JPS638721A - Optical switch device - Google Patents

Abstract

PURPOSE:To simultaneously attain a high on/off ratio and a high coupling efficiency by providing a light condensing grating coupler and providing plane plate electrodes between which a narrow gap is formed so that they cross a collimated guided light three-dimensionally and applying a voltage between electrodes. CONSTITUTION:A divergent light 5 from a semiconductor laser 4 passes an entrance-side substrate end face 6a and is projected to a light condensing grating coupler 3a. The light 5 is converted to a guided light 7 there and is simultaneously collimated by this coupler 3a. The collimated guided light 7 passes under buffer layers 8, and plane plate electrodes 9 are provided on buffer layers 8 and face each other in the same plane with a narrow gap 10 between them. When the voltage from a power source 11 is applied to electrodes 9, the refractive index in the part under the gap 10 of an optical waveguide 2 is reduced, and the guided light 7 is branched into a straight going light 12a and a reflected light 12b. If a width (g) of the gap 10 is narrow, a leak light occurs by the tunnel effect and the straight going light 12a remains. If the voltage is raised, the tunnel leak mode is reduced to attain a high on/off ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to the fields of optical fiber communications, optical applied measurement, and control.

Prior Art FIG. 4 is a bird track diagram showing the prior art. In the figure, a three-dimensional optical waveguide 42 having an electro-optic effect formed on a substrate 41 is a crossing waveguide with a cross section of about several μm, and a narrow gap is formed on the center line of the acute angle of the intersection. Parallel plate electrodes 43 are provided. A buffer layer 44 is provided under the electrode 43 to completely prevent attenuation of light. As a method of coupling light into and out of an optical switch device, prism coupling, end face coupling, etc., as shown in FIG. 4, have been used.

As shown in FIG. 4, prism coupling is performed by pressing a prism 45 onto an optical waveguide 42, and connecting the end face of an input/output optical fiber 46 or a semiconductor laser as a light source to the prism 45 with a lens 47.
This was achieved by configuring an optical system that focuses an image near the pressure contact part. In the end face coupling, optical coupling is achieved by bringing the input/output optical fiber 46 or the output end face of the semiconductor laser as the light source into contact with the exposed end face of the substrate 41 of the three-dimensional optical waveguide 42 . When a voltage signal from a signal source 48 is applied to the electrode 43, an electric field generated under the narrow gap between the electrodes 43 induces an electro-optic effect in the optical waveguide 42, causing a change in the refractive index. Due to this refractive index change, the mode of the guided light propagating throughout the crossed waveguide 42 changes, and the output waveguide is switched. This is equivalent to replacing and connecting all the input optical fibers to the output optical fibers. This is the operating principle of a waveguide optical switch.

Problems to be Solved by the Invention As described above, in the conventional technology, it is difficult to obtain a high coupling efficiency because light is coupled to an optical waveguide whose entire cross-sectional dimension is about several μm. This tendency was particularly noticeable in thin film optical waveguides in which the difference in refractive index between the substrate 41 and the optical waveguide 42 was large. PLZT system (x/y/z > thin film (Pb
' -10[I La+oo (zrJll T110
0”, W.

O3) has a large electro-optic coefficient and PLZT (2010
/100), a force constant of 0.8 x 10'' (m/v)2 is obtained. When used in this thin film all-optical waveguide,
The refractive index of the sapphire substrate is 17-r, PLZT (201
0/1oo) Since the refractive index of the thin film is 2.6, the single condition in the thickness direction results in a thickness of approximately 9311 m or less for the optical waveguide. It is difficult to guide light with high efficiency through such a thin waveguide.

It is generally said that high efficiency can be obtained by prism coupling, but it has poor reproducibility and lacks mass productivity. When coupling to an optical waveguide, the high-efficiency coupling conditions become very strict, making it impractical.Furthermore, in the case of a crossed waveguide structure, the on-wavelength The off-ratio is determined and is usually a value of about 20 dB. In order to obtain a high on-off ratio, the manufacturing conditions for the waveguide structure must be strict, and in practice there is a problem in that the yield is low.

As described above, there has been no optical switch device with a structure that satisfies both high on-off ratio and high coupling efficiency at the same time and is excellent in mass production.

Means for Solving the Problems In a waveguide optical switch using the electro-optic effect, a condensing grating coupler is provided for inputting and outputting the guided light from outside the substrate and for collimating the guided light. Flat plate electrodes are arranged with a narrow gap completely intersecting the two flat plate electrodes, and a voltage applied between the two flat plate electrodes with a narrow gap completely induces a change in the refractive index of the electro-optic material at the bottom of the gap, thereby changing the traveling direction of the collimated guided light. change. The guided light that has passed under the flat electrode is imaged by the output grading coupler and appears as a change in position. The input/output relationship of light from a certain position on the imaging plane changes depending on the voltage applied to the flat electrode.

Further, it is particularly effective when the optical waveguide material is a PLZT thin film.

Furthermore, in order to suppress the attenuation of light under the flat plate electrode, it is effective to provide a buffer layer made of a transparent insulating material having a refractive index lower than that of the optical waveguide between the optical waveguide and the flat plate electrode.

In addition, it is effective in constructing an optical switch if the shape of the planar electrodes is such that they are opposite electrodes on the same plane, or if the gap between the coplanar microstrip lines becomes the gap between the planar electrodes.

Effects By implementing the present invention, a lens for coupling optical input to the optical switch device is not required, and high coupling efficiency can be obtained because the image is formed from the substrate side of the condensing grating coupler. It also has the effect of guiding and collimating the light from the diverging point light source within the optical waveguide plane. The collimated light has a Gaussian distribution shape in the in-plane lateral direction. The electric field generated under the gap between the plate electrodes to which a voltage is applied causes a change in the refractive index of the optical waveguide, and the collimated light is reflected at this narrow portion. The linearly traveling guided light and the reflected light are imaged at different positions outside the substrate by the output condensing grating coupler. By arranging the original fiber and the light receiving element at this position, the output light can be taken out from the I/C. A high on/off ratio can be obtained by combining a condensing grating coupler and a flat plate electrode.

The condensing grating coupler is similar to electrode formation, etc.
Since it is a planar microfabrication process and can be manufactured using a semiconductor process, it is excellent in mass production. In addition, in order to use the interaction between the collimated guided light and the thin linear refractive index change part,
By increasing the magnitude of the applied voltage, total reflection occurs in this portion, making it possible to obtain higher on/off switching than in the past. The manufacturing process of the optical switch involves flat surface processing and board side processing, eliminating the need for low-yield edge processing of the board end face, which was necessary with conventional end face excitation! ll Manufacturing yield is improved.

By using a PLZT thin film as a waveguide material, a high electro-optic effect can be utilized, and a highly efficient optical switch can be constructed. Furthermore, if a buffer layer is formed between the flat plate electrode and the optical waveguide, the original attenuation band at the electrode portion can be reduced.

Furthermore, if the flat plate electrodes have a narrow gap and are opposed in the same plane, the electrode shape is simple and the yield of electrode formation is high.

Furthermore, when the flat plate electrode is used as a traveling wave electrode of a coplanar microstrip line, the difference in phase constant between the guided light and the modulated electric signal (microwave) is reduced, and the modulation bandwidth is widened.

Embodiment FIGS. 1 and 2 show a bird's-eye view and a top view of a first embodiment of the present invention. A detailed explanation will be given in both figures. In order to input and output guided light to the slab optical waveguide 2 formed on the substrate 1, condensing grating couplers 3a and 3bi are used.
It is a provision. Both end faces of the substrate 1 are polished to a desired angle, and the diverging light 5 from a diverging point light source placed nearby, a semiconductor laser 4 in FIG. do. Here, the guided light γ
At the same time, the light is collimated by the condensing grating coupler 3a. The collimated guided photons pass under the buffer layer 8. C.) On top of the F layer 8, a flat plate electrode 9 is placed.
are provided, and are electrodes facing each other in the same plane with a narrow gap 10 in between. Because the light passes through the knockoff layer, there is little attenuation at the electrode 9 due to seepage of the collimated waveguide photons. When a voltage from the power source 11 is applied to the electrode 9, the refractive index of the lower part of the gap 10 of the optical waveguide 2 decreases, and the guided light 7
is divided into straight light 12& and reflected light 12b. Assuming that the angle between the guided light 7 and the gap 10 is θ, and the effective refractive index under the gap is n2 and the total effective refractive index of the other parts is n1, total reflection occurs and becomes reflected light 12b. However, if the width g of the gap 100 is narrow, leakage light occurs due to the tunnel effect, and straight light 12& remains. Furthermore, when the magnitude of the voltage is increased, the tunnel leakage mode is reduced, and a high on/off ratio can be obtained.

This is due to the fact that, unlike in the case of conventional three-dimensional waveguides, the lateral distribution of the guided light 7 has an almost Gaussian distribution shape and propagates almost in parallel, and the condensing grating coupler This is due to light action.

The shape of the condensing grating coupler consists of multiple curves with the same phase difference between the waveguide plane (Gaussian distribution) light and the input and output light, and unevenness is formed on the optical waveguide and the substrate using an electron beam exposure method. Make it. A condensing grating coupler guides and collimates light from a point light source, or vice versa.

A specific example is given below. In FIG. 1, the substrate 1 uses sapphire C-plane (refractive index 1.77)%-, and P L Z
A T (2010/100) thin film with a thickness of about 0.35 μm was created by planar magnetron sputtering. This P
The LZT thin film has a refractive index of 2.6 and becomes the optical waveguide 2. Next, both end surfaces 6a and 6bis of the substrate 1 were polished to about 55 degrees, and a buffer layer 8 was further formed partially on the optical waveguide. For the buffer layer, a TΔ205 thin film (refractive index 2j)'i is used, and the edges on the light input/output side are tapered to about 0 by sputtering.
．． It was formed to have a thickness of 2/1' m. On top of that, a gap of 4 μm,
Length 20+1Lt.

A λg electrode 9 having a depth of about 1 U was formed by photolithography and lift-off. Gap 10 between electrodes 9
A condensing grating coupler for input and output was formed by an electron beam direct writing method so as to form an angle of about 3 degrees.

The grating is an optical waveguide 2 using PMMA resist.
formed on top.

The focal length of the condensing grating was approximately 4 IuL, and the width direction was one skin. Q, 8371 m of light was transmitted, and the obtained coupling efficiency was about 40 factors on one side, far exceeding the coupling efficiency of several φ obtained by the conventional prism method. The switch voltage was about 30 V, and an on-off ratio of 20 dB or more was obtained, and when the voltage was further increased, the on-off ratio improved. this is,
This is a feature of this optical switch device.

In addition, the substrate 1 has LiNb0. Single crystal all around, optical waveguide 2
Similar characteristics were also obtained by thermally diffusing Ti metal. In this case, since the electro-optic effect is small, it was possible to increase the length of the electrode 9 and reduce the crossing angle θ, thereby making it possible to reduce the voltage to several tens of volts.

FIG. 3 is a diagram showing a second embodiment of the present invention.

In the figure, the electrode 21 is a traveling wave electrode and is a coplanar microstrip line, and the microwave supplied from the power source 11 propagates in almost the same direction as the guided wave "5' [7]. The refractive index of the optical waveguide changes.In this case, the operating frequency band of the optical switch is
The number 1oG[Iz is determined by the phase constant difference between the light passing through the entire electrode 21 and the microwave propagating through the electrode 21. 1 in FIG. 3, the diverging point light source includes an optical fiber 22.
This shows the case where . Other features are similar to the first embodiment.

Effects of the Invention By implementing the present invention, optical coupling of several tens of percent can be easily obtained, and an optical switch device with a high on/off ratio can be obtained with good reproducibility. In addition, since the main operating parts of the optical switch device are on the same plane and can be manufactured using the same process as semiconductor processing technology, the structure is suitable for mass production and can be manufactured at low cost.

A perspective view and a top view of the switch, FIG. 3 is a perspective view of the second implementation ψ11, and FIG. 4 is a perspective view of a conventional optical switch.

1...Substrate, 2...Optical waveguide, 3a,
3b... Concentrating grating coupler, 4...
・Semiconductor laser, 5.13...Light beam, 62L, 6
b... End face, completed.

122L, 12b... Reflected light, 8゛°°°° buffer... Electrode.

Name of agent: Patent attorney San Nakao and 1 other person!
- One act level? - Two guiding paths 3a, 3b - A set of grating cassoffs' four and a half body lasers 5.13 - 19. - Gap Shuttle 10-m-Gap No. 2 Figure 21-m-Gap 22-Optical Fiber 23-#Honglow Pit Figure 3

Claims (5)

[Claims] (1) An optical waveguide formed on a substrate, and at least one condensing grating that guides light from a diverging point light source arranged near an end surface outside the substrate and collimates it in the in-plane direction of the optical waveguide. a coupler, a flat plate electrode formed on the optical waveguide and arranged so that a narrow gap that produces an electro-optic effect intersects the collimated waveguide light; and a waveguide light that passes under the flat plate electrode and travels straight. or at least one condensing grating coupler that converges the guided light whose traveling direction is changed by the voltage applied to the electrode and forms an image near the other end surface outside the substrate. Switch device. (2) The optical waveguide material is a PLZT thin film (Pb_1_-_
[_x_/_1_0_0_]La_x_/_1_0_0
(Zr_y_/_1_0_0Ti_z_/_1_0_0
)_1_-_[_x_/_4_0_0_]O_3, O≦
2. The optical switch device according to claim 1, wherein x, y, z≦100, y+Z=100. (3) The optical switch device according to claim 1, characterized in that a buffer layer made of a transparent insulating material having a lower refractive index than the optical waveguide is provided between the optical waveguide and the flat plate electrode. (4) The optical switch device according to claim 1, wherein the flat plate electrodes face each other on the same surface with a narrow gap between them. (5) The flat plate electrode is characterized by comprising a power feeding part for a driving voltage signal and a matching termination part, and comprising the above-mentioned coplanar microstrip line that transmits the driving signal along a narrow gap. An optical switch device according to claim 1.