JP2904442B2 - Optical isolator - Google Patents

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 which 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, after the incident light passes through a first polarizer 1, its polarization plane is rotated by 45 degrees by a Faraday rotator 2. A second polarizer 3 having a polarization plane inclined by 45 degrees with respect to the first polarizer 1
Pass through. On the other hand, as for the reflected return light in the direction opposite to the incident light, only the component whose polarization plane coincides with that of 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. Accordingly, the reflected return light that has passed through the Faraday rotator 2 has its polarization plane rotated by 90 degrees with respect to the first polarizer 1, whereby the reflected light is reflected to the incident side of the incident light. Return light cannot reach it.
As described above, according to the conventional optical isolator, the reflected return light in the reverse direction is blocked, and this kind of optical isolator function is exhibited. By configuring the isolator having the structure shown in FIG. 2 in a plurality of stages, a greater isolation effect can be obtained.

[0003]

However, in such a conventional optical isolator, it is necessary to make the polarization plane of the first polarizer 1 coincide with the polarization plane of the incident light. In an optical transmission system that cannot perform such a function, there is a problem that the function cannot be effectively exhibited. This is because the structure has to depend on the inclination of the plane of polarization of the incident light.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an optical isolator which can function properly as an optical isolator of this kind without considering the state of polarization of incident light at all.

[0005]

SUMMARY OF THE INVENTION An optical isolator according to the present invention has an optical eye having a structure dependent on the plane of polarization of incident light.
The incident side of the formed optical isolator unit and arranged in two pairs in series a first optical system comprising a polarization separating and combining element and a polarization rotator and isolator, and the optical isolator Uni
A second optical system including a polarization rotator and a polarization splitting / combining element is disposed on the output side of the light source, and rotates one polarization plane of the polarization component of the optical path separated in the first optical system. Then, the light is incident on the optical isolator unit such that the polarization planes of the polarization components of the two optical paths separated from each other coincide with the polarization plane of the incident-side polarizer of the optical isolator unit, and the light is emitted on the output side of the optical isolator unit. The polarized light components of the separated optical paths are recombined by the second optical system.

[0006]

According to the present invention, first, the light is separated into two optical paths having polarization components at an angle of 90 degrees with each other by the polarization separation / combination element of the first optical system. Then, after the polarization planes of the polarization components of the two optical paths are matched by the polarization rotator arranged only in one optical path, the polarization rotator of the optical isolator unit is adjusted to the polarization plane of the polarization components of both optical paths. It is made incident. Further, in the second optical system, the polarization plane of the polarization component of the other optical path is orthogonal to the polarization plane of the polarization component of the one optical path by the polarization rotator arranged only in the other optical path among the separated optical paths. After that, these two polarized light components are combined by a polarization separating / combining element. On the other hand, the light in the opposite direction is separated into two optical paths having polarization components forming an angle of 90 degrees with each other by the polarization splitting / combining element of the second optical system, and only one of the two optical paths is separated by the polarization rotating element. After that, they are incident on the optical isolator unit from the opposite direction to the above case. Therefore, the light in the opposite direction cannot return to the incident side on the first optical system side due to the action of the optical isolator unit.

[0007]

DETAILED 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. First, in the drawing, reference numeral 4 denotes two sets each composed of the first polarizer (1), the Faraday rotator (2) and the second polarizer (3) described in the conventional optical isolator (FIG. 2). This is an optical isolator unit configured in series.
A first optical system and a second optical system, which will be described later, are configured on both sides of the optical isolator unit 4. The first optical system is defined as an incident side. Further, in the figure, 5 is a polarization separating / combining element composed of a TiO ₂ (rutile) birefringent plate arranged in the first optical system, and 6 is, for example, a half-wave plate arranged in the first optical system. Polarization rotator,
Reference numeral 7 denotes a polarization rotator configured in the same manner as the polarization rotator 6 in which the second optical system is disposed, and reference numeral 8 denotes a polarization multiplexing / synthesizing element 5 in the second optical system. It is a polarized light separating / combining element configured.

In the above case, parallel light from a semiconductor laser is used as the incident light. First, in the first optical system, the incident light passes through the polarization separating / combining element 5 and passes through the optical path a and the optical path b. Is separated into Also, among the polarized light components of the separated optical paths, only the optical path b passes, and the polarization plane of the polarized light component of the optical path b is rotated by 90 degrees to be coincident with the polarization plane of the polarized light component of the optical path a. The child 6 is arranged. The optical isolator unit 4 is
The polarizer 1 (see FIG. 2) on the incident side is arranged so that the polarization plane of the polarization components of the optical path a and the optical path b to be incident on the polarizer 1 coincide with the respective polarization planes. Further, in the second optical system, the polarization rotator 7 and the polarization separation / combination element 8 are arranged so that the polarization components of the optical path a and the optical path b passing 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 splitting / combining element 5 in the first optical system, and the polarized light splitting / combining element 5 causes the light to enter each other. The light is separated into an optical path a and an optical path b having polarization components forming an angle of 90 degrees.
Therefore, although the polarization planes of the optical paths a and b immediately after passing through the polarization separation / combination element 5 are orthogonal, these optical paths a and b
Of these, only the polarization plane of the polarization component of the optical path b where the polarization rotator 6 is disposed is rotated by 90 degrees, whereby the polarization planes of the polarization components of the optical path a and the optical path b are matched. Further, both the optical paths a and b enter the optical isolator unit 4 in such a state that the polarization planes coincide with each other. In this optical isolator unit 4, the polarization planes of the polarization components of the two optical paths a and b are 90 as described above. Rotated and matched. Next, in the second optical system, an optical path a where the polarization rotator 7 is disposed among the optical paths a and b.
Only the plane of polarization of the polarization component of
As a result, the polarization planes of the polarization components of the optical path a and the optical path b when entering the polarization separation / combination element 8 are orthogonal to each other. And the polarization separation / combination element 8
Are combined again.

On the other hand, the light in the opposite direction that is incident from the second optical system side is first 90
The light is separated into two optical paths a and b having polarization components having an angle of degree, and only the polarization component on one side of the optical path a is rotated by 90 degrees by the polarization rotator 7 and thus each polarization plane is rotated. Are orthogonal to each other, and the optical path a and the optical path b are in the opposite directions from the above case.
Incident on. Therefore, the light in the opposite direction can no longer return to the incident side of the first optical system due to the action of the optical isolator unit 4.

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 the optical path a and the optical path b in the example are exchanged, the same operation and effect as described above can be obtained. Further, by forming the optical isolator unit 4 in 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, the configuration can be simplified by using a conventionally known ordinary optical isolator unit, and the function of the optical isolator unit can be easily achieved. Since the optical isolator unit can be effectively exerted, an extremely high isolation effect can be obtained particularly when the optical isolator unit has a multi-stage configuration. In addition, since it is not necessary to consider the state of the plane of polarization of the incident light at all, the present invention is excellent in practical effects and the like. In addition, it can be used for so-called spatial beam light or optical fiber, but in this case, it can be easily replaced with an existing optical isolator and has advantages such as being extremely useful industrially. .

[Brief description of the 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, 8 Polarization separation / combiner 6, 7 Polarization rotator

Claims (1)

(57) [Claims] 1. A light having a structure dependent on the plane of polarization of incident light.
A first optical system including a polarization splitting / combining element and a polarization rotator is provided on an incident side of an optical isolator unit configured by arranging two sets of isolators in series.
A second optical system including a polarization rotator and a polarization splitting / combining element is provided on the output side of the unit , and one of the polarization components of the polarization component of the optical path separated in the first optical system is rotated. Then, the light is incident on the optical isolator unit such that the polarization planes of the polarized light components of both optical paths separated from each other coincide with the polarization plane of the polarizer on the incident side of the optical isolator unit, and the light is separated on the output side of the optical isolator unit. An optical isolator in which a polarized component of an optical path is re-coupled by the second optical system.