JPS61240227A - Optical switch device - Google Patents

Abstract

PURPOSE:To improve a low crosstalk, a low switch voltage, and a high speed responsiveness by placing symmetrical two-split parallel electrodes on a cross part so as to be positioned in the center of the cross part, through a buffer layer, and impressing voltages whose voltage amplitudes are equal to each other and whose phases are different by 180 deg., between the respective parallel electrodes. CONSTITUTION:As for a cross part 4 of two pieces of cross optical waveguides 2, 3 which is provided on a substrate 1, its effective refractive index becomes higher than the optical waveguides 2, 3. In this case, when a beam P1 is made incident on the optical waveguide 2, it nearly becomes P4, travels straight and goes out, but it partially becomes P3, and a crosstalk is generated. Two pairs of symmetrical parallel electrodes which is provided on the cross waveguide 4 are formed on about a bisector on the cross waveguide. The crosstalk generated by a slight shift of the electrode, a manufacturing condition shift, etc. of the optical waveguide is eliminated entirely by using the split electrode, and driving the voltages whose amplitudes are equal and whose phases are different by 180 deg.C. In this way, a TIR type is made small in size and low in its voltage, the high speed responsiveness is utilized, and also the crosstalk can be decreased by applying an electrical bias.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical switch device in the fields of optical communication, optical information processing, and optical applied measurement that utilize modulating and exchanging light.

2. Description of the Related Art Optical switches that perform optical path switching or modulation are required to have low crosstalk, low switching voltage, and high speed response. Conventionally, from the viewpoint of high-speed response, cross-type waveguide optical switches and total internal reflection (TIR) type optical switches have been actively researched because the switching elements can be made smaller and the electrode capacitance can be reduced. It's here. This type of switch has excellent high-speed response, but has slightly poor crosstalk, so improvements have been made to overcome this problem. This is shown in FIG. In this conventional example, the refractive index of the intersection 4 of the PLZT thin film optical waveguides 2 and 3 is increased to improve crosstalk.

However, in this prior art, the electrode 11a.

The positional accuracy of the gap 11b is severe, and the intersection part 4 2
If the optical waveguide deviates from the equal dividing line, there is a problem in that crosstalk deteriorates due to the asymmetry of the optical waveguide. On the other hand, in a Δβ inversion type directional coupler type optical switch as shown in FIG.
It is easy to obtain low crosstalk, but the electrode length becomes long,
There is a nearly proportional relationship between switch voltage and maximum response time.
It had the disadvantage of being inferior in high-speed response.

Problems to be Solved by the Invention In order to realize an optical switch device with low crosstalk, low switching voltage, and high-speed response, TIR type optical switches are designed to avoid misalignment of electrodes during fabrication and the conditions for fabricating crossed waveguides. Deterioration of crosstalk due to misalignment has been a problem. Further, in the directional coupler type, although the tolerance of manufacturing accuracy has been improved by using the Δβ inversion method, there are problems in that the electrode length becomes long and high-speed response is inferior.

Means to solve the problem In conventional technology, we have to solve the problem of strict manufacturing precision and high-speed response to achieve low crosstalk.
In a crossed waveguide optical switch made of an optical material with a -order electro-optic effect, we have developed a structure in which the effective refractive index of the intersection is increased, and a symmetrical waveguide is placed on the intersection via a buffer layer. The optical path is switched by placing two divided parallel electrodes in the center of the intersection, and applying voltages with the same voltage amplitude and 180 degrees of phase difference between the two divided parallel electrodes between the two parallel electrodes. Provide light switches. In addition, the shape of the optical waveguide is L I
NbOs single crystal formed by increasing the refractive index by Ti diffusion, LiO out-diffusion, or H ion exchange, or P L formed on a transparent substrate.
Z R(x/y/z)X, y, z≦100. y+
z=100)) thin film as the waveguide material, PLZT
The effective refractive index is increased by changing the thickness of the thin film or by loading a transparent ribbon having a higher refractive index than the buffer layer on top of the PLZT thin film. Further, a transparent dielectric thin film or a transparent conductive thin film such as ITO is used for the buffer layer.

Function: In the means of the present invention, by increasing the refractive index of the crossing portion of the crossed optical waveguides, it is possible to reduce crosstalk, and a small crossing angle enables switching voltage, and a short electrode length increases high-speed response. However, it is possible to prevent crosstalk degradation due to asymmetry caused by misalignment of the electrode position during fabrication or misalignment of conditions during fabrication of the optical waveguide, by providing symmetrical two-part parallel electrodes.
By applying equal amplitude voltages with 1800 phase differences to this, crosstalk can be finely adjusted by voltage, as if it were a Δβ inversion type directional coupler, and crosstalk can be reduced. .

Example FIG. 1 is a top view showing an embodiment of the present invention.

In the figure, the intersection 4 of the two intersecting optical waveguides 2 and 3 provided on the substrate 1 has a higher effective refractive index than the optical waveguide 2.3. At this time, when light of Pl enters the optical waveguide 2, most of the light becomes P4 and goes straight out, but some becomes P3 and crosstalk occurs. Two symmetric parallel electrode pairs provided on the crossed waveguide 4, in this example parallel electrode pairs with equal electrode gap and equal length L /2, 6a-sb, 5a-6d
is formed approximately on the bisector of the crossed waveguide via the buffer layer 6. When the same voltage is applied between the electrode pair 5a-5b and six 5 cm layers, almost the same operation as the conventional example is exhibited. Conventionally, the switching operation of this TIR type optical switch was considered as follows. An internal electric field is induced inside the electro-optic material by the voltage applied to the electrode,
It was believed that this internal electric field generates a portion with a low refractive index of about 10@-4 to 10@-3, and that the guided light is totally reflected by this low refractive index portion and is switched.

Through research on crossed optical waveguides, Masuho et al. came to the conclusion that the operating principle of TIR type optical switches is slightly different from conventional ones. This is because when the intersection angle is about 1°, when the waveguide refractive index increase Δn (refractive index increase that contributes to light confinement) is about 10-5, directional coupling occurs when the applied voltage is low. It exhibits a vessel-like operation, in which the straight light and reflected light output repeat periodic reversal as the voltage is increased, so even though it is a TIR optical switch, the propagation constant varies at each location at the intersection. β
I realized that it is more convenient to think of this as coupling between even and odd modes with different coupling coefficients, and to think that applying a voltage changes the coupling coefficient K, resulting in a change in the output. Theoretically, we have obtained results that support this idea, and we have obtained the knowledge that this idea is valid. Based on this knowledge, the authors investigated the Δβ inversion method in directional couplers in detail and found that it can be applied to TIR waveguide optical switches. We have found that by voltage driving, it is possible to completely eliminate crosstalk caused by slight electrode positional deviations, deviations in optical waveguide manufacturing conditions, etc. According to the present invention, a small TIR type.

It has become possible to provide a high-performance optical switch that takes advantage of low voltage and high-speed response, and can further reduce crosstalk by applying an electrical bias9.

The specific switch structure will be described. FIG. 2 shows an optical waveguide formed on a L I N b O3 single crystal substrate 1. In FIG. Intersecting optical waveguides 3 and 4 are formed by TfO thermal diffusion, Li out-diffusion, and H ion exchange, and the waveguides at the intersection have a large Δn. ITO was used for the buffer layer 6 in order to suppress drift. electrodes sa, s
b etc. were formed by vapor deposition using AI. When the split electrode structure of the present invention was used in switches having these structures, it was confirmed that the conventional crosstalk of 10 to 25 dB was reduced to 3 odB or less by applying a voltage of several volts.

3 and 4 show one embodiment in which a PLZT thin film 7 is used in the optical waveguide. In FIG. 3, a thin film of approximately 3,500 layers epitaxially grown on a sapphire substrate 1 (plane 0) by magnetron sputtering using a target with a composition of PLZT (2810/1oo) is etched by approximately SOO, and the light guide excluding the intersection 4 is etched. Waveways 2 and 3 were etched 1000 times to form a ridge-type waveguide. On top of this, a Ta2o6 amorphous film is applied as a buffer layer at approximately 1500A.
They were laminated, and a 4W gap one cabinet length split electrode was formed thereon. The waveguide had a crossing angle of 102 and a width of 10 μm. P
The LZT thin film can have either a first-order or a second-order electro-optic effect depending on the growth conditions, but in this example, a film showing a first-order electro-optic effect was used.

A switch voltage of approximately 5V was obtained, and crosstalk was reduced from 10 dB to 2 odB or less by applying an offset voltage of several volts.

In FIG. 4, a PLZT thin film 7 similar to that in FIG.
Without etching the LZT thin film, a Ta2o5 amorphous film was placed on top of it as a transparent ribbon, and the waveguide hole 3
Approximately 100 people were formed on the surface, and 200 people were formed on the intersection, and approximately 1600 people were formed on the buffer 1 layer 6 using a T a 205 film coated with A12O3, and divided electrodes 5a, 5b, etc. were provided. Ta. The dimensions were the same as in Figure 3. At this time, good results similar to those in FIG. 3 were obtained for both switch voltage and crosstalk, but in the case of FIG. 4, the loss was slightly lower than in the case of FIG. 3.

As described above, the present invention provides low switching voltage.

An optical switch device with low crosstalk and excellent high-speed response has now been provided.

In addition, in the embodiment of the present invention, 1, To, T
a205. Although A6203-added T a 20 s was used, the present invention is not limited to this.

Effects of the Invention According to the present invention, an optical switch device with low switching voltage, low crosstalk, and excellent high-speed response can be easily obtained by applying a bias voltage. In particular, crosstalk was reduced by approximately 5 to 10 dB by applying a bias of several volts, demonstrating the usefulness of the present invention.

[Brief explanation of drawings]

FIG. 1 is a top view showing an embodiment of the present invention, FIG. 2 is a sectional view of an optical switch device using a L I N b Os single crystal showing an embodiment of the present invention, FIGS. The figure is a sectional view showing an optical switch device using a PLZT thin film showing an embodiment of the present invention, and FIGS. 6 and 6 are top views showing a conventional example. 1...Substrate, 2. 3. 12. 13...
-... Optical waveguide, 4... Optical waveguide intersection high refractive index region, 5a, sb. sc, sb, 11a, 11b... Electrode, 6
. . . Buffer layer, 7 . . . PLZT thin film, 8 . . . Transparent ribbon. Name of agent: Patent attorney Toshio Nakao and 1 other person 4.
・・Review the light 31 liquid path, and the painful area SA, 5b, 6t, 5
d-'f, Sulfur Figure 2 Figure 35!1 Figure 4

Claims (4)

[Claims] (1) The intersection of two intersecting optical guides made of an electro-optic material having a first-order electro-optic coefficient has a higher refractive index than other parts of the optical waveguide, and is above the intersection of the optical waveguides. In an optical switch device having two pairs of symmetrical parallel electrodes having equal lengths, the two pairs of parallel electrodes have equal sizes and a phase of 180° through a transparent buffer layer. An optical switch device that switches light by applying an inverted voltage. (2) The optical switch device according to claim 1, wherein the optical waveguide is formed in a LiNbO_3 single crystal by increasing the refractive index by Ti diffusion, Li out-diffusion, or H^+ ion exchange. . (3) Optical waveguide is a composite oxide PL made of lead, zirconium, lanthanum, and titanium formed on a transparent substrate
ZT (x/y/z) thin film (Pb_1_−_x_/_1_0_0La_x_/_1
_0_0(Zr_y_/_1_0_0Ti_z_/_1
_0_0)_x_/_4_0_0O_3, (0≦x,y
, z≦100, y+Z=100)), and the optical waveguide portion has a large film thickness and has a structure of two intersecting ridges, or the optical waveguide portion is made of the PLZT
2. The optical switch device according to claim 1, wherein the effective refractive index of the optical waveguide is increased by two intersecting transparent ribbons having a higher refractive index than the buffer layer on the thin film. (4) The transparent buffer layer is a transparent dielectric thin film or
The optical switch device according to claim 1, characterized in that it is made of a transparent conductive thin film.