JPH0588112A - Optical nonreciprocal circuit - Google Patents

Abstract

PURPOSE:To constitute thin means which multiplex and demultiplex originary light and extraordinary light and to provide the optical nonreciprocal circuit which is made compact in overall size. CONSTITUTION:The 1st, 2nd, and 3rd polarized light demultiplexing and multiplexing means 21, 22, and 23 are composed of couples of birefringent diffraction gratings 21a and 21b, 22a and 22b, and 23a and 23b which are arranged in parallel and equal in diffraction angle and then the respective demultiplexing and multiplexing means 21-23 are shortened in length in the traveling direction of light to make the size of the whole circuit small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical nonreciprocal circuit having a plurality of input / output ports.

[0002]

2. Description of the Related Art As a conventional optical nonreciprocal circuit of this type,
For example, Koga and Matsumoto, "High-isolation optical nonreciprocal circuit with no polarization dependence that can be used as a circulator"
(The Institute of Electronics, Information and Communication Engineers Optical Communication System Study Group, OCS91-
9, May 1991).

FIG. 2 shows the above-mentioned conventional optical nonreciprocal circuit. In the figure, 1, 2 and 3 are birefringent crystal plates, 4 and 5 are quartz clockwise 45 ° rotators, and 6 and 7 are quartz. Counterclockwise 45 degree rotator, 8, 9 are Faraday 45 degree rotators, 11, 12, 1
Reference numerals 3 and 14 are optical input / output ports.

FIG. 3 shows the operation when light is input from the optical input / output port 11 in the circuit of FIG.
2 (a) shows the progress of light when the circuit of FIG. 2 is viewed from above, and FIG. 2 (b) shows the polarization direction and position of light at each position Z0 to Z7 in FIG. 2 (a). This is a view as seen from the input / output port 11 side. Hereinafter, description will be made according to this.

Light L1 input from the light input / output port 11
The (position Z0) is separated into the ordinary light component L11 and the extraordinary light component L12 by the birefringent crystal plate 1 (position Z1). The ordinary light component L11 and the extraordinary light component L12 pass through the crystal clockwise 45-degree rotator 4 and the crystal counterclockwise 45-degree rotator 6, respectively, and their polarization directions are rotated (position Z2), and further the Faraday 45-degree rotator 8 is provided. Through which the polarization direction is rotated (position Z3). Since these light components L11 and L12 are set so as to act as ordinary light on the birefringent crystal plate 2, they travel straight (position Z4). The light components L11 and L12 pass through the crystal counterclockwise 45-degree rotator 7 and the crystal clockwise 45-degree rotator 5, respectively, and their polarization directions are rotated (position Z5).
After passing through the rotator 5 degrees, its polarization direction is rotated (position Z6). Therefore, the light components L11 and L12 both have their polarization directions rotated by 90 degrees with respect to those after passing through the birefringent crystal plate 1 (position Z1), and their polarizations are orthogonal to each other.
These light components L11 and L12 act on the birefringent crystal plate 3 as extraordinary light and ordinary light, respectively, so that they are combined (position Z7) and the light input / output port 12 as light L1 '.
Is output from.

Next, a case where light is input from the light input / output port 12 in the circuit of FIG. 2 will be described with reference to FIG. 4 similar to FIG. However, the polarization direction and position of the light in FIG. 6B are also shown as viewed from the light input / output port 11 side.

Light L2 input from the optical input / output port 12
The (position Z7) is separated into the ordinary light component L21 and the extraordinary light component L22 by the birefringent crystal plate 3 (position Z6). The ordinary light component L21 and the extraordinary light component L22 pass through the Faraday 45-degree rotator 9 and their polarization directions are rotated (position Z5
), And further passes through the crystal clockwise 45 ° rotator 5 and the crystal counterclockwise 45 ° rotator 6, respectively, and their polarization directions are rotated (position Z4). These light components L21 and L22
Acts on the birefringent crystal plate 2 as extraordinary light, and the birefringent crystal plate 2 is set so as to move the extraordinary light downward (-Y direction in FIG. 2).
21 and L22 are both moved downward (position Z3
). Further, the light components L21 and L22 are Faraday 4
After passing through the 5 ° rotator 8, its polarization direction is rotated (position Z2), and further passes through the crystal counterclockwise 45 ° rotator 6 and the crystal clockwise 45 ° rotator 4, respectively, and its polarization direction is rotated. (Position Z1). These light components L21 and L2
When the light beams 2 pass through the birefringent crystal plate 1, they act as extraordinary light and ordinary light, respectively, so that they are combined (position Z0) and the light L
2'is output from the optical input / output port 13.

The light input from the optical input / output port 13 is the same as the light input to the optical input / output port 11,
Finally, the light is output from the optical input / output port 14.

According to the above configuration, the light input from the light input / output port 11 is output from the light input / output port 12, and the light input from the light input / output port 12 is output from the light input / output port 13. The non-reciprocal motion of ... can be performed.

[0010]

In the conventional optical nonreciprocal circuit described above, birefringent crystal plates are used to separate and combine ordinary and extraordinary light, but to prevent the two beams from overlapping. However, the length of the birefringent crystal plate has to be considerably long, and there is a problem that the overall size becomes large. Specifically, when calcite is used as a birefringent crystal plate and the diameter of the beam is 400 μm, calcite having a length of 15 mm is required to obtain a separation width of 1.2 mm, which is three times that of the beam. ..

In view of the above-mentioned conventional drawbacks, it is an object of the present invention to provide an optical nonreciprocal circuit in which means for separating / combining ordinary light and extraordinary light can be made thin and the overall size can be made compact.

[0012]

In order to achieve the above object, the present invention as claimed in claim 1 is set so that an ordinary ray travels straight and an extraordinary ray is diffracted by a predetermined angle, and is separated from each other by a predetermined interval. Three polarization splitting / combining means composed of two birefringent diffraction gratings arranged so as to face each other are arranged along the traveling direction of light, and an electric field of light is placed between the first and second polarization splitting / combining means. A reciprocal and non-reciprocal first group rotor that rotates the vibration direction by the same angle is inserted, and a function similar to that of the first group rotor is provided between the second and third polarization separation / combination means. The direction of separating the ordinary light and the extraordinary light of the second polarization separation / combination means is different from the directions of separation of the first and third polarization separation / combination means by inserting the second group of rotators.
And the separation directions of the third polarization separation / combination means are set to coincide with each other, and the electric field oscillation directions of the ordinary light and the extraordinary light separated by the first polarization separation / combination means are at the input end face of the second polarization separation / combination means. The rotation directions of the reciprocal and non-reciprocal rotors of the first group are set so that they coincide with each other, and
The output end surfaces of the polarized light separating / combining means of
An optical nonreciprocal circuit in which the rotation directions of the reciprocal and nonreciprocal rotators of the second group are set such that the polarization planes of the two lights are orthogonal to each other at the input end face of the third polarization separation / combination means. Item 2, reciprocity in which three polarization separation / combination means are arranged along the traveling direction of light, and the electric field oscillation direction of light is rotated by the same angle between the first and second polarization separation / combination means,
The non-reciprocal first group rotor is inserted, and the second group rotor having the same function as the first group rotor is also inserted between the second and third polarization separation / combination means. First and second light diffracting means are arranged before and after the second polarization separating / combining means, and the first and third polarization separating directions of the second polarization separating / combining means for separating the ordinary light and the extraordinary light are arranged. Different from the separating direction of the combining means, the separating directions of the first and third polarized light separating / combining means are set to coincide with each other, and the electric field oscillation directions of the ordinary light and the extraordinary light separated by the first polarized light separating / combining means are set. The rotation directions of the reciprocal and non-reciprocal rotors of the first group are set so that the two coincide with each other at the input end surface of the second polarization separation / combination means, and at the output end surface of the second polarization separation / combination means. The two planes of polarization of coincidence are located at the input end face of the third polarization splitting / combining means. The rotation directions of the reciprocal and non-reciprocal rotors of the second group are set so as to be orthogonal to each other, and the first light diffracting means diffracts the light diffracted at a predetermined angle by the first polarization separation / combination means. Is set to diffract to the angle before being diffracted, and the second light diffracting means diffracts the light diffracted at the predetermined angle by the third polarization separation / combination means to the angle before diffracting. We propose a set optical nonreciprocal circuit.

[0013]

According to claim 1 of the present invention, the ordinary light is caused to go straight,
First, second and third polarization separation / combination composed of two birefringent diffraction gratings set to diffract extraordinary light by a predetermined angle and arranged to face each other with a predetermined distance therebetween. Since the means is provided, the length of each polarization separation / combination means in the traveling direction of light can be shortened. In addition, claim 2
According to the method, the ordinary light and the extraordinary light separated by the first or third polarized light separating / combining means are made parallel or combined by the light diffracting means provided before and after the second polarized light separating / combining means. The first and third polarized light separating / combining means do not need a length in the traveling direction of light for separating or combining ordinary light and extraordinary light in parallel.

[0014]

1 shows a first embodiment of an optical nonreciprocal circuit of the present invention, in which 21 is a first polarization separation / combination means,
Reference numeral 22 is a second polarization separation / combination means, 23 is a third polarization separation / combination means, and 24 is a first and second polarization separation / combination means 21.
And the first group of rotors inserted between 22 and 25 is the second
And the second group of rotors 31, 32, 33, 34 inserted between the third polarization separation / combination means 22 and 23 are light input / output ports.

First, second and third polarized light separating / combining means 2
Reference numerals 1, 22 and 23 denote two birefringent diffraction gratings 21a, 21b and 22 arranged in parallel and having equal diffraction angles.
a, 22b and 23a, 23b, it is possible to separate ordinary light and extraordinary light and keep the relationship between the ordinary light and extraordinary light parallel, and to combine ordinary light and extraordinary light.

The first group of rotors 24 is a reciprocal rotor for rotating the electric field oscillation direction of light by 45 degrees, that is, a first reciprocal clockwise 45 degree rotor (hereinafter referred to as "first reciprocal right rotation"). 24a and a first reciprocal counterclockwise 45-degree rotator (hereinafter referred to as a first reciprocal left rotator) 24b, and a non-reciprocal that similarly rotates the electric field oscillation direction of light by 45 degrees. Rotor, that is, the first non-reciprocal 45 degree rotor (hereinafter referred to as the first
It is called a non-reciprocal rotor. ) 24c.

The rotor 25 of the second group is the rotor 24 of the first group.
Similarly, the second reciprocal counterclockwise 45-degree rotor (hereinafter referred to as the second reciprocal left rotor) 25a and the second reciprocal right-handed 45-degree rotor (hereinafter, the second reciprocal right rotor). 25b and a second non-reciprocal 45 degree rotor (hereinafter, referred to as a rotor).
This is called the second non-reciprocal rotor. ) 25c.

The above-mentioned reciprocal rotator is an optical element such as quartz, and the non-reciprocal rotator is a YIG crystal or G.
A Faraday rotator using a BIG thin film crystal is used.

The first, second and third polarization separation / combination means 21, 22 and 23 separate the ordinary and extraordinary rays in the first and second directions. Unlike the separating directions of the third polarized light separating / combining means 21 and 23, the separating directions of the first and third polarized light separating / combining means 21 and 23 are set to coincide with each other. In addition, the electric field oscillation directions of the two light components separated by the first polarization separation / combination means 21 coincide with each other at the input end surface of the second polarization separation / combination means 22 as viewed from the first polarization separation / combination means 21 side. Thus, the respective rotation directions of the first reciprocal right rotor 24a, the first reciprocal left rotor 24b, and the first non-reciprocal rotor 24c are set. In addition, the second viewed from the side of the first polarized light separating and combining means 21.
The polarization directions of the two light components that match at the output end face of the polarization separation / combination means 22 of the first polarization separation / combination means 2 are the same.
The second reciprocal left rotator 25 is arranged so as to be orthogonal to each other at the input end face of the third polarized light separating / combining means 23 viewed from the 1 side.
The rotation directions of a, the second reciprocal right rotor 25b, and the second non-reciprocal rotor 25c are set.

The light input / output ports 31 and 33 are provided in the birefringence diffraction grating 21a, and the light input / output ports 32 and 34 are provided.
Is provided on the birefringent diffraction grating 23b.

FIG. 5 shows the operation when light is input from the optical input / output port 31 in the circuit of FIG.
(a) shows how the light travels when the circuit of FIG. 1 is viewed from above, and (b) shows the polarization direction and position of light at each position Z0 to Z7 in (a). This is a view as seen from the input / output port 31 side. Hereinafter, description will be made according to this.

Light L3 input from the optical input / output port 31
(Position Z0) is X- by the first polarization separation / combination means 21.
It is separated into an ordinary light component L31 and an extraordinary light component L32 on the Z plane (position Z1). In the first polarization splitting / combining means 21, the ordinary light component goes straight by the birefringence diffraction grating 21a,
The extraordinary light component is diffracted in a direction inclined by the angle α, and the extraordinary light component is diffracted by the angle −α by the birefringence diffraction grating 21b, and is separated in parallel with the ordinary light component and output. The light component L31 is an ordinary light with respect to the first polarization separation / combination means 21, the light component L32 is an extraordinary light, and the respective polarization directions are orthogonal to vibrate in the Y-axis and the X-axis directions, respectively.

Light components L31 and L3 orthogonal to each other
The vibration directions of the electric field of 2 are respectively the first reciprocal right rotor 2
4a and the first reciprocal left rotor 24b pass through the same direction (position Z2). Where the first
The reciprocal right rotator 24a is in the clockwise direction when the light component L31 is viewed from the input direction, and the first reciprocal left rotator 24b is the light component L.
32 is rotating counterclockwise when viewed from the input direction. Next, the first non-reciprocal rotator 24c causes the light components L31 and L3.
By rotating 2 further clockwise by 45 degrees, the vibration direction of the electric field of these light components L31 and L32 becomes the X-axis direction (position Z3). As a result, the light component L31 rotates 90 degrees, and the light component L32 does not rotate.

Since the second polarized light separating / combining means 22 is arranged so that the two light components L31 and L32 vibrating in the X-axis direction become ordinary light, the light components L31 and L32 are second polarized light separating light. Passes through the synthesizing means 22 as it is (position Z
4) and is input to the rotor 25 of the second group. In this case, the light component L31 is rotated counterclockwise by 45 degrees by the second reciprocal left rotor 25a (position Z5), and is rotated clockwise by 45 degrees by the second non-reciprocal rotor 25c (position Z6).
As a result, the rotation of the polarization direction is canceled out and the polarization direction is not rotated, but the light component L32 is rotated clockwise by 45 degrees by the second reciprocal right rotator 25b (position Z).
5) Then, the second non-reciprocal rotator 25c rotates it 45 degrees clockwise (position Z6), and as a result, the polarization direction rotates 90 degrees. Therefore, 2 at the input end face of the third polarization separation / combination means 23 when viewed from the side of the light input / output port 31.
The vibration directions of the one light component L31 and L32 are orthogonal to each other.

The two light components L31 and L32 are spatially matched and combined with the third polarization separation / combination means 23 because the light component L31 becomes extraordinary light and the light component L32 becomes ordinary light. Z7) and light L3 'are output from the light input / output port 32 and propagate in the Z-axis direction.

Next, the case where light is input from the light input / output port 32 in the circuit of FIG. 1 will be described with reference to FIG. 6 similar to FIG. However, the polarization direction and position of the light in FIG. 7B are also shown as viewed from the light input / output port 31 side.

Light L4 input from the light input / output port 32
The (position Z7) is separated into the light components L41 and L42 on the XZ plane by the third polarization separation means 23 (position Z6).
). Here, the light component L41 is the ordinary light with respect to the third polarization separation / combination means 23, the light component L42 is the extraordinary light, and the respective polarization directions are orthogonal to each other.

The two light components L41 and L42 are the second
It will pass through the rotor 25 of the group. The light component L41 is rotated 45 degrees clockwise (position Z5) by the second non-reciprocal rotator 25c, and is rotated 45 degrees counterclockwise (position Z4) by the second reciprocal right rotator 25b, resulting in the polarization direction. The rotations of are canceled out, and the polarization direction does not rotate.
The light component L42 is rotated clockwise by 45 degrees by the second non-reciprocal rotator 25c (position Z5) and rotated clockwise by 45 degrees by the second reciprocal left rotator 25a (position Z4).
As a result, the polarization direction is rotated by 90 degrees. Therefore, unlike the case of FIG. 5, the electric field of the two light components L41 and L42 oscillates in the Y-axis direction at the output end face of the second polarization separation / combination means 22 as viewed from the light input / output port 31 side. .. This direction becomes extraordinary light with respect to the second polarization separation / combination means 22, so that the light components L41 and L42 are downward (-Y direction in FIG. 1) as they pass through the second polarization separation / combination means 22. Will be moved to (position Z3
).

Two light components L41 and L moved downward
When 42 passes through the rotor 24 of the first group, it receives an action opposite to the polarization action in the case of FIG. In this case, the light component L4
1 is rotated 45 degrees clockwise (position Z2) by the first non-reciprocal rotator 24c and rotated 45 degrees clockwise (position Z1) by the first reciprocal left rotator 24b, resulting in a polarization direction of 90. It will rotate once. Also, the light component L42
Is rotated 45 degrees clockwise (position Z2) by the first non-reciprocal rotator 24c, and is rotated 45 degrees counterclockwise (position Z1) by the first reciprocal right rotator 24a, resulting in rotation of the polarization direction. They are canceled out and the polarization direction does not rotate.

The polarization directions of the light components L41 and L42 at the input end face of the first polarization splitting / combining means 21 as viewed from the side of the light input / output port 31 are the same as those in FIG.
When passing through the first polarized light separating / combining means 21, they act as extraordinary light and ordinary light, respectively, so that they are combined (position Z0), but since the positions of the optical paths are different, the light input / output port 3
1 is not output from the optical input / output port 33 as the light L4 ′.
Will be output from.

As described above, according to this embodiment, the light L3 input from the light input / output port 31 is output as the light L3 ′ from the light input / output port 32, and the light L4 input from the light input / output port 32 is It is possible to realize a non-reciprocal operation in which the light L4 ′ is output from the light input / output port 33 without being output from the light input / output port 31.

Here, the birefringent diffraction grating which constitutes the polarization splitting / combining means will be described. As one of the birefringent diffraction gratings, there is a thin diffraction grating having a rectangular cross section structure. In this diffraction grating, the ordinary light and the extraordinary light are set to have a phase difference of “0” and “π”, respectively, so that all the ordinary light is transmitted and the extraordinary light is diffracted. .. Further, as another birefringent diffraction grating, there is a structural birefringent diffraction grating having a structure with a period of 1/2 or less.

With these birefringent diffraction gratings, the size when the diffraction angle of extraordinary light is, for example, 30 degrees is compared with the case where a conventional birefringent crystal plate is used. In the conventional case, the length required to separate 1.2 mm of light having a beam diameter of 400 μm was 15 mm. In order to separate the beams by 1.2 mm with two birefringent diffraction gratings, even if the diffraction grating thicknesses are estimated to be 1 mm, if the diffraction angle is 30 degrees, only 4 mm is needed, and The size of the reciprocal circuit can be reduced.

FIG. 7 shows a modification of the first embodiment, in which a concrete example of the optical input / output port is shown. That is, in the figure, 41 and 42 are birefringent diffraction gratings 21a, respectively.
Of the lenses provided at the positions corresponding to the light input / output ports 31 and 33 of the birefringence diffraction grating 23b.
Is a lens provided at a position corresponding to the optical input / output ports 32 and 34, and 45, 46, 47 and 48 are optical fibers provided coaxially with the lenses 41, 42, 43 and 44, respectively. is there. The lens 41 and the optical fiber 45 constitute the light input / output port 31, and the lens 4
2 and the optical fiber 46 constitute the optical input / output port 33,
The lens 43 and the optical fiber 47 form the light input / output port 32, and the lens 44 and the optical fiber 48 form the light input / output port 34. The other structure is the same as that of the first embodiment.

Also in this optical nonreciprocal circuit, the same operation and effect as in the first embodiment, that is, the light input from the optical fiber 45 is output from the optical fiber 47, and the optical fiber 47 is output.
The non-reciprocal operation in which the light input from the optical fiber is output from the optical fiber 46 can be realized.

The optical fibers 45 to 48 may be replaced with optical waveguides capable of confining and propagating light energy, and the modes of these optical fibers may be single mode or multimode.

FIG. 8 shows a second embodiment of the optical nonreciprocal circuit of the present invention. The difference between this embodiment and the first embodiment is that the first and third polarization separation / combination means are different from each other. Each of them is composed of only one birefringent diffraction grating 51 and 52, and ordinary light and extraordinary light can be separated and combined, but the two separated lights are not parallel to each other.
The polarized light separating / combining means 22 is inserted between the first and second non-polarizing diffracting means 53 and 54.

First and second non-polarization diffracting means 53 and 5
Reference numeral 4 has a diffraction grating function capable of diffracting light at a predetermined angle regardless of the polarization state of the light.

FIG. 9 shows the operation when light is input from the optical input / output port 31 in the circuit of FIG.
8 (a) shows the progress of light when the circuit of FIG. 8 is viewed from above, and FIG. 8 (b) shows the polarization direction and position of light at each position Z0 to Z7 in FIG. 8 (a). This is a view as seen from the input / output port 31 side. Hereinafter, description will be made according to this.

Light L5 input from the light input / output port 31
(Position Z0) is the first polarization splitting / combining means, that is, the birefringent diffraction grating 51, and the light components L51 and L5 on the XZ plane.
It is separated into two. Here, the light component L51 is an ordinary light component that travels straight, and the light component L52 is an extraordinary light component that is diffracted in a direction inclined by an angle α, and each polarization direction vibrates in the Y-axis and X-axis directions, respectively. Are in an orthogonal state (position Z1).

Light components L51 and L5 orthogonal to each other
The vibration directions of the electric field of 2 are respectively the first reciprocal right rotor 2
4a and the first reciprocal left rotor 24b pass through the same direction (position Z2). Where the first
The reciprocal right rotator 24a is in the clockwise direction when the light component L51 is viewed from the input direction, and the first reciprocal left rotator 24b is the light component L.
52 is rotating counterclockwise as viewed from the input direction. Next, the first non-reciprocal rotator 24c causes the light components L51 and L5.
By rotating 2 further clockwise by 45 degrees, the vibration direction of the electric field of these light components L51 and L52 becomes the X-axis direction (position Z3). As a result, the light component L51 rotates 90 degrees, and the light component L52 does not rotate.

Before passing through the second polarization splitting / combining means 22, the light component L52 is diffracted by the non-polarization diffracting means 53 and travels in the Z-axis direction in parallel with the light component L51. The second polarized light separation / combination means 22 is arranged so that the two light components L51 and L52 oscillating in the X-axis direction become ordinary rays, so that the light components L51 and L52 are the second polarized light separation / combination means. 22 is passed through as it is, and the light component L51 is diffracted by the second non-polarization diffracting means 54, so that the light components L51 and L52 are the second group of the rotor 25.
Will be input to (position Z4). In this case, the light component L51 is rotated counterclockwise by the second reciprocal left rotator 25a.
Rotated 5 degrees (position Z5), second non-reciprocal rotor 25c
Is rotated 45 degrees clockwise (position Z6), and as a result, the rotation of the polarization direction is canceled and the polarization direction is not rotated, but the light component L52 is generated by the second reciprocal right rotator 25b.
Is rotated 45 degrees clockwise (position Z5) by the second non-reciprocal rotator 25c, and rotated 45 degrees clockwise (position Z6) by the second non-reciprocal rotator 25c. As a result, the polarization direction is rotated 90 degrees. Therefore, the oscillation directions of the two light components L51 and L52 are orthogonal to each other on the third polarization separation / combination means viewed from the light input / output port 31 side, that is, on the input end face of the birefringence diffraction grating 52.

The positions of the two light components L51 and L52 coincide with each other on the input end face of the birefringent diffraction grating 52, and the light component L51 becomes extraordinary light, and the light component L52 becomes ordinary light, so that the light component L51 diffracts. The light is received, combined with the light component L52 (position Z7), and converted into the light input / output port 32 as light L5 '.
Will be output from.

Next, a case where light is input from the light input / output port 32 in the circuit of FIG. 8 will be described with reference to FIG. 10 similar to FIG. However, the polarization direction and position of the light in FIG. 7B are also shown as viewed from the light input / output port 31 side.

Optical L6 input from the optical input / output port 32
(Position Z7) is separated into light components L61 and L62 on the XZ plane by the third polarization separating means, that is, the birefringent diffraction grating 52 (position Z6). Here, the light component L61 is the ordinary light with respect to the birefringent diffraction grating 52, the light component L62 is the extraordinary light, and these two light components are angularly separated,
Moreover, the respective polarization directions are orthogonal to each other.

The two light components L61 and L62 are the second
It will pass through the rotor 25 of the group. The light component L61 is rotated 45 degrees clockwise (position Z5) by the second non-reciprocal rotator 25c, and is rotated 45 degrees counterclockwise (position Z4) by the second reciprocal right rotator 25b, resulting in the polarization direction. The rotations of are canceled out, and the polarization direction does not rotate.
The light component L62 is rotated clockwise by 45 degrees by the second non-reciprocal rotator 25c (position Z5) and rotated by 45 degrees clockwise by the second reciprocal left rotator 25a (position Z4).
As a result, the polarization direction is rotated by 90 degrees. The light component L62 is diffracted by the second non-polarizing diffracting means 54 and travels in parallel to the light component L61 in the -Z axis direction. Therefore, unlike the case of FIG. 9, the electric field of the two light components L61 and L62 oscillates in the Y-axis direction at the output end face of the second polarization separation / combination means 22 as viewed from the light input / output port 31 side. .. Since this direction becomes extraordinary light with respect to the second polarization separation / combination means 22, the light components L61 and L62 pass downward through the second polarization separation / combination means 22 (-Y direction in FIG. 8). Will be moved to (position Z3). After passing through the second polarized light separating / combining means 22, the light component L61 is diffracted by the first non-polarizing diffracting means 53.

Two light components L61 and L moved downward
When 62 passes through the rotor 24 of the first group, it receives an action opposite to the polarization action in the case of FIG. In this case, the light component L6
1 is rotated 45 degrees clockwise (position Z2) by the first non-reciprocal rotator 24c and rotated 45 degrees clockwise (position Z1) by the first reciprocal left rotator 24b, resulting in a polarization direction of 90. It will rotate once. Also, the light component L62
Is rotated 45 degrees clockwise (position Z2) by the first non-reciprocal rotator 24c, and is rotated 45 degrees counterclockwise (position Z1) by the first reciprocal right rotator 24a, resulting in rotation of the polarization direction. They are canceled out and the polarization direction does not rotate.

The direction of polarization of these light components L61 and L62 at the first polarization separation / combination means viewed from the light input / output port 31 side, that is, at the input end face of the birefringent diffraction grating 51 is shown in FIG.
This is similar to the case of (1), and when passing through the birefringent diffraction grating 51, they act as extraordinary light and ordinary light, respectively, so that they are combined (position Z0), but since the position of the optical path is different, Instead of being output, the light L6 'is output from the light input / output port 33.

As described above, also in this embodiment, the light L5 input from the optical input / output port 31 is input to the optical input / output port 32.
From the optical input / output port 31 is output as the optical L5 ′ and is output from the optical input / output port 33 as the optical L6 ′, which is a non-reciprocal operation. be able to.

According to this embodiment, the first and second non-polarizing diffracting means 53 and 54 are provided, so that the first
The third and third polarization splitting / combining means can be composed of only one birefringent diffraction grating 51 and 52, respectively, and the size can be further reduced as compared with the first embodiment.

[0051]

According to the first aspect of the present invention, the first and second aspects are provided.
And the third polarization splitting / combining means is constituted by two birefringent diffraction gratings which are set so as to make the ordinary light go straight and diffract the extraordinary light by a predetermined angle, and are arranged so as to face each other at a predetermined distance. Since it is configured, the length of each polarization separation / combination means with respect to the traveling direction of light can be shortened, whereby the size of the optical nonreciprocal circuit can be reduced.

According to the second aspect of the present invention, since the light diffracting means is provided before and after the second polarization separating / combining means, the ordinary light and the extraordinary light are parallel to the first and third polarization separating / combining means. It is not necessary to have a length in the traveling direction of light that is only separated or combined, and therefore, the size of the optical nonreciprocal circuit can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optical nonreciprocal circuit of the present invention.

FIG. 2 is a configuration diagram showing an example of a conventional optical nonreciprocal circuit.

3 is an explanatory diagram showing an operation when light is input from the light input / output port 11 in the circuit of FIG.

4 is an explanatory diagram showing an operation when light is input from the light input / output port 12 in the circuit of FIG.

5 is an explanatory diagram showing an operation when light is input from a light input / output port 31 in the circuit of FIG.

6 is an explanatory diagram showing an operation when light is input from a light input / output port 32 in the circuit of FIG.

FIG. 7 is a configuration diagram showing a modification of the first embodiment of the optical nonreciprocal circuit of the present invention.

FIG. 8 is a configuration diagram showing a second embodiment of the optical nonreciprocal circuit of the present invention.

9 is an explanatory diagram showing an operation when light is input from the light input / output port 31 in the circuit of FIG.

10 is an explanatory diagram showing an operation when light is input from the light input / output port 32 in the circuit of FIG.

[Explanation of symbols]

21, 22, 23 ... Polarization separating / combining means, 21a, 21
b, 22a, 22b, 23a, 23b, 51, 52 ... Birefringence diffraction grating, 24, 25 ... Rotor, 24a, 25b ...
Reciprocal right rotor, 24b, 25a ... Reciprocal left rotor, 2
4c, 25c ... Non-reciprocal rotor, 31, 32, 33, 3
4 ... Optical input / output port, 53, 54 ... Non-polarization diffracting means.

Claims (2)

[Claims] 1. A polarization splitting device comprising two birefringent diffraction gratings which are set so as to make an ordinary ray travel straight and diffract an extraordinary ray at a predetermined angle and are arranged to face each other with a predetermined spacing. Three synthesizing means are arranged along the traveling direction of light, and the reciprocal and non-reciprocal first group of the first and second polarized light separating and synthesizing means rotate the electric field oscillation direction of light by the same angle. A rotator is inserted, and a second group rotator having the same function as the rotator of the first group is inserted between the second and third polarization separation / combination means. The direction in which the ordinary light and the extraordinary light are separated is different from the direction in which the first and third polarized light separating / combining means separate, and the separating directions of the first and third polarized light separating / combining means are set to coincide with each other. Direction of electric field oscillation of ordinary and extraordinary light separated by the polarization separation / combination means 1 The rotation directions of the reciprocal and non-reciprocal rotators of the first group are set so that the input end faces of the second polarization splitting / combining means are coincident with each other, and the rotation directions of the reciprocal and non-reciprocal rotors of the first group are set at the output end face of the second polarization splitting / combining device. The reciprocity of the second group so that the polarization planes of the two light beams are orthogonal to each other at the input end surface of the third polarization separation / combination means.
An optical nonreciprocal circuit characterized by setting the rotation direction of a nonreciprocal rotor. 2. Reciprocity, in which three polarization splitting / combining means are arranged along the traveling direction of light, and the electric field oscillation direction of light is rotated by the same angle between the first and second polarization splitting / combining means. The reciprocal first group rotor is inserted, and the second group rotor having the same function as the first group rotor is also inserted between the second and third polarization separation / combination means. The first and second light diffracting means are arranged before and after the second polarization separating / combining means, and the first and third polarization separating / combining directions in which the ordinary light and the extraordinary light of the second polarization separating / combining means are separated from each other. Different from the separating direction of the means, the separating directions of the first and third polarized light separating / combining means are set to coincide with each other, and the electric field oscillation directions of the ordinary light and the extraordinary light separated by the first polarized light separating / combining means are set. Reciprocity of the first group so that the input end faces of the second polarization splitting / combining means coincide with each other. , The rotation direction of the non-reciprocal rotator is set, and the polarization planes of the two lights that coincide with each other at the output end face of the second polarization separation / combination means are orthogonal to each other at the input end face of the third polarization separation / combination means. Thus, the reciprocity of the second group,
The rotation direction of the non-reciprocal rotor is set, and the first light diffracting unit is set to diffract the light diffracted by the first polarization splitting / combining unit to a predetermined angle before being diffracted. Then, the second light diffracting means is set so as to diffract the light diffracted at a predetermined angle by the third polarization separation / combination means to the angle before being diffracted.