JPS62275226A - Liquid crystal optical switch - Google Patents

Abstract

PURPOSE:To switch traveling directions of light according to whether or not there is a low driving voltage by arranging one liquid crystal cell which has a twisted array when applied with no voltage or an homeotropic array when applied with a voltage between two liquid crystal cells which are put in a homogeneous or homeotropic array. CONSTITUTION:A liquid crystal layer 16 reflects P polarized light, but S polarized light is transmitted through the liquid crystal layer 16 to reach a bevel surface of semitrapezoid prismatic glass 9, and reflected by the bevel and converged by a lens 5 to reach a projection optical fiber 4. When a voltage 3V is applied to the liquid crystal layer 17 of a twist array liquid crystal cell, liquid crystal molecules except liquid crystal molecules very near glass plates 10 and 11 are oriented (in hometropic array) at right angles to the glass surfaces. Light passing through the liquid crystal layer 17, therefore, does not has the vibration direction rotated and reaches the projection optical fiber 3. Light incident from an incidence optical fiber 2 is the same. Namely, when the low voltage of about 3V is applied, light beams of incidence optical fibers 1 and 2 reach projection optical fibers 3 and 4, thus constituting a 2X2 optical switch.

Description

[Detailed Description of the Invention] & Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical switch used in optical communication systems and the like to switch optical paths, and in particular to an electro-optical liquid crystal switch using liquid crystal. It is related to.

[Conventional technology]

Conventionally, optical switches used in optical communication systems include mechanical optical switches that switch optical paths by moving optical fibers or prisms, and electrical optical switches that utilize the electro-optic effect or acousto-optic effect of materials. ing. Among the above-mentioned optical switches, electric optical switches have a fast switching speed, have no abrasion of moving parts, and have little deterioration over time. Furthermore, liquid crystal is easy to use as a material for electric optical switches because it has a large refractive index anisotropy and the polarization direction of light can be easily rotated.

Conventional liquid crystal optical switches of this type include those described in JP-A-56-150725 and Applied Optics, 19.17 (1980), pp. 2921-2925 (Applied Optics). There is.

[Problem that the invention seeks to solve]

The former conventional example takes advantage of the fact that the refractive index of liquid crystal changes depending on whether or not a voltage is applied, but there is a problem in that the applied voltage necessary for switching light becomes higher than several tens of volts. The latter conventional example utilizes the fact that the polarization direction of light passing through a liquid crystal cell changes depending on whether or not a small voltage of several volts is applied, but it requires two polarizing beam splitters and requires a high-speed switch. There was a problem with the price. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to obtain a liquid crystal optical switch that requires a small drive voltage and is inexpensive.

[Means to solve the problem]

The above objective is achieved by using two liquid crystal cell parts that transmit or totally reflect light depending on the polarization direction of the light, and one liquid crystal cell part that changes the polarization direction of light by 90 degrees depending on whether or not a voltage is applied. .

The above-mentioned respective liquid crystal cells are optically connected through trapezoidal glass having a reflective mirror surface.

Liquid crystal cells can be manufactured at low prices by mass production similar to the manufacturing method of liquid crystal display elements in calculators, watches, and the like. Among the above liquid crystal cells, the former assumes a homogeneous arrangement in which liquid crystal molecules are arranged in parallel on a transparent plate such as glass or a homeotropic arrangement in which they are arranged perpendicularly. The latter is the above-mentioned homogeneous arrangement, and is an arrangement in which the upper and lower transparent plates such as glass are twisted 90 degrees to each other, which is called a twisted arrangement. Liquid crystals having each of the above-mentioned arrangements are manufactured by a known method.

Light incident on the homogeneously aligned or homeotropically aligned liquid crystal senses a different refractive index depending on the alignment of the liquid crystal molecules and the polarization direction of the light.

A liquid crystal whose refractive index (no) for ordinary light is smaller than the refractive index (n, ) for extraordinary light is sandwiched between transparent bodies having a refractive index n, and light enters the liquid crystal layer at an incident angle larger than 5in-"!' ni n
・When entering, the liquid crystal molecular arrangement and the direction of vibration of light (polarized light)
Depending on the combination, the polarized light is divided into transmitted polarized light and totally reflected polarized light. Of course, the optical path opposite to the above can also be taken.

[Effect]

A liquid crystal cell in which liquid crystal molecules are arranged homogeneously or homeotropically operates as a polarizing beam splitter because it separates incident light into polarized light that is transmitted and polarized light that is totally reflected, as described above.

In addition, a liquid crystal cell in which liquid crystal molecules are arranged in a twisted manner rotates the direction of light vibration by 90' when no voltage is applied, but operates as an element that does not rotate the direction of light vibration when a voltage is applied. . Therefore, by combining the liquid crystal cells of each arrangement described above, the traveling direction of light can be changed depending on whether or not a voltage is applied, as in the embodiment shown below.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of a liquid crystal optical switch according to the present invention. Single trapezoid columnar glass 6 with a refractive index of 1.75
and 7, 8, and 9fI: Two liquid crystal cells for a polarization beam splinter are manufactured by the method shown below. That is, in order to regulate the arrangement of liquid crystal molecules, S and O□ are formed by oblique vapor deposition on one surface of the above-mentioned single-trapezoidal columnar glass (not shown), and the two single-trapezoidal columnar glasses on which the above-mentioned alignment film has been formed are formed. Glasses are placed one on top of the other so that their vapor deposition surfaces are facing each other, and a liquid crystal material 15 or 16 is placed between a 5 μm thick spacer 14 sandwiched between these two pieces of trapezoidal columnar glass. This was filled to form a liquid crystal cell, and two liquid crystal cells were manufactured. Due to the effect of the 5102 film, the liquid crystal molecules
The long sleeves are oriented on the glass surface and perpendicular to the paper plane of FIG. 1 (homogeneous arrangement).

Input optical fibers 1 and 2, output optical fibers 3 and 4, and a lens 5 are attached to the two liquid crystal cells, respectively. Liquid crystal material 15.16 has n, = 1.75゜n0 = t4
A nematic liquid crystal with a refractive index of 9 is used. The angle of incidence of light that enters the liquid crystal layer is determined by the size of the acute angle of the trapezoidal columnar glass, but the size of the acute angle is appropriate in order to set the angle of incidence at which the specific polarization of the light that enters the liquid crystal layer can be totally reflected. Must be set to . In this embodiment, the angle is set to 55°.

Next, a twisted-aligned liquid crystal cell was formed using glass plates 10 and 11 having a refractive index of 1.75 in the following manner.

That is, In2 is applied to one surface of the glass plate 10 or 11.
After forming a transparent electrode (not shown) by vapor depositing 05-S,,O□, an 810□ film was formed on each of the above electrodes by oblique vapor deposition, so that the direction of the vapor deposition was close to 90°. Lay them on top of each other with their vapor deposition surfaces facing each other. 5 between the above vapor deposition surfaces
A liquid crystal cell was manufactured by filling a liquid crystal material 17 with a spacer 14 having a thickness of μm in between. The liquid crystal molecules have an orientation twisted by 90 degrees (twisted arrangement) as they move from one glass surface to the other glass surface. The above liquid crystal material 1
7 has n, = 1.75. A nematic liquid crystal with a refractive index of n0=1.49 is used. Using the above-mentioned twisted liquid crystal cell and the two above-mentioned homogeneous liquid crystal cells, the twisted liquid crystal cell is placed in the center, and trapezoidal glasses 12 and 13 whose slopes are reflective mirror surfaces and whose refractive index is 1.75 are interposed. Then, two homogeneously aligned liquid crystals were arranged symmetrically to form a liquid crystal optical switch as shown in FIG. The broken lines shown in FIG. 1 are the optical paths of the light, and the respective positions of the above-mentioned components are adjusted so that the optical paths coincide with each other.

The light that passes through the input optical fiber 1, passes through the lens 5, and enters the single-trapezoidal columnar glass 6 is represented by two orthogonal polarized lights (P-polarized light and S-polarized light), and after being made into parallel rays by the lens 5, it becomes a single-trapezoidal columnar glass. The light is reflected by the slope of the columnar glass 6 and enters the interface between the glass 6 and the liquid crystal layer 15 at an incident angle of 70°. The above angle of incidence is larger than the critical angle of total reflection 1.49 sin-' −=5 a 4° when the refractive index of the liquid crystal is n==1.49. 1st
In the figure, P-polarized light, which is polarized light that vibrates parallel to the plane of the paper, and S-polarized light, which is polarized light that vibrates perpendicularly to the paper, have the refractive index of the liquid crystal as n0 = t, 49 and n, = 1.75, respectively. The P-polarized light is totally reflected by the liquid crystal 15, and the S-polarized light is transmitted through the liquid crystal 15. The polarized light is reflected by the slope of the trapezoidal glass 12 and is perpendicularly incident on the glass surface 10 of the twisted liquid crystal cell. When no voltage is applied to the twisted liquid crystal cell, the vibration direction of the light is rotated by 90 degrees, and the P-polarized light changes to S-polarized light, and the S-polarized light changes to P-polarized light. Thereafter, the light is reflected from the slope of the trapezoidal glass 13 and is incident on the interface between the trapezoidal columnar glass and the liquid crystal layer 16 at an incident angle of 70°. As mentioned above, P-polarized light is reflected by the liquid crystal layer 16, and S-polarized light is reflected by the liquid crystal layer 1.
6 and reaches the slope of the trapezoidal columnar glass 9, is reflected from the slope, is focused on the lens 5, and reaches the output optical fiber 4. On the other hand, when a voltage of 3V is applied to the liquid crystal layer 17 of the twisted alignment liquid crystal cell, the liquid crystal molecules are aligned perpendicularly to the glass surface (homeotropic alignment), except for the liquid crystal molecules very close to the glass plates 10 and 11. , no rotation of the vibration direction occurs in the light passing through the liquid crystal layer 17. Therefore, it reaches the output optical fiber 3 for the same reason.

The same applies to the light that enters from the input optical fiber 2.

That is, when no voltage is applied to the twisted array liquid crystal cell, the incident optical fiber and 2 light beams reach the output optical fibers 4 and 3, respectively, and when a low voltage of about 3V is applied, the 5 incident optical fibers and the 2 beams reach the output optical fibers 4 and 3, respectively. The light reaches output optical fibers 3 and 4, respectively, forming a 2×2 optical switch.

In the above embodiments, the liquid crystal material, alignment control material, orientation, refractive index of the glass material, etc., are not limited to the above embodiments, and transparent plastic materials may be used instead of the glass material. .

〔Effect of the invention〕

As described above, the liquid crystal optical switch according to the present invention has two liquid crystal cells arranged in a homogeneous or homeotropic arrangement.
One liquid crystal cell is placed in the middle of the cell, which has a twisted arrangement when no voltage is applied, and a homeotropic arrangement when a voltage is applied, and by combining these, the above homogeneous arrangement or homeotropic arrangement can be achieved. P-polarized light or S-polarized light incident on a tropic-aligned liquid crystal is transmitted or reflected, respectively, and when no voltage is applied, the twisted-aligned liquid crystal layer changes P-polarized light to S-polarized light and S-polarized light to P-polarized light. Since the polarization of the homeotropically aligned liquid crystal layer does not change when a voltage is applied, the traveling direction of light can be switched depending on the presence or absence of a low driving voltage.

Moreover, since the liquid crystal optical switch is manufactured using a liquid crystal manufacturing method that is highly suitable for mass production, it is possible to obtain a liquid crystal optical switch at a low cost.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a liquid crystal optical switch according to the present invention. 6.7, 8.9... Single trapezoid columnar glass 10.11...
- Plate glass 12.13...Trapezoidal glass 14...Spacer 15.16.17...Liquid crystal material. -to,

Claims (1)

[Claims] 1. Place one liquid crystal cell between two homogeneous or homeotropically aligned liquid crystal cells that has a twisted alignment when no voltage is applied and a homeotropic alignment when a voltage is applied. A liquid crystal optical switch constructed by combining them.