JPH0713685B2 - Crossed-waveguide optical switch - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical circuit element, and more particularly to an optical switch having crossed waveguides.

Optical switches currently in practical use generally use a mechanical switching method such as moving a mirror, making it difficult to miniaturize and integrate them, and also require technology for assembling and adjusting individual parts with high precision. Becomes The inventors of the present invention have proposed that the crossed waveguide type optical switch formed on the electro-optic crystal is small in size,
It has been found that it can be driven at a low voltage and has a good extinction ratio [Japanese Patent Laid-Open No. 59-60425].

[Conventional technology]

FIG. 5 is a schematic view of a main part for explaining the structure of a waveguide of a conventional crossed waveguide type optical switch. For example, a strip-shaped pattern is formed on the surface of a substrate 1 made of an electro-optic crystal such as lithium niobate (LiNbO ₃ ). By forming the titanium thin film layer 2 so as to cross it linearly and subjecting it to heat treatment at, for example, 1040 ° C. for 5 hours, the titanium thin film layer 2 diffuses into the substrate 1 and has a larger refractive index than the substrate 1 and is linear. The waveguide 3 that intersects with is formed.

FIG. 6 is a schematic view of a main part for explaining the structure of the crossed waveguide type optical switch already proposed, and a rectangular electrode 4 narrower than the width of the waveguide is provided at the crossing part of two optical waveguides, The side is parallel to the line connecting the intersection angle apex P formed by the edges of the light incident side portions 31 and 32 of the two optical waveguides and the intersection angle apex Q formed by the edges of the light emission side portions 33 and 34, Moreover, it is symmetrical with respect to the line.

In the waveguide type optical switch having the above configuration, the refractive index of the refractive index change region facing the electrode 4 increases (+ Δn effect) or decreases (−Δn effect) depending on the polarity and magnitude of the voltage applied to the electrode 4. ) Do.

Therefore, as is well known, the light propagated on the optical waveguide has 0th order (basic), 1st order, 2nd order, 3rd order with different light distribution states on the waveguide.
It is divided into each mode such as the next one, and the propagation velocity becomes higher as the order becomes higher. In addition, each mode propagates while changing its shape on the waveguide that enables the propagation of that mode, and at each point on the waveguide, the phase also changes with time, and due to the difference in propagation velocity A phase difference occurs.

When, for example, light of the fundamental mode is incident on one of the waveguides on the incident side of the cross waveguide and propagates to the emission side, the shape of the mode on the waveguide is two on the incidence side of the cross waveguide. This corresponds to a composite wave when both the fundamental mode light and the primary mode light are incident on the waveguide and propagated to the exit side.

That is, in one waveguide on the emission side, if the waveforms of the two modes are in the same direction, they are added and emitted, and in the other one waveguide, if the waveforms of the modes are in opposite directions, they are canceled and are not emitted.

If the waveforms of the two modes are added together in the two waveguides on the output side, an optical output can be obtained from either of the waveguides.

In the crossed waveguide type optical switch shown in FIG. 6, the refractive index of the refractive index changing region facing the electrode has not been increased or decreased depending on the polarity and the magnitude of the voltage applied to the electrode 4. As described above, if the refractive index is changed, the propagation velocity changes, which means that the speed of phase change in each mode changes, and the phase difference between modes also changes.

Therefore, in the crossed waveguide type optical switch as shown in FIG. 6, for example, when there is no signal, the straight light output and the branched light output become equal, and when a signal voltage is applied so as to increase the refractive index,
At a predetermined refractive index in the positive direction, the branched light output becomes maximum and the straight light output becomes minimum.

On the other hand, if a signal voltage is applied to reduce the refractive index,
At a given refractive index in the negative direction, the straight light output becomes maximum,
The branched light output becomes a minimum.

In this way, the light changes sinusoidally with the phase on the waveguide due to the increase or decrease of the refractive index, so that it is clear from the operating principle of the crossed waveguide type optical switch that the design conditions of the optical waveguide and electrodes, the signal voltage By setting the size and the polarity differently, it becomes possible to set the output to a straight output state, the branch output state, or the non-output state in the 0 voltage state unlike the above. This can be easily understood.

[Problems to be solved by the invention]

However, in the above-mentioned conventional crossed waveguide type optical switch, a rectangular thin electrode is provided at the crossing portion of two optical waveguides, each of which is usually in the unit of micrometer, and the long side of the electrode enters the two optical waveguides. Crossing angle apex P formed by the side edges of the side portion and crossing angle apex Q formed by the side edges of the light emitting side portion
Since it is provided thinner than the width of the input / output waveguide on the line connecting the two, it is necessary to align the electrodes at the intersection of the waveguides. Difficult to achieve.

In particular, in a crossed waveguide type optical switch, the position of the crossed waveguide and the width of the waveguide at the positions on the left and right sides of the crossed waveguide are different from each other. The change in the refractive index is different from the position of, and the control of the light path between the incident light and the emitted light becomes complicated.

On the other hand, it is possible to arrange the electrodes according to the shape of the intersection, but if there is a slight misalignment in the alignment of the electrodes in the constricted portion of the cross section of the fine-shaped waveguide, the electric field strength is especially high near the electrodes. Since the change is large, there is a problem that a large characteristic change occurs.

[Means for solving problems]

According to the present invention, the above problem includes a waveguide and a substrate in the vicinity thereof in a cross waveguide structure in which two waveguides having a refractive index larger than that of the substrate are linearly crossed on a substrate made of an electro-optic crystal. The electrode to which the signal voltage for controlling the refractive index change of the region is applied has a vertically symmetrical shape parallel to the line connecting the intersection angle vertices, and the electrode surface intersects at a position apart from the intersection and its vicinity. A crossed waveguide type optical switch characterized in that it is arranged on a substrate including a portion.

[Action]

In the above-mentioned waveguide type optical switch, the refractive index changing means for controlling the refractive index change is provided in the whole including the intersection of the two optical waveguides and the vicinity thereof.

That is, with respect to the line connecting the intersection angle vertices of the intersection, an electrode is provided vertically symmetrically in the region including the waveguide and the substrate in the vicinity thereof, and an electric field is applied, or the temperature of the entire region is raised to raise the refractive index. Since an electrode for changing the voltage is provided, high accuracy is not required for positioning the electrode at the intersection of the waveguides, and by selecting the polarity and magnitude of the voltage applied to the electrode,
Incident light can be emitted straight or branched.

Moreover, since the switching operation is realized by the change of the refractive index, it is usually important to switch with a constant voltage, and it is important that the variation of the change of the refractive index is small. I try to move away from the neighborhood.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic view of a main part for explaining the structure of a crossed waveguide type optical switch utilizing the electro-optic effect of one embodiment of the present invention. For example, Y-Cut lithium niobate (LiNbO ₃ ) or the like is used. Two linearly intersecting waveguides 3 having a higher refractive index than the substrate 1 are formed on the surface of the substrate 1 made of an electro-optic crystal by a method similar to the conventional one, and the intersection of the two optical waveguides and the waveguide 3 are formed on the waveguide 3. Except for the input / output section 5 ', the electrodes 5 are provided symmetrically with respect to the line connecting the apexes of the crossing angles so that an electric field due to the refractive index change control signal voltage is formed in the entire area including the vicinity and Except for the output portion 5 ', the electrode surfaces are separated from the intersection and its vicinity.

By applying a signal voltage to the electrode 5, for example, the light incident from the arrow X direction goes straight in the direction of the arrow Y or is branched in the direction of the arrow Z. When the signal voltage is not applied, the light goes straight ahead and branches at the same time. You can also do it.

When the thermo-optic effect is used, the change in the refractive index can be made larger than that of the cross-waveguide type optical switch using the electro-optic effect, so that a cross-waveguide type optical switch with good performance can be obtained.

2, 3, and 4 are a plan view of a main part, a cross-sectional view of a waveguide crossing portion AA ', and a perspective view for explaining a structure of a crossing waveguide type optical switch utilizing a thermo-optic effect. Is a figure,
For example, a thermally oxidized SiO ₂ film 12 is formed on a Si substrate 11, and TixSi is formed on the Si oxide film 12 so that the two waveguides linearly intersect each other.
_{A 1-x} O ₂ waveguide 13 is provided, and a protective layer of a SiO ₂ film 14 covers the waveguide 13. Further, an electrode 15 of a resistor (for example, Ti) is formed as a refractive index changing means on the SiO ₂ film 14 so as to cover the entire crossing portion and its vicinity and is connected to the input / output portion 15 '. The SiO ₂ film 14 is a waveguide of TixSi _1-x O ₂ .
It has a smaller refractive index than 13 and enhances the waveguiding effect, and also serves as optical insulation from the upper electrode 15.

The electrode 15 is vertically symmetrical with respect to the line connecting the apexes of the intersecting corners except for the input / output portion 15 ', and the electrode surface is separated from the intersecting portion and its vicinity except for the input / output portion. By applying a voltage, the temperature of the crossing portion under the electrode 15 rises, and as a result, the refractive index of the refractive index changing region (crossing portion) shows an increase (+ Δn effect), and therefore a signal voltage is applied to the electrode 15. Therefore, the light incident from the direction of the arrow X is reflected by the arrow Y.
Go straight in the direction of or branch in the direction of arrow Z.

In the switch configured as described above, the state of emitting light to the straight side and the state of emitting light to the branch side alternate with the increase of the refractive index of the crossing portion, so that a good switch can be obtained by controlling the temperature rise by the current. Can be configured.

〔The invention's effect〕

As described above, according to the present invention, in the waveguide,
Electrodes to which a signal voltage is applied to control the change in the refractive index of the waveguide and a region including the substrate in the vicinity thereof are provided vertically symmetrically with respect to the line connecting the apexes of the intersection and the intersection and its vicinity. The electrode surface is separated from the crossing portion and its vicinity except the input / output portion so that there is no variation in the change in the refractive index.

That is, since an electric field is applied to the entire area including the intersection and its vicinity or the temperature of the entire area including the intersection and its vicinity is increased, an electrode is provided to change the refractive index evenly. Therefore, there is an effect that a high precision is not required for the alignment, and thus a compact and integrated waveguide type optical switch can be easily manufactured.

[Brief description of drawings]

FIG. 1 is a schematic view of a main part for explaining the structure of a crossed waveguide type optical switch utilizing the electro-optical effect of an embodiment of the present invention, and FIGS. 2, 3, and 4 are thermo-optical effects. FIG. 5 shows the structure of the waveguide of the conventional crossed waveguide type optical switch, and FIG. 5 shows a cross-sectional view and a perspective view of the crossing portion of the waveguide for explaining the structure of the crossed waveguide type optical switch. FIG. 6 is a schematic view of a main part for explaining, and FIG. 6 is a schematic view of a main part for explaining a structure of a conventional crossed waveguide type optical switch. In the figure, 1 and 11 are substrates, 2 is a titanium thin film layer, 3 and 13 are optical waveguides, and 4,5 and
15 is an electrode, 5 ', 15' is an input / output unit for the electrode, 12 and 14 are
SiO ₂ film, 31 and 32 are light incident side portions, 33 and 34 are light emitting side portions,
PQ is the crossing vertex of the optical waveguide.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keiichi Nakajima 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (56) References JP53-96853 (JP, A) JP58- 95330 (JP, A) JP 59-93431 (JP, A) JP 58-142320 (JP, A)

Claims (1)

[Claims] 1. In a crossed waveguide structure in which two waveguides having a refractive index larger than that of the substrate are linearly crossed on a substrate made of an electro-optic crystal, refraction of a region including the waveguide and the substrate in the vicinity thereof. The electrode to which the signal voltage for rate change control is applied is
A crossing waveguide having a vertically symmetrical shape parallel to a line connecting the crossing angle vertices and having its electrode surface arranged on a substrate including the crossing part at a position apart from the crossing part and its vicinity. Type optical switch.