JPH0667219A - Variable optical delay circuit - Google Patents

Abstract

PURPOSE:To simplify device constitution and individually adjust delay times for incident light signals by arranging polarization plane control elements and optical path selecting elements alternately in plural stages. CONSTITUTION:The polarization plane control elements 3-1 to 3-N function to select whether an incident light beam is passed as it is or has its plane of polarization rotated by 90 deg. under electric control. Polarization beam splitters 4-1 to 4-N and 5-1 to 5-N constitute the optical path selecting elements. An incident light beam 10 which has only on S-polarized light component is reflected by a polarization beam splitter 1 and converted by a 1/2-wavelength plate 2 into P-polarized light. The polarization plane control elements 3 selects by which of the optical path selecting elements the light beam is to be reflected. When the light beam which is made incident on the polarization plane control elements 3 have its plane of polarization rotated by 90 deg., the light beam is reflected by polarization beam splitters 4 and 5 in succeeding stages, reflected by a polarization beam splitter 9, and then outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable optical delay circuit which changes the optical path length of one or a plurality of optical signals propagating in a space incident on a circuit and adjusts the delay time of the optical signals.

[0002]

2. Description of the Related Art A delay circuit for adjusting a delay time of a signal is one of basic circuits for signal processing. For example, in a digital circuit that processes a large number of digital signals, a delay circuit is indispensable for performing phase matching between signals and clock synchronization. Further, it can be applied to time slot conversion and a signal demultiplexing circuit.

Focusing on the spatial parallelism of light, optical signal processing for performing various kinds of signal processing through spatially propagating light is being studied. As a variable optical delay circuit using spatially propagating light, one using a movable mirror has been conventionally known. FIG. 3 shows a conventional variable optical delay circuit using a movable mirror. Reference numeral 18 is a first reflection mirror, 19 is a second reflection mirror, 20 is a moving direction of the second reflection mirror 19, and 21 is an incident light beam. The incident light beam 21 is bent at a right angle by the first reflecting mirror 18 and the second reflecting mirror 19
Is incident on. The second reflection mirror 19 reflects the incident light beam 21 twice, and propagates an optical path parallel and different from the incident light beam 21 in the opposite direction. Second reflection mirror 1
The output light beam 9 of FIG. 9 is output again after its optical path is bent 90 degrees by the first reflecting mirror 18. Assuming that the distance between the first reflecting mirror 18 and the second reflecting mirror 19 is L and the moving distance of the light in the input / output direction when passing through the circuit is t, the light beam incident on the circuit is output from the circuit. The delay time td until it is expressed is represented by td = (2L + t) / c (1). Here, c is the speed of light. The delay time can be changed by moving the second reflecting mirror 19 in the moving direction 20 and changing the distance L between the first reflecting mirror 18 and the second reflecting mirror 19.

[0004]

Conventionally, in such a variable optical delay circuit, the delay time is adjusted by moving the second reflecting mirror 19 by using a manual or mechanical method. Therefore, adjustment of the delay time requires a mechanism for moving the second reflecting mirror 19 without any positional or angular displacement, which causes a problem that the device configuration becomes complicated. Further, when a plurality of light beams are incident on the variable optical delay circuit, it is difficult to individually adjust the delay time of each light beam.

In view of the above problems, an object of the present invention is to provide a variable optical delay circuit which enables simplification of the device configuration and allows individual adjustment of delay time for a plurality of optical signals incident on the circuit. To do.

[0006]

In order to achieve the above object, the present invention is directed to one or a plurality of incident signal lights propagating in space by changing the optical path length of the incident signal lights. In a variable optical delay circuit for adjusting a delay time of light, a unit for making each of the incident signal lights into a circuit as a light beam having only one polarization plane of two polarization planes orthogonal to each other, and an incident signal. A polarization plane control element capable of selecting by external control whether to pass each light as it is or output the polarization component of the incident signal light by rotating 90 degrees, and two polarization components of the incident signal light orthogonal to each other. One of the polarized light components is transmitted as it is, and the other polarized light component is reflected in parallel to the incident signal light beam and reflected so as to travel in the opposite direction on an optical path different from the incident signal light beam. It is constituted by the selection device, comprising side by side one stage or plural stages of polarization plane control element and the optical path selection element alternately. According to a second aspect of the present invention, in a variable optical delay circuit that adjusts the delay time of the incident signal light by changing the optical path length of the incident signal light for one or a plurality of incident signal lights propagating in space. Means for injecting each of the incident signal lights into the circuit as a light beam having only one of the two polarization planes orthogonal to each other, and either passing the incident signal lights as they are or A polarization plane control element capable of selecting whether to rotate and output the polarization component by 90 degrees and one polarization component of two polarization components of the incident signal light which are orthogonal to each other are allowed to pass through while the other polarization component is transmitted. The component is an optical path selector that outputs an optical path in the same direction and the same direction as the polarized component that passes through the element as it is after passing the optical path length longer than the polarized component that passes through the element as it is. It is composed of, formed by arranging one stage or plural stages of polarization plane control element and the optical path selection element alternately.

[0007]

[Operation] In the present invention, the polarization plane control elements and the optical path selection elements are alternately arranged in a plurality of stages, and by selecting which optical path selection element uses the polarization plane control element to reflect the light beam, Imposing a delay time on the light beam.

[0008]

FIG. 1 shows a first embodiment of the present invention. In the figure, 1 is a polarization beam splitter, 2 is a half-wave plate, 3-1
˜3-N is a polarization plane control element, 4-1 to 4-N are first polarization beam splitters constituting an optical path selection element, 5-1 to 5-1
5-N is a second polarization beam splitter that constitutes an optical path selection element, 6 is a half-wave plate, 7, 8 and 9 are polarization beam splitters, and 10 is an incident light beam having only an S-polarized component. There is.

The incident light beam 10 having only the S-polarized component incident on the polarization beam splitter 1 is reflected by the polarization beam splitter 1, converted into P-polarized light by the ½ wavelength plate 2, and the polarization plane control element 3-1. Is incident on. The polarization plane control element 3-1 has a function of electrically controlling whether to pass the incident light beam as it is or rotate the polarization plane by 90 degrees. When the light beam 10 incident on the polarization plane control element 3-1 passes through the polarization plane control element 3-1 as it is, the next polarization beam splitter 4-1.
Of the polarization plane control element 3-2 at the next stage. On the other hand, when the light beam 10 incident on the polarization plane control element 3-1 has its polarization plane rotated by 90 degrees, it is reflected by the polarization beam splitter 4-1 at the next stage, and the second polarization beam splitter 5-1. Is reflected again by the polarization plane control element 3
It is incident on -1 in the opposite direction. In that case, the polarization plane control element 3-1 again rotates the polarization plane of the light beam 10 by 90 degrees,
Output as P-polarized light. Output P-polarized light beam 10
Is converted into S-polarized light by the half-wave plate 2, and its optical path is rotated by 90 degrees by the polarization beam splitter 9 to be output from the circuit. In this way, by arranging a plurality of optical path selection elements consisting of the polarization plane control element and the two polarization beam splitters alternately, and selecting which optical path selection element is used to reflect the light beam by using the polarization plane control element. It is possible to impose different optical path lengths or delay times on the light beam.
In FIG. 1, the incident light beam 10 has a polarization beam splitter 4-
It shows a case where the light is reflected by the optical path selection element composed of 2, 5-2 and outputted from the circuit. In the variable optical delay circuit of FIG. 1, the variable delay time has a discrete value, and the variable delay time number corresponds to the number of optical path length adjusting circuits configured by the polarization plane control element and the optical path selection element. Further, the variable delay time amount can be arbitrarily set by the distance between the optical path length adjusting circuits.

There is a liquid crystal spatial light modulator as the polarization plane control device. Such a light modulation element is a surface input / output type and can be easily arrayed. Therefore, for example, if 2
It is also possible to easily control the polarization planes of the individual light beams with respect to the light beam array of the dimensional array so that the delay time is different for each beam by using the circuit shown in this embodiment.

As described above, in the variable optical delay circuit of the present invention, the delay time is electrically adjusted by the polarization plane control element, and there is no mechanical moving part as compared with the optical path adjustment by the manual or mechanical method. The simple structure enables fast and stable delay time adjustment. Furthermore, when a plurality of light beams are made incident on the variable optical delay circuit, it is possible to easily change the delay time of each light beam individually.

FIG. 2 shows a second embodiment of the present invention. In FIG. 2, 11-1 to 11-N are polarization plane control element arrays, 12-1 to 12-N are polarization beam splitters, 13
-1 to 13-N are quarter wavelength plates, 14-1 to 14-N are total reflection mirrors, 15-1 to 15-N are quarter wavelength plates, 1
Reference numerals 6-1 to 16-N denote total reflection mirrors, and 17 denotes an incident light beam.

A pair of quarters facing each other in FIG.
Wave plate and total reflection mirror (13-1 and 14-1, 15-1
And 16-1) act as a reflecting element having a function of reflecting an incident light beam and rotating its polarization plane by 90 degrees. The present embodiment is greatly different from the first embodiment in that the optical path selection element is composed of a polarization beam splitter and the two reflection elements placed at opposite positions with the polarization beam splitter interposed therebetween.

In FIG. 2, the polarization beam splitter 12-
2, 1/4 wavelength plate 13-2, 15-2, total reflection mirror 1
The case where the light beam 17 incident on the circuit is delayed by the optical path selection element composed of 4-2 and 16-2 is shown. When the light beam 17 output from the polarization plane control element 11-2 is P-polarized, the light beam 17 passes through the polarization beam splitter 12-2 as it is and enters the polarization plane control element 11-3 at the next stage. On the other hand, the polarization plane control element 1
When the light beam 17 output from 1-2 is S-polarized, the light beam 17 is reflected by the polarization beam splitter 12-2 and is composed of a quarter wave plate 15-2 and a total reflection mirror 16-2. It is again incident on the polarization beam splitter 12-2 via the element. At this time, the plane of polarization of the light beam 17 which is incident on the polarization beam splitter 12-2 again has undergone 90-degree polarization rotation by the reflecting element, so this time it passes through the polarization beam splitter 12-2 as it is,
The light is incident on the reflection element including the four-wave plate 13-2 and the total reflection mirror 14-2. The light beam 17 incident on the reflection element undergoes 90 degree polarization rotation and is incident on the polarization beam splitter 12-2 again. This time, the light beam reflected on the polarization beam splitter 12-2 and incident on the optical path selection element. It is output in the same optical path and the same direction as 17. In this way, the S-polarized beam input to the element can be delayed by reciprocating once between the reflecting elements arranged at opposite positions with the polarization beam splitter interposed therebetween.

A variable optical delay circuit similar to that of the first embodiment of the present invention can be realized by alternately arranging a plurality of the optical path selection elements and the polarization plane control elements described above. In the variable optical delay circuit of the present embodiment, the variable delay time takes a discrete value, and the adjustable delay time number is n where the number of optical path length adjusting circuits configured by the polarization plane control element and the optical path selection element is 2. matches ⁿ . Further, the variable time amount can be arbitrarily set by changing the distance between the two reflecting elements facing each other with the polarization beam splitter interposed therebetween in each optical path selection circuit. Thus, in addition to the features of the first embodiment of the present invention, this embodiment has the advantage that the adjustable delay time can be significantly increased compared to the first embodiment.

[0016]

As described above, according to the present invention, in the variable optical delay circuit for adjusting the delay time by changing the optical path length of the light beam, the adjustment of the delay time differs from that of the polarization plane control element. Since multiple optical path selection elements are connected alternately and a delay plane is used to select whether or not to impose a delay, there is no mechanical moving part compared to manual or mechanical method for optical path adjustment, and it is simple With such a configuration, high-speed and stable delay time adjustment can be realized. Further, when a plurality of light beams are incident on the variable optical delay circuit, there is an effect that the delay time of each light beam can be easily changed individually.

[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 showing a conventional technique.

[Explanation of symbols]

1 ... Polarizing beam splitter, 2 ... 1/2 wavelength plate, 3-1
To 3-N ... Polarization plane control element, 4-1 to 4-N ... First polarization beam splitter constituting optical path selection element, 5-1 to 5-1.
5-N ... Second polarization beam splitter constituting optical path selection element, 6 ... 1/2 wave plate, 7, 8, 9 ... Polarization beam splitter, 10 ... Incident light beam having S polarization component only, 11-1 11-N ... Polarization plane control element array, 12
-1 to 12-N ... Polarizing beam splitter, 13-1 to 1
3-N ... Quarter wave plate, 14-1 to 14-N ... Total reflection mirror, 15-1 to 15-N ... Quarter wave plate, 16-1 to
16-N ... total reflection mirror, 17 ... incident light beam, 18 ...
First reflecting mirror, 19 ... Second reflecting mirror, 20 ... Moving direction of second reflecting mirror, 21 ... Incident light beam.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takao Matsumoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (2)

[Claims] 1. A variable optical delay circuit for adjusting the delay time of the incident signal light by changing the optical path length of the incident signal light for one or a plurality of incident signal lights propagating in space. A means for injecting each of the signal lights into the circuit as a light beam having only one polarization plane of two polarization planes orthogonal to each other, and a means for passing each of the incident signal lights as they are or a polarization of the incident signal light. A polarization plane control element that can select whether to rotate the component by 90 degrees and output it by external control, and one of the two polarization components of the incident signal light that are orthogonal to each other is allowed to pass as it is and the other polarization component Is an optical path selection element that is parallel to the incident signal light beam and reflects so as to travel in an opposite direction along an optical path different from the incident signal light beam. Variable optical delay circuit which is characterized by comprising arranging one stage or plural stages of optical path selecting device alternately. 2. A variable optical delay circuit for adjusting the delay time of the incident signal light by changing the optical path length of the incident signal light with respect to one or a plurality of incident signal lights propagating in space. A means for injecting each of the signal lights into the circuit as a light beam having only one polarization plane of two polarization planes orthogonal to each other, and a means for passing each of the incident signal lights as they are or a polarization of the incident signal light. A polarization plane control element that can select whether to rotate the component by 90 degrees and output it by external control, and one of the two polarization components of the incident signal light that are orthogonal to each other is allowed to pass as it is and the other polarization component Is an optical path selection element that outputs the same optical path and the same direction as the polarization component that passes through the element as it is after passing the optical path length longer than the polarization component that passes through the element as it is. A variable optical delay circuit, characterized in that the polarization plane control element and the optical path selection element are alternately arranged in one or more stages.