed on a substrate surface, which is an example of a conventional waveguide type optical device. In the figure, light input from the first port 2 when no voltage is applied to the electrode 1 is:
When the power is transferred to the other optical waveguide 4 adjacent to the directional coupler 3 and the light is emitted from the second port 5, the optical waveguide is applied when a certain voltage is applied to the electrode 1. 4 changes, the optical power does not move between the optical waveguides 4 in the portion of the directional coupler 3, and the light is
Out of the port 6 of FIG. Note that the two optical waveguides 4 are formed on the surface of the substrate 7, and the buffer layer 8 is provided on the substrate 7.

For example, in the case of an optical switch used for a measuring device for measuring a break point of an optical fiber, the third port 6 is connected to a light source, the first port 2 is connected to an optical fiber to be measured, and the second port 5 is connected to a light receiving element. . This measuring instrument sends light from the light source to the optical fiber to be measured, measures the return light from the optical fiber to be measured with the light receiving element, and examines the break point of the optical fiber to be measured.
The second port 5 is an output of the signal light. In the case of a modulator, the optical output at the second port 5 is turned on and off by switching the optical path in the directional coupler 3 and propagated as signal light. The light output is similarly turned on and off at the third port 6, but here, the second port 5
Is the signal light output.

In the case of an optical fiber break point measuring instrument using this structure, when a voltage is applied to the electrode 1 and the light is sent from the light source to the optical fiber to be measured, the directional coupler 3 closes the optical waveguide 4. There is a drawback that light leaks and the extinction ratio at the second port 5 is deteriorated. In the case of a modulator, when a voltage is applied to the electrode 1 to turn off the signal light output, that is, when light is output to the third port 6, light leaks into the second port 5. Also, there is a disadvantage that the extinction ratio is deteriorated.

The object of the present invention has been made in view of the above-mentioned disadvantages,
An object of the present invention is to provide a waveguide type optical device in which the extinction ratio of a port from which signal light is output is prevented from being deteriorated.

[Means for solving the problem]

According to a first aspect of the present invention, there is provided a waveguide type optical device including a plurality of optical waveguides formed on a substrate surface and electrodes formed on or near the optical waveguide, wherein the optical waveguide is a waveguide light introduction portion. , A control section, and an output section for signal light. The output section has a wide waveguide, and has a first electrode above or near an optical waveguide constituting a control section for guided light, and has a light guide for the output section. A second electrode for generating an electric field for making the optical waveguide of the output section multi-mode is provided above or near the wave path.

According to a second aspect of the present invention, the first electrode and the second electrode are formed above the optical waveguide via a buffer layer.

[Action]

As described above, according to the present invention, a high extinction ratio of the port from which the signal light is output can be obtained by making the optical waveguide through which the signal light propagates a multi-mode structure having a large propagation loss.

〔Example〕

 Next, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a perspective view showing one embodiment of a waveguide type optical device according to the present invention, and FIG. 2 is a sectional view taken along line II-II of FIG.

This embodiment shows a waveguide type optical device in which optical waveguides 11 and 12 are formed by thermally diffusing Ti into a substrate 10. A first electrode 15 is provided above the directional coupler 13 of the optical waveguides 11 and 12 via a buffer layer 14 in order to change the refractive index of the optical waveguides 11 and 12 using the electro-optic effect of the substrate 10. Is formed. Since the buffer layer 14 is formed directly on the optical waveguides 11 and 12 because the first electrode 15 is a metal film, the power of the TM mode light of the light propagating through the optical waveguides 11 and 12 is reduced by the first electrode 15. It plays a role in preventing the loss from being increased by absorption.

In the present embodiment, silicon oxide (Si
O ₂ ) film is used. The shape of the optical waveguide is
The optical waveguide width of the direct portion from the directional coupler 13 to the second port 16 is widened.

FIG. 3 shows a dispersion curve of the optical waveguide when LiNbO ₃ is used for the substrate 10 for illustrating the operation principle according to the present embodiment. In the figure, Ko is the wave number (2π / λ), d
Is the width of the optical waveguide, Ns is the refractive index of the substrate, Nf is the refractive index of the optical waveguide, and N is the equivalent refractive index {Nf Si Nθ (θ is the angle of incidence of the propagating light on the boundary between the core and the grad)}. The optical waveguide 12 according to the embodiment is designed such that the optical waveguide 12 having the widened waveguide width is at point A (the point B where the waveguide width is not widened is point B).
A second electrode 17 is formed via the buffer layer 14 to change the refractive index of the optical waveguide in this portion.

The light input from the first port 18 is emitted from the second port 16 which is a signal output when no voltage is applied (point A in FIG. 3), and when light is applied (point C in FIG. 3).
Is output from the third port 19 which is a dummy output port. A voltage is applied to the first electrode 15 so that a high extinction ratio can be obtained at the second port 16, and when light is emitted from the third port 19, a voltage is also applied to the second electrode 17,
It is designed so that the refractive index of the optical waveguide 12 changes and a multimode of m = 1 occurs in the optical waveguide 12. The voltage is applied so that an electric field is generated in a direction in which the refractive index of the optical waveguide 12 is reduced.

In general, propagation loss is larger in a multimode than in a single mode (m = 0 in FIG. 3). Therefore, for example, if an optical fiber is connected to the second port 16, the coupling of the light propagating through the optical waveguide 12 to the optical fiber is reduced, and a high extinction ratio is obtained.

As described above, when the light is emitted to the third port 19 which is the dummy port, the optical waveguide 12 of the second port 16 where the signal light is emitted enters the multi-mode state, whereby a high extinction ratio is obtained. Can be For example, in the case of an optical switch used for an optical fiber break point measuring instrument, the third port 19
Is a light source, an optical fiber to be measured is connected to the first port 18, and a light receiving element is connected to the second port 16. This measuring instrument sends light from a light source to an optical fiber to be measured, measures return light from the optical fiber to be measured by a light receiving element, and examines a break point of the optical fiber to be measured. Therefore, as described above, when the optical switch is operating to transmit light from the light source to the optical fiber to be measured, the optical waveguide 12 to which the light receiving element is connected is used.
In the multi-mode, noise to the light receiving element is reduced, and high-resolution measurement can be performed. It is clear 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 or Inp.

〔The invention's effect〕

As described above, according to the waveguide type optical device according to the present invention, the optical waveguide includes a guided light introduction section, a control section, and an output section for signal light, and has a wide waveguide width of the output section. And a second electrode having a first electrode above or near the optical waveguide that forms a control section of the guided light, and generating an electric field for making the optical waveguide of the output section multi-mode above or near the optical waveguide of the output section. With the configuration provided with the electrodes described above, it becomes possible to make the optical waveguide through which the signal light propagates into a multi-mode structure with a large propagation loss, thereby making the extinction ratio of the port through which the signal light is output higher than in the past. It has an excellent effect that it can be raised.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a waveguide type optical device according to the present invention, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. 3 is an operation principle of the optical waveguide according to the present invention. FIG. 4 is a perspective view showing an example of a conventional waveguide type optical device. 10 ... substrate, 11, 12 ... optical waveguide, 13 ... directional coupler, 14 ... buffer layer, 15 ... first electrode, 16 ... second port, 17 ... second electrode , 18 ... first port, 19 ... third port.

Claims (2)

(57) [Claims] 1. A waveguide type optical device comprising: a plurality of optical waveguides formed on a substrate surface; and electrodes formed on or near the optical waveguide, wherein the optical waveguide is an introduction portion for guided light; A control section and an output section for signal light, wherein the output section has a wide waveguide width, and has a first electrode above or near an optical waveguide constituting the control section for the guided light, and has a first electrode. A waveguide type optical device, comprising: a second electrode for generating an electric field for making an optical waveguide of an output section multi-mode above or near the optical waveguide. 2. The waveguide type optical device according to claim 1, wherein said first electrode and said second electrode are formed above said optical waveguide via a buffer layer.