JPS60154237A - Optical switch - Google Patents

Abstract

PURPOSE:To switch light guides by installing a linear multi-mode channel light guide group on a dielectric substrate so that they cross one another across liquid crystal at acute angles, and applying a voltage to the liquid crystal layer. CONSTITUTION:A glass substrate 11 has plural parallel linear light guides 3 on the surface and a glass substrate 2 has a light guide 4 of the same structure with the substrate 1. The substrates 1 and 2 are arranged so that their surface on which the light guides 3 and 4 are formed face each other across a fine gap and the light guides 3 and 4 cross each other at an 1-3 deg. angle theta on the same plane when viewed through the substrates 1 and 2. The liquie crystal 5 is charged in the gap between the substrate 1 and 2. Transparent electrodes 12 and 13 are provided on light guides 10 and 11 along the bisector of the light guides 10 and 11 shown while the intersection part of the light guides 3 and 4 are enlarged. When a voltage is applied between the electrodes 12 and 13, a light wave supplied to the light guide 10 from left is coupled with the light guide 11 through the liquid crystal, and when no voltage is applied, it propagates in the light guide 10 and is switched.

Description

DETAILED DESCRIPTION OF THE INVENTION [Description of the technical field to which the invention pertains] 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.

[Description of prior art]

In optical fiber communication systems, optical switches are widely used for switching between regular and backup lines, switching optical components, and measuring, in order to improve line reliability and facilitate maintenance. In addition, in order to realize an optical switching system that uses optical components to avoid blocked communication channels, select open channels, and connect them to set up a call, it is necessary to have multi-channel switching terminals. A light switch is used. Optical switches are widely used not only in communication systems between long distances, but also in data transmission systems that connect information processing devices within a limited area, such as the connection nodes between highways and terminals on so-called optical data highways. has been done. Optical switches are effective in bypassing routes when it is necessary to avoid a particular terminal, such as when the terminal is out of order, undergoing maintenance or inspection, or when it is not in use.

One type of optical switch that has been developed for this purpose is one that electromagnetically displaces a prism or mirror. This converts the light emitted from an optical fiber into a parallel beam, spatially changes the optical path by inserting a prism or mirror into this optical path, and selects 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,
Although it has the advantage of being easy to use, since it has a mechanical movable mechanism, it is difficult to obtain a high switching speed, and there are concerns about the lifespan for the number of switchings and the reliability for operations with extremely long intervals. For example, there is instability in that the switch remains almost fixed for a long period of time and does not operate correctly when suddenly switched.

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. For example, incident light is passed through a polarization conversion element that has the function of inverting the polarization direction of transmitted light by 90'[g1] by applying a voltage or current, and then a polarization element that changes the direction of the optical path depending on the polarization direction of the light is used. Some guide light to different optical fibers by transmitting it. 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. However, 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 polarizing prisms made of calcite, a material with a long known high birefringence, and prisms made of rutile crystal, which also has a high birefringence. There are some types that are shaped and polished, and others that have a three-layer dielectric film formed on the reflective surface of a total reflection prism made of glass to form a light-loss element. Calcite is a natural stone and is expensive, and the crystal material itself of rutile prism is expensive, and it has a high refractive index, so it is necessary to form a good anti-reflection film on the prism entrance surface. In particular, in polarizing elements made of glass material with a dielectric multilayer film, the wavelength characteristics of the multilayer film are sensitive to incident light, so there are drawbacks such as deterioration of the polarization characteristics when light with a wavelength that deviates from the design wavelength is incident. have

Of course, there is a waveguide-type optical switch that does not use a polarizing element as described above. 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 a switch element structure, electrodes are installed on two adjacent channel waveguides formed flat on the surface of the substrate, and changes in the refractive index caused by an electric field applied to the waveguides via these electrodes are utilized. One method is to control the coupling of light between 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. Other methods have been proposed, such as forming a phase grating and black-reflecting the guided light within a plane, and providing a Y-branch waveguide on the substrate surface and creating a refractive index bias in the branch area to refract the light. . The above switch elements are arranged in multiple stages or in a mesh pattern to configure an optical switch for multiple channels.

The disadvantages of the above-mentioned multichannel optical switch are mechanical,
Because the thermal strength is not very high, the expensive crystal substrate is used, and the available electro-optic effect is extremely small, the voltage required for switching is high, the element length cannot be shortened, and it is difficult to shorten the device length. The problem is that the number of switch elements that can be installed on a single board is limited. For this reason, the number of channels that can be switched is limited. In addition, since the counter electrode required for applying an electric field is installed on a single board, when the number of switch elements increases, the lead electrode becomes a lead wire on the board. This was also one of the factors that limited the number of switch elements that could be installed. Another drawback of this type of waveguide element is that its characteristics change sensitively depending on the optical wavelength used. When used with light, the characteristics cannot be obtained.

Another method of 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 guided light is refracted within a plane, but this method has drawbacks such as difficulty in connecting to an optical fiber because the waveguide is not channelized.

However, in the above-mentioned waveguide type optical switch, in order to obtain sufficient switching characteristics, the guided light must have the spatially lowest order single mode (linearly polarized light). Therefore, as the input optical fiber that can be connected, it is necessary to use a single mode polarization constant optical fiber that has such characteristics for transmitted light. However, there are not many optical information transmission systems in which single-mode polarization-controlled optical fibers are installed, and most use multi-mode optical fibers, which have low system costs. Type optical switches are not applicable.

[Detailed description of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and provide an optical switch that is inexpensive, has a low voltage, has a large number of switching channels, can connect multimode optical fibers, and has a low optical insertion loss.

[Detailed description of the invention]

The present invention has a plurality of linear multimode channel optical waveguides on a surface that do not intersect in a plane, the surfaces on which the optical waveguides are provided face each other, and the two optical waveguide groups intersect at an acute angle. Two dielectric substrates placed so as to match each other, a liquid crystal filled in the gap between the two substrates, and the liquid crystal layer at a portion where the optical waveguides on the two dielectric substrates intersect and overlap υ. In order to apply an electric field, an acute-angled bisection 411 formed by the two optical waveguide groups is formed on the dielectric substrate.
This is an optical switch consisting of an optically transparent electrode formed along the i-th line.

[Explanation of Examples]

The details of the present invention will be explained below 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, in which 1 is a glass substrate having parallel linear waveguides 3 on its surface;
2 is the same glass substrate having the same waveguide 4 as the glass substrate 1, and these two glass substrates 1 and 2 are placed with the surfaces where the waveguides 3 and 4 are formed facing each other with a small gap between them. (2 μm to 10 μm) and form an angle θ of 1 to 3 degrees in the plane, and when viewed through the two substrates 1 and 2, the waveguides 3.4 of each antinode number intersect. are set to match. The gap between the two substrates 1 and 20 is filled with liquid crystal 5.

FIG. 2 is an enlarged view of the intersection of two overlapping waveguides, where 10 indicates the waveguide provided on the lower substrate (1 in FIG. 1), and 11.11 indicates the upper waveguide. 2 shows a waveguide provided on a substrate 2 (2 in FIG. 2) located at . 12
．． 13 represents a transparent electrode provided on each waveguide 10.11. When a voltage is applied between the electrodes 12 and 13, the light wave injected from the left into the waveguide 10 provided on the lower substrate passes through the liquid crystal (not shown) provided between the electrodes, and then passes through the liquid crystal (not shown) provided between the electrodes. The waveguide 11 is coupled to the waveguide 11. 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 upper 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.
, 104 are waveguides provided on the respective surfaces, 106,
107 is a transparent electrode provided on the surface of the waveguide, and 105 is a liquid crystal filled in the gap between the two substrates 101 and 102.
1'08 is a switch, and 109 is a power supply.

This guided light shows a broadened distribution as shown in 110, and is slightly
05 has medium pressure skirt expansion. When no voltage is applied between the electrodes 106 and 107, the liquid crystal 105 exhibits approximately a refractive index of n2 with respect to the light wave injected into the lower substrate 101, and when a voltage is applied, the liquid crystal 105 exhibits a refractive index of n2. The molecular orientation is determined as follows. The two refractive indices have a relationship of n>n. Close the switch 108 and connect the power supply 1 to the two electrodes.
When a voltage of 09 is applied, the refractive index of the liquid crystal 105 increases depending on the light wave, so the electric field distribution of the guided light becomes as shown in 111, and the seepage from the waveguide 103 increases, and the waveguide passes through the liquid crystal 105. Expand the hem to 104. Waveguide 1
Since the waveguide 104 and the waveguide 104 are formed in the same manner, the light wave propagating through the waveguide 103 will pass through the waveguide 104 as it propagates.
join to.

When no voltage is applied between the two electrodes 106 and 107, the light wave does not couple to the waveguide 104 provided on the upper substrate because the electric field distribution of the light wave has a small leakage as shown at 110. Therefore, depending on whether or not a voltage is applied, an optical path conversion is realized in which the light traveling through the lower waveguide is coupled to the upper waveguide 104 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, in order to switch light to a desired upper waveguide 104, the upper waveguide 104 is
This is realized by applying a voltage to a desired pair of electrodes among the pairs of electrodes provided at all positions where the lower waveguide 103 and the lower waveguide 103 intersect.

One of the features of the present invention is that it can also switch multimode fiber light, and this operation is explained as follows. FIG. 4 shows a cross-sectional view taken perpendicularly to the substrate at the intersection of the two waveguides shown in FIG. 2 so as to block the optical waveguide.

The surfaces of the substrates 101 and 102 of the liquid crystal 105 are treated so that the long axis of the molecules is oriented in the light transmission direction, that is, in the two-axis direction in FIG. The liquid crystal 105 shows the refractive index of the light wave transmitted through the waveguide 103 in any mode.

An electric field 109 is applied between the electrodes 106 and 107 by the switch 10.
8. The electrodes 106 and 107 are not vertically opposed to each other, but are set with a gap in the π direction. If the voltage applied between the electrodes 106 and 107 is set correctly, the long axis of the liquid crystal molecules is aligned with the spatial axis Z t y
t g making an angle of 45° to either axis1.
At this time, the liquid crystal is R*(IS*>
%t), and coupling of light into the opposing waveguide 104 occurs as described in the description of FIG. 3 above.

Furthermore, as shown in FIG. 2, since the waveguide 10 on the lower substrate and the upper waveguide 11 intersect in the optical waveguide direction through an angle of 0, the overlap of the two waveguides is in the optical transmission direction. It is not uniform and is changing. This means that when a voltage is applied between the two electrodes, the coupling coefficient of light between the two waveguides is maximized at the center of the intersection of the two waveguides (15 in Figure 2) and in the direction of light transmission. This means that it decreases before and after. Generally, when the coupling coefficient of a coupling waveguide has a distribution in the light transmission direction, when the coupling coefficient is uniform and the coupling length is long, the light coupled from one waveguide to the other waveguide returns to the original waveguide. Since no recombination phenomenon occurs, energy of all modes having different wave numbers, that is, a large number of modes having different degrees of coupling, is unidirectionally transferred from one waveguide to the other waveguide. The structure of this embodiment has switching characteristics with a high switching intensity ratio for a waveguide having a large number of spatial modes with different wave numbers.

The elements of the embodiments of the present invention are realized by design values as shown below, by way of example.

Using BN2 having a refractive index of 1.51 as a glass substrate, a waveguide having a refractive index of about 1.52 is formed by an ion exchange method using silver nitrate or thallium nitrate.

The transparent electrode has an indium tin oxide film of 500 to 100
0^, and as a liquid crystal material n, -1, 63, s, -1
, 50, a good optical switch can be obtained.

[Detailed description of the invention]

As explained above, the optical switch according to the present invention is made of glass material, so it is inexpensive, it is composed of only a straight waveguide, it can switch multiple channels, and it is easy to connect with a multimode optical fiber, and has low optical insertion. It has features such as low loss and low driving voltage due to the use of liquid crystal.

In the above explanation, we have described the case where the ion exchange method is used as a method for forming a waveguide on a glass substrate, but it is also possible to form a waveguide by forming a dielectric layer different from the substrate using the G method, sputtering method, etc. , other waveguide formation methods can be used.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the structure of an embodiment of the present invention, FIG. 2 is an enlarged view of the waveguide intersection in FIG. 1,
3 and 4 show cross-sectional views of the waveguide intersection. 1.2...Substrate, 3,4...Channel optical waveguide,
5...Liquid crystal, 10.11...Channel waveguide, 1
2.13...Transparent electrode, ioi, io2...substrate, 103, 104...optical waveguide, 105...liquid crystal layer Patent applicant NEC Corporation No. 1 Sonochi 2

Claims (1)

[Claims] (1) The surface has a group of linear multi-mode channel optical waveguides consisting of a plurality of optical waveguides that do not intersect in a plane, the surfaces on which the optical waveguide groups are provided face each other, and the two optical waveguide groups intersect each other at an acute angle. In a region where the two dielectric substrates installed as above, the liquid crystal filled in the gap between the two substrates, and the optical waveguide on the two dielectric substrates intersect and overlap,
In order to apply an electric field to the liquid crystal 1@, it is characterized by comprising an optically transparent electrode formed on the dielectric substrate along the bisector of an acute angle formed by the two optical waveguide groups. light switch.