JPH04360119A - Optical isolator - Google Patents

Abstract

PURPOSE:To provide the polarized light nondependence type optical isolator which eliminates the need to consider the pland of polarization of incident light and displays its proper function. CONSTITUTION:A lst optical system consisting of a polarized light separating and synthesiying element 5 and a polarized light rotator 6 is arranged on the side of an optical isolator unit 4 which has structure depending upon the plane of polarization of incident light and a 2nd optical system consisting of two polarized light rotators 7 and 8 and a polarized light saparating and synthesizing element 9 is arranged on the projection side of the optical isolator unit 4; and the plane of polarization of one of the polarized light components of optical paths (a) and (b) separated by the 1st optical system is rotated and then the polarized light component is made incident so that the plane of polarization of the polarized light component matches the plane of polarization of a polarizer on the incidence side of the optical isolator unit 4; and the polarized light components of the separated optical paths (a) and (b) are coupled again by the 2nd optical system on the projection side of the optical isolator unit 4.

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. 3 shows an example of the structure of a conventional optical isolator of this kind. In this optical isolator, after incident light passes through a first polarizer 1, its plane of polarization is changed by a Faraday rotator 2. a second polarizer 3 having a polarization plane rotated by 45 degrees and further tilted by 45 degrees with respect to the first polarizer 1;
pass through. On the other hand, of the reflected return light in the opposite direction to the above-mentioned incident light, only the component whose polarization plane matches the second polarizer 3 passes through the second polarizer 3, and is then processed by 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 its plane of polarization rotated by 90 degrees with respect to the first polarizer 1, and therefore does not reach the incident side of the incident light. become unable to do so. According to such a conventional optical isolator, the above-mentioned reflected return light in the opposite direction is blocked, and the function of this type of optical isolator is exhibited. Note that an even greater isolation effect can be obtained by configuring the optical isolator having the structure shown in FIG. 3 in multiple stages.

0003

[Problems to be Solved by the Invention] However, the optical isolator having the above structure has a characteristic that depends on the inclination of the polarization plane of the incident light, and the polarization plane of the first polarizer 1 is different from the polarization plane of the incident light. Since it is necessary to match the polarization plane of the incident light, there is a problem that the function as an optical isolator cannot be sufficiently effectively exhibited, especially in an optical transmission system where the plane of polarization of incident light cannot be specified in advance.

In view of the above circumstances, it is an object of the present invention to provide a polarization-independent optical isolator that does not require any consideration of the plane of polarization of incident light and is capable of exhibiting its proper function.

[0005]

[Means for Solving the Problems] The optical isolator according to the present invention has a first optical system comprising a polarization separation/synthesis element and a polarization rotator on the incident side of an optical isolator unit having a structure that depends on the plane of polarization of incident light. There are also two polarization rotators and a polarization separation system on the output side of the optical isolator unit.
A second optical system consisting of a combining element is provided, and by rotating one plane of polarization of the polarized light components of the separated optical paths in the first optical system, the polarized light components of both separated optical paths are separated. The polarization plane of the optical isolator unit is made to be incident on the optical isolator unit such that the polarization plane of the polarizer matches the polarization plane of the polarizer on the input side of the optical isolator unit, and the polarization components of the separated optical path are They are combined again by a second optical system.

[0006]

According to the present invention, incident light is first separated into two optical paths having polarization components that are at an angle of 90 degrees to each other by the polarization separation/synthesis element of the first optical system. and,
After the planes of polarization of the polarization components of the two optical paths are matched by a polarization rotator placed only in one optical path, the light enters the polarizer of the optical isolator unit whose plane of polarization is matched to the polarization components of both optical paths. do. Further, the two polarized light components that have passed through the optical isolator unit are returned to the polarization plane in the same direction as when they entered the optical isolator unit by the first polarization rotator of the second optical system, and are then sent to one optical path. The plane of polarization of only the polarized light component of one optical path is rotated by the second rotator disposed in the second rotator, so that the polarized light components of the two optical paths are orthogonal to each other. Then, these polarized light components forming an angle of 90 degrees with each other are combined again by the polarized light separating/combining element of the second optical system. On the other hand, the light in the opposite direction to the above incident light is separated into two optical paths having polarization components at a 90 degree angle with each other by the polarization separation/synthesis element of the second optical system, and the light is separated into two optical paths having polarization components at an angle of 90 degrees to each other. The light enters the optical isolator unit from the opposite direction. Therefore, due to the action of the isolator unit, light in the opposite direction cannot return to the incident side of the first optical system.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the optical isolator according to the present invention will be described below with reference to FIG. 1 and FIG. 3. First, 4
is an optical isolator unit constructed by connecting an odd number of conventional optical isolators (FIG. 3) in series. Each optical isolator constituting this optical isolator unit 4 is composed of a first polarizer, a Faraday rotator, and a second polarizer as in the conventional example, but the incident side of the optical isolator unit 4 is The planes of polarization on the output side and the output side are at an angle of 45 degrees to each other. On both sides of the optical isolator unit 4, a first optical system and a second optical system, which will be described later, are installed.
Although the first optical system is arranged as the first optical system, here, the first optical system is assumed to be on the incident side.

Furthermore, in the figure, numeral 5 is a polarization separation/synthesizing element which is arranged in the first optical system and is made of, for example, a birefringent plate made of TiO2 (rutile), and 6 is arranged in the first optical system. For example, a polarization rotator consisting of a 1/2 wavelength plate, 7
and 8 a first polarization rotator and a second polarization rotator arranged in the second optical system and configured in the same manner as the polarization rotator 6, and 9 a polarization splitter arranged in the second optical system.・It is a composite element.

In the above case, the incident light in the first optical system is separated into two optical paths a and b by the polarization separation/synthesizing element 5, but the polarization rotator 6 separates these separated optical paths. Among the polarized light components, only the polarized light component of the optical path a passes through the polarized light component, and the polarization plane is rotated by 90 degrees to coincide with the polarized light component of the polarized light component of the optical path b. Further, the optical isolator unit 4 has a polarizer 1 (FIG. 3,
The polarizer 1 is arranged so that the plane of polarization of the light beam (see reference numeral 1) coincides with the plane of polarization of each of the polarized light components of the optical paths a and b to be incident on the polarizer 1. Further, the first polarization rotator 7 is configured so that the polarized components of the optical path a and the optical path b that have passed through the optical isolator unit 4 pass through, and the second polarization rotator 8 is configured so that only the polarized component of the optical path b passes through the second polarization rotator 8. It is arranged like this.

Since the optical isolator according to the present invention is constructed as described above, in the first optical system, the incident light first passes through the polarization separation/synthesizing element 5, thereby forming two optical paths having mutually orthogonal polarization components. It is separated into optical path a and optical path b. Then, among the polarized components of these separated optical paths a and b, only the polarized component of optical path a passes through the polarization rotator 6, so that its plane of polarization is rotated by 90 degrees,
As a result, the plane of polarization of the polarized light component of the optical path a matches the plane of polarization of the polarized light component of the optical path b. Further, when the polarized components of the two optical paths a and b pass through the optical isolator unit 4, their polarization planes are both rotated by 45 degrees (or 315 degrees).
, b are first returned to the state of the previous polarization plane of the optical isolator unit 4 by the first polarization rotator 7 in the second optical system. Then, only the polarization component of the optical path b is rotated by 90 degrees by the second polarization rotator 8, thereby
The polarized light components of the two optical paths a and b are orthogonal to each other, and the polarized light components of these optical paths a and b are further combined again by a polarization separation/synthesis element.

On the other hand, the light in the direction opposite to the above-mentioned incident light that enters from the second optical system side is divided by the polarization separation/synthesis element 9 of the second optical system into two polarization components having polarization components forming an angle of 90 degrees to each other. Of these, only the polarized light component of optical path b passes through the polarization rotator 8, and its polarization plane is rotated by 90 degrees. coincides with the polarization plane of the polarization component of optical path a. Then, the polarized light components of the optical paths a and b whose planes of polarization coincide with each other enter the optical isolator unit 4 from the opposite direction according to the reverse procedure to that described above. Therefore, due to the action of the optical isolator unit 4, the light in the opposite direction cannot return to the incident side of the first optical system. In the above case, the same effect can be obtained even if the two optical paths a and b are exchanged.

FIG. 2 shows a second embodiment of the optical isolator according to the invention. In this second embodiment, the optical isolator unit 4 is constructed by connecting an even number of conventional optical isolators (FIG. 3) in series, and the polarization planes on the incident side and the output side make an angle of 90 degrees to each other. I am doing it. The other basic configuration is the same as that of the first embodiment.

According to the second embodiment, the incident light in the first optical system first passes through the polarization separation/synthesizing element 5, as in the case of the first embodiment, so that the incident light has two polarization components orthogonal to each other. The polarization plane of the polarization component of the optical path a is rotated by 90 degrees by passing only the polarization component of the optical path a through the polarization rotator 6. As a result, the polarization plane of the polarization component of the optical path a is coincides with the plane of polarization of the polarized light component. Then, the polarized light components of the two optical paths a and b enter the optical isolator unit 4, but by passing through the optical isolator unit 4, their planes of polarization are both rotated by 90 degrees. The polarized light components of the optical paths a and b that have passed through the optical isolator unit 4 are first returned to the state of the polarization plane before the optical isolator unit 4 by the first polarization rotator 7 in the second optical system. Then, only the polarized light component of optical path b is rotated by 90 degrees by the second polarization rotator 8, so that the polarized light components of the two optical paths a and b are orthogonal to each other. are recombined by the element.

On the other hand, also in the case of light in the opposite direction entering from the second optical system side, the polarization separation/synthesis element 9 of the second optical system separates the two polarization components having polarization components making an angle of 90 degrees to each other.
The light is separated into two optical paths a and b, and enters the optical isolator unit 4 from the opposite direction according to the reverse procedure to the above, but due to the action of the isolator unit 4, the light in the opposite direction is directed to the incident side of the first optical system. I can't go back.

[0015]

As described above, according to the present invention, the plane of polarization can be made to match the plane of polarization of the polarizer on the incident side of the optical isolator unit, especially for optical transmission systems where the plane of polarization of incident light cannot be specified in advance. As a result, the function of the optical isolator can be effectively and fully demonstrated using a conventionally used optical isolator unit without considering the state of the polarization plane. Furthermore, since the optical axes of the incident light and the outgoing light coincide, there are advantages such as excellent practical effects. Of course, it can also be used for spatial beam light and optical fibers, and in that case it has the advantage of being able to easily replace existing optical isolators.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of a first embodiment of an optical isolator of the present invention.

FIG. 2 is an overall configuration diagram of a second embodiment of the optical isolator of the present invention.

FIG. 3 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 First polarization rotator 8 Second polarization rotator 9 Polarization separation/synthesis element

Claims (1)

[Claims] 1. A first optical system comprising a polarization separation/synthesizing element and a polarization rotator is provided on the input side of an optical isolator unit having a structure that depends on the plane of polarization of incident light; A second optical system consisting of two polarization rotators and a polarization separation/synthesizing element is respectively disposed, and one plane of polarization of the polarization component of the optical path separated in the first optical system is rotated. By doing so, the planes of polarization of the polarized light components of both separated optical paths are made to enter the optical isolator unit so that they match the plane of polarization of the polarizer on the input side of the optical isolator unit, and the polarization components on the output side of the optical isolator unit are An optical isolator characterized in that the polarized light components of the separated optical paths are recombined by the second optical system.