JP3199189B2 - Variable optical delay circuit - Google Patents

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 that changes the optical path length of one or more optical signals propagating in a space incident on a circuit and adjusts the delay time of the optical signal.

[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 synchronization between signals and synchronizing clocks. Further, application to time slot conversion and signal demultiplexing circuits is also possible.

Focusing on the spatial parallelism of light, optical signal processing for performing various signal processing via spatially propagating light has been studied. As a variable optical delay circuit using spatially propagating light, a variable optical delay circuit using a movable mirror is conventionally known. FIG. 3 shows a conventional variable optical delay circuit using a movable mirror. Reference numeral 18 denotes a first reflecting mirror, 19 denotes a second reflecting mirror, 20 denotes a moving direction of the second reflecting mirror 19, and 21 denotes 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
Incident on The second reflection mirror 19 reflects the incident light beam 21 twice, and propagates an optical path parallel to and different from the incident light beam 21 in the opposite direction. Second reflection mirror 1
The output light beam of No. 9 has its optical path bent by 90 degrees again by the first reflection mirror 18 and is output. 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 the light passes through the circuit is t, the light beam incident on the circuit is output from the circuit. The delay time td before the operation 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 reflection mirror 19 in the movement direction 20 and changing the distance L between the first reflection mirror 18 and the second reflection mirror 19.

[0004]

Conventionally, in such a variable optical delay circuit, the adjustment of the delay time has been performed by moving the second reflection mirror 19 using a manual or mechanical method. Therefore, adjustment of the delay time requires a mechanism for moving the second reflection mirror 19 without displacement of the position and angle, and there has been a problem that the configuration of the apparatus becomes complicated. Further, when a plurality of light beams are incident on the variable optical delay circuit, it has been difficult to individually adjust the delay time of each light beam.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to provide a variable optical delay circuit capable of simplifying the device configuration and individually adjusting the delay time for a plurality of optical signals incident on the circuit. Is to do.

[0006]

In order to achieve the above-mentioned object, the present invention provides a method for changing the optical path length of one or a plurality of incident signal lights propagating in space by changing the optical path length of the incident signal light. A variable optical delay circuit for adjusting a delay time of light, a means for inputting each of the incident signal lights into the circuit as a light beam having only one of two polarization planes orthogonal to each other; A polarization plane control element that can select whether to pass each of the light as it is or to rotate the polarization component of the incident signal light by 90 degrees and output the same, and two polarization components of the incident signal light that are orthogonal to each other. One of the polarized light components is passed as it is, and the other polarized light component is reflected parallel to the incident signal light beam and traveling in the opposite direction to the optical path different from the incident signal light beam. It is constituted by a selection device, comprising side by side several stages multiple alternating polarization plane control element and the optical path selection element.

[0007]

According to the present invention, a plurality of polarization plane control elements and optical path selection elements are alternately arranged, and different optical path lengths, that is, by selecting which optical path selection element reflects a light beam using the polarization plane control elements. 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 polarizing beam splitter, 2 is a half-wave plate, and 3-1.
3-N are polarization plane control elements, 4-1 through 4-N are first polarization beam splitters constituting optical path selection elements, and 5-1 through 5-1.
5-N denotes a second polarizing beam splitter constituting an optical path selection element, 6 denotes a half-wave plate, 7, 8, and 9 denote polarization beam splitters, and 10 denotes an incident light beam having only an S-polarized component. I have.

The incident light beam 10 having only the S-polarized light component incident on the polarization beam splitter 1 is reflected by the polarization beam splitter 1, converted into P-polarized light by the half-wave plate 2, and converted into a polarization plane control element 3-1. Is incident on. The polarization plane control element 3-1 has a function of selecting whether to pass the incident light beam as it is or to rotate the polarization plane by 90 degrees by electrical control. 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
Pass as it is, and is incident on the next-stage polarization plane control element 3-2. 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 next-stage polarization beam splitter 4-1 and the second polarization beam splitter 5-1. Is reflected again by the polarization plane control element 3
-1 is incident in the opposite direction. In that case, the polarization plane control element 3-1 rotates the polarization plane of the light beam 10 again by 90 degrees,
Output as P-polarized light. The output P-polarized light beam 10
Is converted into S-polarized light by the half-wave plate 2, its optical path is rotated by 90 degrees by the polarization beam splitter 9, and output from the circuit. As described above, by alternately arranging the polarization path control elements and the optical path selection elements composed of two polarization beam splitters in a plurality of stages, and using the polarization plane control elements to select which optical path selection element reflects the light beam. Different optical path lengths or delay times can be imposed on the light beam.
In FIG. 1, the incident light beam 10 has a polarization beam splitter 4-.
2 shows a case where the light is reflected by an optical path selection element composed of 2 and 5-2 and output from a circuit. In the variable optical delay circuit of FIG. 1, the variable delay time takes a discrete value, and the number of variable delay times matches the number of optical path length adjustment circuits formed by the polarization plane control element and the optical path selection element. The variable delay time can be set arbitrarily according to the distance between the optical path length adjustment circuits.

As a polarization plane control element, there is a liquid crystal spatial light modulation element. Such a light modulation element is of a surface input / output type and can be easily arrayed. Thus, for example, 2
It is also possible to easily control the polarization planes of the individual light beams for the light beam array of the dimensional array individually and to set different delay times 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 mechanically movable part as compared with the optical path adjustment by a manual or mechanical method. High-speed and stable delay time adjustment is possible with a simple configuration. Further, when a plurality of light beams are 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,
-1 to 13-N are quarter-wave plates, 14-1 to 14-N are total reflection mirrors, 15-1 to 15-N are quarter-wave plates, 1
6-1 to 16-N represent a total reflection mirror, and 17 represents an incident light beam.

In FIG. 2, a pair of quarters facing each other are shown.
Wave plate and total reflection mirror (13-1, 14-1, 15-1)
And 16-1) function as a reflecting element having a function of reflecting an incident light beam and rotating its polarization plane by 90 degrees. This embodiment is significantly different from the first embodiment in that the optical path selection element is composed of a polarizing beam splitter and two of the above-mentioned reflecting elements disposed at positions facing each other across the polarizing beam splitter.

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 light, the light beam 17 passes through the polarization beam splitter 12-2 as it is and enters the next-stage polarization plane control element 11-3. On the other hand, 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 reflected by a quarter-wave plate 15-2 and a total reflection mirror 16-2. The light is again incident on the polarization beam splitter 12-2 via the element. At this time, the polarization plane of the light beam 17 that is again incident on the polarization beam splitter 12-2 has been rotated by 90 degrees by the reflection element, so that it passes through the polarization beam splitter 12-2 as it is, and
The light is incident on a reflection element composed of a four-wavelength plate 13-2 and a total reflection mirror 14-2. The light beam 17 incident on the reflection element receives the polarization rotation of 90 degrees and is incident again on the polarization beam splitter 12-2. This time, the light beam reflected on the polarization beam splitter 12-2 and incident on the optical path selection element is applied. 17 is output in the same optical path and in the same direction. As described above, the S-polarized beam input to the element can be delayed by making one reciprocation between the reflection elements disposed at positions facing each other 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 optical path selection elements and polarization plane control elements described above. In the variable optical delay circuit of this embodiment, the variable delay time takes a discrete value, and the number of delay times that can be adjusted is n, where n is the number of optical path length adjustment circuits composed of the polarization plane control element and the optical path selection element. ⁿ . Further, the amount of variable time can be arbitrarily set by changing the distance between two reflecting elements that face each other across the polarizing beam splitter in each optical path selection circuit. As described above, in this embodiment, in addition to the features of the first embodiment of the present invention, there is an advantage that the number of adjustable delay times can be greatly increased as compared with 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 is made different from the polarization plane control element and the optical path length. A plurality of optical path selection elements are connected alternately, and whether or not to impose a delay is selected by using a polarization plane control element.Therefore, there is no mechanical moving part compared to manual or mechanical method of optical path adjustment, and it is simple. With a simple configuration, high-speed and stable delay time adjustment can be realized. Furthermore, when a plurality of light beams are incident on the variable optical delay circuit, it is possible to easily change the delay time of each light beam individually.

[Brief description of the drawings]

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

FIG. 2 shows a second embodiment of the present invention.

FIG. 3 is a diagram showing a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Polarization beam splitter, 2 ... 1/2 wavelength plate, 3-1
... 3-N: polarization plane control element; 4-1 to 4-N: first polarization beam splitter constituting an optical path selection element;
5-N: a second polarization beam splitter constituting an optical path selection element; 6, a half-wave plate; 7, 8, 9 ... polarization beam splitters; 10 ... an incident light beam having only S-polarized light components, 11-1. ~ 11-N ... polarization plane control element array, 12
-1 to 12-N: polarizing beam splitter, 13-1 to 1
3-N: 1/4 wavelength plate, 14-1 to 14-N: Total reflection mirror, 15-1 to 15-N: 1/4 wavelength plate, 16-1:
16-N: total reflection mirror, 17: incident light beam, 18:
First reflection mirror, 19: second reflection mirror, 20: moving direction of the second reflection mirror, 21: incident light beam.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Takao Matsumoto 1-6, Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-4-128713 (JP, A) JP-A Heisei 3-48829 (JP, A) JP-A-2-7022 (JP, A) WO 91/14196 (WO, A1) Optics Letters, Vol. 16 No. 4 (February 15, 1991) pp. 255-257 (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/00-1/055 505 G02F 1/29-1/31 G02F 1/13-1/13363 H04Q 3/52-3 / 52 101 JICST file (JOIS)

Claims (1)

(57) [Claims] 1. A variable optical delay circuit for adjusting the delay time of one or a plurality of incident signal lights propagating in a space by changing an optical path length of the incident signal light. Means for injecting each of the signal lights into the circuit as a light beam having only one of two polarization planes orthogonal to each other; and allowing each of the incident signal lights to pass through as it is or the polarization of the incident signal light A polarization plane control element that can select whether to output the component by rotating it by 90 degrees by an external control, and let one of the two orthogonal polarization components of the incident signal light pass as it is, and pass the other polarization component Is constituted by an optical path selection element that reflects so as to travel in an opposite direction to an optical path that is parallel to the incident signal light beam and that is different from the incident signal light beam. Variable optical delay circuit which is characterized by comprising arranging several stages double the optical path selecting device alternately.