JPH05341230A - Optical isolator - Google Patents

Abstract

PURPOSE:To obtain the optical isolator of a polarized wave non-dependence type by disposing in order a Faraday rotator and a polarized light rotator on two optical paths between two elements. CONSTITUTION:A plane of polarization of polarized light components of two optical paths (a), (b) rotates by 90 degrees against a plane of polarization in a state separted at the time of incidence by a Faraday rotator 7 and a polarized light rotator 8, therefore, is not synthesized in a polarized light separating/ synthesizing element 4 of an incident side. In this case, the polarized light component of the optical path (a) is reflected by a reflecting prism 6 for constituting the element 4, passes through a polarized beam splitter 5 as it is and is emitted in the direction for making an angle of 90 degrees against an optical axis of an incident light, therefore, does not return to the incident side. Also, the polarized light component of the optical path (b) is reflected by the splitter 5 for constituting the element 4, and emitted in the direction for making 90 degrees against the optical axis of the incident light in the same as the polarized light component of the optical path (a), therefore, does not return to the incident side. In such a way, a function as the optical isolator is displayed without considering entirely the plane of polarization of an incident light.

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 polarization plane of incident light.

[0002]

2. Description of the Related Art FIG. 2 shows a configuration example of a conventional optical isolator. In this optical isolator, after the incident light passes through the first polarizer 1, the Faraday rotator 2 rotates its polarization plane by 45 degrees, and further has a polarization plane inclined by 45 degrees with respect to the first polarizer 1. It passes through the second polarizer 3. On the other hand, in the reflected return light in the opposite direction to the incident light, only the component whose polarization plane matches 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 45 degrees. Therefore, 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, and thereby reaches the incident side of the incident light. Can not do. As described above, according to the conventional optical isolator, the reflected return light in the opposite direction is blocked, and this type of optical isolator function is exhibited.

[0003]

However, in such a conventional optical isolator, it is necessary to match the polarization plane of the first polarizer 1 with the polarization plane of the incident light. In the optical transmission system which cannot be specified, there is a problem that the function cannot be effectively exhibited. This is because the structure has no choice but to depend on the inclination of the polarization plane of the incident light.

In view of the above situation, it is an object of the present invention to provide a polarization-independent optical isolator capable of exerting its function as an optical isolator without considering the plane of polarization of incident light. And

[0005]

In order to achieve the above object, the optical isolator of the present invention splits a polarized light having an arbitrary polarization plane into two polarizations having polarization planes forming an angle of 90 degrees with each other. One polarized light is emitted on the same optical axis as the incident light, and the other polarized light is emitted on another optical axis parallel to the optical axis. It is characterized in that a Faraday rotator and a polarization rotator are sequentially arranged on the road.

[0006]

According to the present invention, the incident light having an arbitrary polarization plane is first separated by the polarization separating / combining element on the incident side into two polarized lights having polarization planes forming an angle of 90 degrees with each other.
Next, the Faraday rotator rotates the polarization plane of the polarization component of each optical path by 45 degrees, and then the polarization rotator further rotates by 45 degrees, for a total of 90 degrees, so these two polarization components are separated / combined on the output side. It is synthesized by the element.

On the other hand, light in the opposite direction having an arbitrary polarization plane is first split into two optical paths having a specific polarization plane by the polarization splitting / combining element on the output side. Then, the plane of polarization is rotated by 45 degrees by the polarization rotator, and then returned to the original plane of polarization by the Faraday rotator. Therefore, the polarization planes of these two optical paths are rotated by 90 degrees with respect to the polarization planes separated at the time of incidence, and are not combined by the polarization separation / combining element on the incident side. Since the light is emitted in a direction forming 90 degrees with the optical axis, it does not return to the incident side.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing one structural example of an optical isolator according to the present invention. The upper part of the figure shows the arrangement of each element and shows the optical path of the incident light, the middle upper part shows the change of the polarization plane at each stage of the incident light, and the middle lower part and the lower part are for return light. First, in FIG. 1, reference numeral 4 is a polarization splitting / combining element including a polarization beam splitter 5 and a reflecting prism 6. Further, 7 is a Faraday rotator, and 8 is a polarization rotator composed of a λ / 2 plate.

In the above case, the incident light is first split into two polarized lights having specific polarization planes forming an angle of 90 degrees by the action of the polarization beam splitter 5 constituting the polarization splitting / combining element 4. At this time, one of the two polarizations is the optical path b having the same optical axis as the incident light, and the other is the optical paths b and 90.
The optical path a having an optical axis forming an angle of degrees is advanced.

A reflecting prism 6 which constitutes the polarization splitting / combining element 4 is disposed on the optical path a, and the polarized light traveling on the optical path a is reflected by the reflecting prism 6 and has a light axis parallel to the optical path b. Becomes That is, the incident light is separated by the polarization separating / combining element 4 into polarized light components of two optical paths a and b having specific polarization planes forming an angle of 90 degrees with each other and having an optical axis parallel to the incident light. .

Next, the polarization planes of the two separated polarization components are rotated by 45 degrees by the Faraday rotator 7 and further rotated by 45 degrees by the polarization rotator 8 for a total of 90 degrees.
Rotate once. As a result, the polarization planes of the polarization components of the optical paths a and b are in a state where they are just replaced with the separated states. Therefore, the polarization components of the optical paths a and b are combined by the polarization separating / combining element 4 on the exit side, which is configured in the same manner as the polarization separating / combining element 4 on the incident side, and is emitted.

On the other hand, the return light entering from the exit side is first separated by the action of the polarization splitting / combining element 4 into polarization components of two optical paths a and b having specific polarization planes forming an angle of 90 degrees with each other. . Then, the polarization plane is rotated by 45 degrees by the action of the polarization rotator 8, and is returned to the original polarization plane again by the Faraday rotator 7.

Therefore, the polarization planes of the polarization components of the two optical paths a and b are rotated by 90 degrees with respect to the polarization planes separated at the time of incidence.
It is not combined in the combining element 4. At this time, the polarization component of the optical path a is reflected by the reflection prism 6 that constitutes the polarization splitting / combining element 4, and the polarization beam splitter 5
The light does not return to the incident side because it passes through as it is and is emitted in a direction forming 90 degrees with the optical axis of the incident light. Further, the polarization component of the optical path b is reflected by the polarization beam splitter 5 constituting the polarization separation / combination element 4, and is emitted in the direction forming an angle of 90 degrees with the optical axis of the incident light like the polarization component of the optical path a. Do not go back to your side.

[0014]

As described above, according to the present invention, even in an optical transmission system in which the plane of polarization of incident light cannot be specified in advance, the function as an optical isolator is sufficiently effective without considering the state of the plane of polarization. Since it can be demonstrated, it is also excellent in practical effects. In addition, it can be used as a space beam light or an optical fiber, but in that case, it can be easily replaced with an existing optical isolator, which is extremely useful industrially.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of an optical isolator of the present invention.

FIG. 2 is a diagram showing a configuration example of a conventional optical isolator.

[Explanation of symbols]

 1 First Polarizer 2 Faraday Rotor 3 Second Polarizer 4 Polarization Separation / Combining Element 5 Polarization Beam Splitter 6 Reflection Prism 7 Faraday Rotator 8 Polarization Rotator

Claims (1)

[Claims] 1. Polarized light beams having arbitrary planes of polarization are separated from each other by 9
A polarized light that is split into two polarized lights having a plane of polarization that forms an angle of 0 degree, and one polarized light is emitted on the same optical axis as the incident light, and the other polarized light is emitted on another optical axis parallel to the optical axis. An optical isolator, wherein a pair of separation / combination elements are arranged to face each other, and a Faraday rotator and a polarization rotator are sequentially arranged on two optical paths between the two elements.