JPH1138363A - 3 port type optical circulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to realize a high isolation characteristic even if polarization prisms of a low extinction ratio are used. SOLUTION: This circulator is constituted by arranging a 45 deg. Faraday rotator 14 and a half-wave plate 16 between the first and second polarizing prisms 11 and 12, which internally have a polarized light separating film (a) and are provided with a reflection film (b) parallel therewith and coupling the exit light from a first port P1 to a second port P2 and coupling the exit light from the second port P2 to a third port P3 . In such a case, an optical isolator unit 22, in which a polarizer 30 consisting of a wedge type refraction plate, an analyzer 34 consisting of the 45 deg. Faraday rotator 14 and, and a wedge type refraction plate, are arrayed in this order. Further, the similar optical isolator unit 22 is built between the first polarizing prism P1 and the third port P3 as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention disposes a 45-degree Faraday rotator and a half-wave plate between two composite polarizing prisms (polarizing beam splitters) so that light emitted from a first port is emitted. The present invention relates to an optical circulator coupled to a second port, and the output light of the second port is coupled to a third port.
The present invention relates to a three-port optical circulator in which an optical isolator unit is disposed between the optical circulator and a polarizing prism.
This optical circulator is useful, for example, for bidirectional communication and data link in the field of optical communication.

[0002]

2. Description of the Related Art An optical circulator is a multiport passive non-reciprocal element having a function of emitting incident light from a certain port only to another port in a specific direction. As a conventionally known optical circulator, for example, there is a structure shown in FIG. This is because a 45-degree Faraday rotator 14 and a half-wave plate 1 are disposed between a first polarizing prism 10 and a second polarizing prism 12.
6 (for example, Japanese Patent Publication No. 60-49).
887). The polarizing prisms 10 and 12 are formed by joining a right-angled triangular prism and a parallelogram prism so as to sandwich the polarization separating film a inside each other.
This is a structure in which a reflective film b is provided in parallel with the above.

The light emitted from the first port P ₁ enters a first polarizing prism 10 and is separated into P-polarized light and S-polarized light by a polarization separating film a. P-polarized light passes through the polarization separation film a. The S-polarized light is reflected by the polarized light separating film a to form a reflecting film b
Is totally reflected. As a result, the P-polarized light and the S-polarized light become parallel to each other and enter the Faraday rotator 14 and the half-wave plate 16, respectively. At this time, P-polarized light remains P-polarized light, and S-polarized light remains S-polarized light. P-polarized light is totally reflected by the reflecting film b of the second polarizing prism 12, is coupled to the second port P ₂ recombine with S-polarized light by the polarization separation film a.

Light emitted from the _second port P ₂ enters the second polarizing prism 12 and is separated into P-polarized light and S-polarized light by the polarization separation film a. The P-polarized light passes through the polarization separation film a and is totally reflected by the reflection film b. S-polarized light is reflected by the polarization separation film a. As a result, the P-polarized light and the S-polarized light become parallel to each other, and enter the half-wave plate 16 and the Faraday rotator 14, respectively. At this time, the polarization plane rotates in the same direction by 45 degrees, so that the P-polarized light is converted to the S-polarized light, and the S-polarized light is converted to the P-polarized light, and reaches the first prism 10. The P-polarized light is totally reflected by the reflecting film b of the first polarization prism 10, it is coupled to a third port P ₃ recombine with S-polarized light by the polarization separation film a.

[0005]

In such an optical circulator having such a structure, since there are many components in which the P-polarized light is reflected by the polarization splitting films in the first and second polarizing prisms, the isolating ratio is determined by the extinction ratio of the polarizing prisms. Is decided. Therefore, the isolation in the related art is at most about 28 to 30 dB, and it is difficult to achieve higher isolation than that. But,
For use in fields such as recent optical communication, an optical circulator with higher isolation is desired.

An object of the present invention is to provide a three-port optical circulator that can realize high isolation characteristics even when a polarizing prism having a low extinction ratio is used. It is another object of the present invention to provide a three-port optical circulator exhibiting low insertion loss, low polarization dependency, and low crosstalk characteristics.

[0007]

According to the present invention, a 45-degree Faraday rotator, a 1/2 polarization rotator, and a 1/2 polarization prism are provided between the first and second polarization prisms. A two-wavelength plate is arranged, light emitted from the first port enters the first polarizing prism, light emitted from the second polarizing prism is coupled to the second port, and the second port This is a three-port optical circulator in which the light entering the second polarizing prism from the first polarizing prism and the light emitted from the first polarizing prism are coupled to the third port. Here, a polarizer made of a wedge-shaped birefringent plate, a 45-degree Faraday rotator, and an analyzer made of a wedge-shaped birefringent plate are arranged between the first port and the first polarizing prism in that order. The optical isolator unit described above is disposed, and this point is a feature of the present invention.

At a first port adjacent to the first polarizing prism, a polarizer composed of a wedge-shaped birefringent plate, an analyzer composed of a 45-degree Faraday rotator and an analyzer composed of a wedge-shaped birefringent plate are arranged in that order. When the optical isolator unit is arranged, a leak light component generated in each optical component (ie, the first polarizing prism, the Faraday rotator, the half-wave plate, the second polarizing prism, etc.) constituting the optical circulator body is removed. High isolation can be obtained.

According to the present invention, in addition to the above configuration, a polarizer comprising a wedge-shaped birefringent plate, a 45-degree Faraday rotator, and a wedge-shaped birefringent plate are further provided between the first polarizing prism and the third port. An optical isolator unit in which analyzers composed of refraction plates are arranged in that order may be arranged. This configuration can more reliably prevent the return light reflected at the third port from being coupled to the first port.

The optical isolator unit to be incorporated in the three-port optical circulator includes a polarizer composed of a wedge-shaped birefringent plate, an analyzer composed of a 45-degree Faraday rotator and a wedge-shaped birefringent plate, A structure in which parallel flat birefringent plates for compensation are arranged in that order is preferable. In this configuration, by disposing a parallel plate type birefringent plate having a desired thickness, it is possible to eliminate polarization dispersion caused by ordinary light and extraordinary light generated by the polarizer and the analyzer.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A compound polarizing prism (polarizing beam splitter) incorporated in an optical circulator body may have a structure in which a right-angled triangular prism and a parallelogram prism are joined via a polarization separating film, or may be provided via a polarizing separating film. A structure in which two parallelogram prisms are joined may be used. In particular, when the latter composite polarizing prism is used, a parallel opposing optical circulator can be realized, and the optical fiber can be drawn out in the same direction at the first port and the third port. Therefore, there is an advantage that the device can be reduced in size and diameter. is there. As a polarizer and an analyzer incorporated in the optical isolator unit, for example, a tapered rutile single crystal is used.

Each port is composed of an optical fiber, a ferrule, and a collimator lens located at the tip of the optical fiber and ferrule. In practice, the optical circulator body and the optical isolator unit are housed in a housing, and each port is provided on the housing side wall to assemble a three-port optical circulator.

[0013]

FIG. 1 is an explanatory view showing an embodiment of a three-port optical circulator according to the present invention, and FIGS. 2 and 3 are explanatory views of its operation. This optical circulator comprises a combination of an optical circulator body 20 and two optical isolator units 22 and 24.

The optical circulator body 20 is basically provided with a 45-degree Faraday rotator 14 and a half between the first polarizing prism 10 and the second polarizing prism 12 as in the prior art.
This is a configuration in which a wavelength plate 16 is arranged. Double polarizing prism 1
Numerals 0 and 12 have a structure in which a right-angled triangular prism and a parallelogram prism are joined via a polarization separation film a, and a reflection film b is provided in parallel with the polarization separation film a. The first port P ₁ and incorporates a first first between the polarizing prism 10 of the optical isolator unit 22, the second optical isolator unit between the first polarizing prism 10 and the third port P ₃ 24. A second port P ₂ is arranged on the second polarizing prism 12 side. These are assembled in a housing (not shown). Wherein the first port P ₁ is emitted only port, the second port P ₂ is the input-output port, the third port P ₃ is the incident only port. Each port is
It is composed of an optical fiber, a ferrule, a collimator lens, and the like, and is attached to a housing.

The first optical isolator unit 22 and the second optical isolator unit 24 may have the same configuration.
Each of them includes a polarizer 30 formed of a wedge-shaped birefringent plate, a 45-degree Faraday rotator 32, and an analyzer 34 formed of a wedge-shaped birefringent plate.
Are arranged in that order. The optical axis of the analyzer 34 is rotated 45 degrees around the ray direction with respect to the optical axis of the polarizer 30. A first optical isolator unit 22, as in a forward direction with respect to the light emitted from the first port P _1, i.e. polarizer 30 is disposed so as to face the first port P _1. Second optical isolator unit 24, as in a forward direction with respect to the incident light to the third port P _3, i.e. the analyzer 34 is the third port P
Set up to face ₃ .

The light emitted from the _first port P ₁ is coupled to the second port P _{2 as shown} in FIG. Light emitted from the first port P ₁ is incident on the polarizer 30 of the first optical isolator unit 22 receives the different refractive between ordinary light and extraordinary light, the polarization components are emitted separately. The component rotated by 45 degrees by the Faraday rotator 32 becomes an analyzer 34.
, And each polarized light is refracted and emitted as parallel light.
The emitted polarized light component is the first component of the optical circulator body 20.
Are separated into P-polarized light and S-polarized light by the polarization separating film a of the polarizing prism 10, and one is transmitted and the other is reflected. Since the polarization planes of the Faraday rotator 14 and the half-wave plate 16 are rotated in opposite directions by 45 degrees each other, the polarization state is not changed in the second polarizing prism 12, so that the P-polarized light is the transmitted S-polarized light is reflected, condensed on an optical fiber through the second port P ₂ of the lens.

The light emitted from the _second port P ₂ is coupled to the third port P ₃ as shown in FIG. 2B. The light emitted from the second port P ₂ is transmitted to the optical circulator body 20.
Of the second polarizing prism 12, and is separated into P-polarized light and S-polarized light by the polarization separating film a of the second polarizing prism 12, one of which is transmitted and the other is reflected. Since the polarization plane is rotated in the same direction by 45 degrees by the half-wave plate 16 and the Faraday rotator 14, the polarization plane is rotated by 90 degrees when the light enters the first polarizing prism 10. That is, P-polarized light is converted to S-polarized light, and S-polarized light is converted to P-polarized light.
P-polarized light is transmitted through the polarization separation film a of the polarizing prism 10 of FIG.
Since the polarized light is reflected, it goes to the second optical isolator unit 24. Light emitted from the first polarizing prism 10 enters the polarizer 30 of the second optical isolator unit 24, undergoes different refraction between ordinary light and extraordinary light, and is separated and emitted from each polarized component. The component rotated by 45 degrees by the Faraday rotator 32 enters the analyzer 34,
Each polarized light is refracted and output as parallel light, and is condensed on an optical fiber via a lens at a _third port P3.

The light emitted from the _second port P ₂ is originally coupled to the third port P ₃ as described above. But,
Component towards the first port P ₁ of the leaked light component by the second polarizing prism 12 and the first polarizing prism 10 and the like, as shown in FIG. 3, the first optical isolator unit 22 is a reverse to have built way, the first port light towards P ₁ is blocked optical fiber without condensing. That is, the isolation is greatly improved. The return light reflected at the third port P _3, the second optical isolator unit 24 to are integrated at a reverse direction to return to the optical circulator body side without crosstalk is reduced .

Table 1 shows an example of the measurement results. P in the horizontal row
_{1 to} P ₃ indicate ports from which light is emitted, and P
₁ to P ₃ denotes a side port which light is incident. The values in parentheses are measured values by the conventional technique (only the optical circulator body). From Table 1, the insertion loss (from port P ₁ to port P
To _2, and from the port P ₂ to the port P ₃₎ it is not almost increased. On the other hand, isolation (port P
From port ₂ to port P ₁ and from port P ₃ to port P
To ₂₎ is greatly improved, also from cross-talk (port P ₃ to the port P ₁₎ also understood to have been greatly improved. As described above, even if the isolation of the optical circulator body is about 30 dB, high isolation can be obtained by inserting the optical isolator unit 22 between the first port P ₁ and the first polarizing prism 10.

[0020]

[Table 1]

FIG. 4 is an explanatory view showing another embodiment of the three-port optical circulator according to the present invention. The basic configuration is the same as that of FIG. 1 except for the internal structure of the optical isolator unit.
And the corresponding parts are denoted by the same reference numerals and description thereof will be omitted.
Also in this embodiment, the first optical isolator unit 42 is inserted between the first port P ₁ and the first polarizing prism 10 of the optical circulator body 20, and the first polarizing prism 10 and the third port P The second optical isolator unit 44 is inserted between the second optical isolator unit and the _third optical isolator unit. These optical isolator units 42 and 44 include a polarizer 30 composed of a wedge-shaped birefringent plate, a 45-degree Faraday rotator 32, an analyzer 34 composed of a wedge-shaped birefringent plate, and a parallel plate type birefringence for polarization dispersion compensation. Board 36
Are arranged in that order. When viewed in the forward direction, the point different from the previous embodiment is that a parallel plate type birefringent plate 36 is arranged after the analyzer 34. The parallel plate type birefringent plate 3
The optical axis 6 is used by rotating the optical axis of the analyzer 34 by 90 degrees around the ray direction. The parallel plate type birefringent plate 36 may be, for example, a rutile single crystal.

The light emitted from the _first port P ₁ passes through the first optical isolator unit 42 and is coupled to the second port P ₂ by the optical circulator body 20. The light emitted from the second port P ₂ is guided by the optical circulator body 20 in the direction of the second optical isolator unit 44 is coupled to the third port P _3. Of the leak light component of the light emitted from the second port P _{2 in} the optical circulator body 20, the component heading toward the first optical isolator unit 42 is a component that the first optical isolator unit 42 transmits when the leak light component passes. Since they are arranged in the opposite direction,
Leakage light not be coupled to the first port P _1, high isolation can be obtained.

In this embodiment, the light emitted from the _first port P ₁ enters the polarizer 30 of the first optical isolator unit 42 and undergoes different refraction between ordinary light and extraordinary light, and each polarized light component is changed. Separate and emit. The component rotated by 45 degrees by the Faraday rotator 32 enters the analyzer 34, and each polarized light is refracted and emitted as parallel light. That is, the polarizer 3
At 0 and the analyzer 34, the ordinary light and the extraordinary light undergo different refraction and follow different optical paths, so that an optical path difference occurs. The ordinary light and the extraordinary light emitted from the analyzer 34 due to the optical path difference are:
A difference occurs in the propagation speed. Therefore, if a parallel plate type birefringent plate 36 having an appropriate thickness (a thickness corresponding to the difference in the propagation velocities) is provided after the analyzer 34, the extraordinary light becomes the extraordinary light and the extraordinary light passes the ordinary light. . By canceling the difference between the propagation speeds generated by the polarizer 30 and the analyzer 34 by the difference in the propagation speed at that time, an optical circulator having the same propagation speed for each polarized light and having no polarization dispersion can be realized.

FIG. 5 is an explanatory view showing still another embodiment of the three-port optical circulator according to the present invention. The basic configuration is, except for the arrangement of the optical isolator unit.
Since the configuration may be the same as that of the embodiment shown in FIG. 4, corresponding portions are denoted by the same reference numerals and description thereof will be omitted. In this embodiment, the optical isolator unit 42 is inserted between the first port P ₁ and the first polarizing prism 10 of the optical circulator body 20, and the first polarizing prism 10 and the third port P ₃ In particular, no optical isolator unit is inserted between them.

As described above, the light emitted from the _second port P ₂ is originally transmitted to the third port by the optical circulator body 20.
Port but than it binds to P _3, the optical components (second polarizing prism which constitutes the optical circulator body 20 1
2, 1/2 wavelength plate 16, 45 degree Faraday rotator 14,
And leakage light component generated in the first polarization prism 10), part towards the first port P _1. An optical isolator unit 42 but that is inserted, since it is arranged in the opposite direction to the leakage light component, passage of light is not coupled to the first port P ₁ is blocked, therefore isolation characteristics It is greatly improved. This isolation characteristic is the most important, and the isolation from the third port P ₃ to the second port P ₂ or the crosstalk from the _third port P ₃ to the first port P ₁ depends on the use condition. (Because the light emitted from the _third port P3 is not originally assumed), it may not be necessary to make it so large. In such a case, the optical isolator unit
This embodiment, which requires only one unit, is effective.

FIG. 6 is an explanatory view showing still another embodiment of the three-port optical circulator according to the present invention. The basic configuration may be the same as that of the embodiment shown in FIG. 4 except for the internal structure of the optical circulator body. Corresponding portions are denoted by the same reference numerals, and description thereof will be omitted. First polarizing prism 6 of optical circulator body 50
0 and the second polarizing prism 62 are formed by joining two parallelogram prisms via a polarization separating film a, and
This is a structure in which a reflective film b is provided in parallel with the above. 45 between the first polarizing prism 60 and the second polarizing prism 62.
The Faraday rotator 14 and the half-wave plate 16 are arranged. Also in this embodiment, the first optical isolator unit 42 is inserted between the first port P ₁ and the first polarizing prism 60 of the optical circulator main body 50, and the first polarizing prism 60 and the third port P The second optical isolator unit 44 is inserted between the second optical isolator unit and the _third optical isolator unit. These optical isolator units 42 and 44 are composed of a polarizer 3 composed of a wedge-shaped birefringent plate.
An analyzer 34 comprising a 0 and 45 degree Faraday rotator 32 and a wedge-shaped birefringent plate, and a parallel plate type birefringent plate 3 for polarization dispersion compensation.
6 are arranged in that order.

The light emitted from the _first port P ₁ passes through the first optical isolator unit 42 and is coupled to the second port P ₂ by the optical circulator body 50. The light emitted from the second port P ₂ is guided by the optical circulator body 50 to the second optical isolator unit 44 is coupled to the third port P _3. Second port P
Among the leak light components of the light emitted from _{2 in} the optical circulator body 50, the component heading toward the first optical isolator unit 42 is arranged in a direction opposite to the direction in which the first optical isolator unit 42 passes the leak light component. because it is, leakage light is not able to bind to the first port P _1, high isolation can be obtained.

When a polarizing prism combining two parallelogram prisms is used as in this embodiment, the first port P ₁ and the third port P ₃ are arranged, and the second port P ₂ is arranged on them. , A parallel opposing optical circulator can be constructed. Since the optical fibers can be collectively pulled out to both sides, the routing of the optical fibers becomes easy, which is effective for downsizing or reducing the diameter of the device.

[0029]

According to the present invention, an optical isolator unit using a polarizer composed of a wedge-shaped birefringent plate and an analyzer is provided between a first port dedicated for emission and a first polarizing prism of the optical circulator body. By inserting the optical circulator, even if the extinction ratio of each polarizing prism of the optical circulator body is low, the isolation of the entire optical circulator can be increased to almost twice that of the related art. Further, if an optical isolator unit using a polarizer and an analyzer made of a wedge-shaped birefringent plate is inserted between the first polarizing prism of the optical circulator main body and the third port dedicated to incidence, it becomes unnecessary. Crosstalk can also be reduced.

When a parallel plate type birefringent plate is incorporated in the optical isolator unit, an optical circulator having no polarization dispersion can be obtained. By using a polarizing prism of the optical circulator body with a polarization separating film interposed between two parallelogram prisms, a parallel facing type can be obtained.
The arrangement of the optical fiber is facilitated, and there is an advantage that the optical fiber can be reduced in size and diameter.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of a three-port optical circulator according to the present invention.

FIG. 2 shows a first port P ₁ to a second port P
To _2, explanatory views showing the transmission from the second port P ₂ to the third port P _3.

Figure 3 is an explanatory diagram showing a high isolation from the second port P ₂ to the first port P _1.

FIG. 4 is an explanatory view showing another embodiment of the three-port optical circulator according to the present invention.

FIG. 5 is an explanatory view showing still another embodiment of the three-port optical circulator according to the present invention.

FIG. 6 is an explanatory view showing still another embodiment of the three-port optical circulator according to the present invention.

FIG. 7 is an explanatory view showing an example of a conventional three-port optical circulator.

DESCRIPTION OF SYMBOLS 10 First polarizing prism 12 Second polarizing prism 14 45-degree Faraday rotator 16 1/2 wavelength plate 20 Optical circulator main body 22 First optical isolator unit 24 Second optical isolator unit 30 Polarizer 32 45 degree Faraday rotator 34 Analyzer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsuguo Tokumasu 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (72) Inventor Yoichi Suzuki 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd.

Claims (3)

[Claims] 1. A 45-degree Faraday rotator and a half-wave plate are arranged between first and second polarizing prisms each having a polarization separation film inside and a reflection film provided in parallel with the polarization separation film, Light emitted from the first port is incident on the first polarizing prism, light emitted from the second polarizing prism is coupled to the second port, and light emitted from the second port is transmitted to the second polarizing prism. In a three-port optical circulator in which light incident on a polarizing prism and emitted from the first polarizing prism is coupled to a third port, a wedge-shaped birefringence is provided between the first port and the first polarizing prism. A three-port optical circulator, comprising an optical isolator unit in which a polarizer made of a plate, a 45-degree Faraday rotator, and an analyzer made of a wedge-shaped birefringent plate are arranged in that order. 2. A sequence in which a polarizer composed of a wedge-shaped birefringent plate, an analyzer composed of a 45-degree Faraday rotator and a wedge-shaped birefringent plate is arranged between a first polarizing prism and a third port. 2. The three-port optical circulator according to claim 1, wherein the optical isolator units arranged in the above manner are arranged. 3. An optical isolator unit comprising: a polarizer composed of a wedge-shaped birefringent plate, an analyzer composed of a 45-degree Faraday rotator and a wedge-shaped birefringent plate, and a parallel plate-type birefringent plate for polarization dispersion compensation. 3. The structure according to claim 1, wherein the structure is arranged in that order.
The three-port optical circulator according to claim 1.