JPH0833523B2 - Polarization maintaining optical isolator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] An optical isolator in which a constant polarization fiber is used as an input / output optical fiber, and at least one Faraday rotator and two polarization separating / combining elements are arranged between the optical isolator. The polarization plane can be preserved by matching the azimuths of the output constant polarization fiber optical axis and the polarization splitting / combining element optical axis.

[Industrial applications]

The present invention relates to an optical isolator used for optical communication and allowing light to pass in only one direction.

When the output light of the semiconductor laser returns by reflection and is reinjected into the semiconductor laser, its oscillation becomes unstable. Therefore, in order to perform high quality optical communication, an optical isolator must be used to remove the reflected light. used.

[Prior Art] FIG. 3 is a diagram showing one configuration example of a conventional optical isolator. In the figure, 1 and 2 are optical fibers, 3 and 4
Are lenses, 5 and 6 are birefringent crystal wedge-shaped deflecting plates, and 7 is a Faraday rotator. The optical axes of the deflecting plates 5 and 6 are rotated by 45 ° with respect to the traveling direction of light. It is arranged. Then, the light entering from the optical fiber 1 on the left side is separated by the first polarizing plate 5 due to the difference in refractive index between the extraordinary light component 9 and the ordinary light component 8, and then the polarization plane is rotated by the Faraday rotator 7. Due to the refraction at the second deflecting plate 6, the polarization of each polarization component is compensated, and although some positional deviations remain, they become parallel to each other. On the other hand, with respect to the light incident from the optical fiber 2 on the right side, the refraction by the left and right deflecting plates 5 and 6 is not compensated for either polarization component, and the light enters the fiber with an inclination with respect to the optical axis. In this way, when the light travels from left to right (forward direction), the loss is small regardless of the incident polarization, and conversely, when light travels from right to left (reverse direction), it hardly couples to the optical fiber 1. .

[Problems to be solved by the invention]

The optical isolator described above uses a birefringent wedge plate to eliminate the incident polarization dependency, and the light intensity from the input fiber is preserved regardless of the polarization. However, the polarization state is not always preserved.

There is also an optical isolator that uses a polarization-maintaining fiber for input and output, but it can only propagate linearly polarized light in one direction.
However, as the technology of optical communication has advanced, the switching of polarization state has been attracting attention as a basic technology of coherent communication and optical computer, and an optical isolator capable of preserving the polarization state has been demanded.

The present invention was created in view of the above points, and an object thereof is to provide a polarization-maintaining optical isolator capable of preserving the polarization state.

[Means for solving problems]

Therefore, in the present invention, as illustrated in FIG. 1, the first constant polarization fiber 10 and the second constant polarization fiber 11 are used.
And at least a first polarization separation / combination element 12, a Faraday rotator 13, and a second polarization separation / combination element 14 are arranged in sequence, and the optics of the first and second polarization separation / combination elements 12, 14 are arranged. In the optical isolator arranged such that the azimuths of axes are rotated by 45 ° with respect to the traveling direction of light,
Optical axis of the constant polarization fiber 10 and the first polarization splitting / combining element
The azimuths of the optical axes of 12 are matched, the azimuths of the optical axes of the second constant polarization fiber 11 and the second polarization separation / combination element 14 are matched, and two orthogonal polarizations are both passed, and The feature is that the polarization state is preserved.

[Action]

Azimuths of the optical axis of the first polarization maintaining fiber 10 and the optical axis of the first polarization separation / combination element 12, and the second polarization maintaining fiber 11
By making the azimuths of the optical axis of and the optical axis of the second polarization splitting / combining element 14 coincide with each other, it is possible to eliminate the influence of combining the polarized light along the optical axis and the polarized light orthogonal thereto, and It is possible to transmit the polarization state as it is to the output polarization maintaining fiber.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention, in which a is a configuration diagram and b is an enlarged perspective view of a main part of FIG.

In the present embodiment, as shown in FIG. 1A, a lens 15, a lens 15 is provided between a first constant polarization fiber 10 and a second constant polarization fiber 11.
First polarization separation / combination element 12, Faraday rotator 13, second
The fact that the polarization separation / combination element 14 and the lens 16 are sequentially arranged is almost the same as the conventional example described in FIG. A wedge-shaped polarizing plate made of a birefringent crystal is used for the first and second polarization separation / combination elements 12 and 14. The essential point of this embodiment is shown in FIG.
As shown in, the direction of the optical axis of the first polarization-maintaining fiber 10 is aligned with the direction of the optical axis of the first polarization separation / combination element 12, and the direction of the optical axis of the second polarization-maintaining fiber 11 is changed. That is, the azimuth of the optical axis of the second polarization separation / combination element 14 is matched.

In this example configured as described above, since the azimuths of the optical axes of the polarization splitting / combining element and the optical axis of the polarization-maintaining fiber coincide with each other, the polarized light along the optical axis and the polarized light orthogonal thereto are combined. (If the optical axis of the polarization splitting / combining element and the optical axis of the polarization-maintaining fiber do not match, the polarized light along the optical axis and the polarized light orthogonal to it are combined. In this state, the light is incident on the second constant polarization fiber.) As a result, the polarization state of the first constant polarization fiber 10 can be directly transmitted to the second constant polarization fiber 11.

 FIG. 2 is a diagram showing another embodiment of the present invention.

The difference of this embodiment from the previous embodiment is that the direction of travel of light is centered between the lens 15 and the first polarization separation / combination element 12, and between the lens 16 and the second polarization separation / combination element 14. That is, the half-wave plates 17 and 18 that can be rotated are inserted.

The present embodiment configured in this way, the half-wave plate 17 or 1
By rotating 8 it is possible to make adjustments so that the optical axis of the polarization maintaining fiber 10 or 11 and the optical axis of the polarization splitting / combining element 12 or 14 coincide with each other. Other functions and effects are similar to those of the previous embodiment.

〔The invention's effect〕

As described above, according to the present invention, the plane of polarization can be preserved with an extremely simple configuration, which is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing another embodiment of the present invention, and FIG. 3 is a diagram showing one configuration example of a conventional optical isolator. In FIGS. 1 and 2, 10 is a first constant polarization fiber, 11 is a second constant polarization fiber, 12 is a first polarization separating / combining element, 13 is a Faraday rotator, and 14 is a second Polarization separating / combining element, 15, 16 are lenses, 17,
18 is a half-wave plate.

Claims (1)

[Claims] 1. At least a first polarization splitting / combining element (12) and a Faraday rotator (13) are provided between a first constant polarization fiber (10) and a second constant polarization fiber (11). A second polarization separation / combination element (14) is sequentially arranged, and first and second
In the optical isolator arranged such that the azimuths of the optical axes of the polarization splitting / combining elements (12, 14) are rotated by 45 ° with respect to the traveling direction of light, the first constant polarization fiber (10) The azimuths of the optical axis and the optical axis of the first polarization separating / combining element (12) are made to coincide with each other, and the azimuths of the optical axes of the second polarization maintaining fiber (11) and the second polarization separating / combining element (14) are adjusted. A polarization-maintaining optical isolator, which is characterized by matching and passing both orthogonal polarizations and preserving the polarization state.