JPH04188115A - Waveguide type optical device - Google Patents

Abstract

PURPOSE:To obtain high quenching ratio of a port outputting a signal light by constructing an optical waveguide to propagate the signal light into a multimode construction having a large propagation loss. CONSTITUTION:Optical waveguides are constituted out of introducing parts and control parts of wave guided light, and output parts of a signal light, and the width of waveguide of output parts are formed to be wide. First electrodes 15 are provided on the upper part or the vicinity of the optical waveguides 11, 12 of the control part for the wave guided light, and a second electrode 17 to generate electric field for multimode orientating the optical waveguide 12 is provided on the upper part or the vicinity of the optical waveguide 12 of the output part. Hereby. the optical waveguides 11, 12 to propagate the signal light can be constructed into a multimode construction having large propagation loss, and quenching ratio of a port 16 to output the signal light can be made high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a waveguide type optical device, and particularly to the configuration of an optical waveguide.

[Conventional technology]

With the commercialization of optical communication systems, there is a need for higher capacity, multifunctional, and more advanced systems, and new functions such as generation of faster optical signals and switching and switching of optical transmission lines are required. It is said that

In current practical systems, optical signals are obtained by directly modulating the injection current of semiconductor lasers or light emitting diodes. However, direct modulation has drawbacks, such as the difficulty of high-speed modulation at frequencies above several GHz due to effects such as relaxation oscillations, and the difficulty of applying it to coherent optical transmission systems due to wavelength fluctuations. One way to solve this problem is to use an external modulator. In particular, a waveguide type optical modulator that is composed of an optical waveguide formed in an electro-optic crystal substrate has the advantages of small size, high efficiency, and high speed. There is.

On the other hand, optical switches are used as means for switching optical transmission lines and providing network switching functions. Optical switches currently in practical use switch optical paths by mechanically moving prisms, mirrors, fibers, etc., and have drawbacks such as slow speed, large size, and unsuitability for matrix formation. As a means to solve this problem, the development of waveguide type optical switches using optical waveguides is progressing, and they have features such as high speed, ability to integrate multiple elements, and high reliability. In particular, those using ferroelectric materials such as lithium niobate (LtNbOs> crystals) have features such as low light absorption and low loss, and high efficiency because they have a large electro-optic effect. Various types of optical control devices have been reported, such as a directional coupler type optical modulator or optical switch, a total internal reflection type optical switch, and a Matsuhatsu Enda type optical modulator.

In recent years, research and development on high-density integration of waveguide-type optical switches has been actively conducted, and according to a document by Yutaka Nishimoto et al., IEICE OQE8g-147, directional couplers are being developed using LiNbO3 substrates. An 8×8 matrix optical switch with 64 integrated optical switch elements has been obtained. On the other hand, research and development of devices consisting of a single optical switch element, such as external optical modulators, is also actively progressing. Characteristic items of such optical switch devices include switching voltage (power), crosstalk, extinction ratio, loss, switching speed, and stability of operation with respect to environments such as temperature and humidity.

[Problem to be solved by the invention]

FIG. 4 shows a perspective view of an optical switch and modulator consisting of a directional coupler formed on the surface of a substrate, which is an example of a conventional waveguide type optical device. In the figure, when no voltage is applied to the electrode 1, the power of the light input from the first port 2 is transferred to the other adjacent optical waveguide 4 at the directional coupler 3, and the light is transferred to the second optical waveguide 4. When manufactured to emit light from the port 5, when a certain voltage is applied to the electrode 1, the refractive index of the optical waveguide 4 changes, and optical power is transferred between the optical waveguides 4 at the directional coupler 3. does not occur and the light exits from the third port 6. Note that the two optical waveguides 4 are formed on the surface of the substrate 7, and a buffer layer 8 is provided on the top of the substrate 7.

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

In the case of an optical fiber break point measuring instrument using this structure, a voltage is applied to the electrode 10 portion, and when the light is sent from the light source to the optical fiber to be measured, the directional coupler 3 connects the light to the adjacent optical waveguide 4. There was a drawback that the extinction ratio at the second port 5 deteriorated due to the leakage of light. In addition, in the case of a modulator, when a voltage is applied to the electrode l and the signal light output is turned off, that is, when light is output to the third port 6, light leaks into the second port 5. However, there was also the drawback that the extinction ratio deteriorated.

SUMMARY OF THE INVENTION An object of the present invention has been made in view of the above-mentioned drawbacks, and is to provide a waveguide type optical device that prevents deterioration of the extinction ratio of a port through which signal light is output.

[Means to solve the problem]

The invention of claim 1 provides a waveguide type optical device comprising a plurality of optical waveguides formed on a substrate surface and an electrode formed on or near the optical waveguide, wherein the optical waveguide is an introduction part for guided light. , consisting of a control section and a signal light output section, the waveguide width of the output section is formed wide, and a first electrode is provided above or near the optical waveguide constituting the waveguide light control section. A second electrode is provided above or near the optical waveguide for generating an electric field for making the output optical waveguide multi-mode.

According to a second aspect of the invention, the first electrode and the second electrode are formed on the optical waveguide with a buffer layer interposed therebetween.

[Effect]

As described above, according to the present invention, by forming the optical waveguide through which the signal light propagates into a multimode structure with a large propagation loss, a high extinction ratio of the port through which the signal light is output can be obtained.

〔Example〕

Next, the present invention will be explained in detail using the drawings.

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

This example shows a waveguide type optical device in which optical waveguides 11 and 12 are formed by thermally diffusing T1 into a substrate 10. Optical waveguide 11.12 is used to change the refractive index of optical waveguide 11.12 by utilizing the electro-optic effect of substrate 10.
A first electrode 15 is formed on the top of the twelve directional couplers 13 with a buffer layer 14 in between. Since the first electrode 15 is a metal film, this buffer layer 14 is suitable for the optical waveguide 1.
1.12 When formed directly on the top of the optical waveguide 11.12, the size of the TM mode light of the light propagating through the first electrode 15
It plays the role of preventing losses from becoming large due to being absorbed by the water.

In this embodiment, silicon oxide (S) is used as the buffer layer 14.
i02) A membrane is used. Further, the shape of the optical waveguide is such that the width of the straight portion of the optical waveguide 12 from the directional coupler 13 to the second point 16 is wide.

Fig. 3 shows the dispersion curve of the optical waveguide when LiNbO2 is used as the substrate 10 to demonstrate the operating principle of this embodiment. (2π/λ), d is the optical waveguide width, NS is the refractive index of the substrate,
Nf is the refractive index of the optical waveguide, N! Equivalent refractive index (Nf
Si Nθ (θ is the angle of incidence of the propagating light on the boundary between the core and the blood). Optical waveguide 121 with widened waveguide width according to the embodiment, point A (the part where the waveguide width is not widened is at B)
Point) The optical waveguide 12 is designed so that the optical waveguide 12 has a 100-degree angle, and the second electrode 17 is formed via the buffer layer 14 in order to change the refractive index of the optical waveguide in this portion.

When no voltage is applied, the light input from the first port 18 is
Point A in Figure 3) is emitted from the second port 16 which is the signal output, and when voltage is applied (point 0 in Figure 3)
The light is emitted 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 the light is emitted from the third port 19, a voltage is also applied to the 12 electrodes 17, so that the optical waveguide The refractive index of 12 changes, and the optical waveguide 1
It is designed so that m=1 multimode occurs in 2. The voltage is applied so that an electric field is generated in a direction that reduces the refractive index of the optical waveguide 12.

In general, propagation loss is greater in multi-mode than in single mode (m=0 in FIG. 3). Therefore, for example, if an optical fiber is connected to the second port 16, the coupling of light propagated through the optical waveguide 12 to the optical fiber will be reduced, resulting in a high extinction ratio.

In this way, when light is emitted to the third port 19, which is a dummy port, the optical waveguide 12 of the second port 16, which is a signal light emitting port, enters a multimode state, thereby obtaining a high extinction ratio. .

For example, in the case of an optical switch used in a measuring instrument for measuring the break point of an optical fiber, the third port 19 is connected to the light source, the first port 18 is connected to the optical fiber to be measured, and the second port 16 is connected to the light receiving element. . This measuring instrument sends light from a light source to an optical fiber to be measured, and measures the return light from the optical fiber to be measured with a light receiving element to find the break point of the optical fiber to be measured.

Therefore, when the optical switch is working to send light from the light source to the optical fiber under test as described above, by making the optical waveguide 12 to which the light receiving element is connected multi-mode, noise to the light receiving element can be reduced. This makes it possible to perform high-resolution measurements.

It is clear that this structure can also be applied to other waveguide type devices such as total reflection type optical switches and waveguide type optical devices using compound semiconductor substrates such as GaAs and InP.

〔Effect of the invention〕

As explained above, according to the waveguide type optical device according to the present invention, the optical waveguide consists of a guided light introduction part, a control part, and a signal light output part, and the waveguide width of the eight power parts is formed wide. , and has a first electrode on or near the optical waveguide that forms the control section for the guided light, and a first electrode that generates an electric field on or near the output optical waveguide to make the output optical waveguide multi-mode. By adopting a configuration including two electrodes, it is possible to make the optical waveguide through which the signal light propagates into a multi-mode structure with large propagation loss.
This provides an excellent effect in that the extinction ratio of the boat from which the signal light is output can be made higher than in the past.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the waveguide type optical device according to the present invention, FIG. 2 is a sectional view taken along the line ■-■ in FIG. 1, and FIG. 3 is the operating 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 boat, 19... Third port.

Claims (1)

[Claims] 1. In a waveguide-type optical device comprising a plurality of optical waveguides formed on the surface of a substrate and an electrode formed on or near the optical waveguide, the optical waveguide is used for guiding light. It consists of an introduction section, a control section, and a signal light output section, the output section has a wide waveguide width, and a first electrode is provided above or near the optical waveguide constituting the waveguide light control section. 1. A waveguide type optical device, comprising a second electrode that generates an electric field for making the output optical waveguide multi-mode, above or near the output optical waveguide. 2. The waveguide type optical device according to claim 1, wherein the first electrode and the second electrode are formed on the optical waveguide with a buffer layer interposed therebetween.