JPH04324417A - 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 at all. CONSTITUTION:An optical isolator unit 4 is so structured as to depend upon the plane of polarization of the incident light so that the planes of polarization of the incident light and projection light match each other; and a 1st optical system consisting of a polarized wave 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 a polarized light demultiplexing and multiplexing element 8 is arranged on the projection side. The polarized light rotator 6 passes only one polarized light component demultiplexed by the polarized light demultiplexing and multiplexing element 5 to rotate its plane of polarization by 90 deg. and matches its plane of polarization of the other polarized light component which is demultiplexed. The 2nd optical system passes only one of two polarized light components demultiplexed on the projection side of the isolator unit to rotate its plane of polarization by 90 deg., and couples it with the other polarized light component. The optical isolator unit 4 never allows light in the opposite direction to 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. In this optical isolator, incident light passes through a first polarizer 1, and then a Faraday rotator 2 changes the plane of polarization to 45 degrees. The light is rotated 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 planes of polarization are rotated by 45 degrees with respect to each other. 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. As described above, the conventional optical isolator blocks the reflected and returned light in the opposite direction, and exhibits the function of this type of optical isolator. Note that an even greater isolation effect can be obtained by configuring the isolator having the structure shown in FIG. 2 in multiple stages.

0003

However, in the conventional optical isolator having the structure as described above, it is necessary to match the polarization plane of the first polarizer 1 with the polarization plane of the incident light. Particularly in optical transmission systems in which the plane of polarization cannot be specified, there is a problem in that the functions cannot be effectively demonstrated. This is because the structure has no choice but to depend on the inclination of the plane of polarization of the incident light.

In view of the above circumstances, it is an object of the present invention to provide an optical isolator that can function appropriately as this type of optical isolator without taking into account the state of the plane of polarization of incident light at all.

[0005]

[Means for Solving the Problems] The optical isolator according to the present invention includes 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 dependent on the plane of polarization of incident light. Also, a second optical system consisting of a polarization rotator and a polarization separation/synthesis element is provided on the output side of the optical isolator, and one polarization component of the optical path separated in the first optical system is provided. By rotating the wavefront, the polarized components of both separated optical paths are made to enter the optical isolator unit so that their polarization planes match the polarization plane of the polarizer on the input side of the optical isolator unit, and at the output side of the optical isolator unit. The polarized light components of the separated optical paths are recombined by the second optical system. Further, the incident side of the optical isolator unit and the plane of polarization are configured to coincide.

[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 two polarized light components are made to coincide with each other by a polarization rotator disposed in only one optical path, the polarized light components of both of these optical paths are made to enter a combined polarizer of an optical isolator unit. Furthermore, in the second optical system, a polarization rotator disposed only in the other of the separated optical paths causes the plane of polarization of the polarized light component of the other optical path to be orthogonal to the plane of polarization of the polarized light component of the one optical path. After this, these two polarization components are combined by a polarization separation/synthesis element. On the other hand, the light in the opposite direction is separated by the polarization separation/synthesis element of the second optical system into two optical paths having polarization components at 90 degrees to each other, and only the polarization plane of one of the optical paths undergoes polarization rotation. The elements are rotated by 90 degrees, after which they enter the optical isolator unit from the opposite direction to that in the above case. 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 configured by connecting two sets of conventional optical isolators (FIG. 2) in series so that the plane of polarization on the input side and the plane of polarization on the output side match. be. 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 a TiO2 (rutile) birefringent plate arranged in the first optical system, and 6 is a half-wave plate, for example, arranged in the first optical system. 7 is a polarization rotator arranged in the second optical system and configured similarly to the polarization rotator 6;
Reference numeral 8 denotes a polarization separation/combination element 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 and is divided into 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. In addition, the optical isolator unit 4 has a polarizer 1 (Fig. 2
reference) is arranged so that the polarization plane of the polarization component of the optical path a and the optical path b that should be incident on the polarizer 1 coincides with each polarization plane of the polarization components of the optical path a and the optical path b. Furthermore, in the second optical system, a polarization rotator 7 and a polarization separation/synthesis element 8 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 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
It is separated into two parts. Therefore, the polarization planes of optical paths a and b immediately after passing through the polarization separation/synthesizing element 5 are orthogonal;
Of these optical paths a and b, only the polarization plane of the polarization component of the optical path a where the polarization rotator 6 is disposed is rotated by 90 degrees, thereby making the polarization planes of each polarization component coincide. Further, each polarized light component is incident on the optical isolator unit 4, but in this case, in the optical isolator unit 4, the planes of polarization of the polarized light components on both optical paths a and b are maintained in the same state as at the time of incidence. Next, in the second optical system, of the optical paths a and b, only the plane of polarization of the polarization component of the optical path b, in which the polarization rotator 7 is arranged, is rotated by 90 degrees by the polarization rotator 7. The planes of polarization of the polarized light components in optical path a and optical path b when they enter the combining element 8 are perpendicular to each other. Then, they are combined again in the polarization separation/synthesis element.

On the other hand, the lights in opposite directions incident from the second optical system are first separated by 90 degrees from each other by the polarization separation/synthesis element 8.
The light beam is separated into two optical paths a and b having polarization components forming an angle of 100 degrees, and only the polarization component of one of the optical paths b is rotated by 90 degrees by the polarization rotator 7. In this way, the optical paths a and b enter the optical isolator unit 4 from the opposite direction to that in the above case, with their respective polarization planes perpendicular to each other. Therefore, due to the action of the optical isolator unit 4, the light in the opposite direction can no longer return to the incident side of the first optical system.

As described above, by providing the first optical system and the second optical system on both sides of the optical isolator unit 4, the performance of the optical isolator unit 4 can be effectively exhibited. Even when optical path a and optical path b are interchanged, the same effect as described above can be obtained. Moreover, by forming the optical isolator unit 4 into a multi-stage configuration of two or more stages, the isolation effect can be further enhanced.

0012

As described above, according to the optical isolator of the present invention, it can be easily constructed by using conventionally known ordinary optical isolator units, and the functions of such optical isolator units can be improved. Therefore, an extremely high isolation effect can be obtained especially by configuring the optical isolator unit in a multi-stage (even number) configuration. Furthermore, since there is no need to consider the state of the polarization plane of the incident light at all, it is excellent in terms of practical effects and the like. In addition, it can of course be used for so-called spatial beam light and optical fibers, and in that case it has the advantage of being able to easily replace existing optical isolators and being 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]

4 Optical isolator unit 5 Polarization separation/synthesis element 6 Polarization rotator 7 Polarization rotator 8 Polarization separation/synthesis element

Claims (2)

[Claims] Claim 1: An optical isolator unit having a structure dependent on the plane of polarization of incident light has a first optical system comprising a polarization separation/synthesizing element and a polarization rotator on the input side, and an output side of the optical isolator. A second optical system consisting of a polarization rotator and a polarization separation/synthesizing element is respectively disposed, and the polarization plane of one of the polarization components of the optical path separated in the first optical system is rotated to separate the two polarization components. The polarized light component of the optical path is made to enter the optical isolator unit such that the polarization plane of the polarized light component matches the polarization plane of the input side polarizer of the optical isolator unit, and the polarized light component of the separated optical path is made to enter the optical isolator unit on the output side of the optical isolator unit. An optical isolator in which polarized light components are recombined by the second optical system. 2. The optical isolator according to claim 1, wherein in the optical isolator unit, planes of polarization on an incident side and an output side of the optical isolator unit are made to coincide with each other.