JPH05341330A - Multi-terminal optical switch - Google Patents

Abstract

PURPOSE:To decrease switch stages and routing stages in number and facilitate the manufacture of the device by arranging reflecting elements at output terminals of the multi-terminal optical switch and making incident signal light travel and return in the device. CONSTITUTION:Polarization plane control element arrays (switch stages 2-4) and optical path converting elements (routine stages 6-1-6-3) are alternately arranged and the reflecting elements 5 are arranged at the output terminals of the multi-terminal optical switch which controls the polarized states of light beams for switching. The traveling directions of plural collimated lights passed through the multi-terminal optical switch are inverted by 180 deg. and made to travel in the multi-terminal optical switch in the opposite direction from the incident collimated lights, and linear polarized components are mutually exchanged. Further, plural collimated lights which are projected from the device are separated from the light beams which are made incident from the same optical paths and projected to the outside of the device. Consequently, the number of the stages is decreased and the optical paths of the input and output light signals of the devices are aligned with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical switch having a function of arbitrarily changing the order of optical paths of a plurality of light beams propagating in space.

[0002]

2. Description of the Related Art As a switch for wiring between a large number of input terminals and a large number of output terminals, unit switches of 2 inputs and 2 outputs are connected in multiple stages, and between 2n input terminals and 2n output terminals. There has been proposed a method of constructing a switch network capable of realizing all combinations of connecting one-to-one with each other.
FIG. 7 is a diagram showing a wiring example of a switch circuit network of 16 inputs and 16 outputs based on this construction method. In FIG. 7, 23-1 to 23-1
23-16 is a signal input terminal, 24-1 to 24-16 are signal output terminals, 25-1 to 25-7 are switch stages, and 26-1 to 26-6 are wiring stages. The plurality of rectangles forming the switch stage are unit switches of 2 inputs and 2 outputs, and the connection form (through) of input 1-output 1 and input 2-output 2 and input 1-output 2 and input by external control. 2-output 1
One of the connection forms (cross) of FIG. The wiring stages 26-1 to 26-6 are for wiring between the unit switches and are arranged alternately with the switch stages.

In the switch network of FIG. 7, a spatially propagating light beam having polarization planes orthogonal to each other is used as a wiring medium,
There has been proposed a method of constructing a multi-terminal spatial optical switch that realizes the above switch network by using an element that switches the polarization state of passing light as a unit switch.

FIG. 8 shows the structure of such a multi-terminal space optical switch. This configuration is based on K. Nogchi et al.
Uchi et.al), "Reconfigurable multichannel free-space optical switch (Rearrangeabl) using polarization multiplexing technology.
e multichannel free-space optical switch using pola
rization multiplexing technique ”, Electronics Letters, Volume 26, Vol.
No. 17, p. 1325). In FIG. 8, 27 is a collimated signal light beam input port array, and 28 is a collimated light beam output port array. 29-1 to 29-7 are polarization plane control element arrays, and the light beam incident on the elements on the array has its polarization plane rotated by 90 degrees when the element is on, and the passing P wave and S wave are mutually Will be exchanged. On the other hand, when the corresponding element is off, the plane of polarization is not affected and P
Waves and S waves remain as they are. As the polarization plane control element array having such a function, for example, a liquid crystal display can be used. Further, 30-1 to 30-6 are optical path changing elements, which have a function of switching the optical path depending on the polarization plane of the incident light beam. As an optical path changing element having such a function, for example, an element in which polarizing beam splitters are laminated can be used.

Here, each of the polarization plane control element arrays corresponds to one stage of the unit switch of the switch network shown in FIG. 7, and each of the optical path conversion elements corresponds to the wiring network between the switch stages. Reference numerals 31 and 32 in FIG. 8 are polarization beam splitters, which are elements for combining two incident light beams having polarization components orthogonal to each other and separating the beams output in the polarization-multiplexed state for each polarization component. is there.

Usually, the multi-terminal optical switch is constructed by alternately arranging individual switch stages and routing stages. At this time, the switch stage and the routing stage must be arranged with micron-order positional accuracy so that the input and output signal lights do not shift. As the number of input / output channels increases, the number of these switch stages and routing stages also increases. To construct a switch having 2n input / output channels, 2n-1
A switch stage of 2 stages and a routing stage of 2n-2 stages are required. Therefore, in the multi-terminal optical switch, there is a problem that it becomes difficult to accurately align all the elements as the switch scale increases.

[0007]

SUMMARY OF THE INVENTION The present invention provides a multi-terminal optical switch for switching a plurality of light beams propagating in a free space by utilizing the polarization of light to obtain a desired number of input / output channels. Aims to facilitate device fabrication by reducing the number of switch stages and routing stages, and reduce congestion of wiring such as optical fibers by matching the optical paths of input / output optical signals of the multi-terminal optical switch. I am trying.

[0008]

SUMMARY OF THE INVENTION The present invention provides a multi-terminal optical switch in which a polarization plane control element array and an optical path conversion element are alternately arranged to control the polarization state of a light beam for switching. A reflecting element is arranged at the output end of the optical switch so that the signal light incident on the multi-terminal optical switch reciprocates in the device. The feature is that the optical paths of the output optical signals are matched.

[0009]

【Example】

First Embodiment FIG. 1 shows the network configuration of the first embodiment of the present invention. FIG. 1 conceptually shows a case of a 4-input 4-output switching network according to the network configuration. 1-1 to 1-4 are signal input ports,
2-1 to 2-4 are switching elements forming a first switch stage, 3-1 to 3-4 are switching elements forming a second switch stage, and 4-1 to 4-4 are third switches. Switching elements 5-1 to 5-4 are reflective elements, 6-1 to 6-3 are routing steps, and 7-1 to 7-4.
Indicates signal output ports. In this embodiment, the case where all input signals are P-polarized light will be considered. Each switch element logically has two input and two output ports, but structurally has a one input and one output optical input / output terminal, and changes the polarization plane of passing light by 90 degrees. The switching operation is performed by switching whether or not to do so.

In the routing stages 6-1 to 6-3, through connection is provided for P-polarized light, and for S-polarized light, 6-1 is provided with a port two stages above, and 6-2 is provided with one stage below. To the port
In 6-3, a routing element is used so that a cross connection is made so as to be input to the port located two stages below. Collimated light having P-polarized light enters the switching networks from the signal input ports 1-1 to 1-4, respectively. During the first switch stage, the switching elements 2-1 and 2-2 are in the through state, that is, the state in which the polarization does not change at the input / output port,
2-3 and 2-4 are fixed to a cross state, that is, a state where the polarization plane changes by 90 degrees at the input / output port. Therefore, the signal light input to each of the signal input ports 1-1 to 1-4 becomes the switching element 3- of the second switch stage.
Input to 1 or 3-2. Reflective elements 5-1 to 5
At -4, the incident light is reflected and its polarization plane is set to 90
It has a function to rotate it once. This means that the S-polarized light (P-polarized light) incident on the reflecting element is converted into P-polarized light (S-polarized light) and reflected. Therefore, the switching element 4-
The signal light output from the first and the second 4-2 are the reflection elements 5-1 to 5
-4 is inputted to the switching elements 4-3 and 4-4 in the opposite direction to that of the switching elements 2-1 to 2-1.
The signal light is output as S-polarized light from the output ports 7-1 to 7-4 via 2-4.

In FIG. 1, each switching element 3-1 to 3-4 and 4-1 to 4- of the second and third switch stages is provided.
Two input signal lights having polarization components orthogonal to each other and passing through 4 travel in the same direction. That is, in the switching elements 3-1, 3-2, 4-1, 4-2, all the signal light passes from left to right, and the switching elements 3-3, 3-
In 4, 4-3 and 4-4, all the signal lights pass from right to left.

FIG. 1 shows the routes of optical signals transmitted from the signal input port 1-1 to the signal output port 7-1 and from the signal input port 1-3 to the signal output port 7-4, respectively. P-polarized light is shown as a thick line with an arrow, and S-polarized light is shown as a broken line with an arrow. The P-polarized signal light input to 1-1 is input to the reflecting element 5-1 as it is as P-polarized light and output as S-polarized light.
-3, 3-3 after changing the polarization state respectively, 7
It is output as S polarized light from -1. P input to 1-3
The polarized signal light is converted into S-polarized light by the switching element 2-3 and output, and then input to the reflecting element 5-4 as it is as S-polarized light, output as P-polarized light, and passed through each element as it is as P-polarized light. Is input to the switching element 2-4, converted into S-polarized light, and output from 7-4.

FIG. 2 shows the structure of the reflecting element used in the present invention. 8-1 to 8-N are signal lights having only one of two orthogonal polarization components (S polarization and P polarization), 9
Indicates a quarter wave plate and 10 indicates a mirror. The signal lights 8-1 to 8-N incident on the reflecting element are reflected by the mirror 10
And the plane of polarization is rotated 90 degrees by passing through the quarter-wave plate 9 twice. That is, when P-polarized light (S-polarized light) is incident on the present reflective element, the reflected light becomes S-polarized light (P-polarized light). This is the function itself of the reflective element shown in FIG.

FIG. 3 shows the structure of a multi-terminal optical switch which optically realizes the optical switch based on the principle of FIG. 11-
1 to 11-N are polarization plane control elements (for example, liquid crystal displays) used as switch stages, 12-1 to 12-N are routing elements, 13 is a quarter-wave plate, 14 is a mirror, 15 is input signal light, 16 Is an output signal light, and 17 is a polarization beam splitter. The input signal light 15 input to the first switch stage 11-1 passes through the switch body,
The light is reflected by the reflection element composed of the mirror 13 and the mirror 14, passes through the switch body again, and is output from the first switch stage. The input signal light and the output signal light are separated by the polarization beam splitter.

In the conventional multi-terminal optical switch, 2n × 2n switch stages and 2n × 2n switch stages are used to form a 2n × 2n switch.
(N-1) routing stages are required. On the other hand, in the optical switch stage of the present invention, a switch of the same scale can be configured by n switch stages and n + 1 routing stages. However, here, the reflection element and the fixed switch stage of the switch input / output stage are omitted.

FIG. 4 shows the result of calculation of the relationship between the number of channels and the number of stages including switch stages and routing stages for the conventional multi-terminal optical switch and the multi-terminal optical switch of the present invention. For example, in order to realize a switch having 1024 input / output channels, a switch stage is required in a conventional multi-terminal optical switch.
While 19 and 18 routing stages require a total of 37 stages,
With the multi-terminal optical switch of the present invention, a total of 21 stages including 10 switch stages and 11 routing stages, which is about 60% of the number of stages of the conventional multi-terminal optical switch, can realize a switch of the same scale. In the multi-terminal switch of the present invention, since the number of switch stages and routing stages is reduced, the number of switch elements in each switch stage is 2
It is necessary to double the number, but since the switch elements such as a liquid crystal display are integrally formed by using the semiconductor manufacturing technology, the manufacturing thereof is relatively easy even if the number of elements increases.
Therefore, the optical switch of the present invention is more advantageous in the number of stages as the switch scale is larger than that of the conventional multi-terminal optical switch. When all the input signal light is S-polarized light, all of them may be converted into P-polarized light by the switching element in the first stage, or the role may be exchanged with P-polarized light in the routing element and the switching element in the apparatus. When P-polarized light and S-polarized light are mixed in the input signal light, the same function can be realized by converting all input signals into P-polarized light or S-polarized light by the switching element in the first stage.

Embodiment 2 FIG. 5 shows another example of the polarization separation element for separating the input / output channels in the first embodiment of the present invention. 18-1 to 18
-N is an input signal light to the multi-terminal optical switch, and is P-polarized light in correspondence with FIG. Reference numeral 19 is a birefringent crystal such as calcite, and 20-1 to 20-N are output signal lights from the multi-terminal optical switch. As shown in FIG. 5, the input / output signal light occupying the same optical path at the input terminal of the multi-terminal switch can be separated by passing through the birefringent crystal. With such a configuration of the polarization separation element, the signal input port and the signal output port can be formed on the same surface. Therefore, there is an advantage that the light emission and the light receiving element arrays arranged on the same substrate can be connected without using an optical waveguide such as a bundle optical fiber, and the congestion of wiring can be reduced.

Embodiment 3 FIG. 6 shows another example of the polarization separation element for separating the input / output channels in the first embodiment of the present invention. 21-
1 to 21-N are optical waveguide type couplers for separating polarized light,
22-1 to 22-N represent polarization maintaining fibers, respectively. The input signal lights 18-1 to 18-N are optical fibers 22 respectively.
It is guided to the input end of the multi-terminal optical switch by -1 to 22-N and input to the multi-terminal optical switch. On the other hand, the output signal light having the same optical path as the input signal light is the optical fibers 22-1 to 22-2.
The light is guided to the polarization separation element via 22-N and is output from a port different from the input signal light.

[0019]

As described above, according to the present invention, the polarization plane control element array and the optical path changing element are alternately arranged,
In a multi-terminal optical switch that controls the polarization state of a light beam to perform switching, a reflecting element is arranged at the output end of the multi-terminal optical switch, and the signal light incident on the multi-terminal optical switch reciprocates in the device. The structure has an effect of reducing the number of switch stages and routing stages and facilitating device fabrication.

[Brief description of drawings]

FIG. 1 is a diagram showing a network configuration according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a reflective element used in the present invention.

FIG. 3 is a diagram showing a configuration of a multi-terminal optical switch of the present invention.

FIG. 4 is a diagram showing the relationship between the number of channels of the present invention and the conventional multi-terminal optical switch and the number of stages including the switch stages and the routing stages.

FIG. 5 is a diagram showing a second embodiment of the present invention.

FIG. 6 is a diagram showing a third embodiment of the present invention.

FIG. 7 is a diagram illustrating a wiring example of a switch circuit network.

FIG. 8 is a diagram showing a configuration of a conventional multi-terminal space optical switch.

[Explanation of symbols]

1-1 to 1-4 Signal input port 2-1 to 2-4 Switching element 3-1 to 3-4 constituting first switch stage Switching element 4-1 to 4-1 constituting second switch stage 4 Switching elements 5-1 to 5-4 Reflective elements 6-1 to 6-3 Routing stages 7-1 to 7-4 Signal output ports 8-1 to 8-N Two orthogonally arranged switching elements constituting a third switch stage Polarization component (S polarization, P
Signal light having only one of polarized light 9 1/4 wave plate 10 Mirror 11-1 to 11-N Polarization plane control element 12-1 to 12-N Routing element 13 1/4 wave plate 14 Mirror 15 Input Signal light 16 Output signal light 17 Polarization beam splitter 18-1 to 18-N Input signal light to multi-terminal optical switch 19 Birefringent crystal 20-1 to 20-N Output signal light from multi-terminal optical switch 21-1 -21-N Optical waveguide coupler for separating N polarized light 22-1 to 22-N Polarization preserving fiber 23-1 to 23-16 Signal input terminal 24-1 to 24-16 Signal output terminal 25-1 to 25-7 Switch Steps 26-1 to 26-6 Routing step 27 Collimated signal light beam input port array 28 Collimated signal light beam output port array 29-1 to 29-7 Polarization plane control element array 30-1 to 30-6 Optical path conversion element 31 Polarized light Beam Splitter 32 Polarizing Beam Splitter

Claims (3)

[Claims] 1. A means for arranging the optical paths of a plurality of collimated incident signal lights in the direct polarization state in a lattice shape or a row at equal intervals so as to enter the apparatus in parallel to each other, and two means for passing light beams orthogonal to each other. Polarization plane control element array in which a plurality of polarization plane control elements are arranged to control either one of the two linearly polarized light components as they are or the other linearly polarized light components are exchanged with each other. Orthogonal to the light beam for all
It is separated into two linearly polarized light components, the optical path of one of the linearly polarized light components is changed, and this is combined with the other linearly polarized light component of the other light beam that is separated into two linearly polarized light components orthogonal to each other. An optical path conversion element having a function of propagating on the same optical path, and the polarization plane control element array and the optical path conversion element are alternately arranged on the optical paths of the plurality of collimated light beams that have entered the device. In the multi-terminal optical switch described above, the traveling direction of the plurality of collimated lights passing through the multi-terminal optical switch is rotated by 180 degrees, and the multi-terminal optical switch is in the opposite direction to the traveling direction of the incident collimated light. And a means for exchanging linearly polarized light components with each other, and a plurality of collimated light beams emitted from the inside of the device, separated from the light beam incident from the same optical path, outside the device. Multi-terminal optical switch characterized by comprising a means for emitting. 2. A birefringent medium is used to separate each of the plurality of collimated light beams emitted from the inside of the device from the collimated light beams incident from the same optical path and to emit the collimated light beams to the outside of the device. The multi-terminal optical switch according to 1. 3. A polarization preserving fiber and a polarization beam splitter are used to separate each of the plurality of collimated light beams emitted from the inside of the apparatus from the collimated light beam incident from the same optical path and to emit the collimated light beams to the outside of the apparatus. The multi-terminal optical switch according to claim 1, which is characterized in that.