JPS60146230A - Optical switch - Google Patents

Abstract

PURPOSE:To obtain a multi-channel switchable optical switch of low optical insertion loss, which is connected easily to an optical fiber, by combining a linear waveguide made of glass, and liquid crystal. CONSTITUTION:Glass plates 1, 2 having plural parallel linear optical waveguides 3, 4 on the surface of the substrate are provided by making the surfaces on which the waveguides 3, 4 are opposed to each other, having a minute gap, making an angle theta of 1-3 deg. on the surface, and so that plural waveguides cross each other, when seeing through two substrates. The gap of the two substrates is packed with a liquid crystal 105. As for optical wave flowing into a waveguide 103 of the surface of the lower side substrate, when a voltage is applied to two electrodes 106, 107, a refractive index of the liquid crystal to the optical wave increases, therefore, light is coupled to a waveguide 104 through the liquid crystal 105 from the waveguide 103.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical fiber switch that switches the optical path of a light beam traveling through a fiber, and particularly to an electronic optical switch that does not have mechanically movable parts.

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. Also, avoid blocked communication channels,
An optical switch having a multi-channel switching terminal is used to realize a so-called optical switching system that is composed of optical components and that selects and connects an available route to set up a call.

Also, data transmission systems that connect information processing devices within a limited area, including communication systems between distant areas,
Optical switches are also used in so-called optical data highways, such as connection nodes between highways 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, the optical path is spatially changed by inserting a prism or a mirror into this optical path, and the optical fiber on which the light is focused again is selected. 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 high switching speed, and the number of switching cycles is limited. There are concerns about longevity and reliability for extremely long intervals of operation. For example, there is instability in that a device maintains a certain state almost fixedly for a long period of time and does not operate correctly when a switch is suddenly operated. 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 different optical fibers. As the polarization conversion element, electro-optic crystals such as electro-optic crystals and liquid crystals, 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 are expensive or have insufficient characteristics. The above-mentioned polarizing elements that change the optical path depending on the polarization direction of the light include side-light prisms made of calcite, which is a material with a large birefringence that has been known for a long time, and rutile crystal, which is also a material with a large birefringence. There are those that are formed into a prism shape and polished, and those that form a polarizing element by forming a three-layer dielectric film on the reflective surface of a total reflection prism made of glass. 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 anti-reflection film on the prism entrance surface. In a polarizing element made of a dielectric multilayer film, the wavelength characteristics of the multilayer film with respect to incident light are #-like, so there are drawbacks such as the polarization characteristics deteriorate when light of a wavelength deviates from the design wavelength is incident.

An example of an optical switch configured without using a polarizing element as described above is a waveguide type optical switch. A typical waveguide type optical switch uses a lithium niobate single crystal as a substrate and utilizes the electro-optic effect of this crystal (the effect of changing the refractive index in the crystal depending on the applied electric field). be. In other words, as the structure of the switch element, an electrode is installed on two adjacent channel barrel waveforms formed planarly on the surface of the substrate, and the change in refractive index caused by the electric field applied to the waveguide via this electrode is utilized. One method is to control the coupling of light between C-channel waveguides. Another method is to provide two-dimensional intersecting waveguides on the surface of the substrate, form a low refractive region at the intersection using an electric field, and completely reflect the light through this low refractive index region. A method has been proposed in which a phase grating is formed and the guided light is Bragg-reflected within a plane, and a method in which a Y-branch waveguide is provided on the substrate surface and a refractive index bias is formed in the branch region to refract the light. There is. A multi-channel optical switch is constructed by arranging the switch elements in multiple stages or in a mesh pattern.

The key points of the above-mentioned multi-channel optical switch are mechanical,
Because it uses a crystal substrate that does not have very high thermal strength and is expensive, and because the electro-optic effect that can be used is extremely small, the voltage required for switching is high, and the element length cannot be shortened. The number of switch elements that can be installed on a single board is limited, which limits the number of channels that can be switched. Further, since a counter electrode that is capable of applying an electric field is installed on a single substrate, when the number of switch elements increases, the lead electrode becomes a lead wire on the substrate.

This is also one of the factors that limits the number of switch elements that can be installed on one board.

Another method for waveguide-type optical switches uses the fact that liquid crystal is layered on top of a planar dielectric waveguide, and the refractive index for guided light in the waveguide changes in the area where an electric field is applied to the liquid crystal. A method has also been proposed in which the guided light is refracted within the plane, but this method has drawbacks such as difficulty in connecting the original fibers because the waveguide is not channelized.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, to provide inexpensive, low 'tM,
The object of the present invention is to provide an optical switch that has a large number of switching channels, can be connected to an optical fiber array, and has a low optical insertion loss.

According to the present invention, two dielectric substrates each having on their surfaces a group of linear single-mode channel optical waveguides each having a plurality of linear single-mode channel optical waveguides that do not intersect in a plane, and the surfaces on which the optical waveguides are provided face each other. , a liquid crystal filled in the gap between the two dielectric substrates installed so that the two optical waveguide groups intersect with each other, and a portion where the optical waveguides on the dielectric substrate intersect and overlap. An optically transparent polarization formed above and along the optical waveguide to apply an electric field to the liquid crystal layer provides a low voltage, low optical loss, and inexpensive optical switch. can get. m Details of the present invention will be explained based on embodiments and with reference to the drawings.

FIG. 1 is a diagram showing the overall structure of an embodiment of the present invention, where 1 is a glass plate having a plurality of parallel linear waveguides 3 on the substrate surface, and 2 is a glass plate having the same waveguide 4 as the glass substrate 1. These two glass substrates are made of the same glass substrate, and the surfaces forming the waveguide 3.4 are placed facing each other.
2μm-10μm) gap, 1~3° in the plane
When viewed through the two substrates, each of the plurality of waveguides is set to intersect with each other at an angle θ. The gap between the two substrates is filled with liquid crystal. Figure 2 is an enlarged view of the intersection of two overlapping waveguides, where 10 indicates the waveguide provided on the lower substrate (1 in Figure 1), and 11 indicates the upper waveguide. The waveguides provided on the substrate (2 in FIG. 1) located at are shown, and 12 and 13 represent transparent electrodes provided on the respective waveguides. The light wave injected from the left into the waveguide 10 provided on the lower substrate is
A waveguide 11 provided on the upper substrate passes through the liquid crystal between the electrodes with a voltage applied between the electrodes 12 and 13.
join to. When no voltage is applied, the light wave propagates through its own waveguide 10. The reason why light traveling through the waveguide provided on the lower substrate is transferred to the waveguide provided on the first substrate is based on the following principle. FIG. 3 shows a cross-sectional view taken perpendicular to the substrate at the intersection of the two waveguides shown in FIG.

101 is the lower substrate, 102 is the upper substrate, 103.104
106 and 107 are transparent electrodes provided on the waveguide surfaces, and 105 is a liquid crystal filled in the gap between the two substrates. The light wave injected into the lower substrate is a TE wave having an electric field component parallel to the substrate. This guided light has an amplitude distribution shown at 110, and has a slight broadening in the liquid crystal. The liquid crystal 105 is polarized 106 and 1
When no voltage is applied between 07 and TE of L
The molecular orientation is determined so that it exhibits approximately an ordinary refractive index n0 with respect to waves, and an extraordinary refractive index ne when a voltage is applied. The two refractive indices have the following relationship: ne) n. When a voltage is applied to the two electrodes, the refractive index of the liquid crystal increases with respect to the light wave, so the electric field distribution of the guided light becomes 111
As in, the seepage from the waveguide 103 increases,
It extends to the waveguide 104 through the liquid crystal 105. Since the waveguide 103 and the waveguide 104 are formed identically, the light wave propagating through the waveguide 103 is coupled to the waveguide 104 through which it propagates. When no voltage is applied between the two electrodes 106 and 107, the electric field distribution of the light wave has a small leakage as shown at 110, so the waveguide 10 provided on the upper substrate
It does not combine with 4. Therefore, depending on whether or not a voltage is applied, an optical path conversion is realized in which light traveling through the lower waveguide is coupled to the upper waveguide or transmitted through the own waveguide. As shown in the configuration of FIG. 1, a waveguide provided on one lower substrate intersects all upper waveguides. Therefore, switching the light to a desired upper waveguide is achieved by applying a voltage to a pair of electrodes provided at a desired intersection of the upper waveguide and the F-side groove waveguide. Such behavior is −
As an example, using BK7 with a refractive index of 1.51 as a glass substrate realized by the design values shown below,
A waveguide having a refractive index of 1.52 +'4 degrees is formed by an ion exchange method using silver nitrate or chromium nitrate. The transparent electrode contains indium tin oxide with a concentration of 500 to 1000.
Provide level A. For example, as a liquid crystal phase, ne=1.63
, no = 1.50, the tail spread of the light wave in the liquid crystal is equal to the light wavelength 0.
When the voltage is 633μ7n and no voltage is applied, it is 1 μm or less, and when a voltage is applied, it is 2 μm or more F. If the thickness of the liquid crystal layer is about 2 μm, coupling of light waves will occur only when a low voltage is applied. If the nine wavelengths are set in the long wavelength band of 13 to 1.8 .mu.m used for single mode optical fiber communication, good optical switching characteristics can be obtained by making the liquid crystal layer thicker to about 5 .mu.7 nm. In order to form an extremely thin gap between two substrates that holds the liquid crystal, the bonding method previously shown by the present inventor (Japanese Patent Application No. 54-59944, Method of Bonding Piezoelectric Transducers, Japanese Patent Application No. 55-98587, Adhesion method)
In other words, a low melting point metal film is provided on one substrate to be bonded by vapor deposition, etc., a thin film of another metal such as gold is provided on the other substrate, and then the film is heated or laser irradiated to form a layer between the two thin films. By using a method that causes a solid phase reaction, it is possible to perform bonding with high precision in gap spacing.

As explained above, the optical switch according to the present invention uses a glass material, is inexpensive, and is composed of only a straight waveguide.
It has the following features: multi-channel switching is possible, low optical insertion loss that allows easy connection with optical fibers, and low drive KHE due to the use of liquid crystal.

In the above explanation, the ion exchange method was used as a method for forming a waveguide on a glass substrate, but the CVD method,
Other waveguide forming methods can be used, such as forming a waveguide by forming a dielectric layer different from the substrate by sputtering or the like.

[Brief explanation of the drawing]

Figure 1 is a top view showing the structure of one embodiment of the present invention.
is a substrate, and 3 and 4 are channel optical waveguides. FIG. 2 is an enlarged view of the waveguide intersection in FIG. 1, and 10 and 11 are channel waveguides 12 and 13 are transparent electrodes provided on the respective waveguides. FIG. 3 shows a cross-sectional view of the waveguide crossing part, and 101 and 102 are substrates,
103 and 104 are optical waveguides, and 105 is a liquid crystal layer.

Claims (1)

[Claims] Two dielectric substrates each having a plurality of linear single mode channel optical waveguides on their surfaces that do not intersect in a plane and the surfaces on which the optical waveguide groups are provided face each other, and the two
The above two optical waveguide groups are installed so that they intersect with each other.
In order to apply an electric field to the liquid crystal layer at a portion where the liquid crystal filled in the gap between the two dielectric substrates and the optical waveguide on the two dielectric substrates intersect and overlap, An optical switch comprising an optically transparent electrode formed along the waveguide.