JPH0380636A - Optical signal switching method and optical signal transmission line - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is applied to an optical signal transmission line for transmitting optical signals using an optical fiber cable. In particular, it relates to a method for switching an optical signal propagating through one optical fiber to another optical fiber without momentary interruption.

The present invention provides an optical signal switching method for switching the propagation path of an optical signal from a working optical fiber to a backup optical fiber.On the transmitting side, the signal light is linearly polarized and continuously branched steplessly, and on the receiving side, By adjusting the optical path length so that the propagation time of the signal light through the two optical fibers matches and making the polarizations of the two signal lights orthogonal and combining them, no bit errors occur in the transmitted signal and there is no interruption. This is used to switch the optical signal transmission path.

[Conventional technology]

When an optical cable that has already been installed reaches the end of its useful life, it becomes necessary to replace the old cable with a new one. At this time, the optical fiber in the cable in use (hereinafter referred to as "cable A") is reconnected to the optical fiber in the new cable (hereinafter referred to as "cable B"), and then cable A is removed.

Traditionally, switching between optical fibers was done manually by first confirming that no signals were being transmitted. In this operation, the optical fiber of cable A is simply cut and the optical fiber of cable B is fusion-spliced, or the connection portion is connected in advance with a connector and then reconnected. Furthermore, recently, devices have been announced that automatically connect/detach connectors and change connections. With this device, the time required to connect and disconnect connectors is significantly reduced by mechanization compared to manual work, and the time required for signal interruption is reduced to 0.
It can be shortened to about 1 second.

[Problem to be solved by the invention]

However, during the fiber switching, communications for subscribers using cable A are interrupted. To avoid this, conventionally, a date and time is set that will have less negative impact on subscribers, and their consent is obtained not to use the service during that time. However, since it is generally undesirable for wires to be disconnected for a long period of time, it was necessary to take construction measures such as carrying out construction work late at night.

For this reason, there was a drawback that construction work could not be carried out systematically and efficiently.

Even when using a device that automatically connects and disconnects connectors,
The manual work is simply mechanized, and the signal interruption during switching is essentially the same.

With current technology, high-speed transmission of 1.8 Gb/s has also been put into practical use, but at this speed, 0.1 seconds of signal loss will result in zero transmission.
．． 1 second x 1.8 Gb/s = 180 Mb of information loss, which is unacceptable. Therefore, the above-mentioned problems are not solved at all.

When transmitting electrical signals using copper wire cables, methods are already known for seamlessly switching without causing signal errors. In this method, an existing signal transmission line (hereinafter referred to as "copper line A") is replaced with another copper line (hereinafter referred to as "copper line A").
This is connected by contacting it with the copper wire (hereinafter referred to as "copper wire B").

Since both are copper wires, this connection is easy. A variable electrical resistor is attached to copper wire B, and the resistance is initially set to infinity. After installing the copper wire B as a detour route, the resistance of the copper wire B is gradually reduced using a variable resistor. If the resistance of the copper wire B is made smaller than the resistance of the copper wire A, the signal can substantially pass through the copper wire B. After this, the copper wire A is cut.

Although this method is effective for copper wire, there is no method corresponding to the above process for optical fiber. There is no known method of connecting another optical fiber to the side of a signal-carrying optical fiber with low loss and without signal errors. There is also no known method for gradually changing the optical loss within an optical fiber in response to changes in electrical resistance so that the optical loss is smaller than that in the optical fiber during signal transmission. Even if these become possible, the state of propagation of light in an optical fiber is different from the state of propagation of electrical signals in a copper wire, so it is unclear in what state a signal error will occur.

Therefore, it is technically difficult to apply the method described above for copper wires to optical fibers.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide an optical signal switching method for switching an optical signal propagating through one optical fiber to another optical fiber without momentary interruption. A further object of the present invention is to provide an optical signal transmission line suitable for use in this switching method.

[Means to solve the problem]

The first aspect of the present invention is an optical signal switching method, in which the optical branching means and the optical multiplexing means of a working optical fiber are provided with an optical branching means and an optical multiplexing means on the transmitting side and the receiving side, respectively. The input end and the output end of the optical fiber for use are connected, and the signal light is branched so that the signal light propagating to the working optical fiber and the backup optical fiber respectively become linearly polarized light. 4i: The optical path length is adjusted so that the transmitted signal lights reach the optical multiplexing means at the same time, and the polarization of the light incident on the optical multiplexing means is perpendicular to each other. The power of the signal light branched from the fiber to the backup optical fiber is increased, and the working optical fiber is removed from the optical branching means and the optical multiplexing means in a state in which substantially all the signal light power propagates through the backup optical fiber.

Next, the input and output ends of the optical fibers of the new optical fiber cable are connected to the optical branching means and the optical multiplexing means, respectively, so that the signal light propagating to the spare optical fiber and the optical fiber of the new optical fiber cable, respectively, is substantially The optical path length is adjusted so that the signals propagated to the spare optical fiber and the optical fibers of the new optical fiber cable reach the optical multiplexing means at the same time, and the optical multiplexing means is split into linearly polarized light. While controlling the polarizations of the incident light beams to be orthogonal to each other, the signal light power branched from the spare optical fiber to the optical fiber of the new optical fiber cable is increased, so that substantially all the signal light power is The spare optical fiber is removed from the optical branching means and optical multiplexing means while propagating through the optical fiber of the new optical fiber cable.

A second aspect of the present invention is an optical signal transmission line suitable for the above method, which includes at least two optical fibers for signal transmission and backup, and two optical fibers for signal transmission and backup on the transmitting side. An optical branching means to which the fibers can be connected and branches the signal light to these two optical fibers, and a receiving side to which the two optical fibers can be connected and to combine the signal lights propagated to each of the two optical fibers. In the optical signal transmission line equipped with an optical multiplexing means, the optical branching means includes a branching ratio control means for changing the branching ratio to the two optical fibers, and the optical branching means substantially controls the signal light propagating in each of the two optical fibers. a linear polarizing means for adjusting the light to linearly polarized light; an optical path length difference adjusting means for adjusting the optical path length so that the propagation times of the signal light through the two optical fibers substantially match; and an optical multiplexing means from the two optical fibers. It is characterized by comprising a polarization control means for making the polarizations of the incident signal lights orthogonal to each other.

The branching ratio control means can be obtained by using an acousto-optic optical deflection element or a hologram element having optical deflection characteristics.

The linear deflection means is preferably provided before the optical branching means 5), but it may be provided on each of the two optical fibers.

The optical path length difference adjustment means includes means for determining the correlation between the waveforms of the signal lights emitted from the two optical fibers, and means for adjusting the length of at least one of the optical fibers so that this correlation is maximized. is desirable. It is desirable that the means for adjusting the length of the optical fiber changes only the length of the backup optical fiber without changing the length of the signal transmission optical fiber.

As means for adjusting the length of an optical fiber, there are methods that extend and contract the optical path length by applying tension or compression force in the axial direction of the optical fiber, and methods that use materials whose refractive index changes electrically. It's easy.

However, with this structure, the optical path length that can be changed is limited. Therefore, it is desirable to include a plurality of delay leading waveways and a coupling means for cascade-connecting a selected number of delay leading waveways from the plurality of delay leading waveways.

In the configuration using this delay leading wavepath, the optical path length can be varied over a wide range by increasing the number of cascade-connectable waveguides. However, it is not possible to adjust the optical path length shorter than the length of the delay optical waveguide.

Therefore, it is desirable to perform fine adjustment by expanding and contracting the optical fiber in the axial direction, or by using a material whose refractive index changes electrically.

Furthermore, in a configuration using a delay optical waveguide, signal attenuation may occur due to the delay optical waveguide or coupling means. Therefore, it is desirable to use a fiber type optical amplifier as the delay optical waveguide.

For example, an optical fiber doped with erbium Er can be made with a wavelength of 1.48 μm by inputting a pump light with a wavelength of 1.48 μm.
．． It is possible to amplify signal light of 55 μm.

[For production]

By using an acousto-optic optical deflection element or a hologram element having optical deflection characteristics, signal light can be switched from one optical fiber to another optical fiber. On the receiving side, the signal lights propagated through the two optical fibers are combined.

As a result, regardless of the ratio of the optical power propagating through the two optical fibers, the total optical power reaching the receiving side remains approximately constant, excluding the loss caused by multiplexing and demultiplexing. Therefore, in the process of detouring almost all of the signal light power to the bypass, there is no significant change in the received light power. Therefore, by transferring almost all of the signal light of the working optical fiber to the backup optical fiber, the original working optical fiber can be disconnected.

After completing this process, connect the optical fiber of another new cable and use the same operation to switch the signal from the spare optical fiber to the new optical fiber. By executing this for all optical fibers in the cable, the cable can be replaced without any interruption.

At this time, if signal lights propagated through two optical fibers are simply combined on the receiving side, bit errors will occur due to the difference in arrival time of the optical signals and fluctuations in received light power due to interference between optical signal waves.

The difference in arrival time of the optical signals is caused by the difference in length between the two optical fibers. When two optical signals with a difference in arrival time are combined, the desired signal waveform cannot be obtained even though the power hardly changes. Therefore, in the present invention, at least one of the
Desirably, the arrival time difference is offset by controlling the optical path length of the backup optical fiber.

Furthermore, interference between signal waves in the form of sound waves occurs because two signals take different paths and are subjected to different external stresses and temperature changes, resulting in temporal phase fluctuations. Although this phase variation is not large, it generates a beat due to multiplexing, resulting in a large variation in the received light power.

In order to avoid this, in the present invention, the signal light is made linearly polarized in advance on the transmitting side, and the polarizations of the two optical signal waves are made orthogonal on the receiving side. As is well known, two orthogonal waves do not interfere, and the sum of their powers can be obtained.

In this way, the signal propagation path can be switched without momentarily interrupting the signal propagating through the optical fiber and without causing signal bit errors.

〔Example〕

1 and 2 show the structure of an optical signal transmission line according to an embodiment of the present invention and an optical signal switching method using this transmission line.

This optical signal transmission path includes optical fibers 4-1 to 4-n for signal transmission connected between optical signal transmitters 1-1 to l-n and optical signal receivers 2-1 to 2-n. and a spare optical fiber 8, and these optical fibers 4-1 to 4-n and 8 are accommodated in one optical fiber cable 3. Furthermore, this optical signal transmission line includes two optical fibers 4-i, 8 (for signal transmission and for backup) on the transmitting side.
i=1 to n) can be connected, and these two optical fibers 4
-i, 8 are provided with uninterrupted optical demultiplexers 5-1 to 5-n as optical branching means for branching signal light, and two optical fibers 4-i, 8 can be connected on the receiving side. Uninterrupted optical multiplexers 6-1 to 5-n are provided as optical multiplexing means for multiplexing signal lights propagated through two optical fibers 4-1.8, respectively.

Optical fibers 4-1 to 4-n for signal transmission are connected between corresponding uninterrupted optical demultiplexers 5-1 to 5-n and uninterrupted optical multiplexers 6-1 to 5-n, respectively. Connected. These optical fibers 4-1 to 4-n each perform unidirectional signal transmission,
Bidirectional transmission of n/2 pairs is possible with n optical fibers. The spare optical fiber 8 is provided with connectors 9 at both ends, and can be connected to any one of the uninterrupted optical demultiplexers 5-1 to 5-n and the uninterrupted optical multiplexers 6-1 to 6-n, as necessary. 6-n.

Here, the feature of this embodiment is that the uninterrupted optical demultiplexers 5-1 to 5-n change the branching ratio to the two optical fibers connected to the uninterrupted optical demultiplexers 5-1 to 5-n. any one of the optical fibers 4-1 to 4-n (which is connected to the optical fiber 4-n)
-1) and the optical fiber \8 respectively, linear polarizers 7-1 to 7-n are provided as linear polarization means for substantially linearly polarizing the signal light propagating through the two optical fibers 4-i, An optical path length adjuster 11 is provided as an optical path length difference adjustment means for adjusting the optical path lengths so that the signal lights propagated to the two optical fibers 4-i, 8 arrive at the optical multiplexer 5-i at substantially the same time. 8 to uninterrupted optical multiplexer 5-i
A polarization orthogonalizer 10 is provided as a polarization control means for making the polarizations of signal lights incident thereon mutually orthogonal.

The polarization orthogonalizer 10 and the optical path length adjuster 11 each have a force (,
In principle, it is sufficient to provide it only at one end. These polarization orthogonalizer lO and optical path length adjuster 11 are controlled by an optical path length/polarization controller 12. The optical path length/polarization controller 12 is connected to any one of the uninterrupted optical multiplexers 6-1 to 5-n by the connector 9, and controls the polarization orthogonalizer 10 and the optical path length adjuster based on the branched signal light. 11 prevents the occurrence of bit errors in the signal.

Here, an example will be described in which the optical signal transmitted from the optical signal transmitter 1-1 is switched from the optical fiber 4-i to the backup optical fiber 8 (the figure shows the case where i=l).

First, the two connectors 9 of the backup optical fiber 8 are fitted into the uninterrupted optical demultiplexer 5-1 and the uninterrupted optical multiplexer 6-1, respectively, and (The throughput is set using the backup optical fiber 8. Next, the uninterrupted optical demultiplexer 5-1 causes the optical fiber 8 to share the signal propagating through the optical fiber \4-1, and transmits it through the cable. These two signals are combined by an uninterrupted optical multiplexer 6-1 and received by an optical signal receiver 2-i.

At this time, the output of the optical signal receiver 2-1 becomes substantially linearly polarized light by passing through the linear polarizer 7, and this is branched by the uninterrupted optical demultiplexer 5-i to be connected to the optical fiber 4-i. The signal light propagating within the optical fiber 18 becomes substantially linearly polarized light.

In this state, the power of the signal light branched from the optical fiber 4-i to the optical fiber 3 is increased. At this time, on the optical signal receiver 2-i side, the output lights of the optical fibers 4-i and 8 are branched by the uninterrupted optical multiplexer 6-1, and the optical path length and
The polarization controller 12 is manually operated. The optical path length/polarization controller 12 measures the arrival time difference and the angle formed by the polarization of the two human-powered signal lights, and adjusts the optical path lengths of the two optical fibers 4-118 so that the arrival time difference becomes zero, that is, the optical path lengths of the two optical fibers 4-118 match. The optical path length adjuster 11 is controlled so that the two polarization directions are orthogonal to each other, and the polarization orthogonalizer 10 is controlled so that the two polarization directions are orthogonal to each other.

When substantially all the signal light power is propagated through the optical fiber 8, the optical fiber 4-i is removed from the uninterrupted optical demultiplexer 5-i and the uninterrupted optical multiplexer 6-1.

This completes the switching from the working optical fiber 4-1 to the backup optical fiber 8.

Following this, the input and output ends of the optical fibers of the new optical fiber cable are connected to the uninterrupted optical demultiplexer 5-1 and the uninterrupted optical multiplexer 6-i, respectively, and the above-mentioned working optical fiber 4 -i to the spare optical fiber 8, the optical signal is switched from the optical fiber 8 in the existing optical fiber cable to the optical fiber of the new optical fiber cable.

After performing similar operations on all the optical fibers in the optical fiber cable, the changeover from the existing optical fiber cable to the new optical fiber cable is completed.

3 and 4 show the configuration and operation of an example of uninterrupted optical demultiplexers 5-1 to 5-n.

This uninterrupted optical demultiplexer includes an acousto-optic optical deflector 13,
It includes a lead wire 14 for power supply to drive the optical deflector 13, and adapters for fitting connectors provided on both sides of the optical deflector 13.

When there is no need to switch optical signals, the spare optical fiber 8 is not fitted into the optical deflector 13 and the optical deflector 13 is
No drive power is applied to. At this time, the signal light travels straight, enters the currently used optical fiber 4, and propagates through this optical fiber 4.

When switching signals, the connector of the spare optical fiber 8 is fitted into the optical deflector 13, and power is gradually applied to the lead wire 14. The incident signal light is deflected by the characteristics of the optical deflector 13. The deflection angle at this time is determined by the type of acousto-optic material and the angle of incidence of light on the optical axis of this material. In FIG. 4, the polarized light is shown by a broken line, but if the connector 9 of the backup optical fiber 8 is set in advance to be fitted to the output position of this polarized light, the signal light can be created as a backup by applying electric power. can be transferred to the optical fiber 8 for use. Furthermore, as a characteristic of the acousto-optic optical deflector 13, the amount of light to be deflected varies depending on the amount of driving power applied, so by gradually increasing the power, the signal light can be gradually transferred from the optical fiber 4 to the optical fiber 8. It is possible.

FIG. 5 shows the measurement results of the RF driving power applied to the acousto-optic optical deflector 13 and the output optical power from the optical fiber 4.8. Here, the output from the optical fiber 4 when no driving power is applied is assumed to be 100%, and the output from the two optical fibers 4 when the optical deflector 13 is operated by increasing the power is assumed to be 100%.
Shows the percentage of output from 8.

As is clear from this measurement result, by increasing the power, the optical power can be transferred from the working optical fiber 4 to the backup optical fiber 8, and up to about 70% of the optical power can be transferred to the backup optical fiber 8. can be transferred.

As the uninterrupted optical demultiplexer 5, in addition to an acousto-optic element,
A hologram element having light deflection properties can also be used. Such elements are known and are obtained by fixing the change in refractive index necessary to produce the optical deflection in a photosensitive material by means of optical interference fringes. In order to use this hologram element as the uninterrupted optical demultiplexer 5, the change in its refractive index may be set so that the direction of optical deflection can be changed continuously and steplessly.

6 and 7 show the configuration and operation of an example of uninterrupted optical multiplexers 6-1 to 5-n.

This uninterrupted optical multiplexer includes a multiplexing/demultiplexing section 15, which includes a branching section 16 for extracting a part of each signal for monitoring, and a branching section 16 for extracting a part of each signal for monitoring, and a branching section 16 for extracting a part of each signal for monitoring, and a branching section 16 for extracting a part of each signal for monitoring. It includes a multiplexing section 17 that multiplexes light. A connector 9 for two optical fibers 4.8 can be fitted to one end of the multiplexing/demultiplexing section 15.

When there is no need to switch optical signals, there is no need to fit the connector 9 of the spare optical fiber 8, as shown in FIG. At this time, the optical signal propagates from the current optical fiber 4 via the branching section 16 and the multiplexing section 17.

When switching optical signals, the connector 9 of the backup optical fiber 8 and the connector 9 of the optical path length/polarization controller 2 are fitted into the uninterrupted optical multiplexer 6. This state is shown in FIG. At this time, the optical signal is split into two optical fibers 4.8, one for working and one for backup. Current optical fiber 4
The optical signal that has passed through the backup optical fiber 8 is hereinafter referred to as the "main signal", and the optical signal that has passed through the backup optical fiber 8 is hereinafter referred to as the "bypass signal".

The main signal and the bypass signal are multiplexed by a multiplexer 17 and input into the optical signal receiver 2 as one signal. Further, the branching unit 16 extracts a part of each of the main signal and the bypass signal as monitor light, and adjusts the optical path length.
The polarization controller 12 is supplied with the polarization controller 12 .

FIG. 8 shows a detailed configuration of the optical path length/polarization controller 12 and a method of controlling the polarization orthogonalizer 10 and the optical path length adjuster 11 by the optical path length/polarization controller 12.

The optical path length/polarization controller 12 includes two signal monitor sections 18 , a polarization angle measurement section 19 , and an optical path length difference measurement section 20 .

The signal monitor unit 18 includes a known analyzer and a photoelectric conversion unit that converts an optical signal transmitted through the analyzer into an electrical signal, and receives monitor light from the working and backup optical fibers 4.8, respectively.

The inter-polarization angle measuring section 19 measures the polarization direction of the signal to be multiplexed based on the received light output of the signal monitor section 18 .

As the interpolarization angle measuring section 19, a device is used that rotates an analyzer in the signal monitor section 18 and determines the angle at which the optical power transmitted through the analyzer is maximized.

By comparing the polarization directions of the two signal lights, the angle formed by the polarization directions of the two signal lights can be measured.

The polarization orthogonalizer 10 is controlled so that this angle becomes 90 degrees. Two orthogonal light waves do not interfere, so they do not cause bit errors.

The polarization orthogonalizer 10 has a simple structure that bends the optical fiber and changes the magnitude of each polarized component propagating due to birefringence to rotate the polarization direction. The measurement result of the inter-polarization angle measuring unit 19 is fed back to the polarization orthogonal unit 10, and the polarization direction is rotated by the polarization orthogonal unit 10 until the angle measured by the inter-polarization angle measurement unit 19 is orthogonal.

The optical path length difference measurement unit 20 measures the optical path length difference between the two optical fibers 4.8 by comparing the monitor lights. Due to the difference in optical path length, the signal waveforms passing through the two optical fibers 4.8 are shifted in position on the time axis. Therefore, even if these signals are combined as they are, a signal equivalent to the original signal cannot be obtained. Therefore, the optical path length difference is measured by the optical path length difference measuring section 20, and the optical path length adjuster 11 is controlled until the difference becomes zero.

The optical path length difference measurement section 20 uses a computer and uses a configuration that calculates the correlation between two signal waveforms. If the optical path length adjuster 11 is operated in a direction in which the correlation increases and is stopped when the correlation becomes maximum, the two signal waveforms will match on the time axis.

Furthermore, a known interpulse time measuring device can also be used as the optical path length measuring section 20. In that case, pulses with a constant period whose amplitude, pulse width, etc. are varied according to a certain rule are multiplexed into the transmission signal as a biloft signal. These pulses are detected by the optical path length measurement section 20, pulses that were originally the same are identified according to the same rules as those on the transmitting side, and the time difference between the pulses is measured.

As the optical path length adjuster 11, a delay optical circuit as shown in FIG. 8 can be used. This configuration is shown in detail in FIG.

This optical path length adjuster 11 includes a plurality of delay optical fibers 11.
1 and a coupling section 112 that cascades a selected number of fibers from the plurality of delay optical fibers 111.
and a controller 113 for controlling these,
A delay time of a long optical path corresponding to the number of delay optical fibers 111 connected can be given to the signal light.

The coupling unit 112 connects the signal light to the delay optical fiber 1.
11, the number of delay optical fibers 111 is selected according to the required delay time under the control of the controller 113, and the signal light is delayed and then taken out again.

The coupling unit 112 connects the signal optical path to the delay optical fiber 1.
The optical switch 1121 is connected to the optical path of No. 11, and this optical switch 1121 is operated by a signal from a delay controller 1131. Thereby, the optical path through which the signal light passes is switched from the non-delay side optical path 1122 to the delay side optical path 1123. The switched signal is transferred to the delay optical fiber 111.
After passing through, it is coupled to the original optical path by a delay optical coupler 24 in the coupling section 112.

An optical switch 1121 is provided at the junction with each delay optical fiber 111, and by operating the optical switch 1121 according to the required delay time, the optical path length required to obtain the delay time is determined. optical fiber 11
1 can be cascaded.

Here, the delay time obtained by the delay optical fiber 111 is the time it takes for the signal light to propagate once through the optical fiber. Therefore, it is necessary to determine the number of optical switches 1121 to be activated in accordance with the required delay time.

When a delay time shorter than the delay time due to one delay optical fiber 111 is required, the delay time fine adjustment section 112
Adjust with 5. As the delay time fine adjustment section 1125, a component whose waveguide section is made of a material whose refractive index changes electrically, such as LiNbO3, is used. As is well known, the speed of light is inversely proportional to the refractive index of the medium, so the speed of the signal passing through this waveguide, that is, the optical path length, can be electrically controlled.

In addition, in order to prevent signal attenuation during coupling and while propagating through the delay optical fiber 111, the delay optical fiber 11
1, it is effective to use a fiber doped with errium. As is already known, when erbium exists in the fiber core in the state of εr3, when light with a wavelength of 1.48 μm is input into the optical fiber, a signal light with a wavelength of 1.55 μm can be amplified. can.

That is, at the same time as the optical switch 1121 is activated by the delay controller 1131, pump light with a wavelength of 1.48 μm is emitted from the pump light source 1132, is combined with the signal light by the pump light coupling unit 1126, and is connected to the delay optical fiber 111. Propagate. Thereby, the signal light propagating through the delay optical fiber 111 is amplified. Therefore, even when a signal is propagated through a large number of delay optical fibers 111 because a large delay time is required, optical loss due to optical coupling and switching can be offset.

In the above description, an example is shown in which an optical fiber is used as the delay leading waveguide, but a plurality of delay optical waveguides can also be incorporated as an optical circuit on one substrate.

When the optical path length difference is small, as the optical path length adjuster 11,
A simple structure is one in which the optical path length is expanded or contracted by applying tension or compression force in the axial direction of the optical fiber. Also, -
A structure may be used in which the signal light is emitted into space from a star optical fiber, propagated a certain distance in the form of a parallel beam, and then input into the optical fiber again. In this case, the optical path length can be increased by increasing the spatial propagation length.

When replacing a cable, as a practical matter, the current optical fiber 4 and the backup optical fiber 8, or the backup optical fiber 8 and the optical fiber of the new cable are placed along the same route. Therefore, the optical path length difference is as small as 1% or less. Therefore, even a simple configuration such as a configuration in which the optical fiber is expanded and contracted or a configuration in which the optical fiber is propagated through space can be used satisfactorily.

Further, the optical path length adjuster 11 can be configured only by a component using a material whose refractive index changes electrically, such as LiNbO3, in the aforementioned waveguide section, that is, the delay time fine adjustment section 1125.

In order to confirm that no signal bit error occurs when the signal in the optical fiber is switched, the signal error rate was measured using the experimental system shown in FIG. 1O.

The electrical signal generator 21 was capable of generating electrical signals up to 2.4 Gbit/s, and the distributed feedback laser 22 was modulated with the output signal. Bit rate is frequency counter 2
I read it directly in 3. The electric signal generator 21 and the distributed feedback laser 22 correspond to the individual optical signal transmitters 1-1 to 1-n in the embodiment described above.

The modulated light emitted by the distributed feedback laser 22 is transferred to a linear polarizer 7.
The light was adjusted to linearly polarized light and inputted into the optical fiber 4 via the uninterrupted optical demultiplexer 5 using an acousto-optic deflector. This signal was received by the optical signal receiver 2 via the uninterrupted optical multiplexer 6 and the power attenuator 24.

The bit error of the signal converted into an electrical signal by the optical signal receiver 2 was measured by the error rate measuring device 25.

Further, the monitor light was branched by the uninterrupted optical multiplexer 6, the monitor light was converted into an electrical signal by the monitor light receiver 26, this was amplified by the amplifier 27, and the waveform was displayed on the sampling scope 28.

In the middle of the optical fiber 8 is a connector with a lens 29.29'
was provided, the signal light became a substantially parallel beam in the spatial propagation section 30, and was made to enter the optical fiber 8 again. The connector 29' was made movable on the propagation axis of the signal light and operated as the optical path length adjuster 11. Further, the optical fiber 4.8 is provided with a Durham-Thomson type analyzer 31.31' in order to measure the degree of linear polarization of the propagating signal light.

First, the electric signal generator 21 and the distributed feedback laser 22
As a result, a pseudo-random pattern signal light of 1.86 bit/s was generated and propagated only to the optical fiber 4 without operating the uninterrupted optical demultiplexer 5. This signal light is passed through a linear polarizer 7
However, the degree of polarization may deteriorate during propagation through the uninterrupted optical demultiplexer 5 or the optical fiber. Therefore, the degree of linear polarization after propagating through the optical fiber 4 is measured using an analyzer 3.
1. The results are shown in FIG.

The analyzer transmits only the polarized light components that match the transmission axis.

Therefore, in the experiment, the analyzer was rotated and its transmitted power was measured. The length of the optical fiber 4 was changed to 10 m and 26 m.
Measurements were made for the case of +++ in 5. As a result, the 11th
As shown in the figure, periodic fluctuations in transmitted power were measured according to the rotation angle of the analyzer, and the angles at which the power was maximum and minimum were shifted by 90 degrees. From this result, it can be seen that the polarization direction of the signal light is at the angle where the power is maximum. Furthermore, the ratio between the maximum and minimum power, that is, the extinction ratio, is approximately 16 for both fiber lengths.
It was dB. From this result, it is considered that the deterioration of the degree of linear polarization is small even after propagation through a 26.5 km optical fiber.

Next, the uninterrupted optical demultiplexer 5 was operated, and the deterioration of the degree of linear polarization caused by this was evaluated. The signal light was distributed to the two optical fibers 4.8 so that the power ratio was approximately 1:1, and the degree of polarization was measured by rotating the analyzer 31.31'. The results are shown in FIG.

In this case as well, a pattern similar to that shown in FIG. 11 was obtained.

The extinction ratio of the signal light deflected into the optical fiber 8 is approximately 12 dB.
and 16d when the uninterrupted optical demultiplexer 5 is not activated.
Although the value was smaller than that of B, the linear deflection state was maintained.

After confirming that the deflection state is maintained, analyzer 3■,
The bit error rate characteristics due to optical signal switching were measured in a transmission system in which 31' was removed.

First, only the main signal was propagated without operating the uninterrupted optical demultiplexer 5, and the error rate was measured. The results are shown in FIG. In this measurement, the power attenuator 24 was used to change the received light power.

Next, the uninterrupted optical demultiplexer 5 is activated to reduce the signal light power to 1
The optical fibers were separated into two optical fibers 4.8 and propagated into two optical fibers 4.8. The monitor waveform of this signal was displayed on the sampling scope 28, and the connector 29' was adjusted so that the two coincided on the time axis, thereby making the arrival time difference of the signals zero.

Subsequently, the polarization orthogonalizer 10 was adjusted, and the polarization orthogonalizer 10 was fixed at a position where a stable pulse waveform was obtained without interference between the multiplexed signals on the sampling scope. This state is considered to be a state in which the angle between the polarization directions of the two signals is 90 degrees, and the error rate at this time was measured. After this, the polarization orthogonalizer IO
was rotated to shift the polarization directions of the two signals from 90 degrees, and the error rate was similarly measured. The results are also shown in FIG.

As shown in FIG. 13, if the polarization directions of the two signals are orthogonal, the error rate characteristic is equivalent to the case of only the main signal. However, as the angle between the polarization directions deviates from 90 degrees, the error rate decreases.

FIG. 14 shows the measurement results of the arrival time difference and error rate of two signals. In this measurement, the optical path length was changed by sliding the connector 29' with the polarization directions perpendicular to each other, and the difference in arrival time of the two signals at that time was changed. As shown in FIG. 14, as the time difference increases, the error rate deteriorates.

As shown in the above experimental results, even if high-speed signal lights such as 1.86 bit/s are demultiplexed and then combined, the polarization directions of the two signal lights are made orthogonal and their arrival times match. If you do so, no bit errors will occur.

FIG. 15 shows the results of measuring the error rate when the acousto-optic uninterrupted optical demultiplexer 5 is operated when both the polarization orthogonality condition and the zero optical path length difference condition are satisfied. . In this measurement, the received signal light power required to ensure a constant error rate was measured. The signal light power of the optical fiber 4 was set to Pl, the signal light power of the optical fiber 8 was set to P, and the power of the acousto-optic uninterrupted optical demultiplexer 5 was increased to increase the signal light power Pb. Even if the power of the acousto-optic uninterrupted optical demultiplexer 5 is increased, the total received signal light power p, +F'
b was almost constant.

As shown in FIG. 15, even if the signal light power Pb is increased, the received signal light power required to ensure a constant error rate hardly changes. Even when the signal light was transferred from the optical fiber 4 to the optical fiber 8 using the method No. 5, no change in the error rate was observed during the transfer. In FIG. 15, a power ratio of 0% indicates transmission of an optical signal only through the optical fiber 4, and a power ratio of 100%.
indicates transmission through only the optical fiber 8.

〔Effect of the invention〕

As explained above, the optical signal transmission line and the optical signal switching method of the present invention can transfer the signal light from the working optical fiber to the backup optical fiber under conditions where signal bit errors do not occur. . Therefore, even when a subscriber is transmitting a signal, it is possible to replace the cable without causing an error in the signal, and the replacement work can be carried out in a planned and efficient manner.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of an optical signal transmission line according to an embodiment of the present invention and an optical signal switching method using this transmission line. FIG. 2 is a diagram showing another state of the embodiment. FIG. 3 is a configuration diagram showing an example of an uninterrupted optical demultiplexer. FIG. 4 is a diagram showing another state of the uninterrupted optical demultiplexer. FIG. 5 is a diagram showing the measurement results of the output optical power from the optical fiber with respect to the driving power applied to the acousto-optic optical deflector. FIG. 6 is a configuration diagram showing an example of an uninterrupted optical multiplexer. FIG. 7 is a diagram showing another state of the uninterrupted optical multiplexer. FIG. 8 is a diagram showing the detailed configuration of the optical path length/polarization controller. FIG. 9 is a detailed configuration diagram of the optical path length adjuster. FIG. 10 is a configuration diagram of an experimental system for measuring the signal error rate. FIG. 11 is a diagram showing the measurement results of the degree of linear polarization after propagating through an optical fiber. FIG. 12 is a diagram showing measurement results of linear polarization degree deterioration using an instantaneous optical demultiplexer. FIG. 13 is a diagram showing measurement results of bit error chromaticity due to switching of optical signals in a state where the deflection state is maintained. FIG. 4 is a diagram showing the measurement results of the difference in arrival time of two signals and the error rate. FIG. 15 is a diagram showing measurement results of error rate using an acousto-optic type uninterrupted optical demultiplexer. 1-1~1-n...Optical signal transmitter, 2.2-1~2
-n - Optical signal receiver, 3... Optical fiber cable, 4.4-1 to 4-n, 8... Optical fiber, 5.
5-1 to 5-n... Uninterrupted optical demultiplexer, 6.6-1 to 5
-n... Uninterrupted optical multiplexer, 7.7-1 to 7-n...
Linear polarizer, 9.29.29'...Connector, 10.
...Polarization orthogonalizer, 11... Optical path length adjuster, 12...
Optical path length/polarization controller, ■3... Optical deflector, 14...
Lead wire, 15...multiplexing/demultiplexing section, 16...branching section, 1
7... Multiplexing section, ■8... Signal monitoring section, 19...
Polarization angle measuring section, 20... Optical path length difference measuring section, 21.
... Electric signal generator, 22 ... Distributed feedback laser, 2
3... Frequency counter, 24... Power attenuator, 2
5...Error rate measuring device, 26...Monitor receiver, 27
...Amplifier, 28...Sampling scope, 30
...Spatial propagation section, 31.31'...Analyzer, 111
...Delay optical fiber, 112...Coupling unit, 113...Controller, 1121...Optical switch, 1122...Non-delay side optical path, 1123...Delay side optical path, 1124... Delay optical coupler, 1125...
Delay time fine adjustment unit, 1126... Pump optical coupling unit, 1131... Delay controller, ■132...
・Pump light source.

Claims (1)

[Claims] 1. An input end and an output end of a backup optical fiber are connected to the optical branching means and the optical multiplexing means of a working optical fiber, which is provided with an optical branching means and an optical multiplexing means on the transmitting side and the receiving side, respectively. and branched the signal light so that the signal light propagating to the working optical fiber and the backup optical fiber respectively becomes substantially linearly polarized light, and propagating to the working optical fiber and the backup optical fiber. While adjusting the optical path length so that the signal lights reach the optical multiplexing means at the same time and controlling the polarizations of the incident lights to the optical multiplexing means to be orthogonal to each other, the optical fibers are increasing the signal light power branched to the working optical fiber, and removing the working optical fiber from the optical branching means and the optical combining means with substantially all the signal optical power propagating through the spare optical fiber; The input and output ends of the optical fibers of the new optical fiber cable are connected to the optical branching means and the optical multiplexing means, respectively, so that the signal light propagating to the spare optical fiber and the optical fiber of the new optical fiber cable, respectively, is substantially branching the signal light so that it becomes linearly polarized light, and adjusting the optical path length so that the signal light propagated to the spare optical fiber and the optical fiber of the new optical fiber cable reach the optical multiplexing means at substantially the same time. adjusting and controlling the polarizations of the lights incident on the optical multiplexing means to be orthogonal to each other, increasing the power of the signal light branched from the spare optical fiber to the optical fiber of the new optical fiber cable; An optical signal switching method, wherein the spare optical fiber is removed from the optical branching means and the optical multiplexing means in a state in which all signal light power propagates through the optical fibers of the new optical fiber cable. 2. At least two optical fibers, one for signal transmission and one for backup, and an optical branching means to which the two optical fibers, one for signal transmission and one for backup, can be connected on the transmitting side, and the signal light is branched into these two optical fibers. and an optical multiplexing means to which the two optical fibers can be connected on the receiving side and multiplexes the signal lights propagated through the two optical fibers, wherein the optical branching means includes the two optical fibers. linear polarization means, which includes a branching ratio control means for changing the branching ratio into two optical fibers, and substantially linearly polarizes the signal light propagating to each of the two optical fibers, and the signal propagated to the two optical fibers; an optical path length difference adjustment means for adjusting the optical path lengths so that the lights arrive at the optical multiplexing means at substantially the same time; and polarization control for making the polarizations of the signal lights incident on the optical multiplexing means from the two optical fibers orthogonal to each other. An optical signal transmission line characterized by comprising: means.