JPH09318913A - Optical circulator and optical switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-loss, high-isolation, and 3-port optical circulator by providing a polarization beam splitter(PBS) which is inexpensive, small-sized, and easy to manufacture. SOLUTION: Three terminal units 10-1 to 10-3 have mutually upside-down nonreciprocation parts 12 arranged on triangular prisms 13 and parallelogram prisms 14 on the reverse base surfaces of 1st PBSs 11 and the top base surfaces of the PBSs 11 of the respective units 10-1 to 10-3 are input/output ports for light. A 2nd PBS 20a and a PBS 30 for compensation are arranged between the 1st and 2nd terminal units 10-1 and 10-2. The 3rd terminal unit 10-3 is arranged adjacently to the 1st terminal 10-1 and the 2nd PBS 20b is arranged opposite it. Leak light components generated by respective optical elements are reflected by the PBS 30 for compensation, and then projected in directions different from the coupling direction of the ports or further attenuated, so high isolation is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 3-port optical circulator and an optical switch used in an optical communication system or the like.

[0002]

2. Description of the Related Art A typical structure of a 4-port optical circulator is disclosed in Japanese Patent Application Laid-Open No. 5-34633. It is equipped with birefringent plates on both sides of the non-reciprocal part.
Two terminal modules are coupled to each birefringent plate to form a 4-port circuit.

Here, by combining the function of separating the ordinary and extraordinary light paths by two birefringent plates and the non-reciprocity of the non-reciprocal part, the input light of the port 1 is output from the port 2 and the port 2 Input light is output from port 3 and port 3
Input light is output from the port 4 and input light of the port 4 is output from the port 1 to realize the function of the 4-port optical circulator.

In the optical circulator having the above construction, if port 4 is eliminated, the input light from port 1 is output from port 2 and the input light from port 2 is output from port 3, so that 3 ports are provided. Optical circulator is constructed.

[0005]

Since a conventional optical circulator uses a birefringent plate as a polarization separation element for separating ordinary and extraordinary light, in order to sufficiently increase the separation distance between the ordinary light beam and the extraordinary light beam. In this case, the thickness of the birefringent plate must be considerably increased, which causes a problem that the optical circulator becomes large and expensive. When using, for example, a rutile single crystal as the birefringent plate, the ratio of the thickness to the maximum separation distance is about 1:10. Therefore, in order to secure a separation distance of 10 mm, the birefringence plate needs to have a thickness of 100 mm. Become.

Further, since the separation distance between the ordinary light beam and the extraordinary light beam changes depending on the incident angle to the birefringent plate, the mechanical arrangement relationship between the birefringent plate and the input / output port is made highly accurate, It is necessary to keep the incident angle highly accurate and constant. Therefore, the assembly and adjustment of the optical circulator becomes troublesome.

Therefore, it is conceivable to use the polarization beam splitter as the polarization splitting means and the optical path determining means without using the birefringent crystal. The polarization beam splitter is easy to manufacture, inexpensive, and small. However, since the extinction ratio of the polarization beam splitter is not so high, it has been impossible to realize an optical circulator of this type with low loss and high isolation in the past.

The present invention has been made in view of the above background, and an object of the present invention is to solve the above problems and to use a polarization beam splitter which is inexpensive, small, and easy to manufacture, and which has a low loss and a high isolation. The present invention is to provide a 3-port optical circulator and optical switch.

[0009]

In order to achieve the above object, a three-port optical circulator according to the present invention comprises a right-angled isosceles triangular prism (13) and a parallelogram prism (14) having a narrow angle of 45 degrees. And a first composite polarizing beam splitter (11) that is integrated with a polarization separation film (15) between the first surface and the second surface, and the polarization azimuth is 90 degrees when the linearly polarized light passes from one surface to another surface. A non-reciprocal portion (12) having a predetermined size and shape, which is rotated so that its polarization direction is not rotated when passing through in the opposite direction, and a triangle on the lower bottom surface which constitutes the first composite polarization beam splitter. A terminal unit (1) in which the prism and the parallelogram prism are formed by arranging the non-reciprocal parts whose front and back are opposite to each other in parallel.
Three pieces of 0-1, 10-2, 10-3) are prepared.

2 of the 3 terminal units
The first and second terminal units (10-1 and 10-
In 2), the non-reciprocal portions face each other and are arranged at a predetermined distance. Then, two right-angled isosceles triangular prisms (21, 22) are provided between the first and second terminal units.
The second composite polarization beam splitter (20a) integrated with the polarization separation film (23) sandwiched therebetween and the compensating member for blocking the transmission of light in the opposite direction or changing the optical path are arranged in series. At this time, the compensating member is arranged so as to be on the first terminal unit side.

Further, the first terminal unit (10-
The third terminal unit (10-3) is arranged adjacent to 1). Then, the second composite beam splitter (20
another second compound beam splitter (2
0b) facing the third terminal unit and both second composite beam splitters (20a, 20b).
The polarized light separating films (23) are arranged so as to face each other in parallel (claim 1).

The compensating member may be a composite polarization beam splitter in which two right-angled isosceles triangular prisms are integrated with a polarization separation film interposed (claim 2).
A glass polarizer may be used (Claim 3) or a birefringent plate may be used (Claim 4).

Further, the third terminal unit (10-
3) and the second composite polarization beam splitter (20
A glass polarizer (40b) or a birefringent plate (45b) may be inserted and arranged between (b) and (b).

Furthermore, on the premise of the above-mentioned various configurations, it is preferable that some of the constituent elements of the first and third terminal units are constituted by common parts (claim 6).

In the configuration of the optical circulator according to any one of the above, an optical switch can be constructed by using a nonreciprocal optical rotator whose nonreciprocal direction can be switched by electrical means ( Claim 7).

With the above arrangement, in the forward direction, the compound polarization beam splitter of the terminal unit separates the incident light into P-polarized light and S-polarized light, and the polarization plane of one polarization is rotated by 90 ° at the non-reciprocal portion, and the other. Does not rotate the plane of polarization. As a result, polarized light having the same plane of polarization is incident on the second composite polarization beam splitter. Here, the polarization component (leakage light component) perpendicular to it is removed. And the forward light is
The light is transmitted or reflected by the second composite polarization beam splitter, emitted, and then incident on the terminal unit on the emission side. The polarization plane of one of the two lights does not rotate, and the polarization plane of the other light rotates by 90 °. As a result, the first composite polarization beam splitter of the terminal unit on the exit side performs polarization combination, and the light is coupled from the entrance port to the exit port without polarization dependency.

The leaked light component caused by the polarization rotation error at the non-reciprocal part of the exit side terminal unit is the same as the above at the polarization separation film of the first composite polarization beam splitter in the exit side terminal unit. On the contrary, by reflecting and transmitting,
The leaked light is emitted in the direction without the emission port and is not coupled to the emission port.

The leaked light component generated in the composite polarization beam splitter is attenuated at least twice when traveling along the reverse optical path that is coupled to the port on the incident side. Therefore, 2
The damping effect of the power of 2 is exerted, and even if it is coupled to the port on the incident side, it is at a level at which there is no problem.

When a birefringent plate is used as the compensating member, a part of the leaked light component traveling in the reverse direction is shifted to a different optical path with respect to the optical path traveling in the forward direction. Will be emitted in the direction without a port, and will be a slight amount even if not coupled to the port on the incident side or if it is coupled. In this way, high isolation can be obtained by removing the leaked light component generated in each optical element by a compensating member or the like. Therefore, it becomes a high performance optical circulator.

[0020]

1 shows the configuration of an example of an embodiment of a 3-port optical circulator according to the present invention. As shown in the figure, three terminal units (first to third terminal units) 10 corresponding to the three ports 1 to 3 are provided.
-1, 10-2, 10-3 and three composite polarization beam splitters 20a, 20b, 30. Each port is composed of an optical fiber 2 having a coupling lens 1 at its tip. The specific configuration of each part is as follows.

[Structure of Each Terminal Unit 10] The three terminal units 10-1, 10-2, 10-3 basically have the same structure and are mounted by changing their directions.
Therefore, when it is not necessary to distinguish them from each other in the description of each part, they will be referred to as a terminal unit 10. Each terminal unit 10
Is composed of a first composite polarization beam splitter (hereinafter, referred to as “first PBS”) 11 and a non-reciprocal portion 12 including two systems having reverse characteristics.

Each first PBS 11 includes a right-angled isosceles triangular prism 13 and a parallelogram prism 14 having a narrow angle of 45 degrees.
It has a single trapezoidal shape in which the polarization separation film 15 is sandwiched between one surface and the other surface. Then, the lens 1 of the optical fiber 2 is coupled to the upper bottom surface of the first PBS 11, and
The non-reciprocal portion 12 is arranged in proximity to the lower bottom surface of the PBS 11.

The non-reciprocal portion 12 is composed of two half-wave plates 1 each having a planar shape obtained by dividing the lower bottom surface of the first PBS 11 into two.
6 and 17, a Faraday rotator 18 having substantially the same planar shape as the lower bottom surface of the first PBS 11, and a permanent magnet that magnetically saturates the Faraday rotator 18 in the thickness direction. In this example, the Faraday rotator 18 is arranged on the lower bottom surface side of the first PBS 11. Then, the two ½ wavelength plates 1 are laminated so as to be laminated on the surface of the Faraday rotator 18 (on the side opposite to the bonding surface with the first PBS 11).
6, 17 are arranged in parallel.

At this time, the two half-wave plates 16 and 17
Are arranged opposite to each other. Also, 1/2
The optical axes of the wave plates 16 and 17 are ± 22.5 degrees. Further, the Faraday rotator 18 rotates the azimuth of the incident polarized light in the forward direction by 45 degrees counterclockwise.

As shown in FIG. 2, the non-reciprocal portion 12 is constructed such that the half-wave plates 16 and 17 are arranged on the first PBS 11 side and the Faraday rotator 18 is arranged outside thereof. But of course

[Relationship Between Three Terminal Units and Other Composite Polarization Beam Splitter] The first terminal unit 10-1 facing the port 1 and the second terminal unit 10-2 facing the port 2 are The two are in an arrangement relationship in which they face each other while being separated by a predetermined distance. Also, the third terminal unit 10-3 facing the port 3 is the first terminal unit 10-3.
It is adjacent to -1.

Then, in the space formed between the terminal units, the three composite polarization beam splitters 20a, 20
b and 30 are arranged at appropriate positions. That is, between the first terminal unit 10-1 of port 1 and the second terminal unit 10-2 of port 2, a second composite polarization beam splitter (hereinafter, referred to as “second PBS”) 20a and compensation A composite polarization beam splitter (hereinafter, referred to as “compensation PBS”) 30 is arranged in series.

Then, the compensating PBS 30 is positioned on the side of the first terminal unit 10-1, and the first terminal unit 10-1 and the compensating PBS 30 are brought close to each other. Further, the second PBS 20a and the second terminal unit 20-2 are made to be close to each other. On the other hand, the second PBS 20b is provided so as to face the third terminal unit 10-3 of the port 3. At this time, the third terminal unit 20-3 and the second P
The BS 20b is separated by a predetermined distance, and the second PBSs 20a and 20b are adjacent to each other.

The second PBSs 20a and 20b and the compensating PBS 30 have the same structure in the present embodiment, and both of the two right-angled isosceles triangular prisms 2 are used.
The polarization separation film 23 is formed between the bottom surfaces of the 1, 22 (31, 32).
It is formed in an integrated rectangular shape with (33) interposed therebetween. The polarization separation films 23 and 33 are arranged so as to be parallel to each other.

More specifically, the polarization splitting film 33 of the compensation PBS 30 and the polarization splitting film 23 of the second PBS 20a face each other, and the polarization splitting films 23 and 23 of the second polarization splitting films 20a and 20b face each other. I'm trying to face each other.

Next, the operation principle of the optical circulator having the above-mentioned structure, that is, the optical paths in the forward and reverse directions will be described.

[Optical Path from Port 1 to Port 2] This forward optical path is shown in FIG. In the first terminal unit 10-1 of the port 1, the light beam emitted from the optical fiber is collimated by the lens, is incident on the first PBS 11, and is separated into P-polarized light and S-polarized light by the polarization separation film 15. P
The polarization component is transmitted through the polarization separation film 15, and the S polarization component is reflected by the polarization separation film 15 and also reflected by the parallelogram prism 14.

As a result, the P-polarized light and the S-polarized light are converted into the first PBS.
Emitted from 11 in parallel. P polarization direction is 0 degree, 1
Since the optical axis azimuth of the / 2 wave plate 16 is -22.5 degrees, the P-polarized component passes through the 1/2 wave plate 16 and the polarization direction becomes -45 degrees. Conversely, the Faraday rotator 18 counterclockwise. Since it is rotated by 45 degrees in the direction, the polarization azimuth is 0 degree, and it remains P-polarized.

On the other hand, the S-polarization azimuth is 90 degrees and is 1/2
Since the optical axis direction of the wave plate 17 is +22.5 degrees, S
The polarization component passes through the half-wave plate 17 and the polarization direction is -4.
It becomes 5 degrees, and the Faraday rotator 18 rotates counterclockwise by 45 degrees, so that the polarization azimuth becomes 0 degree and the first P
It is converted into P-polarized light when viewed from the BS 11 side.

Therefore, the first terminal unit 10-1
Is emitted as two P-polarized light rays from the non-reciprocal portion 12, passes through the compensating PBS 30 and the polarization separation films 33 and 23 of the second PBS 20a, and goes straight to the second terminal unit 10 of the port 2. It is incident on the half wavelength plates 16 and 17 of -2. Similarly to the non-reciprocal portion 12 on the side of the first terminal unit 10-1 described above, the non-reciprocal portion 12 on the side of the second terminal unit 10-2 also has the 1/2 wavelength plates 16 and 17 and the Faraday rotator 18 in that order. When passing, the plane of polarization rotates 45 degrees in the same direction or 45 degrees in the forward and reverse directions.

That is, in the second terminal unit 10-2 of the port 2, the polarization direction of the P-polarized beam from the port 1 side is -45 degrees as viewed from the output direction of the terminal unit 10-2, and 1 Since the optical axis direction of the / 2 wave plate 17 is +22.5 degrees when viewed from the output direction, the polarization direction of the component transmitted through the 1/2 wave plate 17 becomes 90 degrees, and the parallelogram prism 14 as S polarized light It is reflected by the polarization separation film 15. On the contrary, the optical axis direction of the ½ wavelength plate 16 is −22.5 degrees when viewed from the output direction. Therefore, the polarization direction of the component passing through the ½ wavelength plate 16 becomes 0 degree, and the polarized light is separated as P polarized light. Permeate through the membrane 15. Therefore, the S-polarized light and the P-polarized light are combined into one light beam and are coupled to the port 2 without polarization dependency.

[Optical Path from Port 2 to Port 3] This forward optical path is shown in FIG. Similar to the principle of operation described for the optical path from port 1 to port 2 described above, the light incident from port 2 is the first light of the second terminal unit 10-2.
It is separated into P-polarized light and S-polarized light by PBS 11 of. In each of the non-reciprocal portions 12, the polarization plane of the P-polarized light is rotated by 90 ° to become the S-polarized light, and the S-polarized light is not rotated and remains the S-polarized light in the second PBS.
It is incident on 20a.

The two S-polarized lights are reflected by the polarization splitting film 23 of the second PBS 20a at the center, the optical path is changed by 90 degrees to the lower side in the figure, and the light is incident on the second PBS 20b. . Since the second PBS 20b also has S polarization, it is reflected again by the polarization separation film 23 and proceeds toward the terminal unit 10-3 of the port 3. Thus, the third terminal unit 10 is reflected twice by the polarization separation film 23 and
-3 is incident on the non-reciprocal portion 12.

The light, which is inverted from P-polarized light to S-polarized light in the second terminal unit 10-2, does not rotate the plane of polarization in the nonreciprocal portion 12 of the third terminal unit 10-3 and remains S-polarized light. The light emitted as S-polarized light from the second terminal unit 10-2 is rotated by 90 ° in the non-reciprocal portion 12 of the third terminal unit 10-3 and is inverted into P-polarized light. Therefore,
The light is synthesized by the polarization separation film 15 of the first PBS 11 of the third terminal unit 10-3, is coupled to the port 3 without polarization dependency, and is emitted.

As described above, the light incident from the port 1 is emitted from the port 2, and the light incident from the port 2 is emitted from the port 3.

On the other hand, the causes of deterioration of the isolation characteristics of the optical circulator using the PBS are the polarization to be propagated due to the insufficient polarization separation ability (extinction ratio) of the PBS and the deviation of the rotation angle of the element for rotating the plane of polarization. This is because the orthogonal polarization component contained in the wave becomes leaked light and is coupled. Therefore, the optical path of light (leakage light) traveling in the opposite direction will be described.

[Leakage Route from Port 2 to Port 1] This leakage route is shown in FIG. Second terminal unit 1
In 0-2, the leakage light component due to the extinction ratio of the first PBS 11 and the rotation error of the non-reciprocal portion 12 is P-polarized light. The P-polarized light passes through the second PBS 20a and the compensation PBS 30 as it is, goes straight, and is incident on the nonreciprocal portion 12 of the first terminal unit 10-1. In the non-reciprocal portion 12 of the first terminal unit 10-1, the light transmitted through the half-wave plate 16 does not rotate, and the light transmitted through the half-wave plate 17 has a polarization plane rotated by 90 ° and is S-polarized. become. Therefore, the first terminal unit 10
Since the P-polarized light is transmitted and the S-polarized light is reflected by the polarization separation film 15 of the first PBS 11 in -1, the light is emitted from the first terminal unit 10-1 to the surface without the port 1. In addition,
Even in the polarization separation film 15 of the first PBS 11 of the first terminal unit 10-1, there is light that is reflected / transmitted due to insufficient extinction ratio and proceeds to the port 1 side, but it is on the second terminal unit 10-2 side. Since the light is attenuated at 2, the light is attenuated twice, resulting in a negligible amount of light.

On the other hand, the second terminal unit 10 of the port 2
The forward component emitted from -2 is S-polarized light. As shown in FIG. 4, most of such S-polarized light is the second P-polarized light.
The light is reflected by the polarization separation film 23 of the BS 20a and finally coupled to the port 3. However, there is a component in which part of the P-polarized light is transmitted due to insufficient extinction ratio in the polarization separation film 23 of the second PBS 20a.

Focusing on the optical path of the transmitted leaked light, as shown in FIG. 6, since it enters the compensating PBS 30 and many components thereof are reflected by the polarization separation film 33 in the compensating PBS 30, the port Not combined with 1. Of course, it is not connected to other ports.

Even in the polarization splitting film 33 of the compensating PBS 30, part of the light is transmitted due to the lack of the extinction ratio.
The transmitted P-polarized light is coupled to the port 1 through the optical path indicated by the broken line in the figure. However, since the light is attenuated by a predetermined amount even when passing through the polarization separation film 33, the port 1 is finally attenuated.
The light incident on the first terminal unit 10-1 is transmitted through the two polarization splitting films 23 and 33 of the second PBS 20a and the compensating PBS 30, so that the light can be attenuated to the square and almost no problem occurs. The amount of light that does not exist is emitted from the port 1.

[Leakage Light from Port 3 to Port 2] Third
The leakage light component emitted from the terminal unit 10-3 of S is S
It is polarized light. Therefore, as shown in FIG. 7, the light is reflected twice by the polarization splitting films 23 of the two second PBSs 20b and 20a and is incident on the non-reciprocal portion 12 of the second terminal unit 10-2. Then, the non-reciprocal portion 12 of the second terminal unit 10-2 passes through the ½ wavelength plate 17 and the Faraday rotator 18 to rotate the polarization plane of the light by 90 ° to be P-polarized light. The light that has passed through the wave plate 16 and the Faraday rotator 18 remains S-polarized without being rotated.

As a result, the second terminal unit 10-2
Are combined by the polarization separation film 15 of the first PBS 11 and are emitted to the surface without the port 2. Even in the polarization separation film 15 of the first PBS 11 of the second terminal unit 10-2, there is light reflected by the lack of extinction ratio and traveling to the port 2 side, but it is on the side of the third terminal unit 10-3. Since the light is attenuated at 2, the light is attenuated twice, resulting in a negligible amount of light.

On the other hand, the third terminal unit 10 of the port 3
The forward component emitted from -3 is P-polarized light. Related P
Most of the polarized light passes through the polarization separation film 23 of the second PBS 20b and is emitted to the surface having no port. Then, there is a component that is slightly reflected by the second PBS 20b. However, the reflected leaked light is not coupled to the port 2 unless it is reflected by the polarization separation films 23 and 33 of the two second PBSs 20b and 20a, as shown in the optical path of FIG. Therefore, a sufficient amount of light is emitted from the port 2 without any problem.

As a result, assuming that the leakage light caused by the extinction ratio of PBS and the rotation error of the non-reciprocal portion is 30 dB, the isolation in the reverse direction of the ports 3 → 2 → 1 is as follows.
Since each path is attenuated twice by at least 30 dB, the result is 60 dB, and a sufficiently high isolation can be realized.

Then, a circulator having the above structure was actually prepared, and the insertion loss and isolation between each port were measured. As a comparative example, as shown in FIG. 9, a circulator having a structure in which a ½ wavelength plate 16 and a Faraday rotator 18 are inserted between two PBSs 11 is manufactured, and a forward insertion loss between ports and a reverse direction Isolation was measured.

As a result, in the comparative example, the insertion loss in the forward direction was 1.12 dB ± 0.01, whereas in the product of the present invention, it was 1.52 dB ± 0.01, and the loss was slightly small. Although it grows, it does not pose a problem for practical use. On the other hand, in the reverse direction, as shown in the table below, the comparative example had a value of about 30 dB, while the present invention product has a value of about 30 dB.
It was confirmed that the isolation was improved to more than dB and very high isolation was obtained.

[0052]

[Table 1] FIG. 10 shows a second embodiment of the optical circulator of the present invention. In this example, in the configuration of the first embodiment described above, some of the constituent elements of the two adjacent terminal units are configured by common parts.

Specifically, the terminal units 10-1, 10-2, 10-3 having the structure shown in FIG. 1 are rotated 90 degrees to be laid sideways. Then, the first and third terminal units (10-1
And 10-3), the right-angled isosceles triangular prism 13 and the parallelogram prism 14 constituting the first PBS 11 face each other. Therefore, they were integrated and parts were shared. That is, the elongated right-angled isosceles triangular prism 13 '
And a slender parallelogram prism 14 'with a polarization separation film 1
5'is sandwiched and joined together to form a first PBS 11 '.

In accordance with this, the non-reciprocal portion 12 shown in FIG. 1 is also rotated 90 degrees to be laid sideways. Then, the ½ wavelength plate 16 constituting the two adjacent non-reciprocal portions 12 faces the right-angled isosceles triangular prism 13, and the ½ wavelength plate 17 faces the parallelogram prism 4, Since the non-reciprocal parts 16 and the non-reciprocal parts 17 are vertically arranged, they are integrated. Therefore, as shown in FIG. 10, the half-wave plates 16 'and 17' made of elongated rectangular parallelepipeds are joined to be integrated.

Further, the Faraday rotator 18 is constituted by another member so that the Faraday rotator 18 alternates the rotation directions with respect to the direction of the magnetic field. As a result, one magnet 19 that surrounds the two Faraday rotators can be used in common. Therefore, as shown in FIG.
Each component that makes up the terminal unit is a Faraday rotator 1.
It can be halved except for 8, and the assembly etc. becomes easy.

The second terminal unit 10-2 also uses the same parts as the above-mentioned terminal unit in which the first and third terminal units 10-1 and 10-3 are made common. As a result, regarding the second terminal unit 10-2,
Although the number of parts in the first embodiment and that in the second embodiment are the same, the cost can be reduced by using the same parts and reducing the kinds of parts. In addition, the outer shape of the whole is substantially rectangular, which facilitates assembly and handling.

In the present embodiment, the polarization direction of the polarization splitting film 15 'of the first PBS arranged in the terminal unit is different by 90 degrees from that of the first embodiment shown in FIG. The P-polarized light and the S-polarized light separated by being reflected and transmitted by the polarization separation film 15 'travel in the horizontal plane (in the first embodiment, travel in the vertical plane), and accordingly, the respective PBSs 20a, Even within 20b and 30, it will proceed in a predetermined horizontal plane.

However, only the position of the optical path is different as described above, and the presence or absence of rotation of the plane of polarization in the non-reciprocal portion is the same as in the first embodiment. Therefore, the light is transmitted / reflected by the polarization separation film of each PBS as appropriate, the light travels according to the same operation principle as in the first embodiment, and the light incident from each port is output to the desired port. .

Further, the return light and the leaked light in the opposite directions are emitted from the portion where the port does not exist, or are attenuated twice even if they are coupled to the port, so that there is no problem in practical use. The amount is very small and no malfunction occurs.

FIG. 11 shows a third embodiment of the optical circulator according to the present invention. As shown in the figure,
This embodiment is based on the above-described first embodiment, and a glass polarizer 40a is provided as a compensating member in place of the PBS 30, and the third terminal unit 1 is further provided.
The structure is different in that the glass polarizer 40b is provided close to 0-3. Then, the glass polarizers 40a, 4a
The optical axis of 0b is set so as to pass through the plane of polarization of light in the forward direction that travels between the ports. That is, the configuration of each terminal unit 10-1 to 10-3 is the same as that of the first embodiment.

With this structure, the light in the forward direction passes through the glass polarizers 40a and 40b, so that it travels through the same optical path as in the first embodiment and the light incident from the port 1 is emitted from the port 2. Then, the light incident from the port 2 is emitted from the port 3.

The light in the reverse direction from each port has its polarization plane opposite to that in the forward direction, so that the leaked light cannot pass through the glass polarizers 40a and 40b and is absorbed. Therefore, it cannot return more than the glass polarizers 40a, 40b and is not coupled to the port. In addition, this glass polarizer 4
Although the leaked light generated in 0a, 40b may travel to the terminal unit side, it is attenuated once when passing through the second PBS 20a, 20b before being incident on the glass polarizers 40a, 40b. As a result, the light is attenuated twice, and the amount of the leaked light is extremely small. Therefore, similar to each of the above-mentioned examples, there is no problem in practical use, and high isolation can be exhibited.

Also in the type using the glass polarizers 40a and 40b as in the present embodiment, the structure shown in FIG.
Similarly, the terminal unit can be shared. That is, as shown in FIG. 12, the terminal units 10-1,
Rotate 10-2 and 10-3 90 degrees to the side,
First PBS of the third terminal unit 10-1, 10-3
11 'is shared. Further, the non-reciprocal portion 12 'is also rotated by 90 degrees to be laid sideways, and the half-wave plates 16' and 17 'made of elongated rectangular parallelepipeds are joined to be integrated. Further, the second terminal unit 10-2 side is also configured by using the same component as the common component.

In this way, the parts can be made common and the assembly becomes easy. The operation principle is the same as that of the third embodiment except that the light separated by the polarization separation film of the terminal unit travels in the horizontal plane, and the forward light is emitted from the desired port. Can also be
Light in the opposite direction is absorbed and blocked on the way, and is not coupled to the port.

FIG. 13 shows an optical circulator according to the fourth embodiment of the present invention. As shown in the figure,
The present embodiment is structurally different from the first and third embodiments described above in that birefringent plates 45a and 45b are provided as compensating members. That is, instead of the glass polarizer in the third embodiment, the birefringent plates 45a, 45a
b is provided. The optical axes of the birefringent plates 45a and 45b are set so that the P-polarized light of the second PBS 20a and 20b has an ordinary or extraordinary light relationship with the birefringent plates 45a and 45b (in the present example, The refraction plate 45a side is "ordinary ray" and the birefringence plate 45b side is "extraordinary ray". Since the other configurations are the same as those in the above-described respective embodiments, detailed description thereof will be omitted.

With this configuration, port 1 to port 2
As shown in FIG. 14, since the light emitted from the terminal unit 10-1 is P-polarized light, the light traveling in the forward direction is not shifted by the birefringent plate 45a and goes straight to the second PB.
It is incident on S20a. Therefore, the light incident from the port 1 passes through the same optical path as in the above-described first embodiment and is emitted from the port 2. Also, based on the same principle, port 3
The light incident from the light is not shifted by the birefringent plate 45b, and is emitted from the port 4. Further, the light incident from the port 2 passes through the optical path as shown in FIG. 15 and does not pass through the birefringent plates 45a and 45b. Therefore, the first
The light is emitted from the port 3 in accordance with the same principle as that of the embodiment and the like.

When the optical axes of the birefringent plates 45a and 45b are reversed from those of this embodiment, the birefringent plates 45a and 45b are
The optical path shifts when light in the forward direction passes through 5b,
In this case, each port may be arranged on the path of the shifted optical path.

On the other hand, the leaked light component of light in the opposite direction is basically the same as that in the first embodiment. That is, in the first embodiment, the compensating PBS 3 is used for the leak light component due to the lack of the extinction ratio of the second PBS 20a, 20b.
In contrast to the light reflected at 0 and 30b, in the present embodiment, the leak light component is attenuated by shifting at the birefringent plates 45a and 45b.

Specifically, the return light from the port 2 to the port 1 is a leak component generated in the first PBS 11 and the non-reciprocal portion 12 of the second terminal unit 10-2 on the port 2 side is P-polarized light. Become. Therefore, as shown in FIG.
Of PBS 20a, and reaches the birefringent plate 45a. Since it is P-polarized light, it does not shift even in the birefringent plate 45a and goes straight. Therefore, as in the first embodiment, most of them are emitted in the direction in which the port 1 does not exist, and the light emitted to the port 1 (indicated by the broken line in the figure) is a little attenuated twice. Become.

Further, since the light in the forward direction from the port 2 is S-polarized, it is reflected by the second PBS 20a in this example. However, as shown in FIG. 17, the extinction ratio in the second PBS 20a is insufficient. As a result, part of the attenuated light goes straight. This point is the same as each of the above-described embodiments.

Then, such light is incident on the birefringent plate 45a. Then, since it is S-polarized light, its birefringent plate 45
When passing through a, it is shifted (see FIG. 2B).
After that, since the light travels on the shifted surface having different height positions, it is not coupled to the port 1. Although the shift amount due to the birefringent plate is physically small, it is sufficiently larger than the diameter of the port 1, so there is no problem.

Then, as in this embodiment, the birefringent plate 4
Even in the type using 5a and 45b, the terminal unit can be shared as in the above-described embodiments.
That is, as shown in FIG. 18, the terminal unit 10-
1, 10-2, 10-3 are rotated 90 degrees to be laid sideways, and the first and third terminal units (10-1 and 10-3) and the first PBS 11 'of the second terminal unit 10-2 are arranged. Commonize. Further, the non-reciprocal portion 12 'is also rotated by 90 degrees to be laid sideways, and the half-wave plate 16', 1 made of an elongated rectangular parallelepiped
By joining 7 ', they are integrated.

In this way, the parts can be made common and the assembly is easy. The operation principle is the same as that of the fourth embodiment except that the light separated by the polarization separation film of the terminal unit travels in the horizontal plane, and the forward light is emitted from the desired port. Can also be
The light in the opposite direction shifts its optical path along the way, is absorbed and reflected, and is not coupled to the port.

In the above-described third and fourth embodiments and the modifications thereof (in which the terminal unit is used in common), the compensating member (glass polarizer 40a) faces the first and third terminal units. , 40b, birefringent plates 45a, 45b)
However, the present invention is not limited to this, and the third terminal unit side compensating member (glass polarizer 40b, birefringent plate 45b) may not be provided.

[Application to Optical Switch] In the optical circulator shown in each of the above-mentioned embodiments and modifications,
As the non-reciprocal portions described above, the non-reciprocal direction can be switched by electrical means, so that the ports 1 → 2 → 3
It is possible to switch between a state in which light propagates and a state in which light propagates to ports 3 → 2 → 1. That is, port 2
The light incident from the port 2 can be selectively output to either one of the port 1 and the port 3. In order to exert such a function, the means for applying the magnetic field to the Faraday rotator 18 constituting the non-reciprocal portion is a permanent magnet in each of the above-described embodiments and the like. It can be used as a switch.

[0076]

According to the present invention, since the polarization beam splitter is used as the polarization splitting means and the optical path determining means without using the birefringent crystal, the fabrication is easy and inexpensive, and even if the separation distance is sufficiently large. A small polarization beam splitter is enough. Further, since the extinction ratio of the polarization beam splitter is not so high, it has been impossible to realize an optical circulator and an optical switch with low loss and high isolation in this type, but according to the configuration of the present invention, the extinction ratio is high. High leakage can be realized because leaked light caused by rotation error does not reach other ports.
Further, since the separation distance after passing through the polarization beam splitter does not depend on the incident angle, each component can be easily assembled and adjusted.

Further, according to the present invention, it is possible to realize an optical switch having the above advantages (easy to manufacture, easy to adjust, inexpensive, compact, and high crosstalk).

[Brief description of drawings]

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

FIG. 2 is a diagram showing another configuration of the terminal unit.

FIG. 3 is a first explanatory diagram of the operation of the optical circulator shown in FIG. 1.

FIG. 4 is a second operation explanatory view of the optical circulator shown in FIG.

5 is a third explanatory diagram of the operation of the optical circulator shown in FIG. 1. FIG.

FIG. 6 is a fourth explanatory diagram of the operation of the optical circulator shown in FIG. 1.

FIG. 7 is a fifth explanatory diagram of the operation of the optical circulator shown in FIG.

FIG. 8 is a sixth operation explanatory view of the optical circulator shown in FIG.

FIG. 9 is a diagram showing an optical circulator of a comparative example.

FIG. 10 is a configuration diagram showing a second embodiment of an optical circulator of the present invention.

FIG. 11 is a configuration diagram showing a third embodiment of the optical circulator of the present invention.

FIG. 12 is a configuration diagram showing another embodiment of the optical circulator of the present invention.

FIG. 13 is a configuration diagram showing a fourth embodiment of an optical circulator of the present invention.

FIG. 14 is a first explanatory diagram of the operation of the optical circulator shown in FIG. 13.

FIG. 15 is a second explanatory diagram of the operation of the optical circulator shown in FIG.

FIG. 16 is a third explanatory diagram of the operation of the optical circulator shown in FIG. 13.

FIG. 17 is a fourth explanatory diagram of the operation of the optical circulator shown in FIG. 13.

FIG. 18 is a configuration diagram showing another embodiment of the optical circulator of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coupling lens 2 Optical fiber 10-1 1st terminal unit 10-2 2nd terminal unit 10-3 3rd terminal unit 11 1st compound polarization beam splitter 12 Non-reciprocal part 13 Right-angled isosceles triangular prism 14 Parallelogram prism 15 Polarization separation film 16,17 1/2 wavelength plate 18 Faraday rotator 20a, 20b Second composite polarization beam splitter 21,22 Right-angled isosceles triangular prism 23 Polarization separation film 30 Compensation composite polarization beam splitter ( Compensation member) 31, 32 Right-angled isosceles triangular prism 33 Polarization separation film 40a, 40b Glass polarizer (compensation member) 45a, 45b Birefringent plate (compensation member)

Claims (7)

[Claims] 1. A first composite polarized light integrated with a right-angled isosceles triangular prism (13) and one surface of a parallelogram prism (14) having a narrow angle of 45 degrees with a polarization separation film (15) interposed therebetween. A beam splitter (11) and a predetermined polarization azimuth that rotates the polarization azimuth by 90 degrees when passing from one surface to another and does not rotate the polarization azimuth when passing in the opposite direction. And a non-reciprocal part (12) having a dimensional shape, and the non-reciprocal part with the front and back reversed to each other is arranged in parallel to the triangular prism and the parallelogram prism on the lower bottom surface which constitute the first composite polarization beam splitter. Prepared three terminal units (10-1, 10-2, 10-3), and the first and second terminal units (10-1 and 10-2) among the three terminal units. With the non-reciprocal portion facing, The second right and left isosceles triangular prisms (21, 22), which are arranged at a predetermined distance, are integrated with each other with a polarization separation film (23) interposed between the first and second terminal units. Compound polarization beam splitter (2
0a) and a compensating member that blocks the transmission of light in the opposite direction or changes the optical path, such that the compensating member is on the side of the first terminal unit, and the first terminal unit (10- 1), a third terminal unit (10-3) is arranged, and another second composite beam splitter (20b) having the same configuration as the second composite beam splitter (20a) is connected to the third terminal unit (10-3). Of the polarization beam splitting film (2) of the second composite beam splitters (20a, 20b) facing each other.
3) is an optical circulator, which is arranged so as to face each other in parallel. 2. The compensating member is a composite polarization beam splitter (30) in which two right-angled isosceles triangular prisms (31, 32) are integrated with a polarization separation film (33) sandwiched therebetween. The optical circulator according to claim 1. 3. The compensating member is a glass polarizer (40
The optical circulator according to claim 1, wherein the optical circulator is a). 4. The optical circulator according to claim 1, wherein the compensating member is a birefringent plate (45a). 5. The third terminal unit (10-3)
And the second composite polarization beam splitter (20b) between the glass polarizer (40b) or the birefringent plate (45).
b) is inserted and arranged.
Optical circulator described in. 6. The optical circulator according to claim 1, wherein some of the constituent elements of the first and third terminal units are common parts. 7. The structure of the optical circulator according to claim 1, wherein the non-reciprocal optical rotator has a non-reciprocal direction that can be switched by electrical means. Optical switch.