JPS58202430A - Optical switch - Google Patents

Abstract

PURPOSE:To increase a switching speed, and also to realize a long life and stability of operation, by simple constitution which uses a polarizer of the incident side and the emitting side, consisting of a crystal plate of a high refractive index, and a polarizing rotating element, and has no mechanical movable part. CONSTITUTION:Light emitted from an incident side optical fiber 1 becomes an optical beam 10, is made incident to a polarizer 3 and is separated into a P wave 12 and an S wave 11. As for the incident face of a polarizing rotating element 4, an angle theta of the incident face is set in advance so that the P wave 12 and the S wave 11 which reach there are refracted and become parallel, and also an angle of the emitting end face is set in advance so that two optical beams 13, 14 emitted from the polarizing rotating element 4 cross each other at the same angle theta as the time of incidence. The same polarizer 5 as the polarizer 3 of the incident side is placed at a position where the emitted beams 13, 14 cross each other, and in accordance with a state of the outside field applied to the polarizing rotating element 4, the emitted beam of the incident optical fiber 1 is switched to one of an emitted optical fiber 8 or 9, as an optical beam 15 or 16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical fiber switch for switching the optical path of a light beam transmitted through a 7-eyeper, and <K! i has no mechanically moving parts,
Regarding electronic light switches.

In optical fiber communication systems, optical switches are widely used for switching between regular and backup lines, switching optical components, and for measurement in order to improve line reliability and facilitate maintenance. In addition to communication systems between long distances, there are also optical data transmission systems that connect information processing devices within a limited area.
Optical switches are also used as connection nodes between Heihei and terminals. That is, when it is necessary to avoid a specific terminal, for example, when the terminal is out of order or not being used for maintenance or inspection, the optical switch is used to bypass the route.

One type of optical switch that has been developed for this purpose is one that electromagnetically displaces a prism or mirror. That is, the light emitted from an optical fiber is converted into a parallel beam, and a prism or mirror is inserted into this optical path to spatially change the optical path to select the optical fiber on which the light is focused again. This type of optical switch has the characteristics of high crosstalk and low optical insertion loss, and is easy to use. However, because it has a mechanical movable mechanism, it is difficult to obtain a fast switching speed, and the number of switching is limited. There are concerns about its lifespan and reliability for operation with long distances between poles. For example, there is instability in that the device maintains a certain state almost fixedly for a long period of time and does not operate correctly when suddenly switched during bite. Therefore, it is difficult to use it in optical submarine repeaters, etc., where it is difficult to replace or inspect elements.

The following devices are also known as devices that electronically switch fiber optics without having mechanically movable parts. The incident light is transmitted through a polarization conversion element that has the function of rotating the polarization direction of the transmitted light by 90 degrees by applying a voltage or current, and then transmitted through a polarization element that changes the direction of the optical path depending on the polarization direction of the light. It guides light to 7 different types of lights. As the polarization conversion element, electro-optic materials such as electro-optic crystals and liquid crystals, and magneto-optic materials such as iron garnet crystals and high-concentration lead glass are used. Conventional optical switches of this type have several drawbacks. One of these is that the constituent polarizing elements must be expensive or have insufficient characteristics. The above-mentioned polarizing elements that change the optical path depending on the polarization direction of the light include polarizing prisms made of calcite, which is a material with a large birefringence that has been known for a long time, and prisms made of rutile crystal, which is also a material with a large birefringence. Shaped and polished,
There is one in which a three-layer dielectric film is formed on the reflective surface of a total reflection prism made of glass and used as a light loss element. Calcite is a natural stone and is expensive; the crystal material itself for rutile prisms is expensive; and because it has a high refractive index, it is necessary to form a good reflective film on the prism entrance surface. Polarizing elements that have a dielectric multilayer film as a material have drawbacks such as the polarization properties deteriorate as the wavelength of light that deviates from the design wavelength is incident because the wavelength characteristics of the multilayer film are sensitive to incident light. .

An object of the present invention is to provide a fiber optic switch that eliminates the above-mentioned problems.

According to the present invention, a crystal plate having a high refractive index and optically polished on both sides, and a crystal plate having a high refractive index, and an incident light incident on the crystal plate at a Purster angle,
The angle of the incident end face is set so that both the light beam transmitted through the crystal plate and the light beam reflected are transmitted through the crystal plate, and the two optical axes are parallel to each other within the element.
a polarization rotation element whose output end face is set at an angle such that the two light beams intersect at the same angle as the incident angle, and which rotates the polarization of the transmitted light beam; and the two light beams emitted from the polarization rotation element. An inexpensive, high-performance optical switch can be obtained by using a crystal plate identical to the above-mentioned crystal plate arranged at a position where the optical axes of the optical axis intersect with each other so that the optical axes of the optical axis intersect with each other so that the optical axes of the optical axis intersect with each other so that the optical axes of the optical axis intersect with each other.

Details of the present invention^4(I) will be further explained using examples.

This is a diagram showing the configuration of an embodiment of the present invention shown in FIG. 1, where l is an input optical fiber, 2 is a condenser lens, 3 is a polarizer on the input side consisting of a crystal plate having a high refractive index, and 4 is a polarizer on the input side. polarization rotation element,
5 is a polarizer on the output side having the same configuration as 3, 6 and 7 are lenses, and 8 and 9 are output optical fibers. Input side optical fiber 1
The emitted light becomes a light beam 10 by a condensing lens 2 and enters a polarizer 3. The principle of the polarizer 3 will be described later, but its function is to separate the incident light 10 into a P wave 12 and an S wave 11. The angle θ of the incident surface of the polarization rotation element 40 is set so that the P waves 12 and S waves 11 that reach this surface are refracted and the optical axes become parallel within the polarization rotation element. . The polarization rotation element has a function of controlling the polarization state of transmitted and emitted light to be perpendicular to or the same polarization as that of the incident light, depending on the state of an external field such as an applied voltage or current. Now, the polarization rotation element changes the polarization to 9
If it is in a state of zero rotation, the incident S wave 11 becomes P-polarized light and is emitted as a light beam 13. On the other hand, the incident P wave 12 becomes S-polarized light and is emitted as a light beam 14. The output surface of the polarization rotation element 4 is set so that the output beams 13 and 14 intersect the optical axes, and the angle of intersection is the same as the angle formed by the incident light beams 11 and 12. That is, a polarizer 5, which is the same as the incident side polarizer 3, is placed at a position where the output beams 13 and 14 of the polarization rotation element intersect, which are set to form the same angle θ as the incident plane. The light beams 13 and 14 are set to have a Prusster angle. The light beam 13, which is P-polarized light, exits the polarization rotation element and passes through the polarizer 5, while
The S-polarized light beam 14 is reflected by the back surface of the polarizer 5, and both become light beams 1 and 6, which take almost the same optical path, and are focused by the lens 7 and guided to the output fiber 9. Assuming that the state of the external field applied to the polarization rotation element is different from that described above, that is, the polarization state of the transmitted light is emitted at the same time t as at the time of incidence, then the output beam 13 of the polarization rotation element is The polarized light is S polarized light, which is the same as the incident S wave 11, and the polarized light 14 is P polarized light, which is the same as the incident P wave 12.

The S-polarized light 13 is reflected by the polarizer 5, and the P-polarized light 14 passes through the polarizer 5, becomes a light beam 15, is focused by a lens 6, and is guided to an output 7 eyer 8. Therefore, the output light from the input optical fiber 1 is switched to either the output fiber 8 or 9 depending on the external field condition +m applied to the polarization rotation element 4. A so-called lX2 switch operation is realized.

Next, the operation of the polarizer will be explained. FIG. 2 is a diagram showing the principle of a polarizer, and 100 is a thin single crystal plate of silicon, gallium arsenide, indium phosphide, or the like. These crystals have a light wavelength of 1
It is a crystal that is transparent over a range of about 2 μm. For example, the absorption inspection plate in the region of 1.3 μm to 2 μm of N-type silicon single crystal exhibits extremely good light transmission characteristics of less than (11 (m). Also, the refractive index is extremely high at 3.5 degrees, and the Prusster angle is It is large at 74 degrees.The original beam 101 is 74 degrees (
When the light is incident at a Priest angle of .theta.-16 degrees), reflections from the upper and lower surfaces of the thin crystal plate are combined, and the reflected light 102 becomes only the S-polarized component, with a reflectance of 84%.

Most of the transmitted light 103 is a P-polarized component, and its transmittance is very high because the above-mentioned absorption effect is low.

The S-polarized component contained in this transmitted light 103 is 13%. When three thin crystal plates shown in FIG. 2 are stacked with a space in between, the S polarization component becomes 0.2%, and a polarizing element having sufficient polarization characteristics can be obtained.

As the polarization rotation element 4 in FIG. 1, various conventionally known elements can be used. For example, a polarization rotation element using the electro-optic effect of a niobium-lithium crystal or a polarization rotation element using the Faraday effect of a magneto-optic crystal such as istrium iron garnet (YIG) crystal can be used. The angle of oblique polishing applied to the light incident surface of these crystals is given by a simple geometrical optical force, where n is the refractive index of the crystal. Here, ■ is the Pilster angle of the polarized dung, and when a silicon plate is used as the polarizing element,
From C, for example, the crystal used in polarization rotation elements is YIG.
If it is a crystal and the light wavelength is 1.3 μm, the angle of θ is about -12.5 degrees and -1. FIG. 1 shows an embodiment of a so-called 1.times.2 optical switch that couples one fiber light to either of two output fibers. It is easy to realize a 2×2 optical switch by using two input optical fibers and arranging them in the same manner as the output fibers in the 11k.

As explained above, according to the present invention, the optical switch can be made of inexpensive materials and has a simple structure without any mechanically moving parts, so that an optical switch with high switching speed, long life, stable operation, and high reliability can be achieved. can get.

[Brief explanation of drawings]

Claims (1)

[Claims] A crystal plate with a high refractive index and optically polished on both sides is incident on the crystal plate at the Prusster angle, and both the light beam transmitted through the crystal plate and the light beam reflected are transmitted. The angle of the input end face is set so that the optical axes of the light beams are parallel within the element, and the angle of the output end face is set so that the two emitted light beams intersect at the same angle as when they entered. A polarization rotation element that rotates the polarization of the transmitted light beam by an applied external field, and a position where the optical axes of the two light beams emitted from the polarization rotation element intersect, so that they are incident at a Pourster angle. An optical switch comprising a crystal plate identical to the crystal plate arranged above.