JPH05224151A - Optical isolator - Google Patents

Abstract

PURPOSE:To provide the polarized light independent type optical isolator which has high isolation over a wide temperature range and is compatible with conventional optical isolators. CONSTITUTION:This optical isolator is arranged with 1st, 2nd, and 3rd double refraction flat plates 3A, 3B and 3C, and with Faraday rotators 4A and 4B between the 1st and 2nd, and 2nd and 3rd double refraction flat plates. The separation width ratio of the ordinary and extraordinary light beams of the 1st-3rd double refraction flat plates 3A-3C is set to 1:2sq. rt. 2:1. The angle of rotation of the Faraday rotator 4A is set to +45 deg. and the angle of rotation of the Faraday rotator is set to -45 deg.. Therefore, the optical isolator which has the high isolation over the wide temperature range and has low insertion loss is provided. This optical isolator can be reduced in size almost equally to conventional optical isolators and the deviation width between incident light and projection light is exactly equal.

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 in optical communication and optical transmission, and more particularly to an optical isolator suitable for use between two optical fibers and having no polarization dependence.

[0002]

2. Description of the Related Art An example of an optical isolator conventionally used in optical communication and optical transmission is shown in FIG.

In FIG. 2, 11A and 11B are optical fibers, and 12A and 12B are lenses. 13A, 13B,
13C is a birefringent flat plate, 14 is a Faraday rotator,
The optical isolator is composed of these members and a magnet (not shown). The birefringent flat plates 13A, 13B, 13C
Is the ratio of the separation width of the ordinary ray and the extraordinary ray is √2:
1: 1.

As shown in FIG. 2A, the optical fiber 11
Light L ₁ emitted from A and collimated by the lens 12A
Is separated into two orthogonal light beams by the birefringent flat plate 13A, propagates through the Faraday rotator 14 and the birefringent flat plate 13B in the illustrated polarization state, is combined by the birefringent flat plate 13C, and is coupled to the optical fiber 11A by the lens 12B. Can be combined. Therefore, the light L ₁ traveling in this direction can pass through the optical isolator with almost no loss regardless of the polarization direction.

On the other hand, as shown in FIG. 2 (b), the light L ₂ emitted from the optical fiber 11B and collimated by the lens 12B is separated into two light beams orthogonal to each other by the birefringent flat plate 13C, and then the polarization state shown in the drawing is obtained. Propagate through the birefringent plate 13B, the Faraday rotator 14, and the birefringent plate 13A, but they are not combined by the birefringent plate 13A and are not coupled to the optical fiber 11A by the lens 12A. Therefore, the light L ₂ traveling in this direction cannot pass through the optical isolator.

In this way, a polarization-independent optical isolator becomes possible.

[0007]

However, such a conventional optical isolator has a drawback that the operating temperature range is narrow because the isolation of the Faraday rotator is significantly deteriorated due to the temperature change.

The present invention solves the above conventional problems, has high isolation in a wide temperature range, and
It is an object of the present invention to provide a polarization independent optical isolator compatible with a conventional optical isolator.

[0009]

The optical isolator of the present invention comprises a first, a second, and a third compound arranged such that the ratio of the separation widths of the ordinary ray and the extraordinary ray is 1: √2: 1. Refraction plate,
A first Faraday rotator and a second Faraday rotator arranged between the first and second birefringent flat plates and between the second and third birefringent flat plates, respectively. Of the children, the rotation angle of one Faraday rotator is +4
When it is 5 degrees, the rotation angle of the other Faraday rotator is -45 degrees or +135 degrees, or when the rotation angle of one Faraday rotator is -45 degrees, the rotation angle of the other Faraday rotator is The rotation angle is +45 degrees or -135 degrees.

In the present invention, the rotation angle of the Faraday rotator does not necessarily have to be exactly +45 degrees or -45 degrees or +135 degrees or -135 degrees. ± 3 degrees.

The present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a schematic structure of an optical isolator according to an embodiment of the present invention, a polarization state of light, and a propagation path. FIG. 1A shows a polarization state of light in the forward direction and a propagation path.
(B) shows the polarization state and propagation path of light in the opposite direction.

In FIG. 1, 1A and 1B are optical fibers, and 2A and 2B are lenses. 3A, 3B and 3C are birefringent flat plates, 4A and 4B are Faraday rotators, and the optical isolator of the present embodiment is composed of these members and a magnet (not shown).

In the present invention, the first birefringent flat plate 3
A, first Faraday rotator 4A, second birefringent flat plate 3
B, second Faraday rotator 4B, third birefringent flat plate 3
C are sequentially arranged in this order, and the first birefringent flat plate 3A
A separation width d _3A of the ordinary ray and extraordinary ray, and the separation width d _3B of the ordinary ray and the extraordinary ray of the second birefringent plate-3B, the ordinary and extraordinary rays of separation width d of the third birefringent plate-3C The ratio with _3C is d
_3A : _d3B : _d3C = 1: √2: 1. Further, when the rotation angle of one of the first and second Faraday rotators 4A and 4B is +45 degrees, the rotation angle of the other Faraday rotator is -45 degrees or +135 degrees.
And the rotation angle of one Faraday rotator is -45 degrees, the rotation angle of the other Faraday rotator is +4.
It is 5 degrees or -135 degrees.

In the optical isolator of this embodiment, the optical fiber 1 is used as in the conventional optical isolator.
The light L ₁ emitted from A and collimated by the lens 2A is
In the polarization state shown in FIG. 1A, the birefringent flat plate 3A, the Faraday rotator 4A, the birefringent flat plate 3B, and the Faraday rotator 4B.
Is transmitted, is multiplexed by the birefringent flat plate 3C, and is coupled to the optical fiber 1B by the lens 2B. Therefore, the light L ₁ traveling in this direction can pass through the optical isolator with almost no loss regardless of the polarization direction.

On the other hand, the light L ₂ emitted from the optical fiber 1B and collimated by the lens 2B has a polarization state shown in FIG. , Propagates through the birefringent flat plate 3A, but is not combined by the birefringent flat plate 3A and cannot be coupled to the optical fiber 1A by the lens 2A. Therefore, the light L ₂ traveling in this direction cannot pass through the optical isolator.

In the optical isolator of the present invention, the arrangement of the birefringent plate and the Faraday rotator, the arrangement order of the ratio of the separation width of the ordinary ray and the extraordinary ray of the birefringent plate, and the sign of the rotation angle of the Faraday rotator. Except for adopting
The birefringent plate can be configured in the same manner as the conventional one, and there is no particular limitation on the type of birefringent plate, the value of the separation width of the ordinary ray and the extraordinary ray of each birefringent plate, the type of the Faraday rotator, and the like.

In the present invention, as a method of setting the rotation angles of the two Faraday rotators, the following method can be mentioned.

The same material is used for the Faraday rotator, and the directions of the applied magnetic fields are opposite to each other. Change the material of the Faraday rotator. For example, a combination of bismuth-substituted rare earth iron garnet (rotation angle sign −) and yttrium iron garnet (rotation angle sign +) is applied in the same magnetic field direction. Faraday rotators with rotation angles of 45 and 135 degrees are used.

[0020]

[Function] The ratio of the separation width between the ordinary ray and the extraordinary ray is 1: √2: 1.
Three birefringent flat plates arranged in this order, and the first and second
According to the optical isolator of the present invention, which is composed of two Faraday rotators having a specific rotation angle, which are arranged between the birefringent flat plates and the second and third birefringent flat plates, Since it has no temperature dependence, has excellent characteristics in a wide temperature range, its size is almost the same as the conventional one, and the deviation width of the incident light and the outgoing light is exactly the same, the conventional optical isolator An optical isolator having good compatibility with is provided.

[0021]

EXAMPLES The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

For example, in the following embodiments, a rutile flat plate is used as the polarization separation plate, but a birefringent material such as calcite may be used. Further, as the Faraday rotator, in addition to bismuth-substituted magnetic garnet, yttrium iron garnet can be used.

Example 1 An optical isolator of the present invention shown in FIG. 1 was produced, and the temperature characteristic of its isolation was examined.

As the optical fibers 1A and 1B, single mode optical fibers are used, and birefringent flat plates 3A and 3B,
3C is a rutile birefringent flat plate having separation widths of ordinary ray and extraordinary ray of 420, 600 and 420 μm, respectively.
That is, a separation width ratio of 1: √2: 1 was used. As the Faraday rotators 4A and 4B, bismuth-substituted rare earth iron garnet Faraday rotators are used,
By setting the directions of the applied magnetic fields to be opposite to each other, the rotation angles were set to +45 degrees and -45 degrees, respectively.

The optical isolator thus manufactured has a size of φ6 × 17.5 mm, and the insertion loss in the forward direction is 0.2 dB (however, the transmission loss of the fiber and lens,
And the coupling loss), and the isolation was 58 dB. In addition, the gap between the incident light and the emitted light is 420μ
It was m.

The isolation of this optical isolator was measured in the temperature range from -20 ° C to about 70 ° C, and the results are shown in FIG. As is clear from FIG. 3, the optical isolator of this embodiment has a temperature of 20 ° C. to about 70 °
High isolation of 52 dB or more was obtained in a wide temperature range of ° C.

Comparative Example 1 A conventional optical isolator shown in FIG. 2 was produced and the temperature characteristics of its isolation were examined. The obtained optical isolator had a size of φ6 × 17 mm, a forward insertion loss of 0.2 dB, and an isolation of 44 dB. The deviation width between the incident light and the emitted light was 420 μm.

With respect to this optical isolator, the isolation was measured in the temperature range from -20 ° C to about 70 ° C, and the results are shown in FIG. As is clear from FIG. 3, in the optical isolator of this comparative example, the isolation sharply declines in the low temperature region and the high temperature region, and only the isolation of 27 dB or more is obtained in the temperature range of −20 ° C. to about 70 ° C. I couldn't do it.

[0029]

As described in detail above, according to the optical isolator of the present invention, an optical isolator having a high isolation in a wide temperature range and a low insertion loss is provided. In addition, the size is almost the same as the conventional one, and the size can be reduced, and the deviation width of the incident light and the emitted light is exactly the same as the conventional one. When changing from the optical isolator of the present invention to the optical isolator of the present invention, the system does not require any change, and the industrial utility of the present invention is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an optical isolator according to an embodiment of the present invention, a polarization state of light, and a propagation path, FIG. 1A shows a polarization state of light in a forward direction and a propagation path, and FIG. Indicates the polarization state and propagation path of light in the opposite direction.

2A and 2B are diagrams showing a schematic configuration of a conventional optical isolator, a polarization state of light, and a propagation path, wherein FIG. 2A shows a polarization state of light in a forward direction and a propagation path, and FIG. 2B shows light in a reverse direction. 2 shows the polarization state and the propagation path of.

3 is a graph showing isolation temperature characteristics of the optical isolators manufactured in Example 1 and Comparative Example 1. FIG.

[Explanation of symbols]

 1A, 1B Optical fiber 2A, 2B Lens 3A, 3B, 3C, 3D Birefringent flat plate 4A, 4B Faraday rotator

Claims (1)

[Claims] 1. The ratio of the separation width of the ordinary ray and the extraordinary ray is 1: √
The first, second, and third birefringent plates arranged in the order of 2: 1 and the first and second birefringent plates and the second and third birefringent plates, respectively. First and second
Of the first and second Faraday rotators, if the rotation angle of one Faraday rotator is +45 degrees, the rotation angle of the other Faraday rotator is -45 degrees. Or +135 degrees, or if the rotation angle of one Faraday rotator is -45 degrees, the rotation angle of the other Faraday rotator is +45 degrees or-
An optical isolator characterized by being 135 degrees.