JPS61122624A - Optical isolator - Google Patents

Abstract

PURPOSE:To reduce the number of parts by constituting a titled optical isolator of three polarizers and two Faraday rotors inserted between each polarizer, and constituting said isolator so as to make the direction and the size for translating or refracting and separating the ordinary light and the abnormal light of the polarizer equal in two polarizers, and reverse in direction and two times in size in other one. CONSTITUTION:A titled optical isolator is constituted of the first, the second and the third three polarizers 11, 12 and 13 for translating or refracting and separating an ordinary light and an abnormal light, and the first and the second 45 deg. Faraday rotors 14, 15 inserted between the first and the second polarizers 11, 12, and between the second and the third polarizers 12, 13, so as to make to direction and the size for translating or refracting and separating the ordinary light and the abnormal light of the polarizer equal in two polarizers 11, 13, and as for the remaining one 12, opposite in direction and two times in size comparing with other two 11, 13.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical isolator used in optical communications and the like.

In optical communications, when the light source is a semiconductor laser, if the light is reflected back into the laser by reflection from the laser, which is an oscillator, the oscillation may become unstable or problems involving noise may occur. For this reason, an optical isolator is used to block reflected light and prevent the above-mentioned problems.

[Conventional technology]

A conventional optical isolator has a 45° Farade single rotator 3 such as YIG between a polarizer 1 and an analyzer 2, as shown in Figure 3a.
There is one in which a birefringence polarizer is used as the polarizer 1 and the analyzer 2, as shown in FIG. Both polarizer 1 and analyzer 2 are fixed with their polarization planes different by 45", and the light entering from polarizer 1 is 45".
° The plane of polarization can be rotated by 45" with the Faraday rotator 3, so it can pass through the analyzer 3. On the other hand, the analyzer 2
The plane of polarization of the light entering from the 45° Farade rotator 3 is rotated by 45'', but since the direction makes a 90° angle with the polarization plane of the polarizer 1, it cannot pass through the polarizer 1. In this way, it is possible to function as an isolator by passing light only from one side and blocking light from the other side.In this case, the extinction ratio of a 45° Faraday rotator using YIG is about 40 dB. In order to further increase the extinction ratio, a configuration using two sets of the above configurations as shown in Figure 4 has been devised.
．． 7 is a birefringent deflection plate, and 8 and 9 are 45° Farade single rotators.

[Problem that the invention seeks to solve]

The structure described above requires four birefringent tapered plates, and there is a problem in that the number of parts increases.

[Means for Solving the Problems] The present invention provides an optical isolator that solves the above-mentioned problems. Second. a third three polarizers; a first three polarizers; Second
The first polarizer is inserted between the polarizers and between the second and third polarizers.
and a second 45° Faraday rotator, and the direction and magnitude of translation or refraction separation of the ordinary light and extraordinary light of the polarizer are equal in the two polarizers, and the remaining one is the same as the other two polarizers. This is accomplished by an optical isolator that is opposite in direction and twice the size of the optical isolator.

(Function) In the above optical isolator, two of the three polarizers have the same direction and size for translating or refractively separating the ordinary light and extraordinary light, and the remaining one has the opposite direction to the other two. In addition, by doubling the size, the refraction of both ordinary and extraordinary light in the forward direction is canceled out, and the light is output in the same direction as the input light, while the direction of the light in the opposite direction is changed without canceling out the refraction. , the extinction ratio as an optical isolator is improved.

Also, since only three polarizers are required, the number of parts is small.
It becomes 1.

〔Example〕

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

FIG. 1 is a diagram for explaining one embodiment of the present invention.

In the same figure, 11.12.13 are birefringent deflection plates, 14
．． 15 each indicates a 456 Farade single rotor.

In this embodiment, as shown in FIG. Second. The third three birefringent deflection plates 11, 12.13 and the first. between the second birefringent deflection plate 11.12 and the second birefringence deflection plate 11.12. 45 inserted between the third birefringent deflection plate 12 and 13, respectively.
The first and third birefringent deflection plates 11.13 have the same size and direction for refracting and separating ordinary and extraordinary light, and the second birefringence The deflection plate 12 is formed and arranged so that the size for refracting and separating ordinary light and extraordinary light is twice that of the other two, and the direction is opposite to that of the other two.

The operation of this embodiment configured in this way will be explained using FIG. 2. In this figure, the same parts as in FIG. 1 are designated by the same reference numerals. Further, the solid line and the broken line of the light ray 16 represent ordinary light and extraordinary light within the birefringent deflection plate, respectively.

FIG. 2a shows the optical path when the light ray 16 is incident in the forward direction (from left to right in the figure), and the refraction of both ordinary and extraordinary light is canceled out and output in the same direction as the input light. When the light H16 is incident from the opposite direction, as shown in Figure 2, the ordinary light exiting the third birefringent deflection plate 13 is transformed into the extraordinary light of the second birefringence deflection plate by the second 45° Faraday rotator 15. After being refracted by the second birefringent deflection plate 12, the first 45°
With the Farade rotator 14, it becomes the ordinary light of the first birefringent deflection plate and is emitted from the first birefringence deflection plate 11 in the direction of arrow A.

In addition, the extraordinary light refracted by the third birefringent deflection plate 13 is
At the 45° Faraday rotator 15, it becomes the ordinary light of the second birefringent deflection plate, and after passing through the second birefringence deflection plate 12,
The light becomes extraordinary light of the first birefringent deflection plate at the first 45° Farade rotator 14, is refracted by the first birefringence deflection plate 11, and exits in the direction of arrow B. In this way, both ordinary and extraordinary light rays in the opposite direction are refracted in a direction different from the direction of incidence and exit, so they cannot be coupled to the optical fiber 18 by the lens 17 and become an isolator, and the Faraday rotator is
The extinction ratio can be improved because of the use of the In this example, a birefringent polarizer was used to refract and separate ordinary and extraordinary light, but the same effect can be obtained by using a birefringent flat polarizer that translates ordinary and extraordinary light. . Furthermore, the functions of the three polarizers can be interchanged.

〔Effect of the invention〕

As explained above, according to the present invention, in an optical isolator in which optical isolators using a 45° Farade single rotator are stacked in two stages, only three birefringent flat plates or tapered plates are required as polarizers, whereas conventional The number of parts is reduced compared to the 4 required parts.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an embodiment of the optical isolator of the present invention, FIG. 2 is a diagram for explaining the operation of the embodiment of the present invention, and FIGS. 3 and 4 are diagrams for explaining a conventional optical isolator. FIG. In the figure, 11, 12, and 13 are birefringent deflection plates, and 14° and 15 are 45° Faraday rotators, respectively.

Claims (1)

[Claims] 1. A first and a second device for translating or refractively separating ordinary light and extraordinary light.
, the third three polarizers, and the first and second 45 degrees inserted between the first and second polarizers and between the second and third polarizers.
and a Faraday rotator, and the direction and size of the polarizer for translating or refractively separating ordinary light and extraordinary light are 2.
An optical isolator characterized in that two polarizers are equal, and the remaining one is opposite in direction and twice the size of the other two polarizers. 2. Claim 1, characterized in that the three polarizers are flat plates or tapered plates using a birefringent substance.
Optical isolator as described in section. 3. Claim 1, characterized in that two of the three polarizers have the same translation or refraction separation direction and size for ordinary and extraordinary light, and are the first and third polarizers. The optical isolator described.