JPS6362730B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of an optical switch equipped with a polarizing prism for separating polarized light and a polarizing prism for combining polarized light.

Polarizing prisms for optical devices include those that use dielectric multilayer films and those that use birefringent crystals, but the former has large crosstalk (poor polarization separation), and the latter has a large polarization separation angle. It has the disadvantage of requiring small and large crystals, both of which require improvement measures.

[Conventional technology]

FIG. 5 shows a conventional optical switch using a polarizing prism equipped with a dielectric multilayer polarization separation film.
In the figure, 1 is a polarizing prism for separating polarized light, 2 is a polarizing prism for combining polarized light, 3 ₁ is a polarizing prism for both polarizing prisms 1,
2 is a magneto-optical crystal provided between the two, 3 ₂ is a 1/2 wavelength plate, and 4 ₁ and 4 ₂ are light receiving sections such as optical fibers provided on the output side. The magneto-optic crystal ₃₁ rotates the plane of polarization by 45 degrees to the right when the applied magnetic field is in the same direction as the traveling direction of the light, and rotates the plane of polarization by 45 degrees to the left when the applied magnetic field is in the opposite direction. Further, the 1/2 wavelength plate ₃₂ always rotates the plane of polarization by 45 degrees to the left. Each polarizing prism 1, 2 is
It is provided with polarization separation films 5 and 6 made of dielectric multilayer films.
This figure shows a case where the magnetic field of the magneto-optic crystal ₃₁ is in the direction of the arrow. Polarized light 9 and S polarized light 1 of -●-
0
are separated into a magneto-optic crystal 3 ₁ and a 1/2 wavelength plate 3 ₂
The plane of polarization is not rotated and enters the polarizing prism 2. The light incident on the polarizing prism 2 is combined by the polarizing prism 2, becomes a light beam A, enters the light receiving section ₄₂ , and is combined. In addition, when the magnetic field of the magneto-optic crystal 3 ₁ is set in the opposite direction to that shown in this figure, the light passing through the magneto-optic crystal 3 ₁ and the 1/2 wavelength plate 3 ₂ has a polarization plane.
The light beams rotated by 90 degrees and combined by the polarizing prism 2 are incident on and coupled to the light receiving section 4 ₁ .

[Problem that the invention seeks to solve]

However, because the degree of polarization separation of the polarization separation films 5 and 6 is poor, the S polarization component is included in the P polarization 9, and conversely, the S polarization component is
The polarized light 10 contains a P-polarized light component. In other words, a crosstalk component occurs. Therefore, in the conventional optical switch having such a configuration, when the combined light A, which is a combination of the P polarized light 9 and the S polarized light 10 separated by the polarization combining polarizing prism, enters and combines into one light receiving section, the crosstalk component is removed. There was a drawback that the optical path coincided with the optical path of the other light receiving section, resulting in increased crosstalk. That is, the polarization separation film 6 reflects the P-polarized light 9 and transmits the S-polarized light 10, but the S-polarized light (crosstalk component) contained in the P-polarized light 9 is transmitted, and the P-polarized light (crosstalk component) contained in the S-polarized light 10 is transmitted. is reflected and synthesized crosstalk component B
It is input to the light receiving section ₄₁ as follows. In other words, the crosstalk component B shown by the dotted line in FIG. 5 is obtained when the combined light beam from the polarizing prism 2 is incident on and coupled to the light receiving section ₄₁ (when the magnetic field of the magneto-optic crystal ₃₁ is directed in the opposite direction).
It passes through the optical path.

[Means for solving problems]

The purpose of the present invention is to provide an optical switch capable of solving the above-mentioned problems, and as a means for that purpose, a polarizing prism for polarization separation provided on the light incidence side and a polarization prism provided on the light output side. an optical switch for selectively coupling a light beam combined by the polarization prism for polarization synthesis to two light receiving sections, wherein the polarization prism for polarization separation and the polarization prism for polarization synthesis are provided. In between, a birefringent plate is inserted to cause a translational or angular shift in the crosstalk component so that the crosstalk component is not coupled to the light receiving section on the side where the combined light beam is not coupled.

[Effect]

The crosstalk component of the light beam generated by the polarizing prism is translated or angularly shifted by a birefringent plate inserted between both polarizing prisms, and the optical path of the combined light beam is shifted, so that it is no longer coupled to the light receiving section.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4.

FIG. 1 is a schematic diagram of an optical switch according to the present invention.
In the figure, 11 and 12 are crystal wave plates, and 13 and 14 are flat birefringent plates made of calcite, rutile, or the like. The birefringent plate 13 has a C-axis 13a, and is used for P-polarized light and S-polarized light.
It has a different refractive index depending on the polarized light, and is inserted between the polarizing prism 1 and the magneto-optic crystal ₃₁ .
The wavelength plate 11 is inserted between the polarizing prism 1 and the birefringent plate 13 so as to face the lower part of the birefringent plate 13. The birefringent plate 14 has a C axis 14a,
It is inserted between the magneto-optic crystal 3 ₁ and the polarizing prism 2 . The wavelength plate 12 is inserted between the polarizing prism 2 and the birefringent plate 14 so as to face the upper part of the birefringent plate 14 .

Now, when the magnetic field of the magneto-optic crystal ₃₁ is set in the direction of the arrow and a light beam 15 is made to enter the polarizing prism 1 from the optical fiber 7, the light beam 15 is converted into P-polarized light by the polarizing prism 1. 16 and -●- S
It is separated into polarized light 17. The polarization plane of the P-polarized light 16 is rotated by 90 degrees when passing through the wave plate 11, and the crosstalk component is refracted as shown by the dotted line when passing through the birefringence plates 13 and 14, causing a translational shift. Further, the S polarized light 17 is transmitted through the birefringent plates 13 and 14.
When passing through the wave plate 12, the crosstalk component is refracted as shown by the dotted line, causing a translational shift, and when passing through the wave plate 12, the plane of polarization is rotated by 90 degrees. These lights enter the polarizing prism 2 and are combined into the light beam 18, which enters the light receiving section ₄₂ and is combined. At the same time, however, the crosstalk component that exits the polarizing prism 2 upward causes a translational shift as described above. Light receiving part 4 for
₁ and is not coupled to the light receiving section 4 ₁ .

In addition, as shown in FIG. 2, when the magnetic field of the magneto-optic crystal ₃₁ is set in the opposite direction to that described above and the light beam 15 is incident on the polarizing prism 1 from the optical fiber 7, the light beam 15 is separated by the polarizing prism 1. P polarized light 1
6. The S-polarized light 17 proceeds in the same manner as described above until it passes through the birefringent plate 13, but the plane of polarization is rotated by 90 degrees when passing through the magneto-optic crystal 3 ₁ and the 1/2 wavelength plate 3 ₂ .
Thereafter, these lights are refracted when passing through the birefringent plate 14, and their optical paths coincide with the crosstalk components. Then S
The polarization direction of the polarized light 17 can be changed by 90 degrees by the wave plate 12. In this case, the light beam 19 combined by the polarizing prism 2 and emitted upward is the light receiving part 4 ₁
A crosstalk component that enters and is coupled to the polarizing prism 2 and simultaneously exits to the right from the polarizing prism 2 is not coupled to the light receiving section 4 ₂ .

In this way, even if the crosstalk of the polarization separation film of the polarizing prism is large, the crosstalk component is not coupled to the light receiving section, so that crosstalk can be substantially reduced.

Application examples are shown in FIGS. 3 and 4.

In the case of Fig. 3, the birefringent plate 13 of Figs. 1 and 2,
14 is replaced by wedge-shaped birefringent plates 22 and 23 having C axes 20 and 21. In this case, an angular shift occurs in the passing light, and this angular shift can be used to prevent the crosstalk component from being coupled to the light receiving section as in the previous example.

In the case of FIGS. 4a and 4b, a pair of flat birefringent plates 25 having a C-axis 24 are laminated symmetrically, and a pair of flat birefringent plates 27 having a C-axis 26.
are symmetrically pasted together, and the joining surface is provided in the middle of the two optical paths of the S-polarized light 28 and the P-polarized light 29. In this case, the paths of the coupled components and crosstalk components of each light separated by the polarization separation prism are as shown in the figure, depending on the direction of the magnetic field applied to the magneto-optic crystal. In this example, a wave plate is not required.
Note that each birefringent plate may be arranged so that the plane with the C axis is perpendicular to the plane of the drawing.

〔Effect of the invention〕

As described above, according to the present invention, a translational or angular shift occurs in the crosstalk component of the polarizing prism light beam due to the birefringence plate or the like provided between the polarizing prism for polarizing separation and the polarizing prism for combining polarized light. Since the crosstalk component is not coupled to the light receiving section, it is possible to substantially reduce crosstalk.

[Brief explanation of drawings]

1 to 4 show an embodiment of the optical switch according to the present invention. FIG. 1 shows the structure and operation of the optical switch, and FIG. 2 shows the direction of the magnetic field of the magneto-optic crystal. FIGS. 3 and 4 are explanatory views of the operation of the optical switch when the optical switch is reversed. FIGS. FIG. 5 is an explanatory diagram of the structure and operation of a conventional optical switch. In the figure, 1 is a polarizing prism for polarization separation, 2 is a polarization prism for polarization synthesis, 3 ₁ is a magneto-optic crystal, 3 ₂ is a half-wave plate, 4 ₁ and 4 ₂ are light receiving parts, and 5 and 6 are polarization separation parts. 7 is an optical fiber, 11 and 12 are wavelength plates, 1
3, 14, 22, 23, 25, 27 are birefringent plates,
20, 21, 24, and 26 are C axes.

Claims (1)

[Scope of Claims] 1. A polarizing prism 1 for polarization separation, which is provided on the light incidence side and separates the incident light into two polarized lights, and a polarization plane of the two polarized lights separated by the polarization prism for polarization separation, respectively. Rotating element 3 ₁ that rotates a predetermined angle,
3 ₂ , and a polarization prism 2 for polarization synthesis provided on the output side of the rotating element, and by controlling the rotation element, the light beam combined by the polarization prism for polarization synthesis is sent to two light receiving parts. An optical switch for selectively coupling, the light receiving device on the side that does not couple the combined light beam between the polarizing prism for polarization separation and the rotating element, and between the rotating element and the polarizing prism for combining polarized light. A birefringent plate 1 that causes a translational or angular shift in the crosstalk component so that the crosstalk component is not coupled to the crosstalk component.
An optical switch characterized in that 3, 14, 22, 23 or 25, 27 are inserted respectively.