JPH04359220A - Optical isolator - Google Patents

Abstract

PURPOSE:To provide the polarization nondependence type optical isolator which eliminates the need to consider the plane of polarization of incident light and displays its apprspriate functions. CONSTITUTION:Polarized light demultiplexing and multiplexing elements 6 and 7 are arranged on the incidence and projection sides of two optical isolator units 4 and 5 whose structures depend upon the plane of polarization of the incident light; and the light is made incident on the two optical isolator units 4 and 5 so that the planes of polarization of two optical paths A and B separated by the incidence-side polarized light demultiplexing and multiplexing element 6 match the planes of polarization of the polarizers of the two optical isolator units 4 and 5, and the polarized light components of the separated optical paths A and B separated are multiplexed again by the polarized light demultiplexing and multiplexing element 7 on the light-emitting side of the two optical isolator units 4 and 5.

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. 4 shows an example of the configuration 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 reflected return light in the opposite direction is blocked.
This type of optical isolator function is exhibited. Note that an even greater isolation effect can be obtained by configuring the optical isolator having the structure shown in FIG. 4 in multiple stages.

0003

[Problems to be Solved by the Invention] However, the conventional optical isolator having the above-described structure has a characteristic that depends on the inclination of the polarization plane of the incident light. Since it is necessary to match the planes of polarization, there is a problem that the function as an optical isolator cannot be sufficiently effectively exhibited, especially in optical transmission systems 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 polarization separation/synthesizing elements arranged on each of the input side and output side of two optical isolator units having a structure that depends on the plane of polarization of incident light. The above polarization separation/
Injecting the polarized light components of the two optical paths separated by the combining element into the two sets of optical isolator units so that the polarization planes of the respective polarized light components match the polarization planes of the incident-side polarizers of the two sets of optical isolator units, and On the output side of the two sets of optical isolator units, the polarized light components of the separated optical paths are recombined by the polarized light separation/synthesis element.

[0006]

According to the present invention, incident light is first separated into two optical paths having polarized light components at an angle of 90 degrees to each other by the polarization separation/synthesis element on the incident side. Then, the light is made incident on two sets of optical isolator units in which the polarization plane of the first polarizer is matched to the polarization component of each optical path. Further, the two polarized light components forming an angle of 90 degrees to each other that have passed through the two sets of optical isolator units are combined again by the polarization separation/synthesis element on the output side. On the other hand, light in the opposite direction to the incident light is separated into two optical paths having polarization components at an angle of 90 degrees to each other by the polarization separation/synthesizing element on the output side, and from this opposite direction, the two sets of optical isolator units Inject each into the Therefore, the light in the opposite direction cannot return to the incident side due to the action of the optical isolator unit.

[0007]

Embodiment A first embodiment of the optical isolator according to the present invention will be described below based on FIG. 1 and with reference to FIG. First, in Figure 1, 4 and 5 are conventional optical isolators (Figure 4).
This is an optical isolator unit constructed by connecting an even number of in series. That is, in this example, each optical isolator unit 4, 5 has two optical isolators 4a, 4, respectively.
Each optical isolator 4a, 4b, 5a, and 5b is composed of a first polarizer, a Faraday rotator, and a second polarizer, as in the conventional example. . The polarization planes of the first polarizers (see FIG. 4, reference numeral 1) of these optical isolator units 4 and 5 make an angle of 90 degrees with each other, and at the same time, the polarization planes of the incident side and the output side make an angle of 90 degrees with each other. is doing. Also, 6,
Reference numeral 7 denotes a polarization separation/combining element formed by combining two polarization beam splitters, and as shown in FIG. 1, it is arranged on the input side and output side of the two sets of optical isolator units 4 and 5, respectively.

Since the optical isolator according to the present invention is constructed as described above, the incident light first passes through the polarization separation/synthesizing element 6 on the incident side and is separated into optical path A and optical path B having mutually orthogonal polarization components. be done. The polarized light components of these two separated optical paths pass through the two sets of optical isolator units 4 and 5. At this time, the plane of polarization of the first polarizer (see reference numeral 1 in FIG. 4) on the incident side of each of the two sets of optical isolator units 4 and 5 coincides with the plane of polarization of the polarization components of optical path A and optical path B, respectively. Since the two optical isolator units 4 and 5 are arranged as shown in FIG.
The polarized light components of optical path A and optical path B that have passed through are combined again by the polarization separation/synthesis element 7 on the output side of the optical isolator units 4 and 5.

On the other hand, the light in the opposite direction to the above incident light is first
The polarization separation/synthesizing element 7 on the output side separates the light into two optical paths A and B having polarization components at an angle of 90 degrees to each other. The light enters units 4 and 5. Therefore,
Due to the action of the optical isolator units 4 and 5, such light in the opposite direction can no longer return to the incident side. 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 of the present invention. In this second embodiment, the pair of optical isolator units 4 and 5 have basically the same configuration as in the first embodiment, so that the planes of polarization on the incident side and the output side form an angle of 90 degrees with each other. In addition, the planes of polarization of the first polarizers of the optical isolator units 4 and 5 form an angle of 90 degrees with each other. In this case, unlike in the first embodiment, the direction of the polarization plane of the first polarizer of the optical isolator unit 4 is horizontal in the figure, and the polarization plane of the first polarizer of the optical isolator unit 5 is The direction of each surface is set vertically in the figure.

In each optical path A and optical path B, for example, TiO2 is used on the incident side and the output side of the optical isolator units 4 and 5.
Polarization separation/synthesis elements 8 and 9 made of birefringent plates made of (rutile) are arranged, but the polarization planes of the polarization components of optical path A and optical path B by polarization separation/synthesis element 8 are 2
It is set to match the polarization plane (horizontal direction and vertical direction) of the first polarizer on the incident side of each of the optical isolator units 4 and 5 of the set.

According to the second embodiment of the present invention, the incident light first passes through the polarization separating/combining element 8 on the incident side and is separated into an optical path A and an optical path B having mutually orthogonal polarization components. The polarized light components of these two separated optical paths pass through two sets of optical isolator units 4 and 5. In this case, since the plane of polarization of the first polarizer on the incident side of each of the two sets of optical isolator units 4 and 5 coincides with the plane of polarization of the polarization component of the optical path A and the optical path B, the two sets of optical isolator units 4 and 5 are The polarized light components of the optical path A and the optical path B that have passed through the optical isolator units 4 and 5 are recombined by the polarization separation/synthesis element 9 on the output side of the optical isolator units 4 and 5.

On the other hand, the light in the opposite direction to the above incident light is first
The polarization separation/synthesis element 9 on the output side separates the light into two optical paths A and B having polarization components at an angle of 90 degrees to each other. However, due to the action of the optical isolator units 4 and 5, such light in the opposite direction can no longer return to the incident side.

The optical isolator units 4 and 5 in the first and second embodiments are composed of the first polarizer 1, the Faraday rotator 2, and the second polarizer 3 as described above. (See FIG. 4), when two sets of these optical isolator units 4 and 5 are arranged in the optical path A and the optical path B, the configuration of the conventional optical isolator can be combined into one upper and lower set in parallel. That is, for example, as shown in FIG. 3, in the optical isolator 4a and the optical isolator 5a, the first polarizers 1, 1' and the second polarizers 3, 3' have polarized lights perpendicular to each other with respect to the optical paths A and B. The optical isolator can be made compact by arranging them as polarizers having planes and combining them into one so as to share the Faraday rotator 2. Of course, even with this configuration, the same effects as described above can be obtained, but this is particularly effective when an even number of optical isolator units are connected in series and the number increases.

[0015]

As described above, according to the present invention, the function of an optical isolator can be effectively and sufficiently performed without considering the state of the polarization plane, especially for optical transmission systems where the polarization plane of incident light cannot be specified in advance. It has excellent practical effects. It goes without saying that it can 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 a diagram showing a configuration example of an optical isolator unit according to the present invention.

FIG. 4 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 Optical isolator unit 6 Polarization separation/synthesis element 7 Polarization separation/synthesis element 8 Polarization separation/synthesis element 9 Polarization separation/synthesis element

Claims (1)

[Claims] Claim 1: Two sets of optical isolator units each having a structure that depends on the plane of polarization of incident light are provided with a polarization separation/synthesis element on each of the input side and output side, and the polarization separation/combination element on the input side Inject the two optical isolator units into the two sets of optical isolator units so that the plane of polarization of the polarized light components of the two optical paths separated by coincides with the plane of polarization of the incident-side polarizer of each of the two sets of optical isolator units,
An optical isolator characterized in that the polarized light components of the separated optical paths are recombined by the polarized light separation/combining element on the output side of the two sets of optical isolator units.