JPH02100025A - Liquid crystal optical changeover switch - Google Patents

Abstract

PURPOSE:To prevent a code error from being generated by arranging a polarized light separating means, a cell, and a polarized light composing means so that paths where P-polarized light and S-polarized light pass from the separation point of the polarized light separating means to the composition point of the polarized light composing means become equal in length, and switching the paths with a voltage applied to the cell. CONSTITUTION:Polarization beam splitters 8 and 8a are in a cubic shape with the same dimension, reflecting prisms 10 and 10a are in a shape of an isosceles right-angled triangle, and the length of the sides containing the right angles is equalized to the length of one side of the polarization beam splitters 8 and 8a. Then the paths where the P-polarized light and S-polarized light pass from the separation point of the polarized light separating means to the composition point of the polarized light composing means become equal in length. Light beam which are incident through optical fibers 12 and 12b are therefore dispersed by the polarized light separating means, passed through the cell 1, and put together by the polarized light composing means. Then the paths of the P-polarized light and S-polarized light which enter the optical fibers 12a and 12c are equal, so the incident signal are transmitted as projection signals as they; are. Consequently, the code error generation can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical changeover switch that switches optical paths by utilizing changes in the arrangement state of liquid crystal molecules.

<Prior Art> FIG. 6 shows the structure of a conventional crossbar type 2x2 type optical changeover switch using liquid crystal.

In the figure, 1 is a cell in which a nematic liquid crystal is sealed in a glass electrode, 2.2a is a polarizing beam splitter, 3.
3a is a polarizing film; 4, 4a;

4b and 4c are reflective films, 5, 5a, 5b, and 5c are rod lenses, and 6, 6a, 6b, and 6c are optical fibers.

In such an optical changeover switch, when transmitting an optical signal from the optical fiber 6 to the optical fiber 6a and from the optical fiber 6b to the optical fiber 6C in a bar state, a voltage is applied to the cell 1. In this state, the optical signal of the optical fiber 6 passes through the rod lens 5 and is divided into a P-polarized signal that travels straight at the F)jy11 optical film 3 and an S-polarized signal that heads toward the reflective film 4. Then, the P polarized light signal passes through the cell 1° polarizing film 3a and the rod lens 5a and enters the optical fiber 6a, and the S polarized light signal passes through the reflective film 4° and cell 12 reflective film 4a, is reflected by the polarizing film 3a, and is reflected by the rod lens. 5a and enters the optical fiber 6a as well. On the other hand, the optical signal of the optical fiber 6b is transmitted to the rod lens 5.
It is reflected by the reflective film 4b, and is divided into a P polarized light signal and an S polarized light signal by the polarizing film 3. Then, the P-polarized light signal is transmitted to the reflective film 4. Cell 12 reflective film 4apa optical film 3a.

The S-polarized signal passes through the anti-Itllff 4c and the O-twin lens 5c, enters the optical fiber 6c, and enters the cell 1. Polarizing film 3 a
, reflective film 4c, and optical fiber 6C passing through the orad lens 5C.
to go into.

Furthermore, in the liquid crystal optical changeover switch, when transmitting an optical signal from the optical fiber 6 to the optical fiber 6C and from the optical fiber 6b to the optical fiber 6a in a cross state, by not applying voltage to the cell 1, optical fiber 6
Polarization of the optical signal! [The P and S polarized signals separated by 3 are converted into opposite polarization states when they pass through the cell 1, and the optical signals converted into the S polarization state are sent to the polarizing film 3a,
Reflective film 4c.

The optical signal passed through the rod lens 5C and into the optical fiber 6C, and the optical signal converted into the P polarization state is transmitted to the reflective film 4a, the polarizing film 3a, and the reflective film 4c.

It also passes through the rod lens 5C and enters the optical fiber 6C.

The optical signal of the optical fiber 6b also enters the optical fiber 6 through a similar process, and a cross state is formed.

<Problem to be solved by the invention> In the optical changeover switch according to the above-mentioned prior art, the P is divided into two in both the bar and cross states.
Since the lengths of the paths taken by polarized light and S-polarized light are different, when the optical signal reaches true speed, connecting these switches in series in multiple stages increases the pulse width of the signal and reduces code errors. There were drawbacks that occurred.

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, an object of the present invention is to provide a liquid crystal optical changeover switch that prevents the spread of optical signal pulse width and can be used for high-speed, high-bit-rate optical signal transmission.

Means for Solving the Problems> The configuration of the present invention that achieves the above object includes a polarization separation means constituted by a polarization beam splitter and a total reflection means, and a Plil destination light polarized light separated by the polarization separation means. a liquid crystal cell arranged so as to allow the light to enter the cell, a polarization beam splitter and a total reflection means, and a polarization combining means to which the light passing through the cell is incident; and a polarization separation means for inputting light from the outside to the polarization separation means. In a liquid crystal light changeover switch equipped with a pair of optical fibers and a rod lens, and a pair of optical fibers and a rod lens for extracting light from the polarization combining means to the outside, the polarization combining means The polarized light separating means, the cell, and the polarized light combining means are arranged so that the lengths of the paths taken by the P-polarized light and the S-polarized light to the synthesis point are equal, and the optical path is switched by a voltage applied to the cell. The present invention is characterized in that a plurality of such liquid crystal optical changeover switches are connected in series.

According to the present invention having the above configuration, the light incident through the optical fiber is dispersed by the polarization separation means, passed through the cell, and combined by the polarization synthesis means, and then the Pi-directed light beam enters the optical fiber. Since the paths of the S-polarized light are equal, the input signal is transmitted as is as the output signal.

<Example> Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. As shown in the figure, 7 is a cell in which a nematic or ferroelectric liquid crystal is sealed in a glass electrode, 8.8a is a polarizing beam splitter, 9.9a is a polarizing film, 10.10a is a reflecting prism, 11. lla, llb, llc are rod lenses,
12. IZa, 12b, and 12c are optical fibers. At this time, the polarization beam splitter 8 and the reflection prism 10, which is a total reflection means, form a polarization separation means, and the polarization beam splitter 8a and the reflection prism 10a form a polarization synthesis means, respectively. The polarizing beam splitters 8, 8a are cube-shaped with the same dimensions, and the reflecting prism 10.10a is an isosceles right triangular prism, and the length of the sides that sandwich the right angle is the same as the length of one side of the polarizing beam splitters 8, 8a. . Rod lens 11. 11 a, 11
b.

The 1101 polarizing beam splitters 8 and 8a, the reflecting prisms 10 and 10a, and the self-reflecting prisms are firmly bonded to each other by a refractive index matching adhesive so that there are no gaps, shifts, or inclinations.

In this embodiment having such a structure, the optical fibers 12 and 12b are used as input ports, and the optical fibers 12c and 1
The bar and cross state connections shown in FIGS. 2(a) and 2(b) with 2a as the output port can be switched by applying or not applying voltage to the self.

The operation when using a nematic liquid crystal as the liquid crystal is as follows.
In the bar state shown in Figure (a), no voltage (AC) is applied to the self, so that the optical signal from the optical fiber 12 passes through the rod lens 11 and becomes a P-polarized signal that travels straight through the polarizing film 9. , the reflected Sa1S polarization signal is separated. Among these, the PG optical signal is reflected by the reflecting prism 10, passes through the self-contained light beam, is converted into S-polarized light, is reflected by the polarizing film 9a, passes through the rod lens lie, and is connected to the optical fiber 12C.
Get into it. On the other hand, the 5jyf4 optical signal separated by the polarizing film 9 is converted into P-polarized light through a self-contained beam, and then passes through the reflecting prism 10a.
The light is reflected by the polarizing film 9a, passes through the rod lens llc, and enters the optical fiber 12c. In addition, the optical fiber 12
The optical signal from b is divided into a P-polarized light signal that passes through the rod lens llb and travels straight through the polarizing film 9, and an S-polarized light signal that is reflected. Of these, the P-polarized signal passes through the self-converter and is reflected by the reflecting prism 10a where it is converted into S-polarized light, and then reflected by the polarizing film 9a, passes through the rod lens lla, and enters the optical fiber 12a. On the other hand, the S-polarized light 41 reflected by the polarizing film 9
After being reflected by the reflective prism 10, the signal passes through the self-light beam, passes through the polarizing film 9a, is converted into P-polarized light, passes through the polarizing film 9b, the rod lens lla, and enters the optical fiber 12a.

Next, in the crossed state shown in FIG. Of these, the P-polarized signal is reflected by the reflection prism 10, passes through the self-polarized light, goes straight through the polarizing film 9a as P-polarized light, passes through the rod lens 11a, and enters the optical fiber 12g. , the S-polarized light signal separated by the polarizing film 9 passes through the self-portion, is reflected by the reflection prism 10a as S-polarized light, and is further polarized by the polarized light i9a.
and passes through the rod lens lla to the optical fiber 12
Enter a. The optical signal from the optical fiber 12b is divided into a P-polarized signal that passes through the rod lens llb and goes straight on the polarizing film 9, and an S-polarized signal that is reflected. The light passes straight through the polarizing film 9a, passes through the rod lens llc, and enters the optical fiber 12c. On the other hand, the S-polarized light signal separated by the polarizing film 9 is reflected by the reflecting prism 10, and then passes through the polarizing film 9a.
reflected by the optical fiber 12 and passes through the rod lens llc.
Enter c.

Next, when using a ferroelectric liquid crystal as the liquid crystal, the operation is the same as in the case of a nematic liquid crystal, such as polarization separation/synthesis, switching of the light path by the liquid crystal cell, etc., but the par state and the cross state The difference is that the form of the voltage applied when switching is different, and that the switched state is maintained.

FIG. 3 shows an example of the voltage applied to the liquid crystal cell. Figure 3 (
The case of nematic liquid crystal is shown in a), and the case of ferroelectric liquid crystal is shown in Fig. 3 (bl) and Fig. 3 (C1). In the case of an enhanced F4 liquid crystal, in order to obtain two stable states, the amplitude of one pulse of the alternating voltage is increased on the + side, or the amplitude on the - side is By applying one of these pulses, one of the states can be selected, and the selected state has the opposite sign. It is held until a pulse with an amplitude equal to or greater than the threshold is applied.

The operation described above provides connections in the bar and cross states, but since the length of the path taken by the optical signal from the input port to the output port within the switch is the same in any state, the optical pulse is generated at the output port. The pulse width does not widen due to the deviation. Furthermore, when a ferroelectric liquid crystal is used as the liquid crystal, voltage need only be applied when changing the connection state, and power is not constantly consumed.

FIG. 4 is a block diagram showing a second embodiment of the present invention. In the same figure, 13, 13a are optical fiber transmission lines wired in a loop, star, or path shape; 14, 14a, 1
Reference numeral 4b denotes an optical changeover switch similar to that of the previous embodiment, and these optical changeover switches are ±14.14a and 14a.

Reference numeral 14b indicates that the input or output surfaces of the polarized beam connectors 8 and 8a described in conjunction with the first embodiment are physically and optically connected to each other by bonding with a refractive index matching adhesive. The optical changeover switches 14, 14a, and 14b have the function of taking out and inputting optical signals from the optical fiber transmission line 13, and have the function of taking out and inputting optical signals from the optical fiber transmission line 13.
By connecting various terminals to 5b, various terminals can access the optical fiber transmission line 13.

In such a configuration, an optical fiber pair of 15° and 15 m,
Depending on the circumstances of the terminals connected to 15b, it is often necessary to disconnect some or all of them from the transmission path. The embodiment shown in FIG. 4 can deal with all of them.

First, in order to bring all the terminals into the connected state, all of the optical changeover switches 14, 14a, and 14b may be set to the bar state, and the flow of optical signals at that time is shown in FIG. 5(a).

Next, if you want to disconnect only the terminal connected to the optical fiber pair 15a, set only the optical changeover switch 14a to the cross state, and the signal flow as shown in FIG. can be separated from the transmission line 13.

Furthermore, if you want to disconnect all the terminals, you can set all the optical changeover switches 14 to 14b to the cross state to create a signal flow as shown in Figure 5 tc+, and disconnect by this. . Of course, no matter which operation shown in FIG. 5 is performed, the optical fiber transmission line 1
3.13a, there is no effect on the operation of optical changeover switches similar to those shown in FIG.

As is clear from the above results, in the optical changeover switches 14 to 14b of this embodiment, even if the number of optical changeover switches is increased, especially in the case as shown in FIG. 5(C),
Since the path lengths of the two types of polarized light are the same, the pulse width of the optical signal does not widen. Incidentally, in conventional optical switches, although the spread of the pulse width is relatively small when there are only a few switches, when multiple switches are connected in series, differences in the length of the optical path accumulate. The pulse width becomes very wide.

<Effects of the Invention> As specifically explained above in conjunction with the embodiments, the liquid crystal optical changeover switch of the present invention outputs the input optical signal pulse while maintaining its width. Therefore, there is a strong demand for the mutual transmission of ultrahigh-speed optical signal pulses with very short pulse widths and space intervals between many terminals. It is possible to perform signal transmission that guarantees high reliability with fewer code errors caused by the transmission.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an optical changeover switch according to a first embodiment of the present invention, FIG. 2 is an explanatory diagram showing the connection between a bar state and a cross state, and FIG. 3 is an illustration showing the form of voltage applied to a liquid crystal cell. FIG. 4 is a configuration diagram showing a second embodiment of the present invention in which a plurality of second optical changeover switches of the present invention are connected in series to a transmission line, and FIG. 5 is a waveform diagram showing the optical changeover switch of the present invention. FIG. 6 is an explanatory diagram showing the flow of optical signals when a plurality of optical switches are connected in series, and FIG. 6 is a configuration diagram of a conventional optical changeover switch using a nematic liquid crystal. In the drawing, 1...Cell, 2, 2a...Polarizing beam splitter,
3p 3a=-m light film, 4, 4a, 4b. 4 c - reflective film, 5, 5 a, 5 b, 5 c - rod lens, 6, 6 a, 6 b, 6 c - optical fiber, 7 - cell, 8.8 a - polarized beam Splitter, 9.9a = polarizing film, 10, 10a...reflection prism, 11. lla, llb. 11c...rod lens, 12, 12a, 12b. 12c... Optical fiber, 13, 13a... Optical fiber transmission line, 14, 14a, 14b - Optical changeover switch, 1
5, 15a, 15b--optical fiber pairs. Figure 1 Figure 3 Figure 2 Figure 4 Figure 5 (Q) Figure

Claims (2)

[Claims] (1) A polarized light separating means composed of a polarizing beam splitter and a total reflection means, a liquid crystal cell arranged so that the P-polarized light and the S-polarized light separated by the polarized light separating means can respectively enter, and the polarized beam A polarized light combining means which is composed of a splitter and a total reflection means and into which the light that has passed through the cell is incident; a pair of optical fibers and a rod lens for making light enter the polarized light separating means from the outside; and light from the polarized light combining means. In a liquid crystal optical switch equipped with a pair of optical fibers and a rod lens for extracting the polarized light to the outside,
The polarized light separating means, the cell, and the polarized light combining means are arranged so that the lengths of the paths passed by the polarized light and the S-polarized light are equal, and the optical path is switched by a voltage applied to the cell. LCD light selector switch. (2) A liquid crystal optical changeover switch according to claim 1 is characterized in that one of the incident surfaces of the polarization separation means and one of the output surfaces of the polarization synthesis means are directly bonded to each other to connect a plurality of them. LCD light selection switch group.