JPH06102542A - Spatial optical encoder - Google Patents

Abstract

PURPOSE:To provide the spatial optical encoder of simple constitution which can increase the number of optical branches and obtain a high-speed light signal. CONSTITUTION:A high-speed short pulse train beam is branched by a spatial optical branching part 2 into a light beam having only one of two mutually orthogonal polarized components of plural high-speed short pulse train beams, and plural polarization plane control element arrays 12-1 to 12-3 make a choice of whether plural incident light beams having only one of two mutually orthogonal polarized components are outputted after being converted into the other polarized component or outputted as they are; and the light beams are inputted to a delay part 5 constituted by alternately connecting plural stages of delay elements which pass the incident light beam as it is when the incident light beam is one of the two mutually orthogonal polarized components or delay the incident light beam when the light beam is the other polarized component, and plural output signal light beams which are outputted from the delay part 5 are multiplexed by a spatial optical multiplexing part 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial optical encoder for generating high speed signal light by using a plurality of low speed modulated signals.

[0002]

2. Description of the Related Art In a general optical communication system, a high speed optical signal is generated by multiplexing a plurality of low speed electric signals at a signal transmitting end into a high speed electric signal and modulating light using the high speed electric signal. Originally, light is said to have high speed, and it is said that Tb / s order signal transmission is possible in principle. However, in the current optical communication system, when the transmission speed becomes a high-speed signal exceeding 10 Gb / s, the signal multiplexing processing and the optical modulation mainly control the processing speed of the electric circuit and the band of the electric wiring. It is getting harder and harder. In order to alleviate such problems and generate a higher-speed optical signal, a method has been proposed in which a high-speed short pulse train is used to perform signal modulation and multiplexing processing in the optical region.

FIG. 4 shows the configuration of a conventional example. The configuration of Figure 4 is based on the literature [Rodney S. Tucker, Gadi Eisenstein, and Steven.
K. Korotky, "Optical Time-Division Multiplexing Fo
r Very High Bit-Rate Transmission, "Journal of Lig
htwave Technology, Vol.6, No.11, pp.1737-1749,198
8 "]. In FIG. 4, 1 is a high-speed optical short pulse train input end, 2 is an optical signal branching unit, 3 is an optical gate unit, and 3-1 to 3-4 are An optical gate, 4 is a modulation signal adding unit, 5 is a delay adding unit, 5-1 to 5-4 are optical waveguides such as optical fibers, 6 is an optical signal combining unit, and 7 is an optical signal output terminal. Further, FIG. 5 shows examples of waveforms of the input / output signals IN and OUT and the modulation signals S1 to S4 of the respective optical gates.

In FIG. 4, the high-speed short optical pulse train IN incident on the input end 1 of the circuit is branched into four in the optical signal branching section 2 and input to the optical gates 3-1 to 3-4, respectively. In each of the optical gates 3-1 to 3-4, the incident light is turned on and off by the modulation signals S1 to S4 applied from the outside. The output signal lights from the respective optical gates 3-1 to 3-4 are added with different delays by passing through the optical waveguides 5-1 to 5-4 such as optical fibers having different lengths in the delay adding unit 5. After that, the signals are combined and output in the optical signal combiner 6. By the above operation, the high speed optical signal train OU in which the modulated signals S1 to S4 are multiplexed in time series as shown in FIG.
T can be obtained.

For the generation of a high-speed optical short pulse train, a pulse train having a pulse width of several picoseconds can be obtained relatively easily by the gain switch method or the mode lock method. As the optical gate, a lithium niobate optical modulator or a multiple quantum well structure (MQ
An optical modulator using W) can be used.

In the spatial optical encoder having the configuration of FIG. 4, the optical signal speed that can be formed is given by (possible modulation speed of each optical gate) × (number of optical branches). Therefore, for example, the possible modulation speed of the optical gate controlled by the electric circuit is 1
If 0 Gb / s, it is 1 by setting the number of optical branches to 10.
A high-speed optical signal of 00 Gb / s can be easily obtained by setting the number of optical branches to 100 and a high-speed optical signal of 1 Tb / s.

[0007]

However, in the configuration of FIG. 4, the delay adding section needs optical fibers having different lengths from each other by the number of optical branches, so that congestion of the optical fibers occurs when the number of optical branches increases. There is a problem. In addition, in the optical branching unit and the optical demultiplexing unit, as the number of branches increases, the congestion of the connection occurs, and the whole circuit becomes complicated.

An object of the present invention was made in view of such circumstances, and it is an object of the present invention to provide a spatial optical encoder capable of increasing the number of optical branches with a simple structure and obtaining a high-speed optical signal.

[0009]

In order to solve the above problems, according to claim 1 of the present invention, means for inputting a high-speed short optical pulse train to a circuit as a light beam propagating in a uniform medium,
A plurality of the high-speed optical short pulse train beams split into the high-speed optical short pulse train beam input to the circuit and output as a high-speed short optical pulse train beam array, and each of the plurality of high-speed short optical pulse train beams split by the spatial light splitter An optical gate unit arranged to control whether to pass the high-speed optical short pulse train beam by external control, and a plurality of the high-speed short optical pulse train beams branched by the spatial optical branch unit. Means for converting each of them into a light beam having only one polarization component of two polarization components orthogonal to each other, and a plurality of incident light beams having only one polarization component of two polarization components orthogonal to each other On the other hand, it is possible to select whether to output the polarized light component after converting it to the other polarized light component or to pass it without converting it. The control element array and a plurality of delays in which the incident light beam passes through the element as it is if one of the two polarization components orthogonal to each other and the other polarization component is output with a delay added. It is composed of a delay adding section configured by alternately connecting elements in multiple stages, and a spatial light combining section that combines all of a plurality of output signal light beams output from the delay adding section. Further, in claim 2, in place of the optical gate part according to claim 1, the optical gate part according to claim 1 is arranged for each of the plurality of high-speed short pulse train beams branched by the spatial light branching part, and is controlled by an external source. It was equipped with a reflection type optical switch that can select whether or not to reflect the high-speed short pulse beam.

[0010]

According to the present invention, the high-speed short pulse train is input to the circuit as a spatial light beam, and the modulated signal light is also output from the circuit as a light beam. In the optical signal branching unit and the optical signal combining unit, the number of branches (combining number) can be easily increased by connecting the optical beam branching / multiplexing elements having different output light beam intervals in multiple stages. Further, each polarization beam splitter constituting each light beam branching / multiplexing element is used as a rod, and the light beam branching / multiplexing elements are arranged in the vertical and horizontal directions to easily form and combine a two-dimensional arrayed light beam array. can do. Optical beam branching using such a spatial light beam, and multiplexing is an optical branching using a spatial light beam that uses an optical waveguide such as an optical fiber. A light beam array can be formed and combined, and delay elements with different delays are used in the delay adding section.
By arranging in stages, by controlling the polarization plane rotating element placed in front of the delay element, 2n kinds of delays can be easily added to an arbitrary light beam in the two-dimensionally arranged light beam train. Therefore, when the number of branches is 2n, it is only necessary to connect n stages of delay elements each having a different delay amount, and connection congestion is eliminated and a circuit configuration is eliminated as compared with the conventional example which requires two optical fibers having different lengths. Can be greatly simplified.

[0011]

FIG. 1 shows the configuration of the first embodiment of the present invention. In FIG. 1, 2 is an optical signal branching unit, 3 is an optical gate unit, 4 is a modulation signal adding unit, 5 is a delay adding unit, 6 is an optical signal combining unit, 8 is an incident light beam, 9-1 to 9-4. Is an optical beam branching / multiplexing element, 10-1 to 10-2 are quarter-wave plates, 1
1 is an optical gate array, 12-1 to 12-3 are polarization plane rotating elements, 13-1 to 13-2 are polarization beam splitters, 1
4-1 to 14-4 are quarter wavelength plates, 15-1 to 15-4
Represents a total reflection mirror, and 16 represents an output light beam. S1 to S4 are modulation signals input to each optical gate of the optical gate array 11.

In FIG. 1, a high-speed short optical pulse train incident as a light beam is formed by stacking a plurality of polarization beam splitters in the optical signal branching unit 2, and the light beam splitting / multiplexing elements 9-1, 9-2, And is branched into four using the quarter wave plate 10-1 and is input to each optical gate in the optical gate array 11 in the optical gate unit 3. Each optical gate has modulation signals S1 to S1 applied from the outside in the modulation signal adding section 4.
This is an element for turning on / off the incident light by S4, and specific examples thereof include a surface input / output type optical modulator array having a multiple quantum well structure, a liquid crystal shutter array, and the like. The high-speed short optical pulse trains modulated in each optical gate are input to the delay adding unit 5 in the next stage. The delay adding unit 5 is configured by alternately connecting the polarization plane rotating elements 12-1 to 12-3 and delay elements described in detail later in cascade. Polarization plane rotation element 12
-1 to 12-3 are elements that can select whether to pass two polarization components orthogonal to each other as they are or to convert them and output them. When the delay amount is fixed by the beam path, a 1/2 wavelength plate is used. When the delay amount is changed for each light beam, a liquid crystal or the like can be arranged and used for each light beam. Polarization beam splitter 13-1, quarter wave plate 1
The first delay element composed of 4-1, 14-2 and total reflection mirrors 15-1, 15-2 passes the element as it is when the P-polarized light beam is incident, and the S-polarized light beam. Is incident, a delay is added by passing a longer optical path length than the P-polarized light beam by the distance between the total reflection mirrors 15-1 and 15-2. The second delay element composed of the polarization beam splitter 13-2, the quarter wave plates 14-3 and 14-4, and the total reflection mirrors 15-3 and 15-4 also operates on the same principle as the first delay element. Add a delay.
The first delay element gives a delay of 2t, and the second delay element decides the distance between the total reflection mirrors so as to give a delay of t. Therefore, by changing the polarization of the incident signal light by using the polarization plane rotating elements 12-1 and 12-2 and selecting the optical path, four kinds of delays of t, 2t, 3t, and 4t can be added. Each of the output lights of the delay adding unit 5 includes a polarization plane rotating element 12-3 and light beam branching / multiplexing elements 9-3, 9.
-4 and quarter-wave plate 10-2 optical signal combiner 6
Are multiplexed and output. As explained above, Fig. 1
With the configuration described above, the same operation as that of the spatial light encoder of FIG. 4 can be performed.

In the spatial light encoder of this embodiment, a high-speed short pulse train is input to the circuit as a spatial light beam, and the modulated signal light is also output from the circuit as a light beam. In the optical signal branching unit and the optical signal combining unit, the number of branches (combining number) can be easily increased by connecting the optical beam branching / multiplexing elements having different output light beam intervals in multiple stages. Further, each polarization beam splitter constituting each light beam branching / multiplexing element is used as a rod, and the light beam branching / multiplexing elements are arranged in the vertical and horizontal directions to easily form and combine a two-dimensional arrayed light beam array. can do. Optical beam branching using such a spatial light beam, and multiplexing is an optical branching using a spatial light beam that uses an optical waveguide such as an optical fiber. It has the feature that it can form and combine light beam arrays. Further, in the delay adding unit of FIG. 1, if n stages of delay elements having different delay amounts are arranged, the polarization plane rotating element placed in front of the delay element is controlled to output 2n delays in the two-dimensionally arrayed light beam train. It can be easily added to any light beam. Therefore, in the present embodiment, when the number of branches is 2n, it is sufficient to connect n stages of delay elements having different delay amounts, respectively, in comparison with the conventional example which requires two optical fibers having different lengths. It can be eliminated and the circuit configuration can be greatly simplified.

FIG. 2 shows a second embodiment of the present invention. Figure 2
2, 2 is an optical signal branching unit, 3'is a gate unit and a modulation signal adding unit, 5 is a delay adding unit, 6 is an optical signal combining unit, 8 is an incident light beam, and 9-1 to 9-4 are light beam branching units. Multiplexing elements 10-1, 10-2 are quarter wave plates, 12-1 to 1
2-3 is a polarization plane rotation element, 13-1 to 13-3 are polarization beam splitters, 14-1 to 14-6 are quarter wavelength plates,
Reference numerals 15-1 to 15-6 are total reflection mirrors, 16 is an output light beam, 17 is a reflection type switch array, and 18 is a polarization plane rotation element arranged immediately after the light beam branching / multiplexing element 9-2.
The polarization plane rotation element 18 is the polarization beam splitter 13 at the next stage.
-3 is to make all the polarization of the light beam input to -3 S-polarized, and to add polarization plane rotation to the light beam output as S-polarized from the light beam branching / multiplexing element 9-2. Light beam branching and multiplexing element 9
It is an element that rotates the polarization plane of the light beam output from -2 as P-polarized light by 90 degrees and outputs it as S-polarized light. A liquid crystal light modulator or a half-wave plate can be used as such an element.

In this embodiment, the optical gate array of the first embodiment is replaced with a reflection type switch array. The reflective element is characterized in that the speed of an input light pulse can be determined independently of the switching speed of the element and that a signal can be packetized by using a switching element having hysteresis.

Materials for the switching element include a surface input / output type reflection plate having a multiple quantum well structure and an optical spatial modulator for rotating polarization of reflected light by utilizing ferroelectricity.

Next, the operation of the main part of this embodiment will be described with reference to FIG.

It is assumed that the light beam trains IN1 to IN4 are input from the left side of the drawing and the light beam trains OUT1 to OUT4 are output from the right side of the drawing. The light beam train input from the left side of the drawing is converted into S-polarized light by the polarization plane rotation element 18, and is input to the polarization beam splitter 13-3.
In the polarization beam splitter 13-3, since the input light beam train has all its polarization components S-polarized,
1/4 reflected by the polarization beam splitter 13-3
It is input to the reflection type optical switch array 17 via the wave plate 14-6. The reflection type optical switch array 17 is an element whose reflectance can be controlled by external control. When the reflection type optical switch 17 is controlled to the low reflectance state, the incident light beam is absorbed or scattered by the element and no reflected light appears. On the other hand, the reflection type optical switch 17
Is controlled to a high reflectance state, the incident light beam is reflected, and again enters the polarization beam splitter 13-3 through the quarter wavelength plate 14-6. The light beam reflected as S-polarized light by the polarization beam splitter 13-3 is converted into P-polarized light by passing through the quarter-wave plate 14-6 twice in this way. Therefore, the reflected light from the reflective optical switch array 17 is input to the polarization beam splitter 13-3 as P-polarized light. The reflected light converted into P-polarized light passes through the polarization beam splitter 13-3 as it is, and the quarter-wave plate 14-5, total reflection mirrors 15-5, 1
After passing through the / 4 wave plate 14-5, it is converted into S-polarized light and input to the polarization beam splitter 13-3, where it is reflected and output from the circuit as OUT1 to OUT4.
Other operations are the same as those in the first embodiment.

As described above, the optical encoder can be constructed using the reflection type optical switch array whose reflectance can be controlled by the external controls S1 to S4.

When a reflection type optical switch array of the type that rotates the polarization of reflected light is used, 1 /
The four-wave plate 14-6 becomes unnecessary. That is, when the polarization rotation does not occur in the reflection type optical switch array, the reflected light is reflected by the polarization beam splitter and the light beams IN1 to I
N4 is output in the incident direction. On the other hand, when polarization rotation occurs in the reflection type optical switch array, the reflected light is output light beams OUT1 to OUT1 as described above.
It is output as 4.

In both the first and second embodiments, the input light is modulated by the electric signal, but the optical gate array or the reflection type switch array is used for the input light as the optical signal by using an optical nonlinear medium or the like. It is also possible to add modulation.

[0022]

As described above, according to the present invention, any or all of branching, delay addition, and multiplexing of a high-speed short optical pulse train is performed on a light beam propagating in a space, so that there is no connection congestion. There is an advantage that the number of optical branches can be easily increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the second embodiment.

FIG. 4 is a diagram showing a configuration of a conventional example.

FIG. 5 is a diagram showing an example of input / output and modulation signal waveforms to each optical gate.

[Explanation of symbols]

1 ... High-speed optical short pulse train input terminal, 2 ... Optical signal branching section, 3 ...
Optical gate unit, 3-1 to 3-4 ... Optical gate, 4 ... Modulation signal adding unit, 5 ... Delay adding unit, 5-1 to 5-4 ... Optical waveguide such as optical fiber, 6 ... Optical signal combining unit, 7 ... Optical signal output terminal, 8 ... Incident light beam, 9-1 to 9-4 ... Light beam branching / multiplexing element, 10-1 to 10-2 ... Light beam branching / multiplexing element, 11 ... Optical gate array, 12 -1 to 12-3 ... Polarization plane control element, 13-1 to 13-3 ... Polarization beam splitter, 14-1 to 14-6 ... Quarter wavelength plate, 15-1 to 1
5-5 ... total reflection mirror, 16 ... output light beam, 17 ... reflection type optical switch array.

Claims (2)

[Claims] 1. A means for inputting a high-speed short optical pulse train to a circuit as a light beam propagating in a uniform medium, and a plurality of the high-speed short optical pulse train beams input to the circuit to form a high-speed short optical pulse train beam array. Whether to output the spatial light branching unit and the high-speed short optical pulse train beam, which is arranged for each of the plurality of high-speed short optical pulse train beams branched by the spatial light branching unit, through the external control. And a means for making each of the plurality of high-speed optical short pulse train beams split by the spatial light splitting unit into a light beam having only one polarization component of two polarization components orthogonal to each other. And for each of the plurality of incident light beams having only one polarization component of the two polarization components orthogonal to each other, A plurality of polarization plane control element arrays capable of selecting whether to convert and output the polarized light component or to pass the light as it is without conversion, and one polarized light component of two polarized light components in which the incident light beams are orthogonal to each other. In the case of, the delay element is passed through as it is, and in the case of the other polarization component, it is output from the delay adding section configured by alternately connecting a plurality of delay elements that add delay and outputs. A spatial optical encoder, comprising: a spatial optical multiplexing unit that multiplexes all of a plurality of output signal light beams. 2. The optical gate unit according to claim 1,
A reflection type optical switch which is arranged for each of the plurality of high speed short pulse train beams branched by the spatial light branching unit and which can be selected by external control to reflect or not reflect the high speed short pulse beam. The spatial optical encoder according to claim 1, further comprising: