JPH04324416A - Optical isolator - Google Patents

Abstract

PURPOSE:To provide the polarization nondependence type optical isolator which is usable without considering the plane of polarization of incident light. CONSTITUTION:An optical isolator unit 4 is so structure as to depend upon the plane of polarization of the incident light while the planes of polarization of the incident light and projection light are at 45 deg. to each other; and a 1st optical system composed of a polarized light demultiplexing and multiplexing element 5 and a polarized light rotator 6 is arranged on the incidence side and a 2nd optical system consisting of a polarized light rotator 7 and two polarized light demultiplexing and multiplexing elements 8 and 9 is arranged on the projection side. The polarized light rotator 6 is so arranged as to passes only one polarized light component demultiplexed by the polarized light demultiplexing and multiplexing element 6 and match its plane of polarization with that of the other polarized light component demultiplexed while the plane of polarization is rotated by 90 deg.. The 2nd optical system multiplexes the two polarized light components which are demultiplexed on the projection side of the isolator unit. The optical isolator unit 4 never allows to light in the opposite direction from return to the incidence side of the 1st optical system.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical isolator, and more particularly to a polarization-independent optical isolator that can operate without considering the plane of polarization of incident light.

0002

2. Description of the Related Art FIG. 2 shows an example of the configuration of a conventional optical isolator. The light is rotated by a degree and further passes through a second polarizer 3 having a plane of polarization inclined at 45 degrees with respect to the first polarizer 1. On the other hand, of the reflected return light in the opposite direction to the incident light, only the component whose polarization plane matches the second polarizer 3 passes through the second polarizer 3, and then the Faraday rotator 2 The plane of polarization is further rotated by 45 degrees. Therefore, the reflected return light that has passed through the Faraday rotator 2 has a polarization plane of 9 with respect to the first polarizer 1.
This means that it has rotated by 0 degrees, and as a result, the reflected return light cannot reach the incident side of the above-mentioned incident light. In this manner, the conventional optical isolator blocks the reflected and returned light in the opposite direction, and exhibits this type of optical isolator function. Note that an even greater isolation effect can be obtained by configuring the optical isolator having the structure shown in FIG. 2 in multiple stages.

0003

[Problems to be Solved by the Invention] However, the conventional optical isolator having the above-mentioned structure has a characteristic that depends on the inclination of the polarization plane of the incident light. Since it is necessary to match the polarization planes of the optical isolators 1, there is a problem that the function as an optical isolator cannot be fully demonstrated, especially in optical transmission systems where the polarization plane of the incident light cannot be determined in advance. there were.

In view of these problems, it is an object of the present invention to provide a polarization-independent optical isolator that can be used without considering the polarization plane of incident light at all.

[0005]

[Means for Solving the Problems] The optical isolator according to the present invention is provided on the incident side of an optical isolator unit having a structure in which the polarization plane of the incident light depends on the polarization plane of the incident light and the polarization planes of the incident light and the output light form an angle of 45 degrees to each other. A first optical system consisting of a polarization separation/synthesis element and a polarization rotator is disposed on the output side of the optical isolator unit, and a second optical system consisting of a polarization rotator and two polarization separation/synthesis elements is disposed on the output side of the optical isolator unit. By rotating the plane of polarization of one of the polarization components of the separated optical paths in the first optical system, the plane of polarization of the polarization components of both separated optical paths becomes the plane of polarization of the polarizer on the input side of the optical isolator unit. The polarized light components of the respective optical paths separated on the exit side of the optical isolator unit are recombined by a second optical system.

[0006]

According to the present invention, the incident light is first separated into two optical paths having polarization components forming an angle of 90 degrees to each other by the polarization separation/synthesis element of the first optical system. Then, after matching the polarization planes of the polarization components of the two optical paths with a polarization rotator placed only in one optical path, the polarization planes of the polarization components of both of these optical paths are matched to the polarizer of the optical isolator unit. Make it incident. The polarization planes of the two polarized light components that have passed through the optical isolator unit are each rotated by 45 degrees, and after being made orthogonal to each other by a polarization rotator disposed only on one optical path of the second optical system, the two polarization planes are rotated by 45 degrees. These two polarization components are combined by two polarization separation/combination elements. On the other hand, the light in the opposite direction is separated by the two polarization separation/synthesizing elements of the second optical system into two optical paths having polarization components that are at an angle of 90 degrees to each other. After the planes of polarization are matched by the polarization rotator, the light enters the optical isolator unit from the opposite direction. Therefore, due to the action of the optical isolator unit, the light in the opposite direction cannot return to the incident side of the first optical system.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical isolator according to the present invention will be described below with reference to FIG. 1 and FIG. 2. In FIG. 1, 4 is an optical isolator unit formed by connecting an odd number of conventional optical isolators (FIG. 2) in series, and the polarization planes on the incident side and the output side form an angle of 45 degrees with each other. A first optical system and a second optical system, which will be described later, are arranged on both sides of this optical isolator unit 4. In this case, the side where the first optical system is arranged is defined as the incident side. Furthermore, in the figure, 5 is a polarization separation/synthesizing element made of, for example, a TiO2 (rutile) birefringence plate arranged in the first optical system, and 6 is a polarization separation/synthesizing element, for example, a half wavelength arranged in the first optical system. A polarization rotator made of a plate, 7 is a polarization rotator configured similarly to the polarization rotator 6 arranged in the second optical system, 8, 9
are two polarization separation/combination elements arranged in the second optical system and configured similarly to the polarization separation/combination element 5 described above.

In the above case, parallel light from a semiconductor laser beam is used as the incident light, but first, in the first optical system, the incident light passes through the polarization separation/synthesizing element 5 to separate mutually orthogonal polarization components. It is separated into optical path a and optical path b. Of the polarized light components of these separated optical paths, only the polarized light component of the light path a passes through the polarization rotator 6 so that the plane of polarization is rotated 90 degrees to match the plane of polarization of the polarized light component of the light path b. is located. Further, the optical unit 4 is arranged so that the plane of polarization of the polarizer 1 (see FIG. 2) on the incident side matches the planes of polarization of the polarization components of the optical path a and the optical path b that are to be incident on the polarizer 1. There is. Furthermore, in the second optical system, such an optical isolator unit 4
A polarization rotator 7 and polarization separation/synthesizing elements 8 and 9 are arranged so that the polarization components of optical path a and optical path b that have passed through are combined.

Since the optical isolator according to the present invention is constructed as described above, the incident light is first made incident on the polarization separation/synthesizing element 5 in the first optical system, and the polarization components forming an angle of 90 degrees to each other are separated. Optical path a and optical path b having
separated into Therefore, the polarization planes of the optical paths a and b immediately after passing through the polarization separation/synthesizing element 5 are orthogonal, but the polarization component of the optical path a, where the polarization rotator 6 is arranged, Only the plane of polarization is rotated by 90 degrees, thereby making the planes of polarization of each polarization component coincident. Further, each polarized light component is incident on the optical isolator unit 4, and as described above, the polarization planes of the polarized light components in both optical paths a and b are rotated by 45 degrees. Next, in the second optical system, only the polarization plane of the polarization component of the optical path b, in which the polarization rotator 7 is arranged, is rotated by 90 degrees, and intersects the polarization plane of the polarization component of the optical path a at right angles. The two orthogonal polarized light components are combined again by the polarized light separation/synthesizing elements 8 and 9.

On the other hand, the light in the opposite direction entering from the second optical system side is first separated into two optical paths a and b having polarization components at 90 degrees to each other by polarization separation/synthesis elements 9 and 8. . After only the polarized light component of one of the optical paths a is rotated by 90 degrees by the polarization rotator 7, the optical isolator unit 4 is rotated from the direction opposite to that in the above case.
incident on . Therefore, due to the action of the optical isolator unit 4, such light in the opposite direction can no longer return to the incident side of the first optical system. Note that even if the optical path a and optical path b in the above embodiment are interchanged, the same effects as those described above can be obtained.

[0011]

As described above, according to the present invention, even in an optical transmission system where the plane of polarization of incident light cannot be specified in advance, the plane of polarization can be changed to the polarizer on the incident side of the optical isolator unit 4 (see FIG. 2).
(see). Therefore, the conventionally used optical isolator unit 4 can be used to sufficiently effectively function as an optical isolator without considering the state of the polarization plane, and is excellent in terms of practical effects and the like. It goes without saying that it can be used for spatial beam light or optical fibers, and in that case it can be easily replaced with an existing optical isolator, making it extremely useful industrially.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of an optical isolator according to the present invention.

FIG. 2 is an overall configuration diagram of a conventional optical isolator.

[Explanation of symbols]

1 First polarizer 2 Faraday rotator 3 Second polarizer 4 Optical isolator unit 5 Polarization separation/synthesis element 6 Polarization rotator 7 Polarization rotator 8 Polarization separation/synthesis element 9 Polarization separation/synthesis element

Claims (1)

[Claims] Claim 1: A polarization separation/synthesis element and a polarization rotator are provided on the input side of an optical isolator unit having a structure that depends on the polarization plane of the incident light and that the polarization planes of the input light and the output light make an angle of 45 degrees to each other. A first optical system consisting of a polarization rotator and two polarization separation/synthesizing elements is disposed on the output side of the optical isolator unit, and a second optical system consisting of a polarization rotator and two polarization separation/combination elements is disposed on the output side of the optical isolator unit. The optical isolator rotates one plane of polarization of the polarization components of the separated optical paths so that the plane of polarization of the polarization components of both separated optical paths coincides with the plane of polarization of the incident side polarizer of the optical isolator unit. An optical isolator that allows light to enter the unit and recombines the polarized light components of the separated optical paths on the output side of the optical isolator unit by the second optical system.