JP3043908B2 - Optical path conversion element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical path changing element used for a multi-terminal optical switch having a function of changing the order of the optical paths of a plurality of light beams propagating in space.

[0002]

2. Description of the Related Art The path of a light beam arranged in a two-dimensional array is controlled by using a function of switching the plane of polarization of the light beam by a liquid crystal spatial light modulator and a function of converting a light path of a birefringent material. Techniques for realizing switches are known.
FIG. 1 shows an example of the above technology in a document (Yamaguchi et al., "Prototype of Multi-stage Beam-Shift Type Multi-terminal Optical Switch", Proceedings of the 1992 IEICE Spring Conference, SC-3-8). The basic structure of a multistage beam-shift type optical concentrator switch is shown. In FIG. 1A, reference numerals 11-1 to 11-7 denote polarization control element arrays using liquid crystal, in which the horizontal and vertical polarization components of incident light are exchanged with each other (cross).
It has the function of controlling each cell independently, either in a state of not being exchanged (through). 12-1 to 12
-3 is a birefringent crystal, which allows the horizontal polarization component of the incident light to pass as it is as an ordinary ray, and the vertical polarization component as an extraordinary ray spatially by the cell interval of the liquid crystal spatial modulators 11-1 to 11-7. It has the function of shifting down. 13-1
Reference numerals 13-3 denote birefringent crystals similar to 12-1 to 12-3 rotated by 90 ° about the incident direction of light. The vertical polarization component of the incident light is passed as ordinary light, and the horizontal polarization component is transmitted. Has a function of spatially shifting an extraordinary ray to the near side in the figure by the cell interval of the polarization control element arrays 11-1 to 11-7. The arrows of the optical path conversion elements at each stage in the drawing indicate the directions in which the beams passing through the elements are focused.

FIG. 1B shows birefringent crystals 12-1 to 12-3 and 13.
It shows paths of ordinary rays and extraordinary rays passing through -1 to 13-3. The solid line in the figure indicates the path of the ordinary ray, and the broken line indicates the path of the extraordinary ray. The ordinary ray component of the light beam emitted from each cell of the liquid crystal spatial modulator passes without being shifted, and the extraordinary ray component is shifted by the cell interval of the liquid crystal spatial modulator and emitted from the adjacent cell. It is emitted from the same position as the ordinary ray component.

A horizontally polarized collimated light beam incident from the left side of FIG. 1A is transmitted to the birefringent crystal 12 immediately after the cell of the polarization control element array 11-1 passing therethrough is in a through state. The beam reaches the polarization control element array 11-2 at the next stage without being subjected to the beam shift by -1. When the passing polarization control element array 11-1 cell is in a cross state, the polarization control element array 11-1 is converted into vertically polarized light, and is subjected to a beam shift by the immediately following birefringent crystal 12-1. The next lower cell of 2 is reached. The light beam that has become vertically polarized by the polarization control element array 11-2 is immediately followed by the birefringent crystal 13-.
The beam reaches the next-stage polarization control element array 11-3 at the same position without receiving the beam shift by 1. On the other hand, the horizontally polarized light beam undergoes a beam shift by the immediately following birefringent crystal 13-1, and the next stage polarization control element array 11-3
Is shifted to the adjacent cell in front of. By such control of the polarization plane and the shift of the position, the incident light beam is sequentially converged on the cell below the switch.

[0005] The birefringent crystal used for shifting the light beam in the above-mentioned optical switch has the property that the time required for propagation in the crystal is usually different between an ordinary ray and an extraordinary ray. Here, the propagation time of the ordinary ray and the extraordinary ray passing through the uniaxial crystal in the crystal is

(Equation 4) It is. Here, τ ₀ and τ _e are the propagation times of the ordinary ray and the extraordinary ray in the crystal, t is the thickness of the crystal, and c is the speed of light in vacuum. Also, n ₀ and _ne are the refractive index of light whose vibration direction of the electric field is perpendicular to the principal axis, the principal axis direction, and θ, respectively.
Is the angle between the plane of incidence of the crystal and the main axis of the crystal. As is apparent from this equation, the n _0> n always becomes τ _0> τ _e For _e, n ₀ <n always τ ₀ <τ _e to _e. For Here, calcite typically used for beam shift of the optical switch is a uniaxial crystal, an n _0> n _e. Therefore, in this switch, a light beam that has been subjected to a beam shift in each stage more frequently has a shorter propagation time in the switch than a light beam that has not been subjected to the beam shift. For this reason, a phase difference occurs in the optical signal passing through the switch due to the passing path in the switch. At this time, if the optical signal passing through the switch has a high bit rate and the signals are synchronized with each other, the phase is out of synchronization due to the above-described phase, which adversely affects the transmission characteristics.

FIG. 2 shows another example of an optical switch using the above-mentioned technique, which is described in a literature (Noguchi et al., "Arrangeable multichannel free-space optical switch based on a multistage network configuration." space optical
switch based on multistage network configuratio
n) ", IEEE J. Lightwave Tec
h.), 9, p. 1726), the structure of a multi-stage optical switch is schematically shown. In FIG.
1 to 21-9 are polarization control element arrays using liquid crystal,
It has a function of independently controlling each cell in a state where the horizontal polarization component and the vertical polarization component of the incident light are exchanged with each other (cross) or in a state where they are not exchanged (through). 22-1, 22-2, 23-1, 23-2, 24-1,
Reference numerals 24-2, 25-1, and 25-2 denote polarization routing elements, each of which has a function of shifting one polarization component of a light beam propagating in the same optical path and exchanging these optical paths, and a shift amount of the light beam. The size and the installation direction are different depending on the shift direction.

Each polarization control element array in FIG. 2 corresponds to an array of 2 × 2 switches, and the polarization routing element corresponds to a connection network connecting the switch arrays. A polarization multiplexed optical signal in which the horizontal polarization component and the vertical polarization component are independently modulated enters each cell of the first-stage polarization control element array 21-1. These are spatially separated by the polarization routing element 22-1, and paths are independently set by the respective polarization control element arrays at the subsequent stage. Then, the polarization control signal is finally emitted as a horizontal or vertical polarization component of the polarization multiplexed signal from a target cell of the polarization control element array 21-9 at the final stage.

FIG. 3 shows the structure of a polarization routing element formed by using a birefringent crystal. Fig. 3 (a)-
(d) are the routing elements 22-1 and 22-2 of FIG.
-2, 23-1, 23-2, 24-1, 24-2, 25-1, 25-
2 shows the structure of FIG. In FIG. 3, reference numeral 31 indicates the incident position of the light beam. 32 indicates a birefringent crystal, and the direction of the arrow indicates the shift direction of the extraordinary ray. Reference numeral 33 denotes a polarization plane exchange element, which has a function of exchanging a horizontal polarization component and a vertical polarization component of a passing light beam. Reference numeral 34 denotes an optically isotropic transparent plate having the same shape and refractive index as the polarization plane exchange element 33. As is clear from FIG.
(c) is obtained by rotating (a) by 90 ° about the light incident direction, and (d) is obtained by rotating (b) by 90 ° about the light incident direction.

FIG. 4 shows a path of a light beam propagating through the routing element shown in FIG. In FIG. 4, the solid line indicates the path of the ordinary ray, and the broken line indicates the path of the extraordinary ray. (a) shows the route of (a) and (c) in FIG. 3, and (b) shows the route of (b) and (d) in FIG.
In (a), the shift amount of the extraordinary ray due to the birefringent crystal is equal to the interval between adjacent light beams, and the widths of the polarization plane exchange element and the transparent plate are also equal to the interval between adjacent light beams. Therefore, in (a),
The extraordinary ray on the upper side and the ordinary ray on the lower side of the light beam train adjacent to each other are exchanged. On the other hand, in (b), the amount of shift of the extraordinary ray due to the birefringent crystal is twice the interval between adjacent light beams, and the width of the polarization plane exchange element and the transparent plate is also equal to twice the interval between adjacent light beams. For this reason, in (b), the extraordinary rays of the upper two light beam rows and the ordinary rays of the lower two light beam rows are exchanged while maintaining the spatial positional relationship.

[0010]

By the way, as is apparent from FIG. 4, the distance of the light beam passing through the routing element depends on the incident position and the polarization plane, and the distance that the light beam passes as an ordinary ray and the distance that passes as an extraordinary ray are mutually different. Is different. Therefore, when calcite is used as the birefringent crystal, the switch shown in FIG. 2 has a different propagation time for each incident light beam. For this reason, as in the case of the above-mentioned multi-stage beam shift type optical switch, when the optical signal passing through the switch has a high bit rate and the signals are synchronized, the synchronization is shifted and adversely affects the transmission characteristics. It will be.

In the optical switch shown in FIG. 2, the horizontal polarization component and the vertical polarization component incident on the same cell of the first-stage polarization control element array 21-1 are always changed to the last-stage polarization control element array.
If the paths of the horizontal polarization component and the vertical polarization component emitted from the same cell 21-9 are set so as to be both, the present switch can be applied even when the polarization state of the incident light is indefinite. . However, in this case, even if it is not necessary to synchronize the incident optical signals, if the propagation times of the horizontal polarization component and the vertical polarization component emitted from the same cell in the switch do not match, the propagation of the two components is not performed. Since the time difference becomes the jitter of this signal, it has an adverse effect on high bit rate signal transmission. Therefore, it is necessary to always make the propagation times of these two coincide.

[0012]

SUMMARY OF THE INVENTION The present invention compensates for a propagation time difference between an ordinary ray and an extraordinary ray inherent in the present element for an optical path conversion element that shifts an extraordinary ray using a birefringent crystal. And the resulting phase shift of the optical signal,
Alternatively, the object is to solve the problem of jitter.

The optical path conversion element of the present invention has a first transparent medium having birefringence, the same shape and material as the first transparent medium, and the magnitude of the position shift of the extraordinary ray with respect to the ordinary ray. Is disposed between the second transparent medium and a second transparent medium which is arranged so as to be equal to that of the first transparent medium and the shift direction is opposite to that of the first transparent medium. Converting an ordinary ray emitted from the first transparent medium into an extraordinary ray incident on the second transparent medium, and converting the extraordinary ray emitted from the first transparent medium into the second extraordinary ray.
Is characterized by a polarization plane exchange element that converts an ordinary ray incident on a transparent medium.

[0014] The optical path conversion element of the present invention is characterized in that the polarization plane switching element is constituted by a half-wave plate.

[0015] The optical path conversion element of the present invention is characterized in that the polarization plane exchange element is constituted by an optical rotator for rotating the polarization plane of the passing linearly polarized light by 90 °.

The optical path-changing element of the present invention comprises the first and second
Wherein the transparent medium is composed of calcite or rutile crystals.

An optical path-changing element according to the present invention comprises a first transparent medium having birefringence, the first transparent medium having birefringence, and a magnitude of an ordinary ray refractive index and an extraordinary ray refractive index. The first transparent medium has a refractive index of n ₀₁ , n _e1 , which is a direction in which the vibration direction of the electric field of the first transparent medium is perpendicular to the principal axis, and a direction of the principal axis, respectively. The angle between the plane and the principal axis of the crystal is θ ₁ , the direction of oscillation of the electric field of the second transparent medium is perpendicular to the principal axis, and the refractive indices of light in the principal axis direction are n ₀₂ and _{ne 2} , respectively. When the angle with the main axis is θ ₂ , the thickness t of the first transparent medium is
_{Between 1} and the thickness t ₂ of the second transparent medium.

(Equation 5) The first and second transparent media are arranged so that the following relationship is established.

The optical path-changing element of the present invention comprises the first transparent element.
Angle θ between the plane of incidence of the medium and the principal axis of the crystal ₁But

(Equation 6) The relationship is satisfied.

The optical path-changing element of the present invention is characterized in that the second transparent
Angle θ between the plane of incidence of the medium and the principal axis of the crystal _TwoBut,

(Equation 7) The relationship is satisfied.

The optical path-changing element of the present invention comprises the first and second
Is characterized in that one of the transparent media is composed of calcite.

The optical path-changing element of the present invention comprises the first and second
Is characterized in that one of the transparent media is composed of a rutile crystal.

In the optical path-changing element of the present invention, the first and second optical path-changing elements, in which the magnitude of the shift of the extraordinary ray is equal to each other and the directions thereof are opposite to each other, are arranged in series.
A first optical path conversion element having a width between the first and second optical path conversion elements, the width being equal to an integral multiple of the magnitude of the shift of the extraordinary ray by the first and second optical path conversion elements; Is converted into an extraordinary ray incident on the second optical path conversion element, and an extraordinary ray exiting from the first optical path conversion element is converted into an ordinary ray incident on the second optical path conversion element. A polarizing plane exchange element, and an optically isotropic transparent medium having the same width as the polarization plane exchange element and having the same refractive index as the polarization plane conversion element, alternately in the width direction. It is characterized by being laminated.

The present invention is clearly different from the prior art in that the structure of a birefringent crystal having a structure for compensating for a propagation time difference between an ordinary ray and an extraordinary ray, which has not been studied in the past, is clarified. .

Embodiments of the present invention will be described in detail with reference to the drawings.

[0025]

FIG. 5 shows a first embodiment of the present invention. (a)
Shows the structure of the device according to this embodiment, and (b) shows the path of light passing through the device. In FIG. 5, 51-1 and 51-2
Is a birefringent crystal, and the birefringent crystals 51-1 and 51-2 have the same material and shape, and the shift directions of extraordinary rays are opposite to each other. Reference numeral 52 denotes a polarization plane exchange element, which has a function of exchanging a horizontal polarization component and a vertical polarization component of a passing light beam. Examples of the element having the function of the polarization plane exchange element include a half-wave plate in which the main axis is rotated by 45 ° with respect to the shift direction of the extraordinary ray of the birefringent crystal, or a rotator having an optical rotation angle of 90 °.

As is apparent from FIG. 5, the ordinary ray incident on the present element travels straight through the first birefringent crystal 51-1 and is converted into an extraordinary ray by the polarization plane exchange element 52, and then the second birefringent crystal 51-1. The light is shifted upward by the refraction crystal 51-2 and exits the element. On the other hand, the extraordinary ray incident on this element is shifted downward by the first birefringent crystal 51-1.
After being converted into an ordinary ray by the first birefringent crystal 51-
1 and go out of the device. Each birefringent crystal 51−
Assuming that the shift amount of the extraordinary ray of 1, 51-2 is d, the light beam incident as the ordinary ray shifts upward by d, and the light beam incident as the extraordinary ray shifts downward by d. Therefore, both will receive a relative 2d shift. On the other hand, both light beams pass one of the birefringent crystals 51-1 and 51-2 as an ordinary ray and the other as an extraordinary ray. Therefore, the propagation times required for both light beams to pass through the present element are equal to each other. Therefore, the present element passes both of them with the same propagation time, while maintaining the element's original function of separating and splitting incoming horizontal polarized light and vertical polarized light in parallel.

FIG. 6 shows an example of the configuration of a multi-stage beam shift type optical concentrator switch using the optical path changing element of FIG. In FIG. 6, reference numerals 61-1 to 61-7 denote polarization control element arrays using liquid crystal. Reference numerals 62-1 to 62-3 denote optical path conversion elements shown in FIG.
The vertical polarization component is spatially shifted upward by half of the cell interval of 61-1 to 61-7, and the vertical polarization component is shifted to the liquid crystal spatial modulators 61-1 to 61-7.
Spatially downward by half the cell spacing of 63−
Reference numerals 1 to 63-3 denote rotations of the birefringent crystal similar to those of 62-1 to 62-3 by 90 degrees around the incident direction of the light, and convert the vertical light component of the incident light into liquid crystal spatial modulators 61-1 to 61-1. The horizontal polarization component is spatially shifted by half of the cell interval of the polarization control element arrays 61-1 to 61-7 spatially in the figure by half of the cell interval of −7. Shifts toward the front of. The arrows of the optical path conversion elements at each stage in the drawing indicate the directions in which the beams passing through the elements are focused.

In this configuration, since the propagation time of each optical path conversion element is the same regardless of the polarization state of the incident light, there is no phase difference between the light beams passing through the switch. Therefore, this switch can output these optical signals while maintaining the synchronization of the optical signals. In this configuration, since the optical path conversion elements 62-1 to 62-3 and 63-1 to 63-3 shift both polarization components together, the liquid crystal spatial modulators 61-1 to 6-3 compensate for the shift. 2 to 61-7 are provided with respect to the liquid crystal spatial modulators 61-1 to 61-6 in the preceding stage, by 1 / the cell interval.
It is shifted upward or backward by two. Further, each of the optical path conversion elements 62-1 to 62-3 and 63-1 to 63-3 is
In order to exchange the horizontal and vertical polarization components passing through,
In order to obtain a switch operation equivalent to the case of FIG.
It is necessary to reverse the control of the through state and the cross state of each cell of each of the liquid crystal spatial modulators 61-2 to 61-7 with respect to the case of FIG.

FIG. 7 shows an example in which a routing element having a function equivalent to that shown in FIG. 3 is formed by using the optical path conversion element according to the first embodiment. In FIG.
(a) and (b) correspond to the elements of (a) and (b) in FIG. 3, respectively. Elements equivalent to (c) and (d) in FIG. 3 are (a)
, (B) can be obtained by rotating the element by 90 °. In FIG. 7, reference numeral 71 denotes an incident position of the light beam.
72-1, 72-2, 73-1 and 73-2 indicate birefringent crystals,
The direction of the arrow indicates the shift direction of the extraordinary ray. 74−
Reference numeral 1742 denotes a polarization plane exchange element, which has a function of exchanging a horizontal polarization component and a vertical polarization component of a passing light beam. Numeral 75 denotes a polarization plane exchange element, whose function is the same as that of the polarization plane exchange element 74, but the shape thereof is different. Reference numeral 76 denotes an optically isotropic transparent plate having the same shape and refractive index as the polarization plane exchange element 75. In the configuration of FIG. 7, the birefringent crystals 72-1 and 73-1 and the polarization plane switching element 74-1 constitute an optical path conversion element according to the first embodiment, and the birefringent crystals 72-2 and 73-1. -2 and the polarization plane exchange element 74-2,
Another optical path conversion element according to the first embodiment is constituted. That is, the present configuration is such that, between the two optical path conversion elements according to the first embodiment, a polarization plane exchange element 75 having a width that is an integral multiple of the magnitude of the shift of the extraordinary ray of the optical path conversion element, In this embodiment, optically isotropic transparent plates 76 having the same shape and refractive index are alternately laminated.

FIG. 8 shows the path of the light beam passing through the routing element of FIG. Solid lines in the figure indicate ordinary rays,
Dashed lines indicate extraordinary rays. (A) and (b) of FIG. 8 correspond to the elements of (a) and (b) of FIG. 7, respectively. As is apparent from FIG. 8, these elements have the same routing function as the elements shown in FIG. Further, in FIG. 7, the portions constituting the optical path conversion element according to the first embodiment all pass incident light having any polarization direction with the same propagation time. Therefore, the routing element of FIG. 7 functions as a routing element having no difference in propagation time, and if this routing element is applied to the multi-stage optical switch shown in FIG. , The propagation times through the switches can be made equal to each other, and switching can be performed while maintaining the synchronization of these optical signals.

In order to apply the multistage network type optical switch of FIG. 2 to incident light of asynchronous arbitrary polarization, the horizontal polarization component and the vertical polarization component of the optical signal separated by the first-stage routing element as described above are used. May be combined by the final-stage routing element and emitted from the same optical path. However, at this time, it is necessary that the propagation times of the two coincide with each other. In the example of FIG. 2, one of the two separated optical signals enters the upper two-stage cell of the next-stage polarization control element array, and the other enters the lower two-stage cell. Here, the intermediate part between the first and last routing elements of the present switch has exactly the same structure in the upper two parts and the lower two parts of the polarization control element array. Therefore, if each polarization control element array is set so that the above separated signal passes through the same path in the upper two stages and the lower two stages, even if a conventional device is used as a routing element, The propagation times of the two at the intermediate portion can be made equal to each other. Accordingly, if the propagation times of the first and last routing elements are made equal to each other, the propagation times in both switches can be made equal to each other. In other words, in this case, the routing element according to the present invention shown in FIG. 7 is used for the first and last stage routing elements, and the conventional routing elements are used for the other routing elements. Thus, an optical switch that does not generate signal jitter can be configured.

FIG. 9 shows a second embodiment of the present invention.
(a) shows the structure of the device based on the example, and (b) shows the device
The paths of the passing ordinary and extraordinary rays are indicated by solid and broken lines, respectively.
Indicated by In FIG. 9, reference numeral 91 denotes a refractive index n₀> N_econnection of
For example, there is calcite. Also, 92
Refractive index is n₀<N_eA uniaxial crystal in the relationship
There are rutile crystals. Here, n of the birefringent crystal 91₀, N_e
To n₀₁, N_e1, Thickness t₁, Connected to the entrance surface of the crystal
Angle θ with the crystal main axis₁And n of the birefringent crystal 92 ₀, N
_eTo n₀₂, N_e2, Thickness t_Two, With the entrance surface of the crystal
The angle with the crystal main axis is θ_TwoAnd the optical path conversion element of FIG.
Propagation time of ordinary and extraordinary rays passing through₀, Τ '_e
Are as follows.

(Equation 8) Here, c is the speed of light in a vacuum. From the above equation, in order to make the propagation times of the ordinary ray and the extraordinary ray equal, the ratio of the thicknesses t ₁ and t ₂ of the birefringent crystals 91 and 92 is determined.

(Equation 9) It is only necessary to satisfy the relationship. Generally, the shift amount d of the extraordinary ray due to the birefringent crystal is

(Equation 10) At the maximum, then

[Equation 11] Becomes

Accordingly, the extraordinary ray shift d 'of the element of this embodiment when the extraordinary ray shift of the birefringent crystals 91 and 92 is maximized is expressed by the following equation.

(Equation 12) The condition of the crystal thickness for equalizing the propagation times of the ordinary ray and the extraordinary ray is as follows.

(Equation 13) Becomes

Using the above two equations, the birefringent crystals 91 and 92
By obtaining the thickness, the desired extraordinary ray shift
Optical path change without propagation time difference between ordinary ray and extraordinary ray
A replacement element can be designed. Here, as an example,
Calcite (n₀= 1.658, n_e= 1.486)
Using a rutile crystal (n₀= 2.616, n _e
= 2.903) to design an element with an extraordinary ray shift of 1 mm
An example is shown below. In this case, minimize the extraordinary ray shift amount.
Θ to be large is θ₁= 48.1 °, θ_Two= 42.0 °
You. Here, when the coefficient of the above equation is calculated,

[Equation 14] Is obtained. When the thickness of the birefringent crystal is determined from these values, t ₁ = 5.92 mm and t ₂ = 3.36 mm.

In this embodiment, the birefringent crystal 91 has n ₀ >
In n _e, but birefringent crystal 92 showed a case is n ₀ <n _e, it is obvious that the optical path conversion element having the same function be switched to the both are realized. That is, the present invention does not particularly limit the arrangement order of the birefringent crystals. Further, the present embodiment has shown the case where the birefringent crystals 91 and 92 are uniaxial crystals.
If two of the principal refractive indices are close,
Assuming that the average of two approaches is n ₀ and the other is n _e , it can be regarded as approximately a uniaxial crystal and analyzed using the above equation. As an example, saltpeter (major direction refractive index n
₁ = 1.5064, n ₂ = 1.5056, n ₃ = 1.3346)
_{n 0 = (n 1 + n} 2) /2=1.5060,n e = n 3 = 1.33
As 46, it can be treated approximately as a uniaxial crystal. Therefore, the present invention also includes the optical path conversion element of FIG. 9 configured using such a biaxial crystal.

The function of the optical path changing element shown in FIG. 9 is exactly the same as that of a normal birefringent crystal except that there is no difference in the propagation time between the ordinary ray and the extraordinary ray. Therefore, the birefringent crystals 12-1 to 12-12 of the beam shift type optical switch of FIG.
If -3 and 13-1 to 13-3 are replaced with the present optical path conversion element, an optical switch that does not cause a difference in propagation time depending on the path can be configured as it is. Further, a polarization plane exchange element having a width that is an integral multiple of the magnitude of the shift of the extraordinary ray of the optical path conversion element, and an optical element having the same shape and refractive index as the optical path conversion element. By alternately stacking isotropic transparent plates, a routing element in which the birefringent crystal 32 of FIG. 3 is replaced with the present optical path conversion element is formed. If this routing element is applied to the multi-stage network type optical switch of FIG.
Also, an optical switch in which the propagation time does not differ depending on the path can be configured. Further, by using this element as a routing element applied to the first and last stages of the multistage optical switch shown in FIG. 2, an incident light beam of arbitrary polarization can be passed without jitter.

[0037]

As described above, by applying the optical path conversion element according to the present invention, it is possible to compensate for the propagation time difference between the ordinary ray and the extraordinary ray inherent in the element using the birefringent crystal. The problem of the phase shift or jitter of the optical signal caused by this can be solved.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams showing a basic structure of a multi-stage beam shift type optical concentrator switch, where FIG. 1A is a schematic diagram thereof, and FIG. The paths of the light beam and the extraordinary light beam are shown by a solid line and a broken line, respectively.

FIG. 2 is a diagram schematically illustrating the structure of a multistage optical switch.

FIG. 3 is a view showing a structure of a polarization routing element formed by using a birefringent crystal, and (a) to (d) respectively show the routing elements 22-1 and 22-2 of FIG. 23-1, 23
-2, 24-1, 24-2, 25-1, 25-2 are shown.

FIG. 4 shows the path of a light beam propagating through a polarization routing element, where (a) is the path of (a) and (c) of FIG. 3, and (b) is (b) of FIG. And (d), where the solid and broken lines indicate the paths of the ordinary ray and the extraordinary ray, respectively.

FIGS. 5A and 5B show a first embodiment of the present invention, wherein FIG. 5A is a diagram showing the structure of an element according to the embodiment, and FIG. Are indicated by solid lines and broken lines, respectively.

FIG. 6 is a diagram illustrating a configuration example of a multi-stage beam shift type optical concentrator switch using the optical path conversion element of FIG. 5;

FIG. 7 is a diagram showing a configuration example of a routing element having a function equivalent to that shown in FIG. 3, and (a), (b)
Correspond to the elements of FIGS. 3A and 3B, respectively.

8 shows the path of a light beam passing through the routing element of FIG. 7, wherein solid and broken lines indicate ordinary and extraordinary rays, respectively, and FIGS. 7 of
They correspond to the elements (a) and (b).

FIGS. 9A and 9B show a second embodiment of the present invention, wherein FIG. 9A shows the structure of an element according to this embodiment, and FIG. 9B shows the paths of ordinary and extraordinary rays passing through the element. These are indicated by solid lines and broken lines, respectively.

[Explanation of symbols]

 11-1 to 11-7 Polarization control element array 12-1 to 12-3 Birefringent crystal 13-1 to 13-3 Birefringent crystal 21-1 to 21-9 Polarization control array 22-1, 22-2 Polarization routing Element 23-1, 23-2 Polarization routing element 24-1, 24-2 Polarization routing element 25-1, 25-2 Polarization routing element 31 Light beam incident position 32 Birefringent crystal 33 Polarization plane exchange element 34 Optically Isotropic transparent plate 51-1 and 52-2 Birefringent crystal 52 Polarization plane exchange element 61-1 to 61-7 Polarization control element array 62-1 to 62-3 Optical path conversion element 63-1 to 63-3 Optical path conversion Element 71 Light beam incident position 72-1, 72-2 Birefringent crystal 73-1, 73-2 Birefringent crystal 74-1, 74-2 Polarization plane exchange element 75 Polarization plane exchange element 76 Optically isotropic Transparent plate 91 Birefringent crystal 92 Birefringent crystal

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-120823 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 27/28

Claims (10)

(57) [Claims] 1. A first transparent medium having birefringence, the same shape and material as the first transparent medium, and the magnitude of a position shift of an extraordinary ray with respect to an ordinary ray is the first transparent medium. A second transparent medium disposed so as to be equal to that of the medium and having a shift direction opposite to that of the first transparent medium; and a second transparent medium disposed between the two transparent media, Polarization for converting an ordinary ray emitted from a medium into an extraordinary ray incident on the second transparent medium, and converting an extraordinary ray emitted from the first transparent medium into an ordinary ray incident on the second transparent medium. An optical path conversion element comprising a surface exchange element. 2. The optical path-changing element according to claim 1, wherein said polarization plane switching element is constituted by a half-wave plate. 3. The optical path-changing element according to claim 1, wherein the polarization plane switching element is constituted by an optical rotator that rotates the polarization plane of the passing linearly polarized light by 90 °. 4. The optical path-changing element according to claim 1, wherein the first and second transparent media are made of calcite or rutile crystal. 5. A first transparent medium having birefringence, and a first transparent medium having birefringence, wherein the magnitude relationship between the ordinary ray refractive index and the extraordinary ray refractive index is opposite to the first transparent medium. The first transparent medium has a refractive index of n ₀₁ , n _e1 and n ₀₁ , respectively, in which the direction of oscillation of the electric field of the first transparent medium is perpendicular to the principal axis and the principal axis direction.
The angle between the plane of incidence and the principal axis of the crystal is θ ₁ , the direction of oscillation of the electric field of the second transparent medium perpendicular to the principal axis and the refractive index of light in the principal axis direction are n ₀₂ and _{ne 2} , respectively. the angle between the principal crystal axis in case of a theta _2, Equation 1] between the thickness t ₂ of said first transparent medium having a thickness of t ₁ and the second transparent medium Wherein the first and second transparent media are arranged so that the following relationship is established. 6. The angle θ ₁ between the incident surface of the first transparent medium and the crystal main axis is given by The optical path conversion element according to claim 5, wherein the following relationship is satisfied. 7. An angle θ ₂ between the incident surface of the second transparent medium and the crystal main axis is given by 7. The relationship of claim 5 or claim 6, wherein
An optical path conversion element according to item 1. 8. The optical path conversion device according to claim 5, wherein one of the first and second transparent media is made of calcite. 9. The optical path conversion device according to claim 5, wherein one of the first and second transparent media is made of a rutile crystal. 10. An optical path changing element according to claim 1, wherein the extraordinary rays have the same magnitude of shift and their directions are opposite to each other. And having a width between the first and second optical path conversion elements equal to an integral multiple of the magnitude of the shift of the extraordinary ray by the first and second optical path conversion elements, and
The ordinary ray emitted from the optical path conversion element is converted into an extraordinary ray incident on the second optical path conversion element, and the extraordinary ray emitted from the first optical path conversion element is incident on the second optical path conversion element. A polarization plane exchange element that converts to ordinary light, and an optically isotropic transparent medium having the same width as the polarization plane exchange element and having the same refractive index as the polarization plane exchange element, An optical path-changing element characterized by being alternately stacked in a direction.