JPH0886978A - Optical circulator and light control method - Google Patents

Abstract

PURPOSE: To provide an optical circulator and a light control method with high isolation and capable of transmitting a high bit rate signal. CONSTITUTION: Light inputted from a fiber F1 is outputted to the fiber F2. The light inputted from the fiber F2 is outputted to the fiber F3. Double refraction planes 21-1 to 21-4 are walk-off polarizing beam splitters, and the isolation of the light coupled with respective ports F2, F3 are enhanced. Further, a polarization compensation plate H1 is arranged on a path where no light inputted from a first port F1 is propagated, and it suppresses polarization diffusion when a signal beam inputted from a second port F2 is coupled with a third port F3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical circulator used for optical communication or the like, and more particularly to an optical circulator used for bidirectional communication or data link.

[0002]

2. Description of the Related Art As an optical circulator, a 4-port optical circulator having four input / output ports and a three-port optical circulator having three input / output ports have been conventionally known. A conventional 4-port optical circulator having four input / output ports is disclosed in, for example, Japanese Patent Publication No. 60-498.
The one described in Japanese Patent No. 87 is known. However, the four-port optical circulator and the three-port optical circulator naturally have different requirements for constituting these inventions. Conventionally, a four-port optical circulator and a reflector are equivalently used as a three-port optical circulator. It constituted the circulator. However, such an equivalent optical circulator has a large insertion loss and has many disadvantages in actual optical communication. Therefore, as the 3-port optical circulator, the optical circulators described in JP-A-4-21522 and JP-A-5-323234 have been invented.

[0003]

However, the optical circulator described in the above publication uses one half-wave plate and one Faraday rotator due to the principle of the invention, but in such a configuration, The wavelength dependence and temperature dependence of isolation are rapid. The optical circulator described in the above publication is also an excellent optical circulator in terms of constituting the optical circulator with a small number of parts, but since only one Farade rotator is used, it depends on the wavelength of the isolation. In addition to its rapidity in temperature and temperature dependence, there is an optical path difference in the branched polarized waves, which causes polarization dispersion when the optical signal input from the input port is coupled to the output port. Such polarization dispersion and abrupt wavelength dependence are not suitable for transmission of optical signals of wide wavelength range and high bit rate in the next generation optical communication. Therefore, the present invention has been made in view of these problems, and transmits optical signals in a wide wavelength range at a high bit rate, and these optical signals are high without being coupled to ports other than the target port. An object is to provide a completely new optical circulator capable of having isolation.

[0004]

In order to solve the above problems, the present invention provides a first light input from a first port to a second light source.
The present invention is directed to an optical circulator that outputs to a port and outputs the second light input from the second port to a third port, the first and second polarization beam splitters.
The first to fourth birefringent materials, the demultiplexing birefringent material, the demultiplexing birefringent material, and the demultiplexing birefringent material are included.

The first polarization beam splitter is arranged so that the traveling directions of the ordinary ray and the extraordinary ray of the first light input from the first port are parallel and output, and the first polarization beam splitter is input in parallel. It is arranged so that the ordinary ray and the extraordinary ray are combined and output to the third port.

The second polarization beam splitter is arranged so that the traveling directions of the ordinary ray and the extraordinary ray of the second light input from the second port are parallel to each other, and the parallel polarization is input. It is arranged so that the ordinary ray and the extraordinary ray are combined and output to the second port.

The birefringent material for demultiplexing is arranged between the first port and the first polarizing beam splitter, and separates the first light input from the first port into an ordinary ray and an extraordinary ray. 1 to the polarization beam splitter.

The birefringent material for multiplexing / demultiplexing has a second port and a second port.
The second light input from the second port is separated into an ordinary ray and an extraordinary ray and output to the second polarization beam splitter.
The ordinary ray and the extraordinary ray input from the polarization beam splitter of are combined and output to the second port.

The multiplexing birefringent material is disposed between the third port and the first polarization beam splitter, and combines the ordinary ray and the extraordinary ray input from the second polarization beam splitter to synthesize the third ray. Output to port.

The optical component is disposed between the first polarization beam splitter and the second polarization beam splitter, and
Ordinary ray and extraordinary ray of the first light input from the polarization beam splitter are subjected to first conversion, and are output to the second polarization beam splitter as an extraordinary ray and an ordinary ray, respectively. The ordinary ray and the extraordinary ray of the second light input from the beam splitter are subjected to the second conversion and output to the first polarization beam splitter as the extraordinary ray and the ordinary ray. Here, the polarization compensating plate is arranged between the first polarization beam splitter and the multiplexing birefringent material.

This optical component is disposed so as to face the second polarization beam splitter, and the azimuth of incident polarized light is ± 45.
A second non-reciprocal optical rotation element which is rotated between the first non-reciprocal optical rotation element and the first non-reciprocal optical rotation element and the first polarization beam splitter, and which rotates the azimuth of incident polarized light by ± 45 degrees. Is disposed between the element and the second non-reciprocal optical rotation element and the first non-reciprocal optical rotation element, and the direction of incident polarized light is ± 4
A third non-reciprocal optical rotation element that rotates 5 degrees, and a reciprocal optical rotation element that is disposed between the third non-reciprocal optical rotation element and the second non-reciprocal optical rotation element and that rotates the azimuth of incident polarized light by 45 degrees.
Of the incident light, the ordinary ray advances straight and the extraordinary ray refracts and emits the first birefringent material, and the ordinary ray of the incident light advances and the extraordinary ray refracts and emits the second birefringent material. Ordinary rays of the incident light are made to go straight, and extraordinary rays are made to refract and exit the third birefringent material. Ordinary rays of made incident light are made to go straight and extraordinary rays are made to exit. And a fourth birefringent material.

The third birefringent material is between the second non-reciprocal optical rotation element and the third non-reciprocal optical rotation element, on the propagation path of one polarization of the first light, and The third birefringent material is arranged so that the azimuth of the intrinsic polarization of the third birefringent material substantially matches the azimuth of the other polarization of the first light.

The fourth birefringent material is between the second nonreciprocal optical rotation element and the third nonreciprocal optical rotation element, on the propagation path of the other polarization of the first light, and The fourth birefringent material is arranged so that the azimuth of the intrinsic polarization of the fourth birefringent material substantially coincides with the azimuth of one of the first lights.

The first birefringent material is between the first non-reciprocal optical rotation element and the third non-reciprocal optical rotation element, and through the birefringent material for multiplexing / demultiplexing and the first non-reciprocal optical rotation element. First lever
Is on the propagation path of one polarization of the second light incident on the birefringent material, and the azimuth of the intrinsic polarization of the first birefringence material is the azimuth of the polarization of one of the second lights. , And the polarization direction of one of the first lights.

The second birefringent material is between the first non-reciprocal optical rotation element and the third non-reciprocal optical rotation element, and through the birefringent material for multiplexing / demultiplexing and the first non-reciprocal optical rotation element. Second lever
Is on the propagation path of the other polarization of the second light incident on the birefringent material, and the azimuth of the intrinsic polarization of the second birefringence material is the azimuth of the other polarization of the second light. , And the polarization direction of the other polarization of the first light.

The optical circulator of the present invention comprises the birefringent material for demultiplexing, the birefringent material for demultiplexing, the birefringent material for demultiplexing, the first birefringent material, the second birefringent material, and the third birefringent material. The birefringent material and the fourth birefringent material are flat plates made of the same material. The thickness of each of the first to fourth birefringent materials, the demultiplexing birefringent material, and the demultiplexing birefringent material, It is characterized in that the ratio to the thickness of each birefringent material for multiplexing is √2: 1.

The present invention is also directed to a light control method using such an optical circulator.
After the first light input from the port is spatially separated into an ordinary ray and an extraordinary ray, the polarization planes of the ordinary ray and the extraordinary ray are divided into a second non-reciprocal optical rotation element, a reciprocal optical rotation element, and a third non-reciprocal optical rotation. After sequentially passing through the element and the first non-reciprocal optical rotation element, they are combined and output to the second port, and the second light input from the second port is spatially separated into an ordinary ray and an extraordinary ray. After that, after passing the polarization planes of the ordinary ray and the extraordinary ray through the first non-reciprocal optical rotation element, the third non-reciprocal optical rotation element, the reciprocal optical rotation element and the second non-reciprocal optical rotation element,
This is intended for a method of controlling the light that is combined and output to the third port, in which a birefringent material is arranged on a path where the first light does not propagate, and the second light is spatially anomalous as an ordinary ray. Correcting the optical path difference between these ordinary and extraordinary rays due to this spatial separation, by utilizing the difference in propagation velocity between these ordinary and extraordinary rays in this birefringent material after separation into the ordinary rays. This suppresses polarization dispersion of light output to the second and third ports.

Such an optical circulator according to the present invention comprises a first means for separating the first light input from the first port into an ordinary ray and an extraordinary ray, and a second light input from the second port. Via the second means for separating the ordinary ray and the extraordinary ray into the ordinary ray and the extraordinary ray, and subjecting the ordinary ray and the extraordinary ray inputted from the first port to the first transformation While outputting to the second port,
Second to the ordinary and extraordinary rays input from the second port
And third and third means for converting each of them into ordinary rays and extraordinary rays and outputting them to the third port.
A fourth means is provided on the path of the light propagating between the port and the fourth means for giving a phase difference or an optical path difference between the ordinary ray and the extraordinary ray passing therethrough.

In detail, the first means (D1, 2)
By passing 1-6), a phase difference (φ) or an optical path difference occurs between the ordinary ray and the extraordinary ray. Also, the first
When the light passes through the second means (D2, 21-7), a phase difference (φ) or an optical path difference occurs between the ordinary ray and the extraordinary ray. The first light is emitted by the third means (19-1 to 3, 20, 21).
-1 to 4), the first conversion is applied to the ordinary ray (J)
(First beam) is an extraordinary ray (I)
(Second beam) is converted to ordinary ray (J),
The phase difference generated between the ordinary ray and the extraordinary ray of the first light (between the first beam and the second beam) by passing through the first and second means is φ−φ = 0.

On the other hand, the second light is subjected to the second conversion by the third means, and the ordinary ray (J) (third beam) becomes an ordinary ray (J) and the extraordinary ray (I) (fourth beam). ) Has been converted into extraordinary ray (I), the phase difference between the third beam and the fourth beam of the second light caused by passing through the second means is φ. Further, since the second light passes through the fourth means, -φ is generated between the third beam and the fourth beam.
Therefore, the phase difference between the ordinary ray and the extraordinary ray of the second light coupled to the third port is φ−φ = 0. When the second light is multiplexed and input to the third port, fifth means for combining the input ordinary ray and extraordinary ray between the third port and the fourth means. However, in the case of using the fifth means, the phase difference (φ) when the second light is transmitted through the birefringent material which is the fifth means.
Or, since an optical path difference occurs, the fourth means considers this phase difference (φ) and gives a −2φ phase difference between the ordinary ray and the extraordinary ray of the second light in the fourth means. do it.

If the third means causes a phase difference between these beams, the fourth means also considers the phase difference. That is, the phase difference φ or 2φ compensated by the fourth means is the sum of the phase differences generated by the second means and the third means or the sum of the phase differences generated by the fifth means. However, if the phase difference generated by the third means is negligible with respect to the required polarization dispersion, it is not necessary to consider this phase difference.

[0022]

According to the optical circulator of the present invention, for example,
Coherent linearly polarized light having a wavelength of 1.3 μm or 1.55 μm emitted from the compound semiconductor laser is made incident from the first or second port. These lights incident from the first or second port have high isolation and are output to the second or third port, respectively.
Hereinafter, the propagation of light in the optical circulator when this light (first light) is input from the first port will be described.

The first light incident from the first port first passes through the birefringent material for demultiplexing. The birefringent material for demultiplexing spatially separates the incident light into an ordinary ray and an extraordinary ray and emits the ray. Both the ordinary ray and the extraordinary ray are incident on the first polarization beam splitter. The first polarization beam splitter is preferably a first surface such as a polarization separation film having a transmission selectivity between an ordinary ray and an extraordinary ray arranged at an angle of 45 degrees with respect to these incident lights. It is desirable to have a first reflection film arranged in parallel with the first surface. The ordinary ray incident from the surface of the first surface of the first polarization beam splitter is reflected by the first surface composed of a polarization separation film and the like, but the extraordinary ray incident from the surface of the first surface is The light is transmitted through one surface and is totally reflected by the first reflecting film arranged in parallel with the first surface. Therefore, these ordinary rays and extraordinary rays are emitted in parallel from the first polarization beam splitter.

In this way, the light transmitted through the first polarization beam splitter is incident on the second non-reciprocal optical rotation element. Here, the non-reciprocal optical rotation element is, for example, a Faraday rotator. When the clockwise direction is positive with respect to the traveling direction of light, the second non-reciprocal optical rotation element rotates the polarization planes of these incident lights by approximately -45 degrees (rotates the polarization direction by -45 degrees) and emits them. . The emitted −45 ° ordinary ray and −45 rotation extraordinary ray are incident on the fourth birefringent material and the third birefringent material, respectively. Since the −45 degree ordinary ray and the −45 extraordinary ray are ordinary rays with respect to the fourth and third birefringent materials, these rays are emitted without being walked off. Then, the light emitted from the fourth and third birefringent materials is input to the reciprocal optical rotation element and its polarization plane is rotated by +45 degrees, and then is incident on the third non-reciprocal optical rotation element and its polarized light. The wavefront is rotated by −45 ° and emitted.

Here, the reciprocal optical rotation element is a half-wave plate composed of, for example, rutile crystal. Therefore, the plane of polarization of each polarized light cannot be rotated by passing through the non-reciprocal optical rotation element formed of the set of the reciprocal optical rotation element and the third non-reciprocal optical rotation element.

The first light transmitted through the third non-reciprocal optical rotation element
The light (-45 degree rotation ordinary ray, -45 degree rotation extraordinary ray) is
Since both are extraordinary rays to the second and first birefringent materials, these rays are walked off and emitted by passing through the first and first birefringent materials, and then to the first non-reciprocal optical rotation element. It is incident. The light incident on the first non-reciprocal optical rotation element is emitted with its polarization direction rotated by approximately -45 degrees. The light emitted from these first non-reciprocal optical rotation elements enters the second polarization beam splitter. The second polarization beam splitter has, for example, a second surface that reflects ordinary rays and transmits extraordinary rays, so that the second polarization beam splitter has a second surface such as a total reflection mirror parallel to the second surface.
By changing the traveling direction of one of these lights by the reflecting surface, these lights are incident on the birefringent material for multiplexing / demultiplexing as parallel rays. The birefringent material for multiplexing / demultiplexing combines the incident extraordinary ray and ordinary ray and emits them in the second port direction. Therefore, the light incident from the first port is coupled to the second port. In addition, if the birefringent material for demultiplexing that the first light passes through is made of the same material as the birefringent material for demultiplexing, and the thicknesses thereof are made equal, in the third means,
Since ordinary rays of light are converted into extraordinary rays and extraordinary rays are converted into ordinary rays, the phase difference generated in the birefringent material for demultiplexing and the phase difference generated in the birefringent material for demultiplexing are combined. Therefore, it is possible to compensate for the phase difference between these two separated lights and suppress the polarization dispersion of the light coupled to the second port.

On the other hand, the second light incident from the second port is spatially separated into an ordinary ray and an extraordinary ray by passing through the birefringent material for multiplexing / demultiplexing, and then the ordinary ray. The extraordinary ray is incident from the surface side of the second surface of the second polarization beam splitter together and is incident on the first non-reciprocal optical rotation element. The second surface of the second polarization beam splitter reflects the incident ordinary ray and transmits the extraordinary ray, so that the traveling directions of these rays are changed, and these rays are parallel to each other. Entered in. The first non-reciprocal optical rotation element rotates the polarization planes of the ordinary ray and the extraordinary ray by +45 degrees and outputs them. These +45 degree rotating ordinary rays and +
The 45-degree-rotation extraordinary ray is incident on the first and second birefringent materials, which make these rays ordinary rays, and is input to the third non-reciprocal optical rotation element and reciprocal optical rotation element without walk-off.

These +45 degree rotating ordinary rays and +45 degrees
Since the extraordinary rotation ray passes through the third non-reciprocal optical rotation element and the reciprocal optical rotation element in order, the transmission of these third non-reciprocal optical rotation element and the reciprocal optical rotation element results in polarization of these lights. The wavefront is rotated by +90 degrees and emitted as +45 degree extraordinary ray and +45 degree ordinary ray, respectively. The +45 degree extraordinary ray and the +45 degree ordinary ray are incident on the third and fourth birefringent materials having these rays as ordinary rays, respectively. It is input to the reciprocal optical rotation element. The polarization planes of these lights are rotated by +45 degrees in the second non-reciprocal optical rotation element and are input to the first polarization beam splitter. These lights are output as parallel lights from the first polarization beam splitter, and these lights are combined by being transmitted through the birefringent material for multiplexing and are coupled to the third port. Here, the polarization compensating plate is arranged between the first polarization beam splitter and the combining birefringent material, and the ordinary ray generated by the combining / branching birefringent material and the combining birefringent material is used. It is possible to compensate for the phase difference with the extraordinary ray and thus suppress the polarization dispersion of the light coupled to the third port.

Further, in the present invention, one reciprocal optical rotator and 3
Since the optical circulator is composed of two non-reciprocal optical rotation elements, it is possible to suppress the wavelength dependence of the input light. Further, by using the first to fourth birefringent materials such as the walk-off polarization beam splitter, the amount of light coupled to the unintended port can be reduced, and high isolation can be achieved. If the ratio of the thickness of each of the first to fourth birefringent materials to the thickness of each of the demultiplexing birefringent material, the multiplexing / demultiplexing birefringent material, and the multiplexing birefringent material is √2: 1. , The light input from each port can be efficiently coupled to each other port.

[0030]

EXAMPLES Examples of the optical circulator of the present invention will be described below. In the following description, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a diagram showing the structure of an optical circulator according to an embodiment of the present invention. The optical circulator outputs the first light input from the first fiber (F1) that is the first port to the second fiber (F2) that is the second port, and outputs the first light input from the second fiber (F2). It is an optical circulator that outputs two lights to a third fiber (F3) that is a third port.

The optical circulator of this embodiment comprises a first polarization beam splitter (D1), a second polarization beam splitter (D2), and first to fourth birefringent materials (21-1 to 21-2).
21-4), birefringent material for demultiplexing (21-6), birefringent material for demultiplexing (21-7) and birefringent material for demultiplexing (21
-8).

The demultiplexing birefringent material (21-6) is arranged at a position facing the first port (F1). A spherical lens (L1) is disposed between the first port (F1) and the demultiplexing birefringent material (21-6), and the first port (F1)
The first light input from 1) is made into parallel light by passing through this spherical lens (L1) and is input to the demultiplexing birefringent material (21-6). Birefringent material for demultiplexing (21-
The first light input to 6) is separated into an ordinary ray (J) and an extraordinary ray (I).

The ordinary ray (J) and the extraordinary ray (I) which have passed through the birefringent material for demultiplexing (21-6) are incident on the first polarization beam splitter (D1). First
Of the polarization beam splitter (D1) of the first port (F
The ordinary ray and the extraordinary ray of the first light input from 1) are arranged such that the traveling directions of the ordinary ray and the extraordinary ray are parallel to each other, and the ordinary ray and the extraordinary ray input in parallel are combined to form a third ray. It is arranged to output to the port (F3).

The first polarization beam splitter (D1) is
4 for these lights coming from the first port (F1)
It has a polarization separation film (1112) which is the first surface and is arranged at an angle of 5 degrees. This polarization separation film (111
In 2), ordinary rays are reflected and extraordinary rays are transmitted. The polarization separation film (1112) is arranged on the hypotenuse of the prism (D12) having a right-angled triangular cross section. A prism (D11) having a parallelogrammatic cross section is arranged so as to face the hypotenuse of the prism (D12) having a right triangular shape with the polarization splitting film (1112) interposed therebetween. The parallelogram prism (D11) has a first reflecting surface (M1) parallel to the polarization splitting film (1112).

The ordinary ray (J) and the extraordinary ray incident from the surface of the first surface of the polarization beam splitter (D1) via the birefringent material for demultiplexing (21-6) have advancing directions of +90 degrees. It is bent and emitted in parallel. In detail,
The ordinary ray incident from the surface of the polarization separation film (1112) is reflected by the polarization separation film (1112).
The extraordinary ray incident from the surface of the surface (1112) passes through the first surface (1112) and is totally reflected by the reflecting surface (M1) arranged parallel to the first surface (1112). Therefore, the ordinary ray (J) and the extraordinary ray (1) are emitted in parallel from the first polarization beam splitter (D1). As the configuration of this polarization beam splitter, a polarization beam splitter having a structure shown in FIG. 5 of JP-B-60-49887 may be used.

The combination of the second fiber (F2) which is the second port and the second polarization beam splitter (D2) is the same as the combination of the first port (F1) and the first polarization beam splitter (D1). Is. The details will be described below.

The birefringent material (21-7) for multiplexing / demultiplexing is the second
It is arranged at a position facing the port (F2). Second
A spherical lens (L2) is arranged between the port (F2) and the birefringent material (21-7) for multiplexing and demultiplexing, and the second light input from the second port (F2) receives the spherical light. Lens (L
It is converted into parallel light by passing through 2) and is input to the birefringent material (21-7) for multiplexing / demultiplexing. The second light input to the birefringent material for multiplexing / demultiplexing (21-7) is separated into an ordinary ray (J) and an extraordinary ray (I).

The ordinary ray (J) and the extraordinary ray (I) transmitted through the birefringent material (21-7) for multiplexing / demultiplexing are:
It is incident on the second polarization beam splitter (D2). The second polarization beam splitter (D2) is connected to the second port (F
The ordinary rays and the extraordinary rays of the second light input from 2) are arranged so as to be parallel to each other and output.

The second polarization beam splitter (D2) is
4 for these lights incident from the second port (F1)
It has a polarization separation film (2122) which is the second surface and is arranged at an angle of 5 degrees. This polarization separation film (212
In 2), ordinary rays are reflected and extraordinary rays are transmitted. This polarization separation film (2122) is arranged on the hypotenuse of a prism (D22) having a right-angled triangular cross section. A prism (D21) having a parallelogrammatic cross section is arranged so as to face the hypotenuse of the prism (D22) having a right triangle with a polarization splitting film (2122) interposed therebetween. The parallelogram prism (D21) has a second reflecting surface (M2) parallel to the polarization splitting film (2122).

The second surface (2) of the second polarization beam splitter (D2) is passed through the birefringent material (21-7) for multiplexing / demultiplexing.
The ordinary ray (J) and the extraordinary ray incident from the surface of (122) are emitted in parallel with their traveling directions bent by +90 degrees. More specifically, the ordinary ray incident from the surface of the polarization separation film (2122) is reflected by the polarization separation film (2122), while the extraordinary ray incident from the surface of the second surface (2122) is the second surface. The light passes through (2122) and is totally reflected by the reflecting surface (M2) arranged in parallel with the first surface (2122). Therefore, the second polarization beam splitter (D
From 2), the ordinary ray (J) and the extraordinary ray (1) are emitted in parallel.

Codes (21-1 to 21-4, 19-1 to 1)
9-3, 20) is arranged between the first polarization beam splitter (D1) and the second polarization beam splitter (D2). These optical components perform the first conversion on the ordinary ray and the extraordinary ray of the first light input from the first polarization beam splitter (D1), and make the second polarization as the extraordinary ray and the ordinary ray, respectively. The beam splitter (D2) outputs the second
Ordinary rays and extraordinary rays of the second light input from the polarization beam splitter (D2) are subjected to second conversion, and are output to the first polarization beam splitter (D1) as extraordinary rays and ordinary rays. .

More specifically, this optical component includes a first non-reciprocal optical rotation element (19-1) and a second non-reciprocal optical rotation element (19-).
2), the third non-reciprocal optical rotation element (19-3), the reciprocal optical rotation element (20) and the first to fourth birefringent materials (21-1 to 21-1).
21-4).

The first Faraday rotator, which is the first non-reciprocal optical rotation element (19-1), is arranged so as to face the second polarization beam splitter (D2), and the direction of the incident polarized light is ± 45 degrees. Rotate. Second non-reciprocal optical rotation element (19
-2) which is the second Faraday rotator includes the first non-reciprocal optical rotation element (19-1) and the first polarization beam splitter (D
It is located between 1) and the direction of incident polarized light is ±
Rotate 45 degrees. Third non-reciprocal optical rotation element (19-3)
Is disposed between the second non-reciprocal optical rotation element (19-2) and the first non-reciprocal optical rotation element (19-1), and the incident polarization direction is ± 45 degrees. Rotate. The half-wave plate which is the reciprocal optical rotation element (20) is the third
Is disposed between the non-reciprocal optical rotation element (19-3) and the second non-reciprocal optical rotation element (19-2) and rotates the azimuth of incident polarized light by 45 degrees. Here, the third non-reciprocal optical rotation element (1
9-3) and the reciprocal optical rotation element (20) are combined to form a non-reciprocal optical rotation element (3).
9-3) rotates the polarization plane of polarized light transmitted in the non-reciprocal optical rotation element (20) direction by 90 degrees, and transmits the polarization plane of polarized light transmitted from the reciprocal optical rotation element (20) in the non-reciprocal optical rotation element (19-1) direction. Does not rotate as a result. Then, these Faraday rotators (19-1 to 19-3) are arranged in a magnetic field formed by a cylindrical magnet (MG) arranged so as to surround the optical circulator.

First to fourth birefringent materials (21-1 to 21-21)
-4) is a birefringent material that straightens the ordinary ray of the incident light and refracts the extraordinary ray of the incident light, and outputs the birefringent material, which is composed of a walk-off polarization beam splitter. The first
Birefringent material (21-1) and second birefringent material (21-
In 2), the crystal axes thereof are orthogonal to each other, and the third birefringent material (21-3) and the fourth birefringent material (21-4).
Also, their crystal axes are orthogonal.

The third birefringent material (21-3) is arranged between the second non-reciprocal optical rotation element (19-2) and the reciprocal optical rotation element (20). Similarly, the fourth birefringent material (2
1-4) also includes the second non-reciprocal optical rotation element (19-2) and the third non-reciprocal optical rotation element (19-2).
It is arranged between the non-reciprocal optical rotation element (19-3). The third birefringent material (21-3) is connected to the first port (F
The first light, which is disposed on the propagation path of one polarization of the first light input from 1), is the first polarization beam splitter (D1) and the second non-reciprocal optical rotation element (19-
By passing 2), the extraordinary ray (I ') of -45 degree rotation and the ordinary ray (J') of -45 degree rotation are separated and emitted in parallel.

The third birefringent material (21-3) is
Although the 45-degree rotation extraordinary ray (I ′) is arranged on the propagation path, the orientation of the intrinsic polarization of the third birefringent material (21-3) is −45-degree rotation ordinary ray (J ′) polarization. It is arranged so that it almost matches the azimuth. Therefore, this third
Since the -45 degree rotation extraordinary ray (I ') incident on the birefringent material (21-3) is an ordinary ray with respect to the third birefringence material (21-3), the -45 degree rotation extraordinary ray (I') I
´) will never be walked off.

The fourth birefringent material (21-4) is arranged on the path along which the -45 degree rotating ordinary ray (J ') of the first light propagates. 21-4) is arranged so that the azimuth of the intrinsic polarization substantially coincides with the azimuth of the polarization of the -45 degree extraordinary ray (I ′). Therefore, it is incident on this fourth birefringent material (21-4).
The 5 ° rotating ordinary ray (J ′) is reflected by the fourth birefringent material (2
Since it is an ordinary ray for 1-4), the ordinary ray (J ') rotated by -45 degrees is not walked off.

The first birefringent material (21-1) is arranged between the first non-reciprocal optical rotation element (21-1) and the third non-reciprocal optical rotation element (21-1). 2nd port (F
The second light incident from 2) passes through the birefringent material for multiplexing / demultiplexing and the first non-reciprocal optical rotation element (19-1), so that a +45 degree ordinary ray (J ′) and a +45 extraordinary ray are rotated. It is separated into (I ') and emitted in parallel. The first birefringent material (21-1) is arranged on the path along which the + 45-degree rotating ordinary ray (J ′) propagates, but the intrinsic polarization of the first birefringent material (21-1) is The azimuth is substantially the same as the azimuth of the + 45-degree rotating ordinary ray (J ′) in the second light. Further, the azimuth of the intrinsic polarization of the first birefringent material (21-1) is the azimuth of one polarization of the first light input from the first port (F1), which is a -45 degree rotation ordinary ray. It is arranged so as to substantially coincide with the azimuth of (J ′).

The second birefringent material (21-2) is arranged between the first non-reciprocal optical rotation element (19-1) and the third non-reciprocal optical rotation element (19-3).

The second birefringent material (21-2) passes through the second birefringent material (21-7) for multiplexing / demultiplexing and the first non-reciprocal optical rotation element (19-1). Material (21-
The second birefringent material (2) is arranged on the path through which the + 45 ° extraordinary ray (I ′) incident on 2) propagates.
The azimuth of the intrinsically polarized light of 1-2) substantially coincides with the azimuth of the +45 degree rotation extraordinary ray (I ′) of the second light. Further, the azimuth of the intrinsic polarization of the second birefringent material (21-2) is the azimuth of the other polarization of the first light input from the first port (F1), which is a -45 degree rotation extraordinary ray. (I
It is arranged so as to almost coincide with the azimuth of ´).

The polarization compensating plate (H1) is arranged between the first polarization beam splitter (D1) and the multiplexing birefringent material (21-8). Since the polarization compensator (H1) has its optical axis orthogonal to the incident ordinary and extraordinary rays, the ordinary and extraordinary rays do not change their traveling directions, and the birefringence for combining waves is changed. It is emitted parallel to the material (21-8). The birefringent material for multiplexing (21-8) is
It is arranged to face the third port (F3), and the third spherical lens (L3) is arranged between the multiplexing birefringent material (21-8) and the third fiber (F3). There is. The light input from the multiplexing birefringent material (21-8) to the third spherical lens (L3) is focused on the end face of the third fiber (F3) and coupled to this fiber (F3).

The fibers (F1 to F3) forming the first to third ports are single mode optical fibers,
The spherical lenses (L1 to L3) have a diameter of 2.0 mm. First to fourth birefringent materials (21-1 to 21-4) and demultiplexing birefringent material (21-6), demultiplexing birefringent material (2
1-7), the birefringent material for multiplexing (21-8) has a thickness of 1.0 when the direction of light passing therethrough is the thickness direction.
It is a 0 mm rutile crystal flat plate. The thickness of each of the first to fourth birefringent materials (21-1 to 21-4) is 1.41.
mm. The polarization compensator (H1) has a thickness of 2.
It is a 0 mm rutile crystal flat plate. Reciprocal optical rotation element 1
The thickness of the 1/2 wave plate (20) is 0.09 mm, the outer diameter of the cylindrical magnet (MG) is 7.0 mm, and the length is 7.
It is 0 mm. That is, the demultiplexing birefringent material (21-6), the demultiplexing birefringent material (21-7), the demultiplexing birefringent material (21-8), and the first birefringent material (21-
1), a second birefringent material (21-2), a third birefringent material (21-3) and a fourth birefringent material (21-4).
Is a flat plate made of the same material, the thickness of each of the first to fourth birefringent materials (21-1 to 21-4), the birefringent material for demultiplexing (21-6), and the birefringent material for demultiplexing. Refractive material (21
-7), and the ratio with the thickness of each of the multiplexing birefringent material (21-8) is √2: 1. The ratio of these thicknesses is √2
By setting the ratio to 1, the light can be efficiently coupled to each port and the optical isolation of coupling to each port can be enhanced.

In such an optical circulator, each optical component can be mounted on, for example, a silicon substrate SI as shown in FIG. The optical circulator substrate CI on which the optical circulator is mounted is a normal (001)
After the Si wafer is cut into a rectangular shape by dicing, holes for fixing each optical component are formed by etching, and as shown in the figure, each optical component (19
-1 to 19-3, 21-1 to 21-8, H1, 20, D
1, D2, L1 to L3) are fitted and fixed. For example, the first polarization beam splitter (D1) has a hole (D1).
´) and fix it. If the polarization beam splitter (D1) as one optical component is not sufficiently fixed by the hole (D1 ′), a resin such as epoxy resin or liquid crystal polymer may be poured into the hole (D1 ′) and fixed.
Such a resin may be a thermosetting resin or a photocurable resin that is cured by irradiation with ultraviolet rays or the like. However, when the photo-curable resin is used, the Faraday rotator and the like that compose the optical circulator are not heated, so that deterioration of these delicate elements can be prevented.

Surface SF on which the optical components of FIG.
Is (00 of the silicon crystal that constitutes the silicon substrate SI.
1) surface. Therefore, two surfaces which are perpendicular to this surface SF and which are orthogonal to each other are (100) surface and (0
10) surface. The silicon substrate SI is rectangular (rectangular), and the four sides forming this rectangle are the (100) plane and the (01) plane.
Parallel to the (0) plane, and the (100) and (010) planes are
It is formed by using the cleavage process of a silicon wafer (00
1) A cleavage plane of a silicon wafer.

The present invention is an optical circulator that takes into consideration the influence of polarization dispersion when transmitting an optical signal having a high beat rate, which is performed for the next-generation optical communication. Therefore, highly accurate positioning is required for each optical component that constitutes such a highly accurate optical circulator. Single crystal silicon has silicon atoms arranged in a grid pattern like a grid, and high-precision positioning can be performed by utilizing the array order of this crystal.

The optical fibers (F1, F2, F3) are fixed in V grooves (V1, V2, V3) formed by etching the silicon substrate from the (001) surface. The V shape in the depth direction of the V groove (V1, V2, V3) can be formed by utilizing the etching selectivity of the silicon substrate. Moreover, this V groove (V1, V2, V
The longitudinal direction of 3) is the [001] direction or [01] of the crystal.
[0] direction, and the planes formed by dicing using the cleavage property of the crystal are parallel to these directions. Therefore, V is based on the (100) plane and the (010) plane which are the cleavage planes. The grooves (V1, V2, V3) may be formed. Further, the hole for fixing each optical component can be processed with high accuracy by utilizing the orientation of the silicon crystal. In addition,
Like the (001) silicon wafer, the (111) silicon wafer can be used as the fixed substrate of the circulator. Here, the package PK is composed of a light-shielding member so that ambient light from the outside of the package PK does not enter the inside. In particular, the package PK, which is a light-shielding member, is composed of a light-shielding member that shields light having a wavelength shorter than the wavelength of the signal light incident on the optical circulator.

The optical circulator substrate (CI) may be housed in a package as shown in FIG. 3, for example. This optical circulator device, as shown,
Optical circulator board (CI) housed in package (PK), cylindrical magnet (MG) fitted in hole (PK3) for fixing cylindrical magnet formed in inner wall of package (PK), optical circulator board Fixing members PK1 and PK2 for fixing CI, and a cylindrical member (F1) for fixing each fiber (F1, F3).
′, F3 ′). Fiber (F1, F3)
May be fixed in the through holes of the cylindrical and hollow members (F1 ′, F3 ′) with an adhesive,
In addition, members (F1 ′,
A member having a shape fitting with the inner wall surface of F3 ′) may be fixed, and the member having a fitting shape may be fitted and fixed to the members (F1 ′, F3 ′).

In this optical circulator device, an erbium-doped fiber (EDF) is fitted in a spiral V groove formed on the inner wall of the package (PK). A reflecting mirror (MR) is fixed to one end of the erbium-doped fiber (EDF), and an optical multiplexer / demultiplexer (WDM) is connected to the other end. A second fiber (F1) and a pumping light introducing fiber (FP) are connected to the optical multiplexer / demultiplexer (WDM). Therefore, when the signal light is input from the first fiber (F1) and the pump light is introduced from the fiber (FP), the signal light is amplified in the erbium-doped fiber (EDF) and is reflected by the reflecting mirror (MR). After being reflected, this reflected light is introduced into the optical circulator substrate (CI) from the second fiber (F1). Second fiber (F
The reflected light input from 1) is output from the third fiber (F3). That is, the signal light input from the first port (F1) is amplified and output from the third port (F3).

(Operation of Optical Circulator) Next, the operation of the circulator will be described.

First, the case where the first light is input from the first port (F1) of the circulator will be described with reference to FIGS. The light input from the first port (F1) is first separated into the ordinary ray (J) and the extraordinary ray (I) by passing through the demultiplexing birefringent material (21-6). Next, these lights are input to the first beam splitter (D1). First beam splitter (D
In 1), since the polarization separation film (1112) arranged at an angle of about 45 degrees with respect to the incident direction of these lights is arranged, the extraordinary ray (I) is reflected by the polarization separation film (111).
2) and is totally reflected by the first reflecting surface (M1), and its traveling direction is bent by +90 degrees in a plane parallel to the paper surface of FIG.
It is output from 1). On the other hand, the ordinary ray (J) is reflected by the polarization separation film (1112), its traveling direction is bent by +90 degrees, and emitted from the first polarization beam splitter (D1) in parallel with the extraordinary ray (I). These ordinary rays (J)
And the extraordinary ray (I) are transmitted to the second non-reciprocal optical rotation element (19
-2) is input in parallel. FIG. 5 shows that the ordinary ray (J) and the extraordinary ray (I) are incident on the second non-reciprocal optical rotation element (19-2) and then the first non-reciprocal optical rotation element (1).
9-1) is an explanatory view showing obliquely the states of these polarizations from the output to the output, and the direction of the plane of polarization is circled in the virtual plane formed by being surrounded by the alternate long and short dash line in FIG. It is indicated by a-mark. Further, the + mark in the figure indicates a point on the PP line segment in FIG. In addition, the following FIG. 7, FIG. 9 and FIG.
1 also describes the polarization state using the same expression format as in FIG.

The Faraday rotator (19-2), which is a non-reciprocal optical rotator, has a polarization plane of -45 traveling in the material.
After being rotated by a degree, these (-45 rotation ordinary ray: J ') and (-45 rotation extraordinary ray: I') are output in parallel.

Ordinary rays (J-rotated by -45 degrees) output in parallel
′) And the -45 degree rotation extraordinary ray (I ′) are respectively the fourth walk-off polarization beam splitter (21-4) which is the fourth birefringent material and the third walk-off polarization beam splitter which is the third birefringent material. It is input to (21-3).

These -45 degree rotating ordinary ray (J ') and -45 degree rotating extraordinary ray (I') are ordinary rays to these walk-off polarization beam splitters (21-4) and (21-4), respectively. Therefore, the -45 degree rotating ordinary ray (J ') and the -45 degree rotating extraordinary ray (I') are
The fourth walk-off polarization beam splitter (21
-4) and the third walk-off polarization beam splitter (21-3) without being walked off.

A -45 degree rotating ordinary ray (J) which has passed through the fourth walk-off polarization beam splitter (21-4) and the third walk-off polarization beam splitter (21-3).
′) And the -45 degree rotation extraordinary ray (I ′) are input in parallel to the half-wave plate (20) which is the reciprocal optical rotation element.

The -45 degree rotation ordinary ray (J-) output from the fourth walk-off polarization beam splitter (21-4)
′) Has its plane of polarization rotated by +45 degrees and is output from this reciprocal optical rotation element (20) as an ordinary ray (J). On the other hand, the fourth walk-off polarization beam splitter (2
-45 degree rotation extraordinary ray (I ') output from 1-4)
The plane of polarization is rotated by +45 degrees and is output from this reciprocal optical rotation element (20) as an extraordinary ray (I).

The ordinary ray (J) and the extraordinary ray (I) output in parallel from the reciprocal optical rotation element (20) are input in parallel to the third non-reciprocal optical rotation element (19-3). The third non-reciprocal optical rotation element (19-3) rotates the plane of polarization propagating in the material by -45 degrees to make these -45 rotation ordinary rays (J
′) And the -45 degree rotation extraordinary ray (I ′) are output in parallel.

The -45 rotation ordinary ray (J ') and the -45 degree rotation extraordinary ray (I') output from the third non-reciprocal optical rotation element (19-3) are respectively the second walk-off polarized beam. It is input in parallel to the splitter (21-2) and the first walk-off polarization beam splitter (21-1). These -45 degree rotating ordinary rays (J ') and -4
The 5 degree extraordinary ray (I ′) is reflected by these walk-off polarization beam splitters (21-2) and (21), respectively.
Since it is an extraordinary ray for -2), the -45 degree rotating ordinary ray (J ') and the -45 degree rotating extraordinary ray (I') are respectively the second walk-off polarization beam splitter (21-
2) and the first walk-off polarization beam splitter (2
By passing through 1-1), it is walked off by a distance d in the direction of the polarization direction.

That is, assuming that the direction from the back of the paper surface of FIG. 4 to the front is the reference 0 degree direction and the clockwise rotation with respect to the traveling direction of the light is the positive direction, the ordinary ray of -45 degree rotation ( J ′) is walked off in the direction of +135 degrees (upper left direction in FIG. 5) by the distance d, and the -45 degree rotation extraordinary ray (I
′) Is walked off in the direction of −135 degrees (lower left direction in FIG. 5) by the distance d.

Ordinary ray (-') rotated by -45 degrees and abnormal rotation by -45 degrees output from the second walk-off polarization beam splitter (21-2) and the first walk-off polarization beam (21-1), respectively. The light beam (I ′) is transmitted through the first Faraday rotator (19−) which is the first non-reciprocal optical rotation element.
It is input in parallel to 1). Therefore, the -45 degree rotating ordinary ray (J ') output from each of the walk-off polarization beam splitters (21-2, 21-1) becomes an extraordinary ray (I) by rotating its polarization plane by -45 degrees. , The -45 degree rotation extraordinary ray (I ') output from the first Faraday rotator (19-1) has its polarization plane rotated by -45 degrees and becomes an ordinary ray (J). 19-
It is output in parallel from 1).

These lights (J, I) are input in parallel to the second polarization beam splitter (D2). Ordinary ray (J) input to the second polarization beam splitter (D2)
Is reflected by the second polarization separation film (2122) arranged in the second polarization beam splitter (D2) with an inclination of 45 degrees with respect to the incident direction of the ordinary ray (J), and its traveling direction is It is rotated by −90 ° in a plane including the paper surface of FIG. 4 and output from the second polarization beam splitter (D2). On the other hand, the second polarization beam splitter (D
The extraordinary ray (I) input to 2) is reflected by the second reflecting surface (M2) of the second polarizing beam splitter (D2) having an inclination of 45 degrees with respect to the incident direction of the extraordinary ray (I). It is reflected, its traveling direction is rotated by −90 degrees in the plane including the paper surface of FIG. 4, and it is transmitted through the polarization separation film (2122) arranged in parallel with the surface (M2) and the second polarization beam splitter ( It is output from D2).

The ordinary ray (J) and the extraordinary ray (I) output from the second polarization beam splitter (D2) are input to the flat birefringent material (21-7) for multiplexing and demultiplexing, and the combined ray. The waves are combined in the demultiplexing birefringent material (21-7) and output from the demultiplexing birefringent material (21-7). The light output from the birefringent material for multiplexing / demultiplexing (21-7) is focused on the end face of the fiber (F2) by passing through the spherical lens (L2) and input into the fiber (F2).

Here, the demultiplexing birefringent material (21-6) and the demultiplexing birefringent material (21-7) are set to have the same thickness, and the first input from the first port (F1). One polarization of one light passes through the birefringent material for demultiplexing (21-6) as the ordinary ray (J), passes through the birefringent material for the demultiplexing as the extraordinary ray (I), and the first port ( The other polarized light input from F1) passes through the birefringent material for demultiplexing (21-6) as an extraordinary ray (I) and passes through the birefringent material for demultiplexing (21-7) as an ordinary ray (J). Since they pass through, there is no phase difference or optical path difference between these lights. Therefore,
The first light input from the first port (F1) can be coupled to the second port (F2) without causing polarization dispersion.

Next, the operation when the second light is input from the second port (F2) of the circulator will be described with reference to FIGS. 6 and 7. 2nd port (F2)
The light input from the first, the birefringent material (21
By passing through -7), it is separated into an ordinary ray (J) and an extraordinary ray (I). Next, these lights are input to the second beam splitter (D2).

The second beam splitter (D2) is provided with the polarization separation film (2122) arranged at an angle of about 45 degrees with respect to the incident direction of these lights, so that an extraordinary ray is generated. (I) is transmitted through the polarization separation film (2122) and is reflected by the surface (M2) of the first polarization beam splitter (D2) parallel to the polarization separation film (2122), and the traveling direction thereof is the paper surface of FIG. It is bent by +90 degrees in a plane parallel to and is transmitted through the second polarization beam splitter (D2). On the other hand, the ordinary ray (J) is the polarized light separating film (2122).
Is reflected by the second polarization beam splitter (D) and its traveling direction is bent by +90 degrees in a plane parallel to the paper surface of FIG.
2) is transmitted. Therefore, the ordinary ray (J) and the extraordinary ray (I) are output in parallel from the second polarization beam splitter (D2) and enter in parallel to the first non-reciprocal optical rotation element (19-1). It In FIG. 7, these ordinary ray (J) and extraordinary ray (I) are incident on the first non-reciprocal optical rotation element (19-1) and then emitted from the second non-reciprocal optical rotation element (19-2). It is explanatory drawing which shows the state of these polarized lights up to.

The Faraday rotator (19-1), which is the first non-reciprocal optical rotator, rotates the polarization plane of the polarized light traveling in the material by +45 degrees.
By passing through 1), these extraordinary ray (I) and ordinary ray (J) do not change their traveling directions (+45 degree extraordinary ray: I ') and (+45 degree ordinary ray: J', respectively). ) As parallel outputs from the Faraday rotator (19-1) to the second walk-off polarization beam splitter (21-2) and the first walk-off polarization beam splitter (21-1) as the first birefringent material, respectively. Is entered.

These +45 degree rotation extraordinary ray (I ') and +45 degree rotation ordinary ray (J') are the ordinary rays for these walk-off polarization beam splitters (21-2) and (21-1), respectively. , +45 degree rotation extraordinary ray (I ') and +45 degree rotation ordinary ray (J'),
The second walk-off polarization beam splitter (21
-2) and the first walk-off polarization beam splitter (21-1) to be output from these walk-off polarization beam splitters (21-2, 21-1) without being walked off.

An extraordinary ray (I + 45) rotated by +45 degrees which has passed through the second walk-off polarization beam splitter (21-2) and the first walk-off polarization beam splitter (21-1).
′) And the +45 degree ordinary ray (J ′) are input in parallel to the third Faraday rotator (19-3). Therefore, the + 45-degree rotation extraordinary ray (I ′) and the + 45-degree rotation ordinary ray (J ′) are transmitted through the third Faraday rotator (19-3), so that their polarization planes are rotated by +45 degrees and +45 degrees. The degree-rotation extraordinary ray (I ′) is output as an ordinary ray (J), and the +45 degree rotation ordinary ray (J ′) is output as an extraordinary ray (I) in parallel from the third Faraday rotator (19-3).

Next, these lights transmitted through the third Faraday rotator (19-3) are input in parallel to the half-wave plate (20). Therefore, the third Faraday rotator (19-
The ordinary ray (J) output from 3) has a polarization plane of +4
The extraordinary ray (I) output from the third Faraday rotator (19-3) is rotated by +45 degrees by being rotated by +45 degrees. The abnormal rotation light (I ′) is output from the half-wave plate (20) in parallel.

The + 45-degree rotation ordinary ray (J ') and the + 45-degree rotation extraordinary ray (I') are respectively the fourth walk-off polarization beam splitter (21-4) and the third birefringent material, the third birefringent material. Walk-off polarized beam (21
-3) is input in parallel. These +45 degree rotating ordinary ray (J ′) and +45 degree rotating extraordinary ray (I ′) are respectively generated by these walk-off polarization beam splitters (2 ′).
Since it is an ordinary light for 1-4) and (21-3),
The +45 degree rotation ordinary ray (J ′) and the +45 degree rotation extraordinary ray (I ′) pass through the fourth walk-off polarization beam splitter (21-4) and the third walk-off polarization beam splitter (21-3), respectively. As a result, the walk-off polarization beam splitters (21-4, 21-3) do not output the walk-off signals and output them in parallel.

Further, the + 45-degree rotating ordinary ray (J ') and + 45-degree rotating abnormality output from the fourth walk-off polarization beam splitter (21-4) and the third walk-off polarization beam (21-3), respectively. Ray (I
′) Is input to the second Faraday rotator (19-2). Therefore, the +45 degree rotating ordinary ray (J 4) output from the walk-off polarization beam splitter (21-4)
′) Has its plane of polarization rotated by +45 degrees to become an extraordinary ray (I), and the walk-off polarization beam splitter (2)
Extraordinary ray (I ') rotated by +45 degrees output from 1-3)
Has its plane of polarization rotated by +45 degrees and is an ordinary ray (J).
And is output in parallel from the Faraday rotator (19-2). The ordinary ray (J) and the extraordinary ray (I) output from the second Faraday rotator (19-2) are input to the first polarization beam splitter (D1).

The extraordinary ray (J) input to the first polarization beam splitter (D2) is inclined in the second polarization beam splitter (D2) by 45 degrees with respect to the incident direction of the ordinary ray (J). The second polarization separation film (21
22) and a second polarization beam splitter (D2)
Output from On the other hand, the ordinary ray (J) input to the second polarization beam splitter (D2) has a second polarization beam splitter (D2) inclined by 45 degrees with respect to the incident direction of this ordinary ray (J). Is reflected by the surface (M2) of FIG.
It is rotated by 90 degrees, and thereafter, it is reflected by the polarization separation film (2122) arranged parallel to the surface (M2) and its traveling direction is bent by +90 degrees in a plane including the paper surface of FIG. It is output from the polarization beam splitter (D2) in parallel with the extraordinary ray (I).

Next, these lights (I, J) are input in parallel to the polarization compensating plate (H1). Polarization compensator (H1)
Is arranged so that its incident surface is perpendicular to the traveling directions of the extraordinary ray (I) and the ordinary ray (J) incident on it, and since the optical axis is perpendicular to the traveling direction of the light,
The extraordinary ray (I) and the ordinary ray (J) are given a phase difference without changing their traveling directions and are input in parallel to the birefringent material (21-8) for multiplexing. The ordinary ray (J) and the extraordinary ray (I) input to the birefringent material (21-8) for multiplexing are combined and output, and the third spherical lens (L3).
Is input to The second light input to the third spherical lens is
The light passes through this lens to be focused and coupled to the end face of the third fiber (F3).

Here, the birefringent material for multiplexing / demultiplexing (21-7)
And the phase difference between the separated lights (I, J) generated in the multiplexing birefringent material (21-8) is due to the polarization compensation plate (H
Since the compensation is performed in 1), the second light input from the second port (F2) is input to the third port (F3) without causing polarization dispersion.

As described above, in this embodiment, after the first light input from the first port (F1) is spatially separated into the ordinary ray and the extraordinary ray, the planes of polarization of these ordinary ray and extraordinary ray are The second non-reciprocal optical rotation element (19-2), the reciprocal optical rotation element (20), the third non-reciprocal optical rotation element (19-3), the first
After sequentially passing through the non-reciprocal optical rotation element (19-2),
Combined and output to the second port (F2),
After the second light input from the port (F2) is spatially separated into an ordinary ray and an extraordinary ray, the planes of polarization of the ordinary ray and the extraordinary ray are changed to the first non-reciprocal optical rotation element (19-1), 3 Non-reciprocal optical rotation element (19-3), Reciprocal optical rotation element (2
0), the second non-reciprocal optical rotation element (19-2) was sequentially passed through, and then the light was multiplexed and output to the third port (F3). Here, after the second light is spatially separated into an ordinary ray and an extraordinary ray, the difference in propagation velocity between the ordinary ray and the extraordinary ray in the polarization compensating plate (H1) made of a birefringent material is utilized. By correcting the optical path difference between the ordinary ray and the extraordinary ray due to this spatial separation, it is possible to suppress the polarization dispersion of the light output to the third port (F3).

That is, the first light is transmitted through the demultiplexing birefringent material (21-6) to generate the first beam (J).
And a second beam (I), which results in a second beam
The phase of the beam (I) leads the first beam (J) by + φ degrees (1: 2 = 0 degrees: + φ degrees). After that, these beams pass through the birefringent material (21-7) for multiplexing and demultiplexing, whereby the phase of the first beam (I) is advanced by + φ degrees from the second beam (J) (1: 2 = + Φ degree: + φ degree), second
Polarization dispersion of the light incident on the fiber (F2) can be suppressed.

The second light is a birefringent material (21-
By passing through 7), the beam is separated into the first beam (J) and the second beam (I), which leads the phase of the second beam (I) by + φ degrees relative to the first beam (J). (1: 2 = 0 degree: + φ degree). After that, these beams pass through the polarization compensating plate (H1), so that the phase of the first beam (J) is + 2φ more than that of the second beam (I).
Just proceed (1: 2 = + 2φ degree: φ degree). Further, these beams are transmitted through the birefringent material (21-8) for multiplexing, so that the phase of the second beam (I) is changed to the first beam (J).
More than + φ degrees (1: 2 = + 2φ degrees: + 2φ
Degree), it is possible to suppress the polarization dispersion of the light incident on the third fiber (F3).

Next, a case where the polarized light propagating in the optical circulator does not propagate as desired due to the imperfections of the optical components constituting the optical circulator will be described with reference to FIGS. 8 to 9.

The propagation of light when the second light is input from the second port (F2) will be described below.

FIGS. 8 and 9 correspond to the above-mentioned FIGS. 6 and 7, respectively, which are the second port (F2).
It is a figure for demonstrating a state until the light input from is output to the 3rd port (F3). 2nd port (F
The way in which the light input from (2) is input to the reciprocal optical rotation element (20) is propagated as described in FIGS. 6 and 7. Here, the +45 degree ordinary ray (J ') and the +45 degree extraordinary ray (I') transmitted through the reciprocal optical rotation element (20) are caused by imperfections of optical components, etc. (I ': EXTRA) and +4
It is assumed that a 5 ° rotating ordinary ray (J ′: EXTRA) is included. Then, these extraordinary rays of +45 degree rotation (I ':
EXTRA) and +45 degree ordinary ray (J ': EXT)
RA) is extraordinary light for the fourth walk-off polarization beam splitter (21-4) and the third walk-off polarization beam splitter (21-3), respectively,
The extraordinary ray (I ′: EXTRA) rotated by +45 degrees is walked off by a distance d in the −45 degree direction (upper right direction in FIG. 9) by the fourth walk-off polarization beam splitter (21-4), and is normally rotated by +45 degrees. Ray (J ': EXTRA)
Is a third walk-off polarization beam splitter (21-
By 3), the distance d in the +45 degree direction (the lower right direction in FIG. 9)
Just walked off. Note that, in FIG. 8, the traveling paths of these lights (EXTRA) are indicated by a dashed line.

These lights (EXTRA) are input to the second Faraday rotator (19-2), and their polarization planes are rotated by +45 degrees and output. Thereafter, these lights (EXTRA) are input to the first polarization beam splitter (D1) while maintaining the traveling direction. Of course, the desired light is input to the third port (F3) as described above, but these undesired lights (EXTRA) are
An extraordinary ray (I: EXTRA)
Is reflected by the surface (M1) and then the polarization separation film (1112)
And the ordinary ray (J: EXTRA) passes through the polarization separation film (1
The light is reflected at 112) and input to the birefringent material for demultiplexing (21-6). Unwanted extraordinary rays (I: EXTR
A) is refracted by the sixth birefringent material (21-6), so that the extraordinary ray (I: EXTRA) and the ordinary ray (J: EXTRA) pass laterally of the lens (L2). Therefore, these unwanted lights do not couple to the first port (F1).

FIG. 10 shows the dependency of the isolation (dB) on the temperature (° C.) by the optical circulator of the present embodiment (solid line), the temperature dependency of the isolation of the optical circulator described in JP-B-60-49887. It is a graph which shows the numerical calculation result (dotted line). In addition, FIG.
Is the numerical calculation result of the dependence (solid line) of the isolation (dB) by the optical circulator of this embodiment on the wavelength (nm), and the wavelength dependence of the isolation of the optical circulator described in JP-B-60-49887 ( It is a graph which shows a dotted line. As is clear from these graphs, the optical circulator of this example has high isolation and is not so temperature dependent. Further, the optical circulator of the present embodiment is 1450-
It is possible to transmit light having a wide wavelength of 1650 nm with high isolation without depending on wavelength. The insertion loss of the produced optical circulator was 1.3 dB, the isolation was 70 dB, and the polarization dispersion was less than 0.1 ps.

[0093]

As described above, according to the present invention, since the optical circulator is constituted by using one reciprocal optical rotation element and three non-reciprocal optical rotation elements, the wavelength dependence of the light input to the light is suppressed. Therefore, it is possible to enhance the isolation and simultaneously transmit an optical signal in a wide wavelength range. Also, by arranging it between the polarization compensating plates, it is possible to compensate the phase of the light from all two ports and suppress the polarization dispersion of the output light. Therefore, it is possible to transmit a high bit rate optical signal. You can Further, by using the first to fourth birefringent materials such as the walk-off polarization beam splitter, the amount of light coupled to the ports other than the purpose can be reduced, and the first to fourth birefringent materials can be used. If the ratio of the thickness of each port to the thickness of each of the demultiplexing, multiplexing / demultiplexing, and multiplexing birefringent materials is √2: 1, the light input from each port is efficiently transmitted to each other port. Can be combined. Since the optical circulator of the present invention has excellent characteristics such as high isolation and low polarization dispersion, when used in the field of optical communication systems using optical fiber amplifiers, even in long-distance optical communication. It can transmit low noise, high beat rate optical signals.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of an optical circulator according to an embodiment of the present invention.

FIG. 2 is a perspective view of an optical circulator substrate configured by mounting the optical circulator shown in FIG. 2 on a silicon substrate.

FIG. 3 is a partially cutaway perspective view of an optical circulator device configured by housing the optical circulator substrate shown in FIG. 2 in a package.

FIG. 4 is a structural diagram of an optical circulator for explaining a light propagation path when light is input from a first port of the optical circulator according to the example.

5 is a perspective view for explaining how light propagates in the optical circulator shown in FIG. 4. FIG.

FIG. 6 is a structural diagram of an optical circulator for explaining a light propagation path when light is input from a second port of the optical circulator according to the example.

FIG. 7 is a perspective view for explaining how light propagates in the optical circulator shown in FIG.

FIG. 8 is a structural diagram of an optical circulator for explaining a propagation path of light when light is input from a second port of the optical circulator according to the embodiment and polarization of light propagating in the optical circulator is deviated. Is.

9 is a perspective view for explaining how light propagates in the optical circulator shown in FIG.

FIG. 10 is a numerical calculation of the dependence of the isolation (dB) on the temperature (° C.) by the optical circulator of the present embodiment (solid line), and the temperature dependence of the isolation of the optical circulator described in JP-B-60-49887. It is a graph which shows a result (dotted line).

FIG. 11 is a numerical calculation of the dependence of the isolation (dB) on the wavelength (nm) by the optical circulator of the present embodiment (solid line), and the wavelength dependence of the isolation of the optical circulator described in JP-B-60-49887. It is a graph which shows a result (dotted line).

[Explanation of symbols]

19-1, 19-2, 19-3 ... Faraday rotator, H1
... Polarization compensating plate, 21-1 to 21-8 ... Birefringent flat plate, L
1-L4 ... Lens, D1, D2 ... Polarization beam splitter, 20 ... 1/2 wavelength plate, F1-F4 ... Optical fiber.

Claims (5)

[Claims] 1. A first light input from a first port to a second light
An optical circulator that outputs the second light input to the second port to the third port and outputs the second light input to the third port to the third port, in which traveling directions of ordinary rays and extraordinary rays of the first light input from the first port And a first polarization beam splitter arranged so as to output the parallel beam and the extraordinary ray which are input in parallel and output to the third port. The ordinary ray and the extraordinary ray of the second light input from the two ports are arranged such that the traveling directions of the ordinary ray and the extraordinary ray are parallel to each other and are output, and the ordinary ray and the extraordinary ray input in parallel are combined to each other. A second polarization beam splitter arranged to output to a second port; and the second polarization beam splitter arranged between the first port and the first polarization beam splitter and inputted from the first port.
A birefringent material for demultiplexing that splits light into ordinary rays and extraordinary rays and outputs the ordinary rays and extraordinary rays to the first polarizing beam splitter; and the element is disposed between the second port and the second polarizing beam splitter, and The second input from the second port
The light is separated into an ordinary ray and an extraordinary ray and output to the second polarization beam splitter, and the ordinary ray and the extraordinary ray input from the second polarization beam splitter are combined and output to the second port. Which is disposed between the third port and the first polarization beam splitter, and combines the ordinary ray and the extraordinary ray input from the second polarization beam splitter, The first birefringent material that is input from the first polarization beam splitter and that is disposed between the first polarization beam splitter and the second polarization beam splitter, and the multiplexing birefringent material that outputs to the third port. The ordinary and extraordinary rays of the second polarized beam splitter are output to the second polarization beam splitter as the extraordinary ray and the ordinary ray, respectively. An optical component that performs second conversion on the ordinary ray and the extraordinary ray of the second light input from the optical splitter and outputs the resulting rays to the first polarization beam splitter as the extraordinary ray and the ordinary ray, respectively. An optical circulator, comprising: the polarization beam splitter and the polarization compensating plate disposed between the multiplexing birefringent material. 2. The first non-reciprocal optical rotation element, wherein the optical component is disposed so as to face the second polarization beam splitter, and rotates the azimuth of incident polarized light by ± 45 degrees, and the first non-reciprocal optical rotation element. It is arranged between the element and the first polarization beam splitter, and the azimuth of incident polarization is ± 45
A second non-reciprocal optical rotation element that rotates by a degree, and a third non-reciprocal optical rotation element that is disposed between the second non-reciprocal optical rotation element and the first non-reciprocal optical rotation element and rotates the azimuth of incident polarized light by ± 45 degrees. A non-reciprocal optical rotator, a reciprocal optical rotator arranged between the third non-reciprocal optical rotator and the second non-reciprocal optical rotator, for rotating the direction of incident polarization by 45 degrees; Ordinary rays travel straight, extraordinary rays are refracted and output the first birefringent material, and ordinary rays of the incident light travel straight, and extraordinary rays are refracted and output the second birefringent material, incident Ordinary ray of the incident light goes straight, and extraordinary ray is refracted and emitted, and the third birefringent material, and ordinary ray of incident light goes straight, and extraordinary ray is refracted and emitted, the fourth birefringent material. A material, wherein the third birefringent material is the second non-reciprocal material. Between the optical element and the third non-reciprocal optical rotation element, on the propagation path of one polarization of the first light, and the azimuth of the intrinsic polarization of the third birefringent material is The fourth birefringent material is arranged so as to substantially coincide with the azimuth of the other polarization of the first light, and the fourth birefringent material is formed between the second non-reciprocal optical rotation element and the third non-reciprocal optical rotation element. Is on the propagation path of the other polarization of the first light, and the azimuth of the intrinsic polarization of the fourth birefringent material is the polarization of the one polarization of the first light. The first birefringent material is arranged so as to substantially coincide with the azimuth, and the first birefringent material is between the first nonreciprocal optical rotation element and the third nonreciprocal optical rotation element, One of the second light incident on the first birefringent material through the material and the first non-reciprocal optical rotation element. Is on the propagation path of the other polarization, and the azimuth of the intrinsic polarization of the first birefringent material is the azimuth of the one polarization of the second light, and the one of the first light. The second birefringent material is arranged between the first non-reciprocal optical rotation element and the third non-reciprocal optical rotation element, and Is on the propagation path of the other polarization of the second light incident on the second birefringent material through the second birefringent material and the first non-reciprocal optical rotation element, and the second The birefringent material is arranged such that the azimuth of the intrinsic polarization of the birefringent material substantially matches the azimuth of the other polarization of the second light and the azimuth of the other polarization of the first light. The optical circulator according to claim 1, which is characterized in that. 3. The birefringent material for demultiplexing, the birefringent material for demultiplexing, the birefringent material for demultiplexing, the first birefringent material, the second birefringent material, and the third birefringent material. The birefringent material and the fourth birefringent material are flat plates made of the same material, and the thickness of each of the first to fourth birefringent materials,
The optical circulator according to claim 2, wherein the ratio of the thickness of each of the demultiplexing birefringent material, the demultiplexing birefringent material, and the demultiplexing birefringent material is √2: 1. . 4. The first light input from the first port is spatially separated into an ordinary ray and an extraordinary ray, and the polarization planes of the ordinary ray and the extraordinary ray are converted into a second non-reciprocal optical rotation element and a reciprocal optical rotation. After passing through the element, the third non-reciprocal optical rotation element and the first non-reciprocal optical rotation element in order, they are combined and output to the second port, and the second light input from the second port is spatially ordinary ray. And the extraordinary ray are separated, and then the planes of polarization of the ordinary ray and the extraordinary ray are sequentially passed through the first non-reciprocal optical rotation element, the third non-reciprocal optical rotation element, the reciprocal optical rotation element and the second non-reciprocal optical rotation element. In the method of controlling light that is combined and output to a third port, a birefringent material is arranged on a path where the first light does not propagate,
After the second light is spatially separated into an ordinary ray and an extraordinary ray, the ordinary velocity and the extraordinary ray in the birefringent material are utilized to make use of the difference in propagation velocity between the ordinary ray and the extraordinary ray, and these ordinary rays are separated by the spatial separation. A method of controlling light, characterized in that polarization dispersion of light output to the second and third ports is suppressed by correcting an optical path difference between a light ray and an extraordinary ray. 5. In an optical circulator, first means for separating the first light input from the first port into an ordinary ray and an extraordinary ray, and the second light input from the second port as an ordinary ray. A second means for separating into an ray and an ordinary ray and an extraordinary ray inputted from the first port, which are subjected to a first conversion to be an extraordinary ray and an ordinary ray, respectively, and the second means through the second means. Third means for outputting to the port, outputting second and third ordinary and extraordinary rays to the third port as ordinary and extraordinary rays while outputting to the third port; Means for providing a phase difference or an optical path difference between an ordinary ray and an extraordinary ray that are transmitted, the fourth means being disposed on the path of light propagating between the means and the third port. Optical circulator.