JPS61113032A - By-pass optical switch - Google Patents

Abstract

PURPOSE:To reduce the size and the electric power consumption of a by-pass optical switch and to increase its reliability by using liquid-crystal cells as a switching element. CONSTITUTION:A nonpolarization beam splitter 24, a beam splitter 25 for polarization demultiplexing which separates incident signal light into two orthogonal polarized light components, a liquid-crystal cell 29 which transmits incident linear polarized light while rotating its plane of polarization by 90 deg. or transmits it as it is according to an external applied voltage, and a beam splitter 26 for polarization multiplexing which multiplexes linear polarized light transmitted through the liquid-crystal cells are arranged in a line along the optical axis of the image formation optical system wherein convergent rod lens 11 and 12 are arranged opposite each other. Further, right-angled prisms 27 and 28 and convergent rod lenses 19 and 22 are arranged in contact with the beam splitters for polarization demultiplexing and polarization multiplexing.

Description

[Detailed description of the invention] [Industrial application field] This invention uses a liquid crystal cell as an active medium.

The present invention relates to an electronic bypass optical switch for switching and connecting one of optical signals transmitted through two optical fibers to an output optical fiber using an external control signal.

[Conventional technology]

Recently, communication terminals and information processing terminals installed within a limited area, such as within the same building or the same factory site, are connected via optical fiber communication lines to make a single communication.

Optical LAN (0pti) is used as a network for information processing.
A system called "cal local area network" has been put into practical use.

Examples of such optical LAN configurations include star configuration, bus configuration, loop configuration, and ring configuration. - As an example, an optical LAN system with a loop configuration is shown in FIG. FIG. 5 is a block diagram showing a conventional loop-configured optical LAN system. The basic configuration of this optical LAN system is that a control station 1 and a plurality of terminal stations are connected in a ring with an optical fiber 2.Here, for convenience of explanation, terminal station A (3)
, terminal station B (4), and terminal station C (5) are illustrated. The control station 1 is comprised of a computer 6 that monitors and controls the communication status, an optical transmitter 7, and an optical receiver 8.

Further, each terminal station A(3) to C(5) processes information.

It is composed of a terminal 9 that performs display, etc., an optical transmitter 7, an optical receiver 8, and a bypass optical switch IO, which will be described in detail later.

In the above-mentioned optical LAN system, in order to maintain high reliability, when a failure occurs in any one of the many terminals 9, a failure isolation method is provided so as not to affect the entire other end station system. It is common to have In order to take measures against such failures, as shown in terminal station C (5), a bypass optical switch I is used to bypass the transmitted optical signal.
0 to pass through terminal station C (5).

FIG. 6 is a configuration diagram showing a bypass optical switch in the optical LAN system of FIG. 5. As shown in the figure, the bypass optical switch having a mechanical configuration has two converging rod lenses 11 and 12 arranged at a specific distance in the optical axis direction.
A one-to-one imaging optical system is formed in which optical fibers FA113 and TAN4 are connected to both ends of each of the converging rod lenses 11 and 12, respectively, and between each of the converging rod lenses 11 and 12, , reflect about 50 beams of signal light parallelized by the focusing rod lens 11,
A moving core 17 with a half mirror 15 that transmits the other 50% and one reflecting mirror 16 is inserted.

In the above optical LAN system, as shown in FIG.
If each terminal 9 is operating normally, the
), a current is applied to the electromagnet 18.

The moving core 17 is moved to the upper position shown in the figure. After converting the signal light transmitted through the optical fiber (a) 13 into parallel light using the converging rod lens 11,
5, the reflected light is incident on a focusing rod lens 19, focused on an optical fiber (e) 20, and received by an optical receiver (not shown in FIG. 1). On the other hand, the light that has passed through the mirror 15 is blocked by the moving core 17 and is not output to the optical fiber (a>14).

The signal light transmitted from the optical transmitter (not shown in the figure) is
Focusing rod lens 22 through optical fiber (bJ 21
After the light is input into the camera and converted into parallel light, the optical path is bent by 90 degrees by a single reflecting mirror 16, and outputted to an optical fiber (DJ 14) by a converging rod lens 12.

Next, as shown in FIG. 5, if a failure occurs in one of the terminals 9, as shown in FIG. Move it to the lower position shown. As explained in FIG. 6(A), about 50% of the signal light transmitted through the optical fiber (al13) is received by the optical receiver.

The other approximately 50% passes through the half mirror 15 and is then output to the optical fiber (d) 14 by the convergent rod lens 12. On the other hand, the signal light transmitted from the optical transmitter.

After being reflected by the reflection mirror 16, it is absorbed by the absorber 23 and is not output to the optical fiber (dH4).

[Problem that the invention seeks to solve]

In the mechanical bypass optical switch used in the conventional optical LAN system as described above, the moving core 17 is moved using the electromagnet 1B, so the device itself is large and consumes a large amount of power. There was also a problem that the operating life was short. In addition, half mirror 15 and reflective mirror 1
6 is in contact with the atmosphere, so there were problems such as the reflective film of each mirror being corroded by temperature, gas, etc.

This invention was made to solve this problem, and uses a liquid crystal cell as a switching element,
The object of the present invention is to obtain an optical bypass optical switch which is an electronic bypass optical switch without moving parts, and which achieves miniaturization, low power consumption, and high reliability of the device itself.

[Means for solving problems]

The bypass optical switch according to the present invention has an optical axis of an imaging optical system in which first and second converging rod lenses are arranged facing each other at both ends of an input optical fiber a and an output optical fiber d, respectively. Along the line, there is a non-polarizing beam splitter having a predetermined transmittance and reflectance, a polarization separation beam splitter that separates the incident signal light into two orthogonal polarized lights, and a polarization plane of the incident linearly polarized light by an externally applied voltage. A liquid crystal cell that transmits the linearly polarized light while rotating it by 90 degrees or transmits it as is, and a beam splitter for polarization synthesis that polarizes and synthesizes the linearly polarized light that has passed through this liquid crystal cell are arranged in a row, and the polarized light is polarized with respect to the optical axis. The optical path of the linearly polarized light emitted vertically from the separation beam splitter is bent at right angles.
A first right-angle prism that makes the light enter the liquid crystal cell, and a second right-angle prism that bends the optical path of the linearly polarized light that has passed through the liquid crystal cell at right angles and makes the light enter the polarization combining beam splitter from a direction perpendicular to the optical axis. Placed in contact with each beam splitter for polarization separation and polarization synthesis.

and a third focusing rod lens that outputs the reflected light from the non-polarizing beam splitter to an output optical fiber C, and a fourth focusing rod lens that inputs the reflected light from the input optical fiber B to the polarization separation beam splitter. are arranged in contact with a non-polarization beam splitter and a polarization separation beam splitter, respectively.

[Effect]

In the bypass optical switch of the present invention, a liquid crystal cell is used as a switching element to constitute an electronic bypass optical switch with no moving parts, and by such a bypass optical switch, light transmitted through two optical fibers is By switching and connecting one of the signals to an optical fiber on the output side using an external control signal, the device itself can be made smaller, have lower power consumption, and have higher reliability.

〔Example〕

FIG. 1 is a block diagram showing a bypass optical switch according to an embodiment of the present invention. The same parts as in FIG. 6 are designated by the same reference numerals, and detailed explanation thereof will be omitted. In the figure, 24 is a non-polarizing beam splitter having a predetermined transmittance and reflectance, 25 is a polarization separation beam splitter that separates the incident signal light into two orthogonal polarized lights, and 26 is a polarization-synthesizer of linearly polarized light. Beam splitter for polarization synthesis, 2
7 and 28 are rectangular prisms, and 29 is a liquid crystal cell that transmits incident linearly polarized light while rotating its plane of polarization by 90 degrees or transmits it as is. others.

% focusing rod lens 11 to original fiber (d) 14. The valley focusing rod lens 19 to the absorber 23 are shown in FIG.
N and IB). Here, to simplify the explanation, FIG.

Figure 1 (C1
The input signal light is divided into two parts for each of +DJ and +DJ.

First, the first
Figure FA) and iBl will be explained. As shown in FIG. 1A), the signal light transmitted through the optical fiber +al 13 is converted into parallel light by the converging rod lens 11, and is reflected at a predetermined rate by the non-polarizing beam splitter 24. Optical fiber t using converging rod lens 19
Output to el20. On the other hand, the signal light transmitted through the non-polarizing beam splitter 24 is converted into a P-polarized light component (a linearly polarized light component parallel to the incident plane of each polarized-light separating and polarization-combining beam splitter 25 and 26) by a polarization separating beam splitter 25. The light 30 is separated into light 31, which is an S-polarized light component (a linearly polarized light component perpendicular to the plane of incidence of each of the polarization separation and polarization synthesis beam splitters 25 and 26). P-polarized light 30 and S-polarized light 31 totally reflected by the right-angle prism 27.

The light enters the liquid crystal cell 29. At this time, as will be described in detail later, if a liquid crystal cell 29 is used that has the function of rotating the plane of polarization of the incident linearly polarized light by 90 degrees under the applied voltage vL, then the linearly polarized light transmitted through the liquid crystal cell 29 In the light of , P polarization becomes 8 polarization.

The S-polarized light is each converted to P-polarized light. Among these, the light that has been converted from the 8 polarized lights to the P polarized light is combined by the right angle prism 28, and the light that has been converted from the P polarized light to the S polarized light is combined by the polarization combining beam splitter 26. The parallel light thus synthesized travels in a direction perpendicular to the optical axis passing through each of the converging rod lenses 11 and 12 and is absorbed by the absorber 23.

Next, in FIG. 1+B), the signal light transmitted from the optical transmitter of the local station will be explained. As shown in the figure, the signal light is input from the optical fiber (BL 21).

The light is converted into parallel light by the converging rod lens 22 and input to the polarization separation beam splitter 25, where it is separated into P-polarized light 30 and 8-polarized acid light 31.

When the S-polarized light 31 and the P-polarized light 30 totally reflected by the right-angle prism 27 are incident on the liquid crystal cell 29,
As explained in FIG. 1 (8), since the plane of polarization is rotated by 90 degrees, S-polarized light is converted to P-polarized light, and P-polarized light is converted to S-polarized light. Of these, the light converted from P polarized light to 8 polarized light is totally reflected by right angle prism 4, and the light converted from 8 polarized light to P polarized light is combined with the beam splitter 2 for polarization synthesis.
6 is synthesized. Then, this combined signal light travels in a direction parallel to the optical axis passing through each of the converging rod lenses 11 and 12.

The light is output from the converging rod lens I2 to the optical fiber (d) 14.

Next, fc1 and iDl in FIG. 1, which show states corresponding to the case where a failure occurs in the terminal 9, will be explained. Figure 1 f
As shown in c1, the signal light transmitted through the optical fiber +al 13 is converted into parallel light by the convergent rod lens 11, and then converted into non-polarized light, in exactly the same way as explained in Figure 1 tA). It is reflected and transmitted by the beam splitter 24 at a predetermined ratio, one of which is reflected by the focusing rod lens 1.
9 to an optical fiber tc+ 20, and the transmitted light is output to a beam splitter 25 for polarization separation. The parallel light input to the polarization separation beam splitter 25 is P
The light is separated into polarized light 30 and light 31 of eight polarized acids. P-polarized light 30 and S-polarized light 31 totally reflected by the right-angle prism 27.

The light enters the liquid crystal cell 29. At this time, when a voltage vH is applied to the liquid crystal cell 29, the incident linearly polarized light is transmitted through the optical surface without changing, as will be explained in detail later.

2 sets'13- 1 Kunru. Therefore, the light 31 of 8 polarized acids transmitted through the liquid crystal cell 29 is totally reflected by the right angle prism 28.

P-polarized light component 30 and beam splitter 26 for combining polarized light
When combined, the combined parallel light travels in a direction parallel to the optical axis passing through each convergent rod lens 11 and 12, and is outputted to an optical fiber (d) 14 by the convergent rod lens 12. be done.

Next, in FIG. 1(D), since a failure has occurred in the terminal 9, the signal light from the optical transmitter of the own station is normally not transmitted, but if noise-like light is transmitted, , the light input from the optical fiber (BL 21).

The light is converted into parallel light by the converging rod lens 22.

The polarization separation splitter 25 separates the light into P-polarized light 30 and 8-polarized acid light 31. At this time, a voltage vH is applied to the liquid crystal cell 29, and the incident linearly polarized light is only transmitted without changing its polarization plane.

P-polarized light 30 is passed through two right-angle prisms 27 and 28.
The beam splitter 26 for polarization synthesis repeats total reflection at
On the other hand, the S-polarized light component 31 travels straight and is input into the polarization combining beam splitter 26.
4- The light of people is synthesized. Then, this combined light travels in a direction perpendicular to the optical axis passing through each convergent rod lens 11, 12, is absorbed by the absorber 23, and passes through the optical fiber (
d) There is no output on 14.

In the above explanation, the signal light transmitted through the optical fiber (AL 13) and the signal light transmitted from the optical transmitter of the local station were explained separately, but in reality, two signal lights are transmitted at the same time. This is what is input.

FIG. 2 is a configuration diagram showing an example of a liquid crystal cell that is a switching element of the bypass optical switch shown in FIG. 1.

The liquid crystal cell 29 shown in the figure has a twisted nematic cell (TN cell) configuration, and as shown in the figure,
A spacer 34 made of a material such as a polymer compound is inserted between a glass substrate 33 on which a transparent electrode 32 such as In2O, -8nO, or a film is deposited, and the spacer 34 is made of a material such as a polymer compound. 35 type nematec liquid crystal molecules are enclosed. In a state where a voltage vL as shown in FIG.
It is set so that it twists 90' in between. In this state,
When the plane of polarization of the linearly polarized light incident on the long sleeve alignment direction of the L-type nematec liquid crystal molecules 35 is made parallel or perpendicular.

The plane of polarization rotates according to the twist of the upper nematic liquid crystal molecules 35, and rotates exactly 90 degrees between the input and output planes.

Next, when voltage vH is applied between the transparent electrodes 32 of this liquid crystal cell 29, as shown in FIG. Since the signal light is oriented parallel to , the signal light is transmitted without changing its plane of polarization.

FIG. 3 is a configuration diagram showing another modification of the liquid crystal cell which is the switching element of the bypass optical switch shown in FIG. 1. The liquid crystal cell 29 shown in FIG. This is a π cell configuration that utilizes the condition that π. In the figure, the transparent electrode 32 to the G-type nematic liquid crystal molecules 35 are exactly the same as those explained in FIG. 2 above. Figure 3 (voltage vL as shown in N)
In the state where 1g upper matic liquid crystal molecules 3
Oblique deposition or rubbing treatment is performed so that the long axis of the glass substrate 5 forms a tilt angle ψ of several degrees with respect to the glass substrate 33, and the glass substrate 33 is set to have a tilted orientation on both sides.

FIG. 4 is a diagram showing the operating principle of the liquid crystal cell having the π cell configuration shown in FIG. As shown in the figure, the long axes of the P-type nematic liquid crystal molecules 35 are arranged in a direction at an angle of 45° with respect to a direction parallel or perpendicular to the polarization plane of the incident linearly polarized light, and the linearly polarized light is incident light. As shown in FIG. 4, the long axes of the upper nematic liquid crystal molecules 35 are uniformly aligned from z=0 to z=d by 45 degrees with respect to the X and y axes.
It is oriented at an angle of .degree., and linearly polarized light 36 whose polarization direction is parallel to the X axis is incident on it in biaxial directions. At this time,
When o<z<ct, the electric field components in the X-axis and y-axis directions are EX.

When expressed as Ey, Ex and Ey have the following relationship.

However, Eo is the electric field strength* "lS e" is the refractive index of the upper nematic liquid crystal molecule 35 in the long- and short-axis directions, respectively.

λ is the wavelength, and δ is the retardation. Depending on the value of δ, as linearly polarized light propagates in the z-axis direction, the polarization state changes from ellipse to ellipse to linearly polarized light, as shown in Figure 4. The direction of linearly polarized light also changes.

That is, if the refractive index (n, -n□) in the long and short axis directions of the 1g upper matic liquid crystal molecule 35 and the thickness d of the liquid crystal layer are set to appropriate values so that δ=π, the liquid crystal cell 2
The plane of polarization of linearly polarized light that passes through 9 can be rotated by 90 degrees.

Next, when voltage vH is applied between the transparent electrodes 32 of the liquid crystal cell 29, as shown in FIG.
Because the long axis of is oriented parallel to the electric field direction.

The signal light is transmitted without changing its polarization plane.

As explained above, the bypass optical switch according to the present invention uses the liquid crystal cell 29 as a switching element, and can achieve a predetermined operation by simply switching the voltage applied to the liquid crystal cell 29, unlike the conventional mechanical bypass optical switch. As there are no moving parts, it has a long lifespan,
Further, since the power consumption is only about 1 μW, low power consumption can be achieved.

Furthermore, each convergent rod lens 11 which is a component,
The dimensions of 12, 19, and 22 are approximately 2 mm in diameter and 6 mm in length, and the beam diameter when converted into parallel light using a stiff focusing rod lens is approximately 2 mm or less. ,
Non-polarizing beam splitter 24. The length of each side of the beam splitters 25 and 26 for polarization separation and polarization synthesis, and the 1n-angle prisms 27 and 28 can be reduced to about 3 mm, and the device itself can be made smaller.

Furthermore, a non-polarizing beam splitter 24. The reflective films of the beam splitters 25 and 26 for polarization separation and polarization synthesis are joined by two right-angle prisms 27 and 28, so they do not come into contact with the atmosphere, and the bypass light has excellent moisture and corrosion resistance. A switch can be realized.

): In the embodiment described above, a case has been described in which the bypass optical switch is applied to an optical LAN system with a loop configuration. However, the present invention is not limited to this, and can be applied to optical LAN systems such as a bus configuration and a ring configuration. Usable.

〔Effect of the invention〕

As explained above, this invention uses a liquid crystal cell as a switching element in a bypass optical switch, and has an electronic bypass optical switch structure with no moving parts. In comparison, the device itself can be made smaller, have a longer lifespan, have lower power consumption, and have higher reliability, and also has the excellent effect of realizing a bypass optical switch with good moisture and corrosion resistance. It is.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a bypass optical switch which is an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a liquid crystal cell which is a switching element of the bypass optical switch of FIG. 1, and FIG. , FIG. 4 is a diagram showing the operating principle of the liquid crystal cell having the π cell configuration shown in FIG. 3, and FIG. is a conventional loop-configured optical LAN
FIG. 6 is a block diagram showing a bypass optical switch in the optical LAN system of FIG. 5. FIG. In the figure, 11, 12, 19, 22... focusing rod lenses, 13, 14, 20, 21...
・Optical fiber, 24...Non-polarizing beam splitter, 2
5...Beam splitter for polarization separation, 26...Beam splitter for polarization synthesis, 27, 28...Right angle prism, 29...Liquid crystal cell, 30...P polarization component light, 3
1... S-polarized light component, 32... Transparent electrode, 33.
. . . Glass substrate, 34 . . . Spacer, 35 . . . Shaped nematec liquid crystal molecules. In each figure, the same reference numerals indicate the same or equivalent parts.

Claims (3)

[Claims] (1) Out of the signal light input from the two input optical fibers a and b, part of the signal light input from the input optical fiber a is outputted to the constant output optical fiber c, A bypass optical switch that outputs either the remaining signal light of the signal light or the signal light input from another input optical fiber b to another output optical fiber d according to an external control signal. In the input optical fiber a
and a first and second optical fiber at both ends of the output optical fiber d, respectively.
A non-polarizing beam splitter having predetermined transmittance and reflectance separates the incident signal light into two orthogonal polarized lights along the optical axis of the imaging optical system, which has converging rod lenses arranged facing each other. a beam splitter for polarization separation; a liquid crystal cell that rotates the plane of polarization of incident linearly polarized light by 90 degrees and transmits it or transmits it as is by an externally applied voltage;
A beam splitter for polarization synthesis that polarizes and synthesizes the linearly polarized light transmitted through this liquid crystal cell is arranged in a row, and an optical path of the linearly polarized light emitted from the beam splitter for polarization separation in a direction perpendicular to the optical axis is arranged. a first rectangular prism that is bent at a right angle and made to enter the liquid crystal cell; and a first right angle prism that bends the optical path of the linearly polarized light that has passed through the liquid crystal cell at a right angle and makes it enter the polarization combining beam splitter from a direction perpendicular to the optical axis. a third rectangular prism arranged in contact with each of the beam splitters for polarization separation and polarization synthesis, respectively, and outputs the reflected light from the non-polarization beam splitter to the output optical fiber c. A focusing rod lens and a fourth focusing rod lens input from the input optical fiber b to the polarization separation beam splitter are arranged in contact with the non-polarization beam splitter and the polarization separation beam splitter, respectively. A bypass optical switch characterized by: (2) The liquid crystal cell is a twisted nematec cell in which the long axes of nematec liquid crystal molecules are oriented parallel or perpendicular to the polarization plane of the incident straight light beam and twisted by 90 degrees between two glass substrates. 2. A bypass optical switch according to claim 1, characterized in that a liquid crystal cell having the following structure is used. (3) The liquid crystal cell is oriented at 45 degrees with respect to the polarization plane of the incident linearly polarized light, and the long axes of the nematic liquid crystal molecules are oriented in a certain direction between the two glass substrates, and the two orthogonal incident polarized lights are The bypass optical switch according to claim 1, characterized in that a liquid crystal cell having a π cell configuration that generates a condition where the phase difference is π is used.