JP2857502B2 - 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 used for optical communication and the like. More specifically, the present invention relates to a fiber input / output type optical isolator having no polarization dependence and using a wedge-shaped uniaxial single crystal as a polarizer.

[0002]

2. Description of the Related Art In optical communication, an optical isolator is used to remove reflected return light to a laser light source.
There are various types of optical isolators. One of them is an input / output fiber type optical isolator that uses a uniaxial single crystal (birefringent polarizing plate) such as a wedge-shaped rutile single crystal as a polarizer and eliminates polarization dependence. is there.

FIG. 2 shows an example of the configuration. In each case, a 45-degree Faraday rotator 12 is mounted in a cylindrical permanent magnet 10, and polarizers 14 made of wedge-shaped uniaxial single crystals are arranged on both sides of the permanent magnet 10 so that their optical axes are staggered by 45 degrees. Further, a lens 16 and a fiber 18 are arranged on both sides of the fiber 16 to form a polarization-independent optical isolator for input and output of the fiber.

[0004] Such an optical isolator is conventionally assembled in the following order. A non-reciprocal element 15 is assembled by using two permanent magnets 10, a Faraday rotator 12, and two polarizers 14 each formed of a wedge-shaped rutile single crystal. As shown in FIG. 3, the two rutile single crystals are arranged so that their optical axes (denoted by A) are different from each other by 45 degrees to maximize the isolation of the optical isolator. The input / output fiber 18 is fixed to an optical isolator housing (not shown). By adjusting the position of the lens 16, the coupling between the fibers is established so that the amount of light passing through in the forward direction is maximized. The lens 16 is fixed to the optical isolator housing.

[0005]

The above-mentioned method has a drawback that the assembling and adjusting steps are increased because the assembly of the nonreciprocal element and the coupling between the fibers are performed in separate steps. Specifically, the adjustment of the nonreciprocal element 15 is performed by the arrow R in FIG.
As shown by, one of the polarizers is rotated relative to the other polarizer, and the coupling adjustment between the fibers is performed for both lenses in three axes as shown by coordinates X, Y, and Z in FIG. Do. For this reason, an increase in assembly and adjustment costs is inevitable.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to assemble a non-reciprocal element and to couple fibers together at the same time, to reduce the number of assembling and adjusting steps and to reduce the cost. An object of the present invention is to provide an optical isolator having a structure that can be easily manufactured.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided a fiber input / output unpolarized fiber in which a Faraday rotator is mounted in a cylindrical permanent magnet, and wedge-shaped uniaxial single crystal polarizers are disposed on both sides of the Faraday rotator. It is a dependent optical isolator. In order to achieve the above object, the present invention uses a cylindrical holder,
A lens is accommodated therein, a polarizer is mounted on one end of the cylindrical holder, and a ferrule with a fiber is inserted from the other end to obtain a fiber collimator with a polarizer. The end face of the fiber is adjusted to the focal length of the lens. Then, the cylindrical permanent magnet incorporating the Faraday rotator and two sets of the fiber collimator with a polarizer are inserted and fixed in the circular through hole of the optical isolator housing.

Here, the cylindrical holder has a sufficient concentricity between the inner peripheral surface and the outer peripheral surface, and the inner diameter of the cylindrical holder matches the outer diameter of the ferrule. The circular through-hole of the optical isolator housing is designed so that its diameter matches the outer diameter of the cylindrical holder. It is preferable that the fiber end face located at the tip of the ferrule is polished obliquely.

[0009]

The angle shift between two uniaxial single crystals serving as polarizers does not significantly affect the forward insertion loss, but greatly affects the isolation. Insert the fiber collimator with polarizer into the circular through hole of the optical isolator housing,
The coupling between the fibers is achieved by rotating the ferrule relative to the cylindrical holder and adjusting the ferrule so that the amount of light passing therethrough is maximized in the forward direction. The non-reciprocal element unit is assembled by rotating the cylindrical holder relative to the optical isolator housing and adjusting it so that the isolation is maximized.

If the fiber end face located at the tip of the ferrule is polished obliquely, the deviation of the optical path propagating in space in the non-reciprocal element from the central axis can be corrected, and the reflection in the optical isolator itself can be reduced.

[0011]

1 is a sectional view showing an embodiment of a fiber input / output polarization independent optical isolator according to the present invention.
Basically, as in the prior art, a 45-degree Faraday rotator 12 made of a magneto-optical crystal or the like is mounted in a cylindrical permanent magnet 10, and a uniaxial single crystal such as a wedge-shaped rutile single crystal is mounted on both sides thereof. A polarizer 14 composed of a refracting polarizing plate)
Arrange them so that their optical axes are staggered by 45 degrees,
In this configuration, fibers 18 are provided at both ends.

In this embodiment, a cylindrical holder 20 having a sufficient concentricity between the inner peripheral surface and the outer peripheral surface is used. At one end of the cylindrical holder 20, a concave portion 22 for mounting a polarizer having an inclined surface having a joining surface side equal to the wedge angle is provided so that the plane side of the wedge-shaped polarizer 14 is perpendicular to the central axis. Keep it.
The lens 16 is press-fitted into the cylindrical holder 20, and the polarizer 14 is bonded to the concave portion 22 at one end. Further, a ferrule 24 with a fiber is inserted into the cylindrical holder 20 from the other end side. The ferrule with fiber 24 is the fiber 18
Is inserted into and adhered to the ferrule 24, the outer diameter of the ferrule 24 is equal to the inner diameter of the cylindrical holder 20, and the tip including the fiber is obliquely polished. Then, the fiber end face is adjusted to the focal length of the lens 16 to obtain a fiber collimator 26 with a polarizer. The feature of the present invention resides in that the polarizer 14, the lens 16, and the fiber 18 are assembled as an integral structure.

Further, in this embodiment, the outer diameter of the fiber collimator 26 is made equal to the outer diameter of the cylindrical permanent magnet 10.
The Faraday rotator 1 uses an optical isolator housing 30 having a circular through-hole 28 having a diameter equal to the outer diameter of the Faraday rotator 1.
2 and the two sets of the fiber collimator with polarizer 26 are mounted on the optical isolator housing 3.
The optical isolator is inserted and fixed in the 0 circular through hole 28.

The basic operation of the optical isolator of the present invention is as follows.
This is exactly the same as the conventional optical isolator. If one of the two polarizers 14 functions as a polarizer in a narrow sense, the other functions as an analyzer. In case of forward direction, the first
The light input from one of the (one) fibers is output directly from the second (the other) fiber, but in the opposite direction,
Light input from the second fiber is not output from the first fiber. That is, a non-reciprocal operation is performed. As a result, the light output from the laser light source is output to the optical transmission line, but the reflected light can be prevented from returning to the laser light source.

The angular deviation of the optical axis between uniaxial single crystals serving as polarizers does not significantly affect the forward insertion loss. However, the angle shift has a great effect on isolation. Fiber collimator with polarizer 26
Into the circular through hole 28 of the optical isolator housing 30,
The ferrule 24 is rotated relative to the cylindrical holder 20 and moved in and out so that the amount of light passing through in the forward direction is adjusted to be maximum. Thereby, the coupling between the fibers is established. Further, the cylindrical holder 20 is relatively rotated with respect to the optical isolator housing 30 to adjust so as to maximize the isolation. Thus, the non-reciprocal element section is assembled.
The fixing between the ferrule 24 and the cylindrical holder 20 and the fixing between the cylindrical holder 20 and the optical isolator housing 30 are performed by bonding, welding, press fitting, or the like depending on the material. That is, in the present invention, a structure in which the assembly of the non-reciprocal element portion and the coupling between the fibers can be performed at the same time.

Further, in this embodiment, the fiber end face at the tip of the ferrule is polished obliquely. The inclination angle is set so that the amount of deviation from the central axis of the optical path that is spatially propagated in the non-reciprocal element portion can be exactly offset. Also, the reflection in the optical isolator itself can be reduced by this oblique polishing.

[0017]

As described above, according to the present invention, the polarizer, the lens, and the fiber are inserted into the optical isolator casing as an integral structure in which the cylindrical holder is incorporated. Can be performed at the same time, the number of assembling / adjusting steps is reduced, and the manufacturing becomes easier. As a result, an optical isolator with high assembling accuracy, good isolation characteristics, and stable accuracy can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a sectional view showing one embodiment of a fiber input / output polarization independent optical isolator according to the present invention.

FIG. 2 is an explanatory view of a conventional fiber input / output polarization independent optical isolator.

FIG. 3 is an explanatory view of a conventional non-reciprocal element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Permanent magnet 12 Faraday rotator 14 Polarizer 15 Non-reciprocal element 16 Lens 18 Fiber 20 Cylindrical holder 24 Ferrule 26 Polarizer-equipped fiber collimator 28 Circular through hole 30 Optical isolator housing

Continuation of front page (72) Inventor Akihiro Masuda 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) G02B 27/28 G02B 6/27 G02B 6/32

Claims (1)

(57) [Claims] A fiber-independent input / output polarization-independent optical isolator in which a Faraday rotator is mounted in a cylindrical permanent magnet, and a wedge-shaped uniaxial single crystal polarizer is arranged on both sides of the Faraday rotator. A lens is accommodated in a holder, a polarizer is mounted on one end of the cylindrical holder, and a ferrule with a fiber is inserted from the other end to form a fiber collimator with a polarizer. An optical isolator characterized in that a cylindrical permanent magnet incorporating a rotor and two sets of the fiber collimator with a polarizer are inserted and fixed in a circular through hole of an optical isolator housing.