JPH04360118A - Optical isolator - Google Patents

Abstract

PURPOSE:To provide the polarization nondependence type optical isolator. CONSTITUTION:A 1st optical system consisting of two polarized light separating and synthesizing elements 5 and 6 and a polarized light rotator 7 is arranged on the incidence side of an optical isolator unit 4, and a 2nd optical system consisting of a polarized light rotator 8 and two polarized light synthesizing elements 9 and 10 is arranged on the projection side; and the plane of polarization of one of polarized light components of optical paths (a) and (b) separated by the 1st optical system is rotated and the polarized light component is made incident on the optical isolator unit 4 so that the plane of polarization matches the plane of polarization of a polarizer on the incidence side of the optical isolator unit 4. Further, the polarized light components of the separated optical paths (a) and (b) are coupled again on the projection side by the 2nd optical system and the optical axes on the incidence side of the 1st optical system and the projection side of the 2nd optical system are aligned with each other.

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 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. be 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. 2 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] An optical isolator according to the present invention comprises an optical isolator unit having a structure that depends on the plane of polarization of incident light, and which includes two polarization separation/synthesizing elements and a polarization rotator on the incident side of the optical isolator unit. 1 optical system, and a second optical system consisting of a polarization rotator and two polarization separation/synthesis elements are disposed on the output side of the optical isolator unit, and the first optical system separates and combines the polarization elements. By rotating the polarization plane of one of the polarization components of the separated optical paths, the light is At the same time, the polarized light components of the separated optical paths are recombined by the second optical system on the output side of the optical isolator unit, and the polarization components of the optical paths separated on the output side of the optical isolator unit are recombined. The optical axes are made to coincide on the output side of the 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 two polarization separation/synthesis elements of the first optical system. Then, the polarization planes of the polarization components of the two optical paths are matched by a polarization rotator disposed only on one of the separated optical paths, and then an optical isolator unit whose polarization plane is matched with the polarization components of these optical paths is formed. incident on the polarizer. Further, the two polarized light components that have passed through the optical isolator unit are made orthogonal to each other by a polarization rotator disposed only on one side of the second optical system, and then recombined by two polarization separation/synthesis elements. At this time, the optical axis before entering the first optical system and the optical axis emitted from the second optical system coincide. 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 a direction opposite to that described above. 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 A first embodiment of the optical isolator according to the present invention will be described below with reference to FIG. 1 and FIG. 2. First, Figure 1
4, an optical isolator unit is constructed by connecting an even number of conventional optical isolators (FIG. 2) 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 The planes of polarization on the output side coincide or form an angle of 90 degrees with each other. A first optical system and a second optical system, which will be described later, are arranged on both sides of the optical isolator unit 4, but here, the side of the first optical system is assumed to be the incident side. Further, in the figure, numerals 5 and 6 are arranged in the first optical system, and are polarization separation/combining elements each made of a birefringent plate made of TiO2 (rutile), for example, and 7 is arranged in the first optical system. 8 is a polarization rotator arranged in the second optical system and configured in the same manner as the polarization rotator 7, and 9 and 10 are the second optical system. This is a polarization separation/synthesis element placed in the

In the above case, first, in the first optical system,
The incident light passes through two polarization separation/synthesizing elements 5 and 6 and is separated into optical path a and optical path b, which have mutually orthogonal polarization components. The polarization rotator 7 separates these separated optical paths. Of the polarized light components, only the polarized light component of the optical path a passes through, and the polarization plane is rotated by 90 degrees to match the polarization plane of the polarized light component of the optical path b. Further, the optical isolator unit 4 has a polarizer 1 (FIG. 2, reference numeral 1) on its incident side.
(see) such that the plane of polarization of the polarizer 1 coincides with the plane of polarization of the polarization components of the optical path a and optical path b that are to be incident on the polarizer 1. Furthermore, in the second optical system, the polarization rotator 8 and the polarization separation/combining elements 9 and 10 are arranged so that the polarization components of the optical path a and the optical path b that have passed through the optical isolator unit 4 are combined. .

Since the optical isolator according to the present invention is constructed as described above, the incident light first enters the two polarization separation/synthesizing elements 5 and 6, which separate the polarization components forming an angle of 90 degrees with each other. The beam is separated into an optical path a and an optical path b. Therefore, these two polarization separation/synthesis elements 5,
Immediately after passing through 6, the polarization planes of optical paths a and b are orthogonal, but among these optical paths a and b, only the polarization plane of the polarization component of optical path a, where polarization rotator 7 is arranged, is rotated by 90 degrees. death,
The planes of polarization of the polarized light components of both optical paths a and b match. Further, each polarized light component is incident on the optical isolator unit 4. Next, in the second optical system, only the polarization plane of the polarization component of the optical path b, in which the polarization rotator 8 is arranged, is rotated by 90 degrees to be orthogonal to the polarization plane of the polarization component of the optical path a. The two polarized light components, which are orthogonal to each other, are combined again by the two polarized light separation/synthesizing elements 9 and 10, but at this time, the optical axes of the incident light and the outgoing light coincide.

On the other hand, the light in the opposite direction that enters from the second optical system side is first divided into optical paths a and b, which have polarized components making an angle of 90 degrees to each other, by the two polarization separation/synthesizing elements 10 and 9. separated into And these optical paths a,
Of b, only the polarized component of optical path b is polarized by polarization rotator 8.
After rotating by 0 degrees, the light enters the optical isolator unit 4 from the opposite direction to that described above. 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. In addition, in the above case,
Similar effects can be obtained even if the two optical paths a and b are switched.

[0011]

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 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 separation/synthesis element 7 Polarization rotator 8 Polarization rotator 9 Polarization separation/synthesis element 10 Polarization separation/synthesis element

Claims (1)

[Claims] Claim 1: An optical isolator unit having a structure that depends on the polarization plane of incident light has two polarization separation plates on the incident side.
A first optical system consisting of a combining element and a polarization rotator, and a polarization rotator and a second optical system on the output side of the optical isolator unit.
A second optical system consisting of two polarized light separation/combining elements is respectively provided, and by rotating one plane of polarization of the polarized light components of the optical path separated in the first optical system, the two polarized light components are separated. The optical path is made to enter the optical isolator unit such that the plane of polarization of the polarized light component of the optical path coincides with the plane of polarization of the polarizer on the input side of the optical isolator unit, and the optical path is separated on the output side of the optical isolator unit. An optical isolator characterized in that the polarized light components of are recombined by the second optical system so that the optical axes thereof coincide on the input side of the first optical system and the output side of the second optical system. .