JPH0756118A - Optical variable delay line - Google Patents

Abstract

PURPOSE:To facilitate the size reduction of the optical variable delay line, which delays a light signal and can have its delay time varied and set and to adjust the delay time over a wide variation range with high precision and accuracy. CONSTITUTION:This delay line is equipped with an input/output separating means 50 which separates an input light signal and an output light signal and a birefringent plate 11 which makes a light signal, made incident through the input/output separating means 50, travel straight or obliquely according to its polarized light direction and projects it on the input/output separating means 50 finally. Further, the delay line is equipped with polarized light rotating and reflecting means 20 and 30 which are arranged on both the surfaces of the birefringent plate 11 and reflect a light signal traveling out of the top surface of the birefringent plate 11 to the inside and also rotate their planes of polarization by a specific angle to make the light signal straight and obliquely by turns in the birefringent plate and a reflecting means 40 which moves together with the polarized light rotating and reflecting means 20 and 30 and reflect the light signal traveling out of the top surface of the birefringent plate 11 to the inside and send the light signal, traveling straight or obliquely in the birefringent plate 11, to the same optical path.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical delay line capable of variably setting a delay time in an optical delay line for delaying an optical signal.

[0002]

2. Description of the Related Art In an electric circuit for processing a high speed signal, a variable delay line for adjusting a propagation delay time of a signal is used in order to adjust a phase between different signals. In the case of processing a high-speed optical signal also in an optical circuit, a similar variable optical delay line for adjusting the propagation delay time between signals is required.

In order to adjust the propagation delay time of an optical signal, it is necessary to directly or indirectly change the optical path length, which is the length of the optical path through which the optical signal propagates. For example, when an optical fiber is used as a transmission medium, a direct method is to switch optical fibers having different lengths with an optical switch to change the delay amount. Further, as an indirect method, there is a method in which a mechanical, electromagnetic, thermal, or other external force is applied to the optical fiber to change the propagation constant of the optical fiber to adjust the delay amount.

[0004]

However, since it is not easy to adjust the length of the optical fiber with an accuracy of a centimeter or less by the direct method, it is possible to obtain a delay with high accuracy and high accuracy of about several tens of picoseconds. I couldn't adjust the time. further,
The optical switch used in combination with the optical fiber has a limit in terms of downsizing because the switching mechanism which is available at the present time and has high stability and low loss is limited to the mechanical type.

On the other hand, in the indirect method, since the rate of change of the propagation constant with respect to the external force of the optical fiber is small, it is possible to adjust the delay time with high accuracy of picoseconds or less, but conversely, a time of the order of several hundred picoseconds is required. It was difficult to adjust the delay time in the area.

The present invention is easy to miniaturize, has high accuracy,
An object of the present invention is to provide an optical variable delay line capable of adjusting a delay time with high accuracy and a wide variable range.

[0007]

According to a first aspect of the present invention, in an optical variable delay line for adjusting a propagation delay time of an optical signal, an input / output separating means for separating an input optical signal and an output optical signal, and an input / output separating means are provided. The birefringent plate is arranged on both sides of the birefringent plate and the birefringent plate which makes the optical signal incident through the output separating means go straight or skew according to the polarization direction and finally emits to the input / output separating means. Polarization rotation reflection means for reflecting an optical signal going out from the surface of the inside toward the inside, rotating its polarization plane by a predetermined angle and alternately going straight and obliquely inside the birefringent plate, and polarization rotation reflection. And a reflecting means for moving an optical signal traveling from the surface of the birefringent plate toward the outside and reflecting the optical signal toward the inside thereof, and for returning an optical signal traveling straight or obliquely through the birefringent plate to the same optical path.

According to a second aspect of the invention, in the variable optical delay line according to the first aspect, there is provided a plurality of polarization control elements capable of individually controlling the polarization rotation characteristics, and the polarization rotation reflection means and the reflection means. This is a configuration in which the polarization control element that functions as is arbitrarily set.

According to a third aspect of the present invention, in the variable optical delay line according to the first or second aspect, an optical signal is separated into two polarization components orthogonal to each other and is incident on a birefringent plate, and each polarization component is polarized. An optical path length adjusting means for adjusting the delay amount of the light returning from the optical path divided for each component and multiplexing the light is provided.

According to a fourth aspect of the present invention, in an optical variable delay line that adjusts the propagation delay time of an optical signal, the incident optical signal is made to go straight or oblique according to its polarization direction.
The two birefringent plates and the two birefringent plates, which are integrated, are arranged on both sides to reflect an optical signal from the surface of the birefringent plate to the outside toward the inside and to set its polarization plane to a predetermined value. And a polarized light rotating / reflecting means for rotating the birefringent plate alternately to advance straight and obliquely, and a polarization plane of an optical signal passing at a predetermined position, which is arranged between the two birefringent plates, by a predetermined angle. And a polarization control element for rotating.

According to a fifth aspect of the present invention, in the variable optical delay line according to any one of the first to fourth aspects, the light entering and exiting is collected on the optical path of at least one surface of the birefringent plate. Place a illuminating lens.

[0012]

First, the function of the birefringent plate which is a basic constituent element of the variable optical delay line of the present invention will be described with reference to FIG.

In FIG. 21, a light beam vertically incident on the birefringent plate 11 goes straight or obliquely through the birefringent plate according to its polarization direction (or polarization plane). For example,
As shown in (1), the input light 1 having an electric field oscillation direction perpendicular to the paper surface goes straight through the birefringent plate 11 as an ordinary ray (a ray that follows the law of refraction). Further, as shown in (2), the input light 1 having an electric field oscillation direction parallel to the paper surface and the plane of incidence of the birefringent plate passes through the birefringent plate 11 as an extraordinary ray (a ray that does not follow the law of refraction). It runs obliquely along the axis 15. Therefore, by controlling the polarization direction of the light beam incident on the birefringent plate 11, the optical path in the birefringent plate 11 can be selected to be either straight or oblique. When the light beam incident on the birefringent plate 11 is elliptically polarized light having both polarization components or the like, light in each polarization direction travels by separating each optical path.

Next, with reference to FIG. 22, a light transmission mechanism by the birefringent plate and the polarization rotation reflection means will be described. In FIG. 22, by providing polarization rotation reflecting means 20 and 30 for reflecting light and rotating the polarization plane by 90 degrees on both sides of the birefringent plate 11, the light incident from one end of the birefringent plate 11 can be placed at any place. It is possible to realize a light transmission mechanism that guides light to.

(1) shows the case where the linearly polarized input light 1 which becomes an ordinary ray in the birefringent plate 11 enters from the point A of the birefringent plate 11. The input light 1 goes straight through the birefringent plate 11 and reaches point B on the other surface. Then, the light is reflected by the polarization rotation reflection means 20 and returned to the inside of the birefringent plate 11, and at the same time, the polarization plane is rotated by 90 degrees and converted into an extraordinary ray. as a result,
The light obliquely travels in the birefringent plate 11 and reaches the point C. In the figure, for convenience, the optical path of the ordinary ray is shown by a solid line, and the optical path of the extraordinary ray is shown by a broken line. Next, the light is reflected by the polarization rotating / reflecting means 30 and returned to the inside of the birefringent plate 11, and at the same time, the plane of polarization is rotated by 90 degrees, and becomes an ordinary ray again. As a result, the light goes straight through the birefringent plate 11 toward the point D. In the same manner, the light travels to the right of the paper while being sequentially reflected on both sides of the birefringent plate 11, and finally exits from the birefringent plate 11 as the output light 2 from point E where there is no polarization rotation reflection means. To be done. In this way, a mechanism for transmitting light from the point A to the point E can be realized.

(2) shows the case where the linearly polarized input light 1 which becomes an extraordinary ray in the birefringent plate 11 enters from the point A of the birefringent plate 11. Point a, point b, point c, point d, point e correspond to point A, point B, point C, point D, and point E, respectively. That is, only by changing the order of the ordinary ray and the extraordinary ray, the light sequentially proceeds on the left side of the paper while being reflected by both surfaces of the birefringent plate 11, and finally the output light 2 from the point e where there is no polarization rotation reflection means. Is emitted as.

Next, the basic principle of the variable optical delay line of the present invention constructed by using the above basic components will be described. FIG. 1 shows a basic configuration of the variable optical delay line according to claim 1 or 2. In the light transmission mechanism including the birefringent plate 11 and the polarization rotation reflection means 20 and 30, the reflection means 40 that reflects the polarization plane to the predetermined position of the birefringence plate 11 without rotating the polarization plane (at the rotation angle of the polarization plane of 0 degree). Is arranged and the position of the reflection means 40 is moved to change the delay amount. The reflection means 40 may be one that reflects the rotation angle of the polarization plane at an integral multiple of 180 degrees.

(1) shows the case where the linearly polarized input light 1, which becomes an ordinary ray in the birefringent plate 11, enters from the point A of the birefringent plate 11. The input light 1 is reflected while sequentially rotating the plane of polarization at points B, C, and D of the polarized light rotating / reflecting means 20, 30 and reaches the point E as an extraordinary ray. If the reflection means 40 is arranged at this E point, the extraordinary ray is reflected,
The optical path is the same as that before reflection and goes in the opposite direction to return to point D. Similarly, at points D, C, and B, the polarization plane is sequentially rotated and reflected, and the output light 2 is emitted from point A to the outside of the birefringent plate 11. The input / output separating means 50 separates the input light 1 and the output light 2. In this way, by arranging the reflection means 40 at the point E, the point E becomes the turning point of light. In addition,
Even if the reflecting means 40 is arranged at another position, it becomes a turning point of light.

By the way, the delay time of the output light 2 with respect to the input light 1 is determined by the optical path length up to the reflecting means 40 which is the turning point of the light. Therefore, the delay time is discretely changed by moving the position of the reflecting means 40. Can be changed.
For example, the reflection means 4 is provided at the point E and at the point D.
In the case where 0 is arranged and the light is turned back at the point D, the time required for the light to travel back and forth between D and E is the difference in delay time.

(2) shows the case where the linearly polarized input light 1 which becomes an extraordinary ray in the birefringent plate 11 enters from the point a of the birefringent plate 11. Point a, point b, point c, point d, point e correspond to point A, point B, point C, point D, and point E, respectively. The point e at which the reflection means 40 is arranged is different from the case (1) in that it is reflected as an ordinary ray.

FIG. 2 shows a basic configuration of an optical variable delay line that does not depend on the polarization state of the input light 1 in the optical variable delay line according to claim 1 or 2. That is, the input light 1
Corresponds to elliptically polarized light having both polarization components and other cases.

This basic configuration is a combination of the variable optical delay lines corresponding to the respective polarization directions shown in FIGS. 1 (1) and 1 (2). A
When the input light 1 is made incident on the birefringent plate 11 from the point (a), the light of each polarization component is divided into right and left and proceeds. here,
For example, if the reflecting means 40 is arranged at the points E and e, the light is turned back at the points E and e, returns to the point A, and is combined and emitted as the output light 2. The input / output separation unit 50 is configured to receive the input light 1
And the output light 2 are separated. Since the optical path lengths to the reflecting means 40 at the points E and e are the same, there is no problem even if they are combined as they are. By moving the position of the reflection means 40 symmetrically, the delay time can be discretely changed without depending on the polarization state of the input light 1.

However, for example, when the reflecting means 40 is arranged at the points D and d, ABCD and abc are provided.
The optical path lengths of -d are different. This is due to the difference in the number of light that goes straight and light that travels obliquely. Therefore, the light returning to the point A has a different delay time for each polarization direction,
The output light 2 cannot be combined as it is.

Therefore, when the reflecting means 40 is arranged on the side opposite to the incident position of the input light 1 (on the side of the polarization rotation reflecting means 20), the phase of the light that has been separated and returned in each polarization direction is adjusted. Need to combine. That is, a means for adjusting the optical path length is required. The basic configuration corresponding to claim 3 is shown in FIG.

The means for adjusting the optical path length is composed of a birefringent plate 61 having the same thickness as the birefringent plate 11 and a ½ wavelength plate 62 for rotating the polarization plane of light by 90 ° and passing it. The input light 1 is incident on the point α of the birefringent plate 61, and is divided into an extraordinary ray that obliquely travels and an ordinary ray that travels straight according to two orthogonal polarization components. Furthermore, with the half-wave plate 62,
The polarization plane is rotated by 90 degrees, and is incident on the birefringent plate 11 from points A and a, respectively. Here, for example, if the reflecting means 40 is arranged at the points D and d, the light in each polarization direction is D
The process returns to the points A and a at the points d and d. Then, due to the rotation of the plane of polarization of 90 degrees by the half-wave plate 62, the light returning to the point A in the birefringent plate 61 skews, the light returning to the point a goes straight, and at the point α. The light is combined and emitted as output light 2. At this time, the optical path lengths corresponding to the respective polarization directions match. The input / output separation unit 50 is configured to receive the input light 1
And the output light 2 are separated.

As described above, even if the reflection means 40 is arranged on the side opposite to the incident position of the input light 1 (on the side of the polarization rotation reflection means 20), the optical path length by the birefringence plate 61 and the half-wave plate 62 is adjusted. By using this means, it is possible to realize an optical variable delay line that does not depend on the polarization state of the input light 1.

FIG. 4 shows the basic configuration of the variable optical delay line according to the fourth aspect. A polarization rotation means 70 for rotating the polarization plane of light by 90 degrees and passing it is sandwiched between a part of the two birefringence plates 11 and 12, and the light is reflected on the outer surfaces of the birefringence plates 11 and 12 and polarized. Polarization rotation reflection means 20 and 30 for rotating the surface by 90 degrees
And a mechanism for changing the amount of delay by moving the position of the polarization rotation means 70.

(1) shows the case where the linearly polarized input light 1 which becomes an ordinary ray in the birefringent plate 12 enters from the point A of the birefringent plate 12. The input light 1 goes straight in the birefringent plate 12, and further goes straight from the point P in the birefringent plate 11 to reach the point B. Then, the light is reflected by the polarization rotation reflection means 20 and returned to the inside of the birefringent plate 11, and at the same time, the polarization plane is rotated by 90 degrees,
Converted to extraordinary rays. As a result, the light obliquely travels in the birefringent plate 11, and further obliquely travels in the birefringent plate 12 from the point Q.
Reach the point. Next, the light is reflected by the polarization rotating / reflecting means 30 and returned to the inside of the birefringent plate 12, and at the same time, the plane of polarization is rotated by 90 degrees and becomes an ordinary ray again. As a result, the light travels straight in the birefringent plate 12 and the polarization rotation means 70 arranged at the point R.
Is incident on and is converted into an extraordinary ray by the rotation of the plane of polarization of 90 degrees. Therefore, the light that has passed through the polarization rotation means 70 obliquely travels inside the birefringent plate 11 and reaches the point D. Similarly, at points D, C, and b, the polarization plane is sequentially rotated and reflected, and the output light 2 is emitted from the point a to the outside of the birefringent plate 12.

(2) shows the case where the linearly polarized input light 1 which becomes an extraordinary ray in the birefringent plate 12 enters from the point A of the birefringent plate 12. The input light 1 obliquely travels in the birefringent plate 12, and further travels straight in the birefringent plate 11 from the point p to reach the point d.
Then, the light is reflected by the polarization rotation reflection means 20 and returned to the inside of the birefringent plate 11, and at the same time, the light is rotated by 90 degrees on the plane of polarization and converted into an ordinary ray. As a result, the light is reflected by the birefringent plate 11.
Go straight inside, and from point q, go straight inside the birefringent plate 12 to reach point c. Next, the light is reflected by the polarization rotation reflecting means 30 and returned to the inside of the birefringent plate 12, and at the same time, the plane of polarization is rotated by 90 degrees, and again becomes an extraordinary ray. As a result, the light travels straight in the birefringent plate 12, enters the polarization rotating means 70 arranged at the point r, is rotated by 90 degrees of the plane of polarization, and is converted into an ordinary ray. Therefore, the light that has passed through the polarization rotation means 70 travels straight in the birefringent plate 11 and reaches point f. Similarly, the light is reflected while being sequentially rotated by the polarization planes at the points f, a, and b, and is emitted from the point C as the output light 2 to the outside of the birefringent plate 12.

In this way, the polarization rotation means 70 is applied to the R and r points.
By arranging, the R and r points become the turnaround points of light, and the position determines the delay time. In addition, other P, p
Even if the polarization rotation means 70 is arranged at a point, a point Q, a point q, or another position, it becomes a light turning point, and the delay time can be discretely changed according to the position.

The feature of this structure is that the optical paths of the forward path and the return path are different. Therefore, the input / output separating means for separating the input light 1 and the output light 2 is unnecessary. Also,
By removing the polarized light rotating and reflecting means 20 from the position of the point b, the point b can be used as the emission point of the output light 2.

FIG. 5 shows a basic configuration of the variable optical delay line that does not depend on the polarization state of the input light 1 in the variable optical delay line according to the fourth aspect. This is a combination of the variable optical delay lines corresponding to the respective polarization directions shown in FIGS. 4 (1) and 4 (2). When the input light 1 is made incident on the birefringent plate 12 from the point A, the light of each polarization component is divided into right and left and proceeds. here,
For example, if the polarization rotating means 70 is arranged at the R point and the r point, the light is turned back at the R point and the r point, reaches the b point, is combined, and is emitted as the output light 2. In addition, A → P → B → Q → E
→ R → D → Q → C → P → b optical path length and A → p → d → q
Since the optical path lengths of → c → r → f → q → a → p → b are the same, there is no problem even if they are combined as they are. By shifting the position of the polarization rotating means 70 symmetrically, the input light 1
It is possible to discretely change the delay time without depending on the polarization state of.

By the way, when the optical variable delay line is constructed by the above-described method, the delay time of the optical signal (the required time from the point A to the point A, the point α and the point α) is returned. (Required time from the point A to the point b) is the reciprocal optical path length to the turning point, the birefringent plates 11, 12, 61, the polarization rotation reflection means 20, 30,
It is determined by the propagation speed of each light in the reflection means 40, the half-wave plate 62, and the polarization rotation means 70. When the delay time is variable, the delay steps are mainly the birefringent plates 11, 12,
It depends on the thickness of 61. Therefore, the birefringent plate 1
By reducing the thickness of 1, 12, 61, the delay step can be shortened to the order of several picoseconds to tens of picoseconds. Furthermore, by increasing the lateral length (or area) of the birefringent plates 11 and 12 and increasing the number of delay steps, it is possible to extend the variable range from several tens of picoseconds to several hundreds of picoseconds or more. . Further, since it is easy to set the processing accuracy and the assembly accuracy of the birefringent plate and other optical parts to several tens of micrometers or less, it is possible to easily obtain the setting accuracy of the delay time of picoseconds or less.

[0034]

EXAMPLE FIG. 6 shows an example configuration of the variable optical delay line according to the first aspect. The present embodiment corresponds to the basic configuration shown in FIG. 1, and first, the correspondence relationship between the respective parts will be described. The input light 1, the output light 2, and the birefringent plate 11 correspond as they are. The quarter-wave plate 21 and the reflection film 22 correspond to the polarization rotation reflection means 20, and the quarter-wave plate 31 and the reflection film 3 are provided.
Reference numeral 2 corresponds to the polarization rotation reflection means 30. The isotropic transparent medium 41 and the reflecting film 22 correspond to the reflecting means 40. The quarter-wave plate 21, the reflection film 22, and the isotropic transparent medium 41 are integrally movable in the left-right direction. The polarization beam splitter 51 and the Faraday rotator 52 correspond to the input / output separating means 50.

Reference numerals A to H denote light incident and exit points on the surface of the birefringent plate 11, and reference numerals B'to H'represent light reflection points on the reflection films 22 and 32. X is the incident point of the input light 1, and Y is the outgoing point of the output light 2. The optical path 81 shown by a solid line is an optical path of an ordinary ray, and the optical path 82 shown by a broken line is an optical path of an extraordinary ray.
A solid arrow 83 indicates a forward light propagation direction in the birefringent plate 11, and a broken arrow 84 indicates a backward light propagation direction in the birefringent plate 11.

The functions of the polarization beam splitter 51 and the Faraday rotator 52 will be described with reference to FIG. 6 (2). The p-polarized input light 1 passes through the polarization beam splitter 51 and enters the Faraday rotator 52. The light is incident on the birefringent plate 11 with its plane of polarization rotated by 45 degrees by the Faraday rotator 52. Therefore, at point A of the birefringent plate 11, the plane of polarization of the incident light is in the direction perpendicular to the plane of the paper, and goes straight through the birefringent plate 11 as an ordinary ray.

On the other hand, the light emitted from the point A passes through the Faraday rotator 52 and enters the polarization beam splitter 51. The emitted light at point A is an ordinary ray and has a plane of polarization perpendicular to the plane of the paper, so that the plane of polarization is changed by the Faraday rotator 52.
By rotating it by 45 degrees, it becomes s-polarized light having a polarization plane rotated by 90 degrees with respect to the input light 1. This s-polarized output light 2
Is reflected by the reflection surface of the polarization beam splitter 51 and is separated from the input light 1.

Next, the path of the light incident on the point A of the birefringent plate 11 will be described. Incident light (ordinary ray) travels straight through the birefringent plate 11 to reach point B, and is further passed through the quarter-wave plate 2
1 and then reflected at the point B ′ of the reflection film 22 and again 1/4.
It passes through the wave plate 21 and returns to point B. At this time, the light is 1 /
Since it reciprocates through the four-wave plate 21, its plane of polarization rotates 90 degrees. As a result, the ordinary ray is converted into an extraordinary ray, and the light incident on the birefringent plate 11 obliquely travels inside the birefringent plate 11 and reaches the point C. At point C, the quarter wave plate 31 and the reflection film 3
At 2, the plane of polarization is rotated by 90 degrees and is reflected, then becomes an ordinary ray again. As a result, the light goes straight through the birefringent plate 11 toward the point D. Similarly, the light travels zigzag in the order of D → E → F → G → H while alternating the two states of the ordinary ray and the extraordinary ray by rotating the planes of polarization 90 degrees on both sides of the birefringent plate 11. To do.

The ordinary ray reaching the point H passes through the isotropic transparent medium 41, is reflected at the point H ′ of the reflection film 22, passes through the isotropic transparent medium 41 again, and returns to the point H. At this time, the plane of polarization of the light does not rotate, so that the ordinary light enters the birefringent plate 11 again from the point H. As a result, the light goes straight through the birefringent plate 11 and returns to the point G. Similarly, light is G → F → E →
It proceeds from D → C → B, returns to point A, and is emitted as an ordinary ray. Therefore, the light reciprocates with the reflection point H ′ of the reflection film 22 as the turning point.

Now, the optical signal is the polarization beam splitter 51.
The time required from the point X to the point Y to be emitted from the point Y is defined as the delay time t of the delay line. In order to change the delay time t, the isotropic transparent medium 41 located at the turning point may be moved along the surface of the birefringent plate 11. As a result, the optical path length between X and Y changes, and the delay time changes. The amount of change in the delay time at this time is discrete with the round-trip propagation time between the reflection films 22 and 32 as a unit. For example, when the isotropic transparent medium 41 is moved to the position of point D, the turning point of light becomes the reflection point D'of the reflection film 22, and the delay time becomes shorter by the round-trip propagation time between D'-H '. .

Here, the delay time t is the propagation time of X → A → Y is t ₀ , the propagation time of A → B ′ → A is t ₁ , and it is between two adjacent points (for example, between B ′ and D ′). The round-trip propagation time (unit delay time) is Δt, and the number of delay steps when the point B is the origin (for example, 2 at point F) is n, then t = t ₀ + t ₁ + Δt × n (1) be able to. The unit delay time Δt mainly depends on the thickness of the birefringent plate 11. Now, as the birefringent plate 11, a calcite having a thickness of 5 mm is used, and the quarter-wave plates 21 and 3 are used.
When a crystal having a thickness of 100 μm is used as 1, the unit delay time Δt is about 100 picoseconds.

Further, the birefringent plate 11 in the present embodiment is not limited to calcite and may be any material having the same birefringence and satisfying the necessary conditions. 1/4 wave plate 2
The materials 1, 31 are not limited to quartz, and any material that can serve as a wave plate may be used as long as it satisfies the necessary conditions. Reflective film 22,
As 32, a metal thin film or a dielectric multilayer film that is usually used in optical components can be used. As the polarization beam splitter 51 and the Faraday rotator 52, those generally used as optical components can be used. The Faraday rotator 52 is a magneto-optical rotator,
In reality, a magnet that gives a magnetic field parallel to the optical path is required, but it is omitted in the figure for simplicity.

FIG. 7 shows the configuration of a first embodiment of the variable optical delay line according to the second aspect. In the embodiment shown in FIG. 6, 1 /
The four-wave plate 21, the reflection film 22, and the isotropic transparent medium 41 are integrally moved in the left-right direction to change the delay time. In the present embodiment, instead of the quarter-wave plate 21 and the isotropic transparent medium 41, a plurality of polarization control elements 23 capable of individually controlling polarization rotation characteristics are arranged in an array, and each polarization control element 23 It is characterized by controlling the state. Therefore, the plurality of polarization control elements 2 arrayed
3 and the reflection film 22 correspond to the polarization rotation reflection means 20 and the reflection means 40. Other configurations are similar to those of the embodiment shown in FIG.

Here, referring to FIG. 8, the polarization control element 23
The configuration and function of will be described. Polarization control element 23
Is a structure in which the liquid crystal 24 and the spacer 25 are sandwiched by the transparent electrode 26 and the isotropic transparent medium 27 as shown in (1). Further, as shown in (2), if a reflective film 28 is inserted between the liquid crystal 24 and one transparent electrode 26, the reflective film 22
Is a substitute for. That is, the polarization control element 23 shown in (2)
In the case of using, the reflection film 22 is not necessary as the polarized light rotating / reflecting means 20 and the reflecting means 40. The reflective film 2
The electrode paired with 8 may be a normal electrode, and both functions can be shared by using a metal film or the like.

In such a liquid crystal cell (for example, a twisted nematic (TN) liquid crystal cell), the birefringence of the liquid crystal 24 changes depending on the voltage and polarity applied to the transparent electrode 26.
Therefore, by designing the thickness of the liquid crystal layer, it can function as a quarter-wave plate for the applied voltage V ₁ and can be made equivalent to an isotropic transparent medium for the applied voltage V ₂ . . That is, when the light incident on the polarization control element 23 travels back and forth through the liquid crystal 24, the polarization plane is rotated by 90 degrees when the applied voltage is V ₁ , and the polarization plane is not rotated when the applied voltage is V _2. To be done. It should be noted that as a material replacing the liquid crystal 24, for example, a dielectric crystal, PLZT or other transparent ceramics may be used.

A plurality of such polarization control elements 23 are arranged, and the applied voltage of the polarization control element 23 at the position (point H in the present embodiment) which is the light turning point is controlled to V ₂ and other polarization control is performed. By controlling the applied voltage of the element 23 to V ₁ ,
An optical variable delay line similar to that of the embodiment shown in FIG. 6 can be realized.

Further, 1 arranged on the lower surface of the birefringent plate 11
Also for the / 4 wavelength plate 31, by changing the same polarization control elements 23 arranged in an array, the turning point of light can be set on either side of the birefringent plate 11. FIG. 9 shows a configuration example thereof (a second embodiment of the variable optical delay line according to claim 2). In this example,
The turning point of light is set to point G, and the polarization control element 3 at that position is set.
The applied voltage of 3 is controlled to V ₂ , and the other polarization control elements 23,
The applied voltage of 33 is controlled to V ₁ .

As described above, by setting the turning point of light on the lower surface of the birefringent plate 11, it is possible to construct an optical variable delay line which does not depend on the polarization state of the input light 1 as shown in FIG. Details will be described later as a third embodiment.

Further, by setting a light turning point on the upper surface or the lower surface of the birefringent plate 11, the delay step can be halved. That is, the unit delay time Δt is determined by the unit delay time Δt between two adjacent points (for example, B ′ in the above embodiment).
Although the round trip propagation time is between -D ', the round trip propagation time is between two opposing points (for example, between B'and C') in this embodiment. In the figure, since the separation angle between the optical path where the ordinary ray travels straight and the optical path where the extraordinary ray travels is emphasized, the optical path length between B'-C 'and C'-D' is emphasized. The difference is increasing. However, actually, even if calcite having the largest separation angle of about 6 degrees is used as the birefringent plate 11,
The difference is less than 1%. Therefore, the delay steps are halved almost equally.

FIG. 10 shows the configuration of a third embodiment of the variable optical delay line according to the second aspect. This embodiment corresponds to the basic configuration shown in FIG. 2 and is an embodiment of the variable optical delay line that does not depend on the polarization state of the input light 1. That is, it can be applied to linearly polarized light in any direction, elliptically polarized light, non-polarized light, and light whose polarization state changes.

The path of the light incident on the point A of the birefringent plate 11 will be described. In the present embodiment, the light turning point is set to G and g, the applied voltage of the polarization control element 33 at that position is controlled to V ₂ , and the applied voltage of the other polarization control elements 23 and 33 is V _1. To control. Birefringent plate 1 from point A (a)
When the input light 1 is incident on 1, the light of each polarization component is split left and right and proceeds. That is, the ordinary ray is A → B ′ →
C '→ D' → E '→ F' → G '→ F' → E '→ D' →
Fold back as C '→ B' → A. Extraordinary ray is a → b ′ → c ′
→ d '→ e' → f '→ g' → f '→ e' → d '→ c' →
Turn back b '→ a. Here, since the round-trip optical path lengths to the G point and the g point are the same, it is possible to perform the multiplexing as it is at the A (a) point. By controlling the applied voltage of the polarization control element 33 at the position where the light turns back to V ₂ and the applied voltage of the other polarization control elements 23 and 33 to V ₁ , the delay corresponding to the turning point is delayed. An optically variable delay line of time can be realized.

Further, the input / output separating means 5 used in this embodiment
0 is required to have no polarization dependence, and for example, a half mirror can be used. However, in that case, a theoretical loss of 3 dB occurs. To prevent such a loss, a known circulator circuit shown in FIG. 11 may be used.

Input light 1 having an arbitrary plane of polarization, which is incident on the circulator circuit from point X, is split into two polarization components (p-polarized light and s-polarized light) orthogonal to each other by a polarization beam splitter 51 ₁ and polarized independently. It passes through a Faraday rotator 52 that rotates the surface by 45 degrees and a half-wave plate 55.
Here, the polarization planes of the respective polarization components are rotated together by 90 degrees, the p-polarization component is converted into s-polarization, and the s-polarization component is converted into p-polarization. These lights are returned to the polarization beam splitter 51 again.
_They are combined at ₂ , and are incident on point A of the birefringent plate 11. Incidentally, 56 ₁ and 56 ₂ are right-angle prisms.

On the other hand, the light emitted from the point A of the birefringent plate 11 and having an arbitrary polarization plane is polarized beam splitter 51 ₁
Are separated into two polarization components (p-polarized light and s-polarized light) orthogonal to each other, and are independently passed through a ½ wavelength plate 55 and a Faraday rotator 52 that rotate the polarization plane by 45 degrees. At this time, in the Faraday rotator 52, the polarization plane rotates 45 degrees in the same direction as the forward path with respect to the traveling direction, but the half-wave plate 55
Then, the polarization plane rotates 45 degrees in the direction opposite to the forward direction with respect to the traveling direction. Therefore, the polarization rotation is canceled by passing through the half-wave plate 55 and the Faraday rotator 52, and as a result, the p-polarized component remains as p-polarized light and the s-polarized component remains as s-polarized light by the polarization beam splitter 51 ₁ . It is waved and emitted as output light 2 from point Y. In the figure, the polarization components of the return path are denoted by p'and s' to distinguish them from the outward path.

FIG. 12 shows the configuration of the first embodiment of the variable optical delay line according to the third aspect. The present embodiment is an embodiment of the variable optical delay line that does not depend on the polarization state of the input light 1, but the light turning point is set on the upper surface of the birefringent plate 11 (in this embodiment, H point and h point). Corresponding to the case.

In this embodiment, the input light 1 that has passed through the input / output separating means 50 has a birefringent plate 61 having the same thickness as the birefringent plate 11.
And a half-wave plate 62 that rotates the polarization plane by 90 degrees and passes it.
The light is made incident on the points A and a of the birefringent plate 11 via and. The input light 1 having an arbitrary plane of polarization incident on the point α of the birefringent plate 61 is divided into an extraordinary ray that obliquely travels and an ordinary ray that travels straight according to two orthogonal polarization components. Further, each of the half-wave plates 62 is rotated by 90 degrees in the plane of polarization, so that the extraordinary ray is converted into an ordinary ray and is incident on the birefringent plate 11 from the point A, and the ordinary ray is converted into an extraordinary ray. The light enters the birefringent plate 11 from the point a. Similarly, the light traveling to the H point and the h point is turned back to A
Go back to point and point a. The ordinary and extraordinary rays emitted from points A and a are 90
The ordinary ray becomes an extraordinary ray by the rotation of the plane of polarization, and the extraordinary ray becomes an ordinary ray and is incident on the birefringent plate 61. Therefore, in the birefringent plate 61, the light returning to the point A skews, the light returning to the point a goes straight, is combined at the point α, and is incident on the input / output separating means 50. A known circulator circuit shown in FIG. 11 can be used as the input / output separating means 50.

As described above, by interposing the birefringent plate 61 and the half-wave plate 62, the optical path length of X-A-B and the optical path length of X-a-b can be made equal, and an ordinary ray and an abnormal ray can be obtained. The delay times for the rays can be matched. In addition,
Other configurations and functions of the variable optical delay line are similar to those of the above-described embodiment.

In the structure of this embodiment, the birefringent plate 61 is used.
The optical path of A to H and the optical path of a to h can be overlapped with each other in the depth direction by rotating the direction of 90 degrees about the vertical direction as an axis.

FIG. 13 shows the configuration of the second embodiment of the variable optical delay line according to the third aspect. The feature of this embodiment is that FIG.
The configuration of the input / output separating means 50 in the first embodiment shown in is changed. The configuration and operation of the input / output separating means 50 used in this embodiment will be described below with reference to FIG. In addition, in FIG. 14, (1) is a plan view,
(2) is a front view and (3) is a side view.

[0060] Input light 1 with arbitrary polarization plane incident from point X, is separated into p-polarized light by the birefringent plate 57 ₁ (ordinary ray) and s-polarized light (extraordinary ray), with respect to the birefringent plate 57 ₁ And is incident on the birefringent plate 57 ₂ arranged at a right angle. Therefore, in the birefringent plate 57 ₂ , the p-polarized light obliquely travels as an extraordinary ray and the s-polarized light travels straight as an ordinary ray. The p-polarized light is converted into s-polarized light by rotating the plane of polarization by 90 degrees at the wave plate portion (hatched portion) of the split 1/2 wave plate 58 ₁ . Further, the s-polarized light passes through the isotropic transparent medium (the portion without hatching) of the split half-wave plate 58 ₁ as it is as the s-polarized light.
Both s-polarized light pass through the Faraday rotator 52 via the polarization beam splitters 51 ₁ and 51 ₂ , and their polarization planes are
It becomes s'polarized light rotated by 45 degrees. Furthermore, both s 'polarized light is incident on split half-wave plate 58 _2, one wavelength plate portion polarization plane through the (hatched portion) is rotated 90 degrees, p where the p-polarized light is rotated 45 degrees' It becomes polarized light and is emitted from point W. The other passes through the isotropic transparent medium (portion without hatching) and is emitted from point V as it is as s'-polarized light. The p'-polarized light and the s'-polarized light emitted from the point W and the point V are oblique and straight as an extraordinary ray and an ordinary ray in the birefringent plate 61, respectively.

On the other hand, the light having the respective polarization planes emitted from the point W and the point V of the birefringent plate 61 is divided into half-wave plates 58 ₂
Incident on s ', the s'-polarized light passes through as it is, and the p'-polarized light is s'.
It is polarized into polarized light, passes through and is incident on the Faraday rotator 52. In the Faraday rotator 52, the respective polarization planes are rotated by 45 degrees, so that they both become p-polarized light and pass through the polarization beam splitter 51 ₂ . Furthermore, these are divided into 1/2
The light passes through the wave plate 58 _3, is combined through the birefringent plates 57 ₂ and 57 _1, and is emitted from the point Y as the output light 2.

FIG. 15 shows the configuration of the first embodiment of the variable optical delay line according to the fourth aspect. The present embodiment corresponds to the basic configuration shown in FIG. 4, and first, the correspondence relationship between the respective parts will be described. Input light 1, output light 2, birefringent plates 11, 12
Corresponds as it is. Quarter wave plate 21 and reflective film 2
Reference numeral 2 corresponds to the polarization rotating / reflecting means 20, and a quarter wavelength plate 31
The reflection film 32 corresponds to the polarization rotation reflection means 30.
A plurality of polarization control elements 71 arranged in an array between the birefringent plates 11 and 12 correspond to the polarization rotating means 70. An isotropic transparent medium 72 is arranged at one end thereof.

A to G, a and b are incident and outgoing points of light on the surfaces of the birefringent plates 11 and 12, B'to G 'and b'are reflected points of light on the reflecting films 22 and 32, and P. Symbols S to S are points of entry and exit of light to and from the polarization control element 71. X is the incident point of the input light 1, and Y is the outgoing point of the output light 2. Optical path 8 shown by the solid line
Reference numeral 1 is an optical path of an ordinary ray, and optical path 82 shown by a broken line is an optical path of an extraordinary ray.

Here, referring to FIG. 16, the polarization control element 7
The configuration and function of No. 1 will be described. Polarization control element 7
1 has a structure in which the liquid crystal 73 and the spacer 74 are sandwiched between a transparent electrode 75 and an isotropic transparent medium 76. Such a liquid crystal cell (eg, TN (twisted nematic) liquid crystal cell, super TN liquid crystal cell, ferroelectric liquid crystal cell) is
The birefringence of the liquid crystal 73 changes depending on the voltage and polarity applied to the transparent electrode 75. Therefore, by designing the thickness of the liquid crystal layer, _{1 is} applied to the applied voltage V ₁ (voltage zero).
It can function as a 1/2 wave plate and can be made equivalent to an isotropic transparent medium with respect to the applied voltage V ₂ (AC voltage of about several volts). That is, in the light passing through the polarization control element 71, the polarization plane rotates 90 degrees when the applied voltage is V ₁ , and the polarization plane does not rotate when the applied voltage is V ₂ . As a material replacing the liquid crystal 73, for example, a dielectric crystal, PLZT or other transparent ceramics may be used.

A plurality of such polarization control elements 71 are arranged, the applied voltage of the polarization control element 71 at the position where the light is turned back is controlled to V ₁ , and the applied voltage of the other polarization control elements 71 is V _2. To control. The isotropic transparent medium 72 is for allowing light to pass through without changing the polarization state, and in addition to the isotropic transparent material such as glass, the polarization control element 71.
The voltage V ₂ may be constantly applied to. Hereinafter, the path of light incident on the point X (A) of the birefringent plate 12 will be described. The voltage applied to the polarization control element 71 at the point S is V ₁
And the voltage applied to the other polarization control element 71 is V ₂ .
The incident light (ordinary ray) travels straight in the birefringent plate 12 and passes through the polarization control element 71 at the point P, then further travels straight in the birefringent plate 11 and enters the quarter-wave plate 21 from the point B. . The quarter-wave plate 21 and the reflection film 22 constitute the polarization rotating / reflecting means 20 as in the embodiment shown in FIG. 6, and the incident light is reflected by rotating the polarization plane by 90 degrees. As a result, the ordinary ray is converted into an extraordinary ray, and the light incident on the birefringent plate 12 obliquely travels through the birefringent plate 11 and passes through the polarization control element 71 at the point Q.
Further, the light passes obliquely through the birefringent plate 12 and enters the quarter-wave plate 31 from the point C. The quarter-wave plate 31 and the reflection film 32 also constitute the polarization rotating / reflecting means 30 in the same manner as the embodiment shown in FIG. 6, and the incident light is reflected with its polarization plane rotated by 90 degrees, and again the ordinary ray. become. As a result, the light goes straight through the birefringent plate 12 toward the point R. In the same manner, the light is reflected by the birefringent plate 1
The polarization planes are rotated by 90 degrees on both surfaces of 1 and 12, and the two states of ordinary ray and extraordinary ray are alternately taken, and the process proceeds as R → F ′ → S.

The extraordinary ray reaching point S has its polarization plane rotated 90 degrees by the polarization control element 71 at point S, which functions as a half-wave plate. Therefore, the light that has passed through the polarization control element 71 at the point S travels straight inside the birefringent plate 12 toward the point G. Therefore, after that, R → D ′ → Q → C ′ → P → b ′
→ p → a, and the light is emitted from point Y. Therefore, the light is reflected by the polarization control element 71 at the point S.

Now, in order to change the delay time from when the optical signal enters the point X to when it exits the point Y, the applied voltage of the polarization control element 71 at the turning point is set to V ₁
It only has to function as a two-wave plate. This allows XY
The optical path length between them changes, and the delay time changes. The delay time t is given by equation (1). However, t ₀ is 0, t ₁ is the propagation time of A → P → b ′ → p → a (Y), and the unit delay time Δt is the round-trip time between adjacent polarization control elements (for example, between P and Q). (P-> B '->Q->C'-> P), and the delay step number n has the origin at the point P (for example, 3 at the point S).

The point b can be set as the emission point Y of the output light 2 by removing the quarter-wave plate 21 and the reflection film 22 from the point b. In that case, in the equation (1), t ₁ is the propagation time of A → P → b (Y).

FIG. 17 shows the configuration of the second embodiment of the variable optical delay line according to the fourth aspect. This embodiment corresponds to the basic configuration shown in FIG. 5 and is an embodiment of an optical variable delay line that does not depend on the polarization state of the input light 1. In this embodiment, the S point, s
The voltage applied to the polarization control element 71 at that point is V ₁ , the voltage applied to the other polarization control element 71 is V ₂ , and the points S and s are turn points.

When the input light 1 is made incident on the birefringent plate 12 from the point X (A), the lights of the respective polarization components are divided into left and right and proceed, and as described above, they are folded back at the points S and s to b.
The light reaches the point (Y), is combined, and is emitted as output light 2. In addition, A-P-B-Q-E-R-D-Q-C-P-
b optical path length and Ap-d-q-c-r-f-q-a-
The optical path length of p-b is the same. By moving the position of the polarization control element 71 serving as the turning point symmetrically, the delay time can be discretely changed without depending on the polarization state of the input light 1.

FIG. 18 shows the configuration of the third embodiment of the variable optical delay line according to the fourth aspect. In the figure, (1) is a front view, (2) is a bottom view, and (3) is a side view. A feature of this embodiment is that the optical variable delay line shown in FIG. 17 has a sufficient thickness in the depth direction to realize an optical variable delay line having a plurality of inputs and outputs. As shown in the figure, the optical path is spatially parallel to a plurality (8 channels) of input light 1.

By extending the polarization control element 71 by the number of channels in the depth direction, it is possible to construct a parallel type optical variable delay line that gives the same amount of delay time to each channel. Further, by arranging the polarization control elements 71 in a two-dimensional array and controlling each independently, it is possible to configure a parallel optical variable delay line in which a different delay time can be set for each channel. Also, in each of the configurations of the above-described embodiments, by arranging a plurality of channels in the depth direction,
A similar parallel variable optical delay line can be constructed.

FIG. 19 shows the configuration of an embodiment of the variable optical delay line according to the fifth aspect. Although the present embodiment is applied to the variable optical delay line shown in FIG. 17, it can be similarly applied to the configurations of the above-described embodiments.

The feature of this embodiment is that the lens 9 for suppressing the spread of the light beam is provided on the upper and lower surfaces of the birefringent plates 11 and 12.
1 are arranged in an array. In the above-described embodiments, the light beam is assumed as the input light 1. However, when the dimension of the polarization control element 71 is reduced in order to reduce the delay time step, the diameter of the light beam also decreases, and the spread of the light beam due to the diffraction phenomenon cannot be ignored. The spread of the light beam increases the loss and causes crosstalk to the adjacent polarization control element. In the case of a delay line, this crosstalk means that an optical signal having an unnecessary delay time is superimposed on an optical signal having an originally necessary delay time. Therefore, as shown in this embodiment, it is necessary to use the lens 91 to suppress the spread of the light beam.

The function of the optical variable delay line of this embodiment is as follows.
It is exactly the same as described above. Therefore, here, only the function of the lens 91 will be described with reference to FIG. The lens 91 is arranged at a position corresponding to the position of each polarization control element 71. The input light 1 can be regarded almost as a point light source like the light emitted from the single mode optical fiber, and is converted into a light beam 92 by the lens 91 at the X point. After that, the light beam 92 is condensed by the facing lens 91, forms a spot on the reflection films 22 and 32 and is reflected at the same time, and becomes a light beam again and propagates through the birefringent plate.
In this way, by propagating the light beam 92 while repeating the condensing by the lens 91, it is possible to suppress the spread of the light beam due to diffraction as compared with the case where the lens 91 is not provided. As a result, the interval between the polarization control elements 71 can be narrowed and the delay time step can be shortened.

In this embodiment, the lens 91 is 1
It may be arranged between the quarter wave plates 21 and 31 and the reflection films 22 and 32. In that case, a gap or a spacer may be inserted to adjust the gap between the reflection films 22 and 32 and the lens 91. Further, in the present embodiment, the array-shaped lenses 91 are arranged on both sides, but when the spread of the light beam is not remarkable, they may be arranged on only one side or appropriately thinned out.

[0077]

As described above, according to the present invention, the size of the delay line can be easily reduced as compared with the delay line using the optical fiber, and the delay time can be adjusted with high accuracy and high accuracy and in a wide variable range. In addition, the variable optical delay line that does not depend on the polarization state of the input light can be easily configured.

Further, the optical variable delay line can be easily parallelized. That is, it is possible to provide a configuration in which the same amount of delay is collectively applied to each channel or a configuration in which the delay time is independently set for each channel, and it is possible to realize a compact and high-density optical variable delay line. .

Furthermore, the unit delay time (delay step) is achieved by suppressing the spread of the light beam in the variable optical delay line.
Can be shortened, the total delay time can be extended, and crosstalk and loss can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of an optical variable delay line according to claim 1 or 2.

FIG. 2 is a diagram showing a basic configuration of an optical variable delay line that does not depend on a polarization state of input light 1 in the optical variable delay line according to claim 1 or 2.

FIG. 3 is a diagram showing a basic configuration of the variable optical delay line according to claim 3;

FIG. 4 is a diagram showing a basic configuration of the variable optical delay line according to claim 4;

5 is a diagram showing a basic configuration of an optical variable delay line that does not depend on a polarization state of input light 1 in the optical variable delay line according to claim 4. FIG.

FIG. 6 is a diagram showing the configuration of an embodiment of the variable optical delay line according to claim 1;

FIG. 7 is a diagram showing a configuration of a first embodiment of the variable optical delay line according to claim 2;

FIG. 8 is a diagram showing a configuration of a polarization control element 23.

FIG. 9 is a diagram showing a configuration of a second embodiment of the variable optical delay line according to claim 2;

FIG. 10 is a diagram showing the configuration of a third embodiment of the variable optical delay line according to claim 2;

FIG. 11 is a diagram showing a configuration of a known circulator circuit used as an input / output separating means 50.

FIG. 12 is a diagram showing a configuration of a first embodiment of the variable optical delay line according to claim 3;

FIG. 13 is a diagram showing the configuration of a second embodiment of the variable optical delay line according to claim 3;

FIG. 14 is a diagram showing another configuration of the input / output separating means 50.

FIG. 15 is a diagram showing a configuration of a first embodiment of the variable optical delay line according to claim 4;

16 is a diagram showing the configuration of a polarization control element 71. FIG.

FIG. 17 is a diagram showing the configuration of a second embodiment of the variable optical delay line according to claim 4;

FIG. 18 is a diagram showing the configuration of a third embodiment of the variable optical delay line according to claim 4;

FIG. 19 is a diagram showing a configuration of an embodiment of the variable optical delay line according to claim 5;

FIG. 20 is a diagram illustrating the function of the lens 91 in the variable optical delay line according to claim 5;

FIG. 21 is a view for explaining the function of a birefringent plate which is a basic constituent element of the variable optical delay line of the present invention.

FIG. 22 is a view for explaining a light transmission mechanism by a birefringent plate and a polarization rotation reflection means.

[Explanation of symbols]

 11, 12, 61 Birefringent plate 20, 30 Polarization rotation reflection means 21, 31 1/4 wavelength plate 22, 32 Reflection film 23, 33 Polarization control element 40 Reflection means 41 Isotropic transparent medium 50 Input / output separation means 51 Polarization Beam splitter 52 Faraday rotator 62 1/2 wavelength plate 70 Polarization rotating means 71 Polarization control element

Claims (5)

[Claims] 1. An optical variable delay line for adjusting a propagation delay time of an optical signal, wherein an input / output separating means for separating an input optical signal and an output optical signal, and an optical signal incident through the input / output separating means are provided. A birefringent plate that goes straight or obliquely according to the polarization direction and is finally output to the input / output separating unit, and an optical signal that is arranged on both sides of the birefringent plate and goes out from the surface of the birefringent plate. A polarization rotation reflection means for reflecting the light toward the inside and rotating the polarization plane by a predetermined angle alternately to advance straight and obliquely in the birefringence plate, and to move together with the polarization rotation reflection means, An optical variable device comprising: a reflecting means for reflecting an optical signal going outward from the surface of the refracting plate toward the inside thereof, and returning an optical signal traveling straight or obliquely through the birefringent plate to the same optical path. Delay line. 2. The variable optical delay line according to claim 1, further comprising a plurality of polarization control elements capable of individually controlling polarization rotation characteristics, and a polarization control element functioning as a polarization rotation reflection means and a reflection means. An optical variable delay line, which is configured to be set arbitrarily. 3. The variable optical delay line according to claim 1 or 2, wherein an optical signal is separated into two polarization components orthogonal to each other and is incident on a birefringent plate, and an optical path separated for each polarization component is formed. An optical variable delay line comprising an optical path length adjusting means for adjusting a delay amount of light that has returned and combining them. 4. An optical variable delay line for adjusting the propagation delay time of an optical signal, comprising two birefringent plates for advancing or skewing an incident optical signal according to its polarization direction, and the two birefringent plates. The birefringent plate is arranged on both sides of the birefringent plate when integrated, reflects an optical signal going outward from the surface of the birefringent plate toward the inside, and rotates its polarization plane by a predetermined angle. A polarization rotation reflection means for alternately going straight and obliquely inside, and a polarization control element arranged between the two birefringent plates for rotating a polarization plane of an optical signal passing at a predetermined position by a predetermined angle. A variable optical delay line characterized in that 5. The variable optical delay line according to any one of claims 1 to 4, wherein a lens that collects incoming and outgoing light is arranged on the optical path of at least one surface of the birefringent plate. Optical variable delay line characterized by.