JPH04320205A - Optical switch - Google Patents

Abstract

PURPOSE:To provide the optical switch which has good electric power efficiency, operates surely at a high speed and allows integration to a high scale. CONSTITUTION:This switch has an optical waveguide 30 which is formed on an Si substrate 11 and is constituted by coating a core 32 to allow the propagation of light with a clad 31 having the refractive index lower than the refractive index of the core, a gap 40 which is formed in the mid-way of the core 32 and holds a liquid 41 having the refractive index approximately equal to the refractive index of the core 32, and a semiconductor electrothermal element 21 which is formed on the surface of the Si substrate 11 and heats the liquid 41 in the gap 40. The switch controls the progressing direction of the light within the optical waveguide 30 by evaporating the liquid 41 in the gap 40 by heating or condensing the evaporated liquid 41 by stopping the heating, thereby changing the refractive index in the gap 40.

Description

[Detailed description of the invention]

The present invention relates to an optical switch for switching the optical path of propagating light.

0002

[Prior Art] As a conventional optical switch, FIGS. 4 and 5
The optical waveguide structure shown in FIG. Note that this was previously proposed by the present inventors.

As shown in FIGS. 4(a) and 4(b), this optical switch consists of an optical waveguide consisting of a core 32 with a rectangular cross section and a cladding 31 with a low refractive index covering the core 32 on a quartz (SiO2) substrate 10. A gap 40 is formed in the middle of the optical waveguide 30 so as to cut the core 32, and the gap 40 is filled with a liquid 41 having a refractive index substantially equal to that of the core 32. It has a special structure in which an electric heating body 20 for heating the liquid 41 is formed. As shown in FIG. 5, the core 32 is formed by intersecting two linear cores in a cross shape, and then forming the gap 40 by diagonally crossing the intersection, resulting in L Two cores 32a bent in a letter shape,
It is cut at b.

This optical switch operates as follows in FIG.

When no current is flowing through the electric heating element 20, the gap 40 is filled with the liquid 41. Therefore, at this time, the refractive index within the gap 40 is
2a and 2b, the light incident from the first input port 50 travels straight through the gap 40 and is output to the first output port 51.

When a current is passed through the electric heating element 20, the gap 40
The liquid 41 inside is heated and vaporized, leaving only gas inside the gap 40. At this time, since the refractive index within the gap 40 is smaller than that of the core 32a, the light incident from the first input port 50 is totally reflected at the bent end face of the core 32a exposed within the gap 40. The output is then switched to the second output port 52.

When the electric heating element 20 is de-energized, the temperature in the gap 40 decreases and the gas condenses, so the gap 40 is filled with the liquid 41 again, and the incident light goes straight to the first The output is switched to the output port 51 of.

Similarly, when no current is flowing through the electric heating element 20, the incident light from the second input port 53 goes straight and is output to the second output port 52, and when no current is flowing through the electric heating element 20, the incident light is outputted to the second output port 52. Sometimes, the light is totally reflected at the end face of the bent portion of the core 32b exposed within the gap 40 and is output to the first output port 51.

Since this optical switch utilizes total reflection of light at the bent end faces of the cores 32a, b exposed within the gap 40, the loss of light during switching can be kept to an extremely low level. Furthermore, it is easier to downsize compared to conventional optical switches using other methods. Further, an electric heating element 2 for heating the liquid 41 within the gap 40
0 and the wiring 22 are arranged on the optical waveguide 30, so there is an advantage that they can be easily formed by a method such as metal vapor deposition.

0010

[Problems to be Solved by the Invention] By the way, the electric heating body 20
By turning on/off the current to the gap 40
The gap 40 is switched between an empty state and a filled state with the liquid 41 by vaporizing or condensing the liquid 41 within the gap 40, and switching is performed using the change in the refractive index within the gap 40 at that time. type of optical switch, in order to speed up the switching operation, the electric heating element 20
When a current is applied to the gap 40, the liquid 41 needs to be quickly discharged from the gap 40. This includes a gap of 40
It is desirable to have a structure in which the liquid 41 is first vaporized from the bottom of the gap 40, and the remaining liquid 41 is pushed up and discharged out of the gap 40.

However, in the structure of the conventional optical switch described above, the liquid 41 inside the gap 40 is heated from the upper part of the gap 40 by the electric heating element 20 disposed on the upper surface of the optical waveguide 30. Vaporization begins. Therefore, it is difficult for the gas initially generated at the bottom of the gap 40 to become a mechanism for pushing up the liquid 41. Also,
The liquid 41 will remain in the gap 40 until the entire gap 40 is heated and the liquid 41 at the bottom is vaporized. For this reason, the liquid 4
It takes a long time for 1 to be discharged from the gap 40, making it difficult to increase the switching speed. Furthermore, since the conventional optical switch does not have a structure in which the liquid 41 is reliably discharged from the gap 40, there is also a problem in the reliability of the switching operation.

In an optical switch having such a conventional structure, if an attempt is made to speed up the vaporization of the liquid 41 within the gap 40, the amount of heat required of the electric heating element 20 increases, resulting in extremely low power efficiency. Furthermore, it is difficult to form a circuit for controlling the electric heating body 20 of an optical switch on the same chip, and therefore it is difficult to achieve high integration of this optical switch.

The present invention was devised to solve the above problems, and its purpose is to provide an optical switch that has good power efficiency, operates quickly and reliably, and can be highly integrated.

[0014]

[Means for Solving the Problems] In order to achieve the above object, an optical switch according to the present invention comprises an optical waveguide formed on a Si substrate, in which a core through which light propagates is covered with a cladding having a lower refractive index than the core. and a gap formed in the middle of the core to sandwich a liquid having a refractive index substantially equal to that of the core, and a semiconductor electric heating element formed on the surface of the Si substrate to heat the liquid in the gap. The direction in which light travels within the optical waveguide is controlled by changing the refractive index within the gap by vaporizing the liquid or by stopping the heating and condensing the vaporized liquid.

The electric heating element may be formed by partially doping the Si substrate with n-type or p-type dopants. It is desirable that the electric heating element be driven with a constant current.

Further, the core of the optical waveguide may be formed in a lattice shape, and the gap and the electrothermal element may be provided at each lattice point position of the core.

[0017]

[Operation] The semiconductor heating element and the wiring for driving it can be easily formed on a Si substrate using ordinary integrated circuit technology such as planar technology. When manufacturing the optical switch, the semiconductor electrothermal element is formed on the surface of the Si substrate in alignment with the position where the gap is formed, and then the optical waveguide is formed on the Si substrate. As a result, a semiconductor electric heating element is formed directly under the gap formed in the optical waveguide.

[0018] If the electric heating element is placed directly under the gap, the liquid in the gap can be heated from below by passing a current through the electric heating element, and the liquid can be vaporized first from the bottom of the gap. As a result, the remaining liquid in the gap is pushed up by the rise of the gas generated on the lower side and is quickly discharged from the gap, thereby achieving faster and more reliable optical switching. The semiconductor electric heating element is Si
Since it is formed by partially adding impurities to the surface of the substrate, the lower surface of the optical waveguide can be made smooth, and the optical waveguide formed on the electrothermal element will not have any adverse effects such as distortion. Further, since the semiconductor heating element has a characteristic that the resistance value decreases as the temperature rises, constant current driving self-stabilizes the temperature when generating heat, thereby simplifying temperature control of the heating element. Furthermore, since functional components such as transistors can be easily formed on a Si substrate using ordinary integrated circuit technology, a large number of optical switches can be arranged in a matrix to drive circuits for each electric heating element on the same substrate. High integration can be achieved by mounting the device on the device.

[0019]

[Examples] Examples of the present invention will be described below.

[Embodiment 1] In the optical switch shown in FIGS. 1 and 2, an optical waveguide 30 consisting of a core 32 having a rectangular cross section and a cladding 31 with a low refractive index covering the core 32 is formed on a Si substrate 11. A gap 40 is formed in the middle of the optical waveguide 30 so as to cut the core 32, and the gap 40 is filled with a liquid 41 having a refractive index substantially equal to that of the core 32.
Semiconductor electric heating element 2 for heating liquid 41 directly below 0
It is mainly composed of 1.

The core 32 is formed by forming an optical waveguide 30 having cores crossed in a cross shape as shown in FIG. As a result, the cores 32a and 32b are cut into two L-shaped bent cores 32a and 32b. At the tip of the bent portion of these L-shaped cores 32a, b,
end surfaces 35a exposed within the gap 40 and facing each other;
b is formed.

In the semiconductor electric heating element 21, before the optical waveguide 30 is formed, the surface of the Si substrate 11 is partially doped with an n-type or p-type dopant in accordance with the position where the gap 40 is formed. formed by. The electric heating element 21 is connected to a wiring 22 formed on the Si substrate 11 by metal vapor deposition or the like.

This optical switch operates as follows in FIG.

[0024] When no current is flowing through the heating element 21,
The inside of the gap 40 is filled with the liquid 41. Therefore, at this time, since the refractive index within the gap 40 is equal to the refractive index of the cores 32a and 32b, the light incident from the first input port 50 goes straight through the gap 40 and reaches the first output. It is output to port 51.

When a current is passed through the heating element 21, the gap 4
The liquid 41 in the gap 40 is heated and vaporized, leaving only gas in the gap 40. At this time, since the refractive index within the gap 40 is smaller than that of the core 32a, the light incident from the first input port 50 is totally reflected at the bent end surface 35a of the core 32a exposed within the gap 40. The output is then switched to the second output port 52.

When the electric heating element 21 is de-energized, the temperature in the gap 40 decreases and the gas condenses, so the gap 40 is filled with the liquid 41 again.
The incident light goes straight and the output is switched to the first output port 51.

Similarly, the incident light from the second input port 53, when no current is flowing through the heating element 21, goes straight and is output to the second output port 52, and when no current is flowing through the heating element 21, Sometimes, the light is totally reflected by the bent end face 35b of the core 32b exposed in the gap 40 and is output to the first output port 51.

In the above optical switching operation, since the electric heating element 21 is provided directly under the gap 40,
The liquid 41 in the gap 40 is heated from below, and vaporization starts from the bottom of the gap first. The liquid 41 within the gap 40 is pushed up by the rise of the gas, and is quickly discharged from the gap 40. Therefore, the operation of the optical switch shown in this embodiment is much more efficient, faster, and more reliable than conventional switches.

[Embodiment 2] FIG. 3 shows an example in which an optical switch matrix and a drive circuit are integrated.

An optical waveguide with cores 32 formed in a lattice shape is formed on the Si substrate. Each grid point 3 of the core 32
By arranging the gap 40 and the semiconductor heating element 21 at position 4, a large number of optical switches 80 are formed in a matrix. The upper surface of the optical switch matrix is filled with a liquid having the same refractive index as the core 32 of the optical waveguide, so that the gap 40 is filled with this liquid. Each optical switch 80 has a structure similar to that of FIGS. 1 and 2.

A transistor 70 is arranged near the optical switch 80 to drive these separately. A control signal 7 is placed around the optical switch matrix.
2, the optical switch 80 via the transistor 70
A switch control circuit 71 is arranged to control the. These transistors 70 and switch control circuit 71 are
Together with the semiconductor heating element 21, it is formed on a Si substrate by common integrated circuit technology. The semiconductor heating element 21 of the optical switch 80 is driven with a constant current. A power supply line 90 for optical switch drive is connected to all optical switches 80 and transistors 70.

Since functional components such as the transistor 70 can be easily formed on the Si substrate 11 using ordinary integrated circuit technology, a large number of optical switches 80 are arranged in a matrix to connect each semiconductor heating element 21. By mounting two drive circuits on the same substrate, high integration can be achieved. As explained in the first embodiment, the operation of each individual optical switch 80 is fast and reliable, and this integrated optical switch has extremely high performance. Furthermore, since the semiconductor heating element 21 has a negative temperature coefficient of resistance,
By driving the electric heating element 21 with a constant current, the electric heating element 21
Since the temperature during heat generation is automatically stabilized, there is no need for a circuit for temperature stabilization.

[0033]

[Effects of the Invention] In summary, according to the present invention, high efficiency,
A high-speed, reliable optical switch can be realized, and a highly integrated optical switch can be easily constructed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of an optical switch according to the present invention, in which (a) is a longitudinal cross-sectional view, and (b) is an I-I diagram of (a).
FIG.

FIG. 2 is a plan view of the optical switch shown in FIG. 1.

FIG. 3 is a plan view showing another embodiment of the present invention.

FIG. 4 is a diagram showing a conventional optical switch, in which (a) is a longitudinal cross-sectional view, and (b) is a cross-sectional view taken along the line IV-IV in (a).

FIG. 5 is a plan view of the optical switch shown in FIG. 4.

[Explanation of symbols]

11 Si substrate 21 Semiconductor heating element 30 Optical waveguide 31 Clad 32 core 34 Lattice points 40 Gap 41 Liquid

Claims (4)

[Claims] 1. An optical waveguide comprising a core formed on a Si substrate through which light propagates is covered with a cladding having a lower refractive index than the core, and a liquid formed in the middle of the core and having a refractive index substantially equal to that of the core. and a semiconductor electric heating element that is formed on the surface of the Si substrate and heats the liquid in the gap, and can vaporize the liquid in the gap by heating or condense the vaporized liquid by stopping the heating. An optical switch characterized in that the optical switch is configured to control the traveling direction of light within the optical waveguide by changing the refractive index within the gap. 2. The optical switch according to claim 1, wherein said electric heating element is formed by partially doping said Si substrate with an n-type or p-type dopant. 3. The optical switch according to claim 1, wherein the electric heating element is driven with a constant current. 4. The core of the optical waveguide is formed in a lattice shape, and the gap and the electric heating element are provided at each lattice point position of the core. light switch.