JPH06250122A - Optical isolator independent of polarization - Google Patents

Abstract

PURPOSE:To save the handing time of alignment and to reduce the reflection and absorption losses for an ordinary ray and to improve a characteristic by arranging a birefringence plate for correcting a beam position only on one side optical path of separated beams. CONSTITUTION:This isolator is constituted so that a second birefringence plate 4 is actuated only to separated beam, and is constituted so as to be arranged in order of a first birefringence plate 2 separating the beam to two linear polarization according to a polarization direction, a Faraday rotator 3 imparting a nonreciprocal rotation to a polarization surface, the second birefringence plate 4 for correcting the beam position and a third birefringence plate 5 synthesizing a separated polarization. Then, the birefringence plate 4 is arranged on an optical path of only one side of the separated beam. The beam is separated to the normal beam fa-1 and an abnormal beam fb-1 by the birefringence plate 2 in a forward direction (A). Only the fb-2 is made incident on the birefringence substrate 4, and the position of the beam is shifted (fb-3). In a backward direction (B), the incident beam 6 is separated to the normal beam bb-1 and the abnormal ba-1, and the bb-1 is made incident on the birefringence substrate 4 and the beam position is shifted.

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 fiber communication or the like, and more particularly to a polarization independent isolator mounted between optical fibers.

[0002]

2. Description of the Related Art A conventional polarization-independent optical isolator is shown in FIG. In the figure, (A) shows light traveling in the forward direction,
(B) represents light traveling in the opposite direction, 1 is an incident light beam, 2 is a birefringent plate, for example, a uniaxial crystal cut out so that its optical axis is inclined to the surface and polished into a parallel plate, which is perpendicular to the parallel plate. The light beam incident on is split into two linearly polarized lights that are perpendicular to each other. At this time, the linearly polarized light that goes straight through the birefringent plate is called an ordinary ray, and the one that receives birefringence and goes obliquely is called an extraordinary ray. These lights propagate in parallel after passing through the birefringent plate. Reference numeral 3 denotes a Faraday rotator formed of YIG or the like, which rotates the plane of polarization by 45 ° about the light propagation direction as an axis. Four
Is a second birefringent plate 2 installed so that the optical axis forms an angle of 45 ° with the birefringent plate 2 about the light propagation direction. Reference numeral 5 indicates the first birefringent plate 2 about the light propagation direction. Is a third birefringent plate installed so that the optical axis of 5 and the optical axis of 5 form −45 °.

FIGS. 2A and 2B are side views of how light travels in this device. The position and polarization direction of the beam in FIG. 2 are the directions of the first birefringent plate 2. 3A and 3B are viewed from above. The arrow indicates the direction of the plane of polarization. The case where the light is incident from the first birefringent plate 2 is defined as the forward direction, and the case where the light is incident from the third birefringent plate 5 is defined as the reverse direction. For further simplification, the linearly polarized light split into two is a and b respectively, and the forward direction is fa and fb, and the reverse direction is b.
Represented as a and bb. The numbers correspond to the respective positions in FIG.

The operating principle of the isolator will be described with reference to FIGS. 2 and 3. Light incident in the forward direction becomes two linearly polarized lights which are perpendicular to each other as shown in FIG. 2 and travel in parallel. Fa-1 is the ordinary light and fb-1 is the extraordinary light. When the light passes through the Faraday rotator (fa-2), the plane of polarization (fb-2) rotates 45 ° clockwise. In the second birefringent plate 4, the optical axis is rotated by 45 ° so that fa-2 becomes ordinary light and fb-2 becomes extraordinary light corresponding to the rotated plane of polarization, so only extraordinary light is refracted. It becomes like fb-3. On the other hand, in the third birefringent plate 5, the optical axes are set so that fa-3 becomes extraordinary light and fb-3 becomes ordinary light. Therefore, two orthogonal polarized lights are combined as fa-4 and fb-4. Emitted from the device without loss of power.

On the other hand, in the opposite direction, the light 6 incident on the third birefringent plate 5 is separated into two orthogonal polarizations such as ba-1 (extraordinary light) and bb-1 (ordinary light). Since the optical axis of the second birefringent plate 4 is orthogonal to that of the third birefringent plate 5, ba-1 goes straight as an ordinary ray to ba-2 and bb-1 becomes an extraordinary ray to be refracted bb. -It becomes like 2. The Faraday rotator rotates non-reciprocal polarization planes ba-3, b
The light that has become b-3 is refracted to ba-4 by the first birefringent plate 2 because ba-3 is extraordinary light and becomes bb-4 because it is an ordinary light and goes straight to bb-4. Therefore, the light is emitted at a position different from the forward incident position, cannot be coupled to the optical system on the forward side, and is blocked.

[0006]

However, in the above-mentioned prior art, since three expensive birefringent elements are used, the cost becomes high as a whole. Further, when entering and exiting the birefringent element, there are two beams, an ordinary ray and an extraordinary ray, both of which must be accurately aligned at the same time, and since there are three birefringent elements, alignment is very troublesome. Therefore, the cost is increased.

[0007]

In order to solve the above-mentioned problems, referring to FIG. 3 of a conventional example, a forward fa-
Since 2 → fa-3 and ba-1 → ba-2 in the opposite direction have not undergone any conversion with respect to the angle of the plane of polarization and the position of the beam,
It can be seen that the entire function of this portion does not change even without the birefringent element. Therefore, in the present invention, the second birefringent plate 4 is structured so as to act only on the separated light b, and the first birefringent plate that separates the light into two linearly polarized lights according to the polarization direction and the non-reciprocal polarization plane. A polarization-independent optical isolator in which a Faraday rotator that gives various rotations, a second birefringent plate for beam position correction, and a third birefringent plate that combines the separated polarized lights are arranged in this order. Therefore, it is a polarization-independent optical isolator in which a birefringent plate for correcting the beam position is arranged on the optical path of only one of the separated beams.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the structure of a polarization-independent isolator according to the present invention, in which a second birefringent plate 4 is arranged so as to act on only one of the separated lights. The operation will be described with reference to FIG. 1. In the forward direction (A), the first birefringent plate 2 separates the ordinary light fa-1 and the extraordinary light fb-1. The two beams have their polarization planes rotated by the Faraday rotator 3 to become fa-2 and fb-2. Only fb-2 is incident on the second birefringent plate 4, and the position of the beam is displaced (fb
-3). fa-2 goes straight on and the third birefringent plate 5
Incident on. In the birefringent plate 5, fa-2 is extraordinary light and fb-
Since 3 becomes ordinary light, only fa-2 is refracted and combined.

On the other hand, in the reverse direction (B), the incident light 6 is the ordinary light b.
It is separated into b-1 and extraordinary light ba-1. ba-1 goes straight, bb-1 is incident on the birefringent plate 4, and the beam position is displaced (bb-2). The Faraday rotator undergoes non-reciprocal rotation of the plane of polarization, and specifically, it moves in the same direction as when passing in the forward direction.
The 5 ° plane of polarization is rotated to become ba-2 and bb-3. Since ba-2 is extraordinary light with respect to the first birefringent plate 2, it is refracted,
Since bb-3 is an ordinary light, it goes straight and becomes ba-3 and bb-4, so that the light is blocked because the axis is deviated from the forward incident light. As described above, the rotation of the polarization plane and the positional relationship of the beams are the same as in the conventional case.

[0010]

As described above, according to the configuration of the present invention, the size of the birefringent plate is reduced, so that the cost can be reduced, and the alignment of the second birefringent plate can be performed only for extraordinary light. It reduces the trouble of alignment, and
The only light passing through the second birefringent plate is extraordinary light, which reduces the reflection and absorption loss of ordinary rays and improves the characteristics.

[Brief description of drawings]

1A and 1B are schematic diagrams showing an operation of forward incident light and an operation of backward incident light, respectively, in an embodiment of an optical isolator of the present invention.

FIG. 2 shows an example of a conventional polarization-independent optical isolator,
6A is a schematic diagram showing an operation with respect to forward incident light and FIG.

FIG. 3 is a schematic diagram showing a polarization direction and a beam position when the conventional example FIG. 2 is viewed from the direction of the first birefringent plate 2.

[Explanation of symbols]

 1 incident light 2,4,5 birefringent plate 3 Faraday rotator

Claims (1)

[Claims] 1. A first birefringent plate that separates light into two linearly polarized lights according to a polarization direction, a Faraday rotator that gives non-reciprocal rotation to a polarization plane, and a second birefringent plate for correcting beam position. And a third birefringent plate for synthesizing the separated polarized light in this order, in a polarization-independent optical isolator, a birefringent plate for correcting a beam position is provided on the optical path of only one of the separated beams. A polarization-independent optical isolator, characterized in that