JPS62127829A - Waveguide type liquid crystal matrix switch - Google Patents

Abstract

PURPOSE:To realize a low loss and to reduce a crosstalk by bringing a liquid crystal to a molecular orientation in the direction of a bisector of a cross angle made by two waveguides, and setting a refractive index of the liquid crystal at the time when an electric field is impressed and when it is not impressed between electrodes, to a value being equal to a refractive index of the waveguide. CONSTITUTION:A liquid crystal cell 1s is field with a liquid crystal, and this liquid crystal has an anisotropy in its refractive index, but brought to a molecular orientation so that the refractive index becomes equal against input use and output use waveguides 10a2, 11a2. That is to say, an empty cell 12 for inserting the liquid crystal has an oriented layer which has been formed on the upper face of a substrate, and this oriented layer is brought to rubbing in the direction of a bisector of a cross angle made by two waveguides 10a2, 11a2, and the liquid crystal is brought to a molecular orientation in the direction in which the rubbing has been executed. Also, a refractive index of the waveguides 10a2, 11a2 is set so as to become roughly equal to a refractive index of the liquid crystal in case when an electric field is not impressed between the upper and lower electrodes of the liquid crystal cell 12. In this way, at the time of a switching operation, a large deflection angle is obtained, a crosstalk is reduced and an insertion loss becomes small.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a waveguide type liquid crystal light beam (IJ) used for optical path switching in optical fiber transmission circuits, terminal devices, etc.

(Prior Art) A liquid crystal optical matrix switch that uses liquid crystal in a cladding layer is conventionally known. FIGS. 6 and 7 show such a conventional liquid crystal optical matrix switch, in which a flat waveguide 3 made of 5iO2-TazOs is formed on the surface of a Si substrate 1 serving as a lower electrode via a 5iOz buffer yN2. Then, on the outer surface of the flat waveguide 3, SiO
□A liquid crystal cladding N5 is provided via the alignment layer 4, and a 5iO1 upper substrate 6 is further provided as an outer layer thereof. One (for example, two) parallel rays 8a, 8b (Fig. 6) enter the above-mentioned flat plate waveguide 3, and this parallel ray 8a
, 8b, in addition to the above-mentioned lower electrode l, an upper electrode 7 formed on the outer surface of the upper substrate 6 is provided, and a predetermined electric field is applied between the upper and lower electrodes 7.1. The optical path is switched by applying the voltage. That is, when an electric field is applied to the liquid crystal 5, its crystal structure changes and the refractive index changes. As a result, the effective refractive index of the waveguide in the optical path changes, and a refractive index interface B (Fig. 5) is created between the electric field applied part and the non-applied part, the optical path of the propagating light is deflected, and the output light beam 9a .

9b is obtained. In this way, by providing n tree input/output terminals and providing pattern electrodes at each intersection of the manual optical path and the output optical path, an nxn optical matrix switch is obtained.

(Problems to be Solved by the Invention) The thicknesses of the flat tit wave path 3 and the cladding (liquid crystal) layer 5 of the conventional optical matrix switch are approximately 0.5 μm and 9 μm, respectively.
．． When the wavelength of light is 1.3 μm, the refractive index of waveguide 3 is 1.741. 1.60 in the long axis direction of the liquid crystal molecules
9. It is 1.492 in the minor axis direction. In such an optical matrix switch, it is difficult to obtain perfectly parallel light rays due to the lens system, so if the optical path distance from the input end to the output end is long, the light flux will spread and crosstalk will increase. It was difficult to increase the number and increase the size.

Furthermore, since the waveguide 3 is thin, the optical signal loss is large.

The present invention was made in order to solve such problems, and an object of the present invention is to provide a liquid crystal optical matrix switch that can be connected to an optical fiber with low heating, has a small insertion TFI, and has low crosstalk. .

(Means for Solving the Problem) According to the present invention, in order to achieve the above-mentioned conditions, a liquid crystal cell is provided at each intersection of the waveguide, and upper and lower electrodes of the liquid crystal cell are provided, and each liquid crystal The liquid crystal filled in the cell is oriented substantially in the direction of the bisector of the intersection angle formed by the two waveguides, and the liquid crystal is oriented either when an electric field is applied or when no electric field is applied between the upper and lower electrodes. There is provided a waveguide type liquid crystal optical matrix switch characterized in that the refractive index of the waveguide is set to a value substantially equal to the refractive index of the waveguide.

(Function) The liquid crystal provided at each intersection of the waveguides of the waveguide-type liquid crystal optical matrix switch according to the present invention and filled in the liquid crystal cell has a refractive index that changes either when an electric field is applied or when no electric field is applied. It is set to a value that is substantially equal to the refractive index of the waveguide, and when the refractive index of the liquid crystal and the waveguide are equal, the optical signal propagating through the waveguide is propagated through the waveguide without being deflected by the liquid crystal cell. I will do it. On the other hand, the reversal of the electric field state creates an interface between the refractive index of the liquid crystal and the waveguide, at which the optical signal propagating through the waveguide is reflected or refracted, and the waveguide through which the optical signal propagates is switched.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show zero input waveguides 10 (10a).

1oan) and n output waveguides 11 (11a+-1lan) intersecting these are arranged in a lattice pattern, each waveguide 10a, 10an , 1la1
~1 lan is 50μm thick, 5o wide, as described later.
It consists of Sift-Tag's (silicon dioxide/tantalic acid type) with a square cross section of μm, and 4 wave paths 108 for each input.
1 to 10an and each output waveguide 11al=11an are arranged to intersect with each other at a predetermined angle θ (for example, 246).

Further, the interval between each waveguide of the input waveguides 10a+ to 1Oan and the interval between each waveguide of the output waveguides flat to 1lan are each set to approximately 0.5 mm. And each intersection,
Moreover, an empty cell 12 for inserting a liquid crystal is formed in the optical path of the waveguide. More specifically, the empty cell 12 for inserting the liquid crystal is formed at the predetermined angle θ with respect to the optical axis of the input waveguide 10a2.
It is arranged at an angle of half (12°),
In addition, they are arranged at an angle (12°) at the same angle with respect to the optical axis of the output waveguide 11a2. One side 12a of the liquid crystal cell 12 faces the upstream side of the input waveguide 10a2 and the downstream side of the output waveguide 11a2.

The liquid crystal cell 12 has a liquid crystal (for example, Pct (1132, refractive index is 1.609 in the long axis direction of the molecule for a wavelength of 1.3 μm).
．． 1.492 ) in the short axis direction, and this liquid crystal has anisotropy in the refractive index, but the input and output waveguides 1
The molecules are oriented so that the refractive index is equal to 0az and 1laz. That is, the empty cell 12 for inserting the liquid crystal has an alignment layer formed on the upper surface of the substrate, as will be described in detail later, and this alignment layer has substantially the same angle of intersection between the two waveguides 10az and 1lai. The liquid crystal is rubbed in the direction of the rays, and the molecules of the liquid crystal are oriented in the direction of the rubbing.

The refractive index of the waveguides 10az and 1laz is determined by the upper and lower electrodes of the liquid crystal cell 12 (in FIG.
The refractive index is set to be approximately equal to the refractive index of the liquid crystal when no electric field is applied between them.

Therefore, when no electric field is applied to the upper and lower electrodes, no refractive index interface is generated between the waveguides 10az, 1laz and the liquid crystal, so that the waveguides 10a2. The optical signal propagating through the flat propagates straight without being refracted or reflected at the interface between the waveguides 10az, 1laz and the liquid crystal (the above-mentioned negative side surface 12a, etc.). On the other hand, when an electric field is applied to the upper and lower electrodes, the liquid crystal molecules are aligned perpendicularly to the electrodes, the refractive index becomes smaller, and a refractive index interface (12a) is created between the waveguide 10at and the liquid crystal. At this interface 12a, the optical signal that has propagated through the waveguide 10a undergoes total reflection, and its optical path is switched to the output waveguide 11a2.

Thus, by controlling the electric fields of the upper and lower electrodes of the liquid crystal cell at each intersection of the waveguides using a known method, an nxn matrix switch can be realized.

Next, details of the configuration of the liquid crystal optical matrix switch according to the present invention will be explained with reference to the steps for forming the waveguide and liquid crystal cell shown in FIGS. 3 and 4.

When forming the cladding layer 19 on both sides of the waveguide 10, the lower thin film electrode 1 is formed on the SiO□ substrate 15 (FIG. 3(a)).
After depositing the cladding layer 19" (FIG. 3(b)),
is deposited ((C) in the same figure). The core portion of this cladding layer 19', that is, the portion 1 where the waveguide 10 is formed.
9' is etched by a sputter etching method (see Figure (d)), and a 5iOt-Ta205 waveguide iii
The waveguide layer 101 is formed by sputter etching, leaving the waveguide forming portion 19°1, as shown in FIG.
' is etched to form the waveguide 10 (FIG. 1(f)).
). Note that the portion of the cladding layer 19 below the waveguide 10 functions as the alignment layer 17.

Next, the waveguide 10 of FIG. 3 formed as described above is
Then, an empty cell 12 for inserting a liquid crystal at the intersection position is formed by etching (FIG. 4(a)). Then, in order to align the molecular orientation of the liquid crystal in the above-described certain direction, the alignment layer 17 in the liquid crystal cell 12 portion is subjected to a rubbing process (alignment process) in the certain direction. Next, an upper SiO□ substrate 20 on which an upper thin film electrode 13a is deposited and a liquid crystal injection port 21 is formed is formed.
are bonded to the waveguide 10 with the electrode deposition surface facing down and aligned with the empty cell 12 for inserting the liquid crystal. A liquid crystal injection port 21 is inserted into the thus formed empty cell 12 for inserting the liquid crystal.
A liquid crystal 24 is injected from the tank and sealed liquid-tightly by a sealing member 22 . The lower thin film electrode 13b functions as a common electrode, the upper (single film) electrode 13a functions as a pattern electrode, and the leads drawn out from each upper electrode 13a are connected to a control circuit (not shown) to perform known switching control. executed.

Further, the shape of the upper electrode 13a is set to have a length of 350 μm and a width of 1.
Assuming that the distance between each waveguide is 0.5 mm (Fig. 2), the distance between the electrodes will be approximately 1 m, so
Even if the lead width is 100 μm, it can be integrated into a 10×10 matrix switch.

Furthermore, the liquid crystal optical matrix switch of the present invention has a waveguide 1
By variously changing the external shape of 0.11, it can be applied to both 5M optical fiber and GI optical fiber.

Furthermore, in the above-described embodiment, the refractive index of the liquid crystal filled in the liquid crystal cell 12 was set to be approximately equal to the refractive index of the waveguide 10° 11 when no electric field was applied. Without limitation, the refractive index of both may be set to be equal when an electric field is applied. In this case, the optical signal propagating through the input waveguide when no electric field is applied will be reflected at the interface between the waveguide and the liquid crystal. Since the beam is bent, the output waveguide may be arranged in the direction of this bending.

(Effects of the Invention) As described in detail above, according to the waveguide forming part matrix switch of the present invention, a liquid crystal cell is provided in the optical path at each intersection of the waveguide, and liquid crystal molecules filled in the liquid crystal cell are provided. The alignment is made substantially in the direction of the bisector of the intersection angle formed by the two waveguides, and the refractive index of the liquid crystal is determined by changing the refractive index of the liquid crystal when an electric field is applied or when no electric field is applied between the upper and lower electrodes. Since the refractive index is set to a value substantially equal to the refractive index of , a large deflection angle can be obtained during the switching operation, and excellent effects such as small crosstalk, small insertion member, and low loss connection to the optical fiber can be achieved.

[Brief explanation of drawings]

1 to 4 show one embodiment of the present invention, FIG. 1 is a cross-sectional view showing a liquid crystal cell formed at a waveguide intersection of a waveguide-type liquid crystal optical matrix switch, and FIG. 2 is an input 3 is a process diagram for explaining the waveguide formation procedure, and FIG. 4 is a vertical cross section of a liquid crystal cell formed in the waveguide. figure,
FIGS. 5 and 6 are configuration diagrams of a conventional liquid crystal optical matrix switch. 10... Waveguide for human power, 11... Waveguide for output, 1
2...Liquid crystal cell, 13a...Upper (thin film) electrode, 1
3b... Lower (thin film) electrode, 17... Orientation layer, 24
···liquid crystal. Applicant: Furukawa Electric Co., Ltd. Patent attorney: Kanji Nagato Figure 1 Figure 2 Figure 3 (a) (b) (c)
(d) Figure 4 (a) (b) Figure 5 Figure 6

Claims (1)

[Claims] 1. A liquid crystal cell and upper and lower electrodes of the liquid crystal cell are provided at each intersection of the waveguides, and the liquid crystal filled in each liquid crystal cell is The molecules are oriented substantially in the bisector direction, and the refractive index of the liquid crystal is made to be substantially equal to the refractive index of the waveguide either when an electric field is applied or when no electric field is applied between the upper and lower electrodes. A waveguide type liquid crystal optical matrix switch characterized by: 2. The waveguide type liquid crystal optical matrix switch according to claim 1, wherein an alignment layer is provided on at least one of the upper and lower parts of each of the liquid crystal cells, and the alignment layer is subjected to alignment treatment.