JPH1117261A - Loss-compensating light selector and optical network - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the optical surge of optical amplifying means by providing a loss compensating selector having a function of relaxing the increase of the optical intensity with the optical switching; the amplifying time const. of the amplifying means being less than the switching time of optical switching means. SOLUTION: An optical switch 202 for distributing optical signals from optical transmission lines 101 to optical transmission lines and optical amplifiers 201 form a losscompensating selector as a basic constitution. Part 404 of the signal from a control circuit 301 is sent to an optical amplifier drive circuit 304 through a timing circuit 303 to stop the optical switch operation and resume an optical amplifying operation after the optical switch operation. This delay time is set on account of the switching time const. of optical switching means, if long enough, the rise of the optical light intensity is relaxed to suppress the optical source in the optical amplifying means laid on an optical transmission line at the downstream of the optical selector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical selector used in the field of optical communication and an optical network system using the same.

[0002]

2. Description of the Related Art An optical long-distance transmission technology using an optical fiber has made it possible to greatly improve the quality and broadband of a signal as compared with a conventional long-distance transmission technology using a microwave. For this reason, the optical long-distance transmission technology using an optical fiber is being rapidly applied to the entire communication network including the backbone communication network.

[0003] The remarkable widening of the signal band in the optical transmission technology has made it possible to rapidly reduce the communication cost, but on the other hand, the amount of traffic carried by each optical fiber has increased rapidly. On the contrary, when the optical transmission line is disconnected, the influence on society is becoming enormous. In addition, the optical long-distance transmission technology is inherently vulnerable to natural disasters and man-made disasters such as road construction, since optical fibers as transmission paths must be laid over long distances. Up to now, there have been many reports of optical fiber disconnection accidents, and there is an urgent need to establish an optical communication network to cope with such an optical transmission path failure.

In order to cope with such a situation, an optical network having a plurality of optical transmission lines between individual nodes has been proposed. In such an optical network, an optical signal from an optical transmitter is bridged between a plurality of optical transmission lines by an optical demultiplexer or an optical switch in order to reduce the number of expensive optical transmission line terminating devices. A configuration is adopted in which an optical signal transmitted through a plurality of optical transmission lines is selected by an optical switch placed immediately before the optical receiver. For example,
Reference "Fiber Network Service Survivability" (Wu, Ts
(ong-Hu, 1992, Norwood, MA, USA) use a mechanical optical switch that selects the transmission path through which the optical signal passes by mechanically displacing the optical medium that carries the optical signal. Examples are given.

[0005]

The mechanical optical switch as described above surpasses other optical switches in terms of insertion loss, crosstalk characteristics and optical wavelength band, but the rise time of an optical signal is 1 mm. Seconds to milliseconds are reported. Although the rise time of this optical signal is shorter than the time required for the system to switch the transmission line from the working fiber to the backup fiber when the optical transmission line fails, it is necessary to adapt to the actual optical transmission system. Has the following problems.

After an optical amplifier, such as a rare earth-doped fiber optical amplifier, placed at a relay point for compensating for a transmission path loss, becomes a no-signal state due to an optical fiber disconnection accident or the like, the above-mentioned one to several milliseconds is not used. When an optical signal having a rise time is input, a strong optical pulse called an optical surge is generated. This optical surge may cause an accident to destroy the optical transmission device after the optical amplifier, in the above example, the rare earth doped fiber optical amplifier.

According to the present invention, there is provided an optical amplifying means for compensating for attenuation of an optical signal in an optical transmission line, and an optical switching means for selecting a transmission path through which an optical signal should pass from among a plurality of optical transmission lines. The present invention provides a loss-compensating optical selector comprising:
In particular, the present invention provides a loss-compensating optical selector that suppresses the occurrence of optical surge in an optical amplifying unit laid on an optical transmission line downstream of the optical selector.

[0008] The present invention also provides an optical network using the loss compensating optical selector and a system therefor.

[0009]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, typical ones will be outlined as follows.

(1) Optical amplification means for compensating for attenuation of an optical signal in an optical transmission line, and optical switching means for selecting a transmission path through which an optical signal should pass from among a plurality of optical transmission lines. A loss compensating optical selector, wherein the time constant of amplification of the optical amplifying means is smaller than the switching time of the optical switching means, and the function of alleviating an increase in light intensity due to optical switching is added. It is an optical selector. As the optical amplifying means, a known one can be used. Further, as the optical switching means, various conventional ones such as a mechanical optical switch, a semiconductor optical switch, and a dielectric optical switch can be used.

Incidentally, the time constant (τ) of the amplification of the optical amplification means is usually
o) is μs-ms, switching time (τs) is ns-m
This is the order of s.

(2) As the optical amplifying means, there are a fiber Raman amplifier, a resonance type laser amplifier, an injection locking type laser amplifier and the like, but a waveguide or a fiber optical amplifier doped with a doped material capable of being stimulated emission is practically used. Moreover, it is simple and useful. In this optical amplifier, an optical input signal is supplied to an input waveguide together with a predetermined pump light. The waveguide is doped with a doping material that absorbs the excitation light and exhibits a stimulated emission process at the signal light wavelength. The signal light is amplified by this stimulated emission process.

(3) A typical example of the present invention is a rare-earth-doped fiber optical amplifier for compensating for attenuation of an optical signal in an optical transmission line, and transmission of an optical signal through a plurality of optical transmission lines. An optical switch for selecting a path, and a loss compensating optical selector having a function of alleviating a sudden increase in light intensity due to optical switching, thereby providing an optical transmission path downstream of the optical selector. This suppresses the occurrence of an optical surge in the installed rare earth-doped fiber optical amplifier.

(4) When the optical amplifier uses pump light and signal light, the optical switch for selecting a transmission path through which an optical signal should pass from among a plurality of optical transmission paths is used. Particularly useful is a loss compensating optical selector where the pump light for the amplifier is selected to follow the same path as the optical signal. Since the optical amplification is started only after the pump light is incident, the optical surge at the beginning of switching is suppressed. And
In this case, it is extremely easy to select the pump light so as to follow the same path as the optical signal. The optical switch for selecting a transmission path through which an optical signal should pass from among a plurality of optical transmission paths so that all or a part of the pumping light for the optical amplifier passes through the same path as the optical signal. Select the configuration. An optically active medium such as a rare-earth-doped fiber is disposed in each of the paths leading to the plurality of optical transmission lines, and the optically active medium is selected by the optical switch so as to pass through the same path as the optical signal. The medium is configured to take either the light amplification state or the light absorption state.

(5) In this case, the optical switch for selecting a transmission path through which the optical signal should pass from among the plurality of optical transmission paths causes pumping light passing through a path other than the same path as the optical signal to be excited. By blocking, it is preferable that the photoactive medium connected to a transmission path other than the transmission path through which the optical signal should pass is in a light absorbing state.

(6) The loss compensating optical collector according to any one of (1) to (4), wherein a photoactive medium is disposed in each of the paths from the optical switch to the plurality of optical transmission lines. Preferably, the photoactive medium is in either a light-amplified state or a light-absorbed state by the excitation light selected by the optical switch to follow the same path as the optical signal.
The photoactive medium in the light absorbing state can absorb the optical noise flowing into this transmission line and improve the crosstalk characteristics.

(7) More specifically, the configuration of the item (5) is described below. A multiplexer for multiplexing the pump light parallel to the optical signal with the optical signal along the transmission direction of the optical signal. , A rare earth-doped fiber amplifier connected thereto, a 1-input N-output optical switch connected thereto, and a rare-earth-doped fiber connected to each of the N output terminals.

(8) The operation will be described below in accordance with an actual operation. When operating the optical switch to switch the transmission path through which the optical signal should pass from the transmission path (A) to the transmission path (B),
By selecting all or a part of the pumping light so as to pass through the same path as the optical signal, the photoactive medium connected to the transmission path (B) changes from the light absorption state to the light amplification state. If the time constant of this state change is sufficiently slow, the rise of the signal light intensity that flows through the transmission line (B) due to the optical switching is reduced, and the light laid in the optical transmission line downstream of the optical selector is reduced. Generation of an optical surge in the amplifying means can be suppressed.

(9) Further, the optical switch according to the above items (1) to (7), wherein the optical switch for selecting a transmission path through which an optical signal should pass from among a plurality of optical transmission paths. Alternatively, an optical switch may be used in which the amount of return loss at the time of state setting and switching operation exceeds the gain of the optical amplifier.

In particular, it is possible to use an optical switch that selects a transmission path through which an optical signal passes by mechanically displacing the optical medium that carries the optical signal.

In the following embodiment, an example in which the loss compensating optical selector is provided in one stage is shown. However, in a system in which the optical compensating optical selector is provided in another stage, the optical surge associated with the above-described optical switching is applied by using the present invention. Needless to say, the effect of suppressing the above is obtained.

The loss compensation optical selector of the present invention is extremely useful for an automatic protection system used in an optical network having a plurality of optical transmission lines for avoiding a failure in the optical transmission line. Of course, the loss compensating optical selector of the present invention may be used in an optical cross-connect system used for controlling an optical network having a plurality of optical transmission lines. An optical network can be configured using these systems.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 is a configuration diagram showing one embodiment of a loss compensation optical selector according to the present invention. An optical switch 202 for distributing an optical signal from the optical transmission line 101 to a plurality of optical transmission lines 103
And the optical amplifier 201 are basic components. The control of the optical switch 202 is performed in response to a switching request signal 401 from the outside. Specifically, an optical switch is performed by a control circuit 301 that performs predetermined signal processing according to a switching request signal 401 from the outside and an optical switch driving circuit 302 that responds to the control signal.

In this embodiment, by transmitting a part 404 of the signal from the control circuit 301 to the optical amplifier driving circuit 304 via the timing circuit 303, the optical amplification operation of the optical amplifier is stopped during the operation of the optical switch. After the end of the optical switch operation, the optical amplification operation is restarted. This delay time is set in consideration of the switching time constant of the optical switching means. Thus, a function of alleviating a sudden increase in light intensity due to optical switching is provided.

Embodiment 2 FIG. 2 shows an embodiment of a loss compensating optical selector using a waveguide doped with a doped material capable of being stimulated emission as an optical amplifying means. In this embodiment, a rare earth-doped fiber (more specifically, a europium-doped fiber) is used as the waveguide to which the doped material capable of being stimulated-emitted is added.

The loss compensating optical selector is connected to a rare earth doped fiber as an optical amplifying means, a pumping means for exciting the fiber, an optical switch, and a rare earth doped fiber corresponding to the first and second states of switching, respectively. It is composed.

The optical switch 202 distributes an optical signal from the optical transmission line 101 to a plurality of optical transmission lines 1031 and 1032. The optical amplification unit includes a drive circuit 304 for an optical amplifier, a light source 2011 for generating pump light, a multiplexer 2012 for coupling the generated pump light to a transmission line, and rare-earth-doped fibers 2013, 2014, and 2015. ing.

When the optical switch 202 is set on the side of the optical transmission line 1031 as shown in the figure, a part of the signal light pumping light and the signal light flow in the optical transmission line 1031 side. The rare-earth-doped fiber 2014 is excited by the excitation light supplied through the multiplexer 2012 and serves as an optical amplification medium. On the other hand, the rare-earth-doped fiber 20 on the optical transmission line
15 is in a ground state and is a light absorbing medium.

FIG. 3 shows an optical switching waveform of the optical switch.
FIG. 4 illustrates an optical switching waveform after passing through a conventional optical amplifier, and FIG. 5 illustrates an optical switching waveform after passing through a loss compensation optical selector. The optical switching waveform as shown in FIG.
After passing through a conventional optical amplifier, the optical switching waveform is as shown in FIG. That is, an optical surge at the time of switching occurs. This phenomenon occurs remarkably when the switching time (τS) of the optical switching unit is shorter than the time constant of amplification of the optical amplification unit. In the case of a rare earth-doped fiber, the time constant corresponds to the spontaneous emission lifetime (τa) of the level forming the population inversion. In FIG. 5, the time constant of the optical switching of the loss compensation optical selector is longer than the switching time (τS) of the optical switching, and no optical surge occurs.

The configuration of the present example produced two effects. One is that when the optical switch 202 is switched to the optical transmission line 1032 side, the optical transmission line 10
That is, the optical amplification operation does not start until the population inversion is formed in the rare-earth-doped fiber 2015 by the excitation light flowing on the 32 side. As a result, the sudden increase in the light intensity accompanying the optical switching was automatically mitigated. Another effect is that the rare-earth-doped fiber on the side where no optical signal flows serves as a light-absorbing medium, thereby absorbing optical noise leaking into the transmission line and improving crosstalk characteristics.

Embodiment 3 This embodiment describes an example in which the loss compensating optical selector of the present invention is applied to a self-rescue type optical network. Prior to describing a specific example, a configuration of a general self-repair optical network will be briefly described.

FIGS. 6 to 8 show three examples of an optical transmission system to which the loss compensating optical selector of the present invention can be applied. FIG.
FIG. 4 is a diagram illustrating a 4Fiber BLSR (Bidirectional Line Switching Ring). 115-118 are transmission devices (nodes). Working transmission line 119-122 and protection transmission line 1
23-125 are connected in a ring shape. Each of the transmission devices has a transmission switching capability, and these transmission devices transmit signals bidirectionally on the working transmission line and the protection transmission line.

In such an optical transmission system, when a failure occurs in the working transmission line 122, a signal is relieved using the backup transmission line 126. In addition, the working transmission line 122
If a failure occurs in both the backup transmission line 126 and the backup transmission line 126, a detour is used because of the ring type. The signal is relieved using the spare transmission lines 123-125.

FIG. 7 shows an example of a network in which another self-rescue can be rescued. The illustrated self-rescue network includes first to fifth transmission devices 200, 201, 202,
Each of these transmission devices is connected in a series chain, that is, a single chain by four spare transmission lines. Here, the first to fifth transmission devices 200 to 2
04, transmission device A, transmission device B, transmission device C,
The transmission device D and the transmission device E. Each transmission device has a transmission line switching capability. In these transmission devices, the working transmission line and the protection transmission line transmit signals bidirectionally. In the figure, 205-210 is an active transmission line, and 211-215 is a standby transmission line.

When a failure occurs in a network having such a configuration, when a failure occurs, (1) the transmission path in which the failure has occurred, and (2)
Switching is performed by determining the importance of the transmission path and (3) the order of occurrence.

For example, when a first failure having a priority of 3 occurs in the working transmission line 206, the working transmission line 206 is relieved by using the protection transmission line 212. The higher the importance value, the higher the priority.

When a second fault having a priority of 1 occurs in the working transmission line 209, the working transmission line 209 is repaired by using the protection transmission line 213.

FIG. 8 shows a ring network.
In this example, the backup transmission lines are connected in a ring shape. The illustrated self-rescue network is the first to fifth transmission devices 2.
00, 201, 202, 204 and 205, and each of these transmission devices is connected in a ring by five spare transmission lines. Here, the first to fifth transmission devices 2
Reference numerals 00 to 205 denote transmission devices A, B, C, D, and E, respectively, and the current transmission line numbers of the current transmission lines 205, 206, 209, and 210 are 1
And the active transmission line numbers of the active transmission lines 207 and 210 are 2
And

The working transmission lines 205 to 210 are connected as shown in FIG. Each of the transmission devices has a transmission line switching capability, and these transmission devices are configured such that a signal is transmitted bidirectionally through an active transmission line and a backup transmission line.

In a ring-shaped network, a method of relieving a working transmission line in which a failure has occurred is to predetermine a spare transmission line to be used when the working transmission line is abnormal.

The loss compensation selector of the present invention is advantageously applied to switching of the transmission line in such a case.

Although a general self-relieving optical fiber network has been outlined above, a specific example in which the loss compensation selector of the present invention is used in such a network will be described. 1 is a specific example of an embodiment of an optical cross-connect system provided by the present invention.

FIG. 9 shows an example of the configuration of an optical cross-connect system for coping with an optical transmission line failure. 101WU (1
.. N) are n working transmission lines connected to the optical receiver, 101
WD (1... N) are n working transmission paths connected to the optical transmitter, and 101PU (1,2) 101PD (1,2) are protection transmission paths. The optical cross connect system
(1) Optical receiver 701 directly connected to optical preamplifier 7012
(2) optical transmitters 7021 and n directly connected to the optical booster amplifier 7022, between one and n active optical transmission lines 101WU;
It is installed between the current optical transmission line 101WD of the book. FIG.
Reference numeral 801 denotes a loss compensation optical selector according to the present invention. The figure shows an optical amplifier and an optical switch at least included in the loss compensation optical selector.

The failure recovery by the optical cross-connect system is performed as follows.

As for a node transmitting to the failed optical transmission line, for example, when a failure occurs in the n-th transmission line in the optical transmission line 101WD, the optical matrix switch 6022 The n-th optical transmitter is connected to the spare optical transmission line 101PD. For a node that is receiving from the failed optical transmission line, for example, when a failure occurs in the n-th transmission line in the optical transmission line 101WU, the n-th optical The transmitter is switched to the spare optical transmission line 101PU. Thus, the optical signal is transmitted to the spare optical transmission path 101PU, 1
01PW flows, and the fault is recovered.

The above-described example of the failure recovery is a case where there is a spare optical transmission line parallel to the failed optical transmission line. However, in general, there may be no spare optical transmission line parallel to the failed optical transmission line. In this case, the failure recovery is performed using a spare optical transmission line that runs on a completely different complicated path from the failed optical transmission line. In general, since the spare optical transmission line passes through a plurality of nodes, the optical cross-connect system prepares the spare optical transmission lines 101PD and 1PD in case the own node becomes a relay node.
It is necessary to provide a path 901 that can connect to 01PU. That is, the optical cross-connect system includes (1)
When the own node is the terminal station of the faulty optical transmission line and the spare optical transmission line is connected to the optical terminator, (2) the own node is the relay station of the spare optical transmission line and the spare optical transmission Must be prepared for connecting roads. In this configuration example, the loss compensation optical selector 801 according to the present invention and the path 90
1 and the optical switch 601 enable connection in both cases.

In particular, the loss compensation optical selector 80 of the present invention
By using No. 1, it was possible to compensate for the optical transmission loss, which is a problem when relaying the spare optical transmission line, and to perform the optical path switching according to the above two cases at once.

The configuration of the loss compensation optical selector 801 itself is the same as that shown in the second embodiment.

When a sudden rise in light intensity occurs during optical transmission via an optical switch, there is a risk that an optical surge may occur in the optical preamplifier 7012 or the like. The 801 has a function of alleviating a sudden increase in light intensity due to optical switching, and this danger can be greatly reduced.

[0050]

The present invention provides a loss compensating optical selector capable of suppressing the occurrence of an optical surge in the optical amplifying means laid on the downstream optical transmission line. Further, by using the loss compensating optical selector of the present invention, an optical network corresponding to an optical transmission line failure and a system therefor are provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a loss compensation optical selector according to a first embodiment.

FIG. 2 is a configuration diagram of a loss compensation light optical selector according to a second embodiment.

FIG. 3 is a diagram showing an optical switching waveform of an optical switch.

FIG. 4 is a diagram showing an optical switching waveform after passing through an optical amplifier having a conventional configuration.

FIG. 5 is a diagram showing an optical switching waveform after passing through a loss compensation optical selector according to the present invention.

FIG. 6 is a diagram illustrating an example of an optical transmission system.

FIG. 7 is a diagram illustrating another example of the optical transmission system.

FIG. 8 is a diagram illustrating another example of the optical transmission system.

FIG. 9 is a diagram showing a configuration of an optical cross-connect system using a loss compensation optical selector according to the present invention.

[Explanation of symbols]

101, 103, 1031, 1032: optical transmission line, 20
2: optical switch, 201: optical amplifier, 2011: light source for generating pump light, 2012: multiplexer for coupling pump light to the transmission line, 2013, 2014, 2015: rare earth doped fiber, 301: control circuit, 302: switch driving circuit, 304: optical amplifier driving circuit, 101WU: n active optical transmission lines, 101PU, 101PD: spare optical transmission lines, 7012: optical preamplifier, 7011: optical receiver,
7022: optical booster amplifier, 7021: optical transmitter, 6
211, 6022: Optical matrix switch, 801: Loss compensating optical selector according to the present invention, 601: Optical switch 115-118, 200-204: Node, 119-1
22, 205-210: working transmission line, 123-125,
211-215: standby transmission path,

Claims (13)

[Claims] 1. An optical amplifying means comprising: at least a desired optical amplifying means; and an optical switching means for selecting a transmission path through which an optical signal should pass, wherein the amplification time constant of the optical amplifying means is set to A loss compensating optical selector which is shorter than the switching time and has a function of alleviating a sudden increase in light intensity accompanying optical switching. 2. An optical amplifier comprising a waveguide doped with a doped material capable of being stimulated emission, and at least an optical switching means for selecting a transmission path through which an optical signal should pass,
A loss compensating optical selector in which the time constant of amplification of the optical amplifier comprising the waveguide doped with the stimulated emission is smaller than the switching time of the optical switching means; A loss-compensating optical selector characterized by having a function of alleviating a sudden increase in light intensity. 3. An optical amplifier having at least a rare earth-doped fiber optical amplifier and an optical switching means for selecting a transmission path through which an optical signal should pass, and wherein the time constant of amplification of the rare earth-doped fiber optical amplifier is the optical switching. A loss compensating optical selector which is shorter than a switching time of the means, wherein a function of alleviating a sudden increase in light intensity accompanying optical switching of the optical switching means is provided. 4. An optical switch for selecting a transmission path through which an optical signal should pass from among a plurality of optical transmission paths, wherein at least a part of the pump light for the optical amplifier has the same path as the optical signal. 4. The loss-compensating optical selector according to claim 2, wherein the selector is selected so as to pass through. 5. A loss compensating optical selector according to claim 1, wherein an optically active medium is disposed on each of the paths leading to the plurality of optical transmission lines of the loss compensating optical selector, and an optical signal is transmitted by the optical switching means. A loss compensation optical selector, wherein the photoactive medium takes one of an optical amplification state and an optical absorption state depending on the presence or absence of the excitation light selected to pass through the same path as that of the optical active medium. 6. A multiplexer for multiplexing an excitation light transmitted in parallel with an optical signal with an optical signal along a transmission direction of the optical signal, an optical amplifier connected thereto, and an optical amplifier connected to the optical amplifier. A loss-compensating optical selector, comprising: an optical switching means; and an optically active medium connected to an output end thereof. 7. A multiplexer for multiplexing an excitation light transmitted in parallel with an optical signal with an optical signal along a transmission direction of the optical signal, a rare-earth-doped fiber connected to the multiplexer, and the rare-earth-doped fiber. A 1-input N-output optical switch connected to a fiber,
A loss compensating optical selector comprising: a rare earth doped fiber connected to each of the N output terminals. 8. An optical switch for selecting a transmission path through which an optical signal passes is used to block an excitation light passing through a path other than the same path as the optical signal, thereby transmitting an optical signal through which the optical signal passes. 8. The loss compensating optical selector according to claim 2, wherein the photoactive medium connected to a transmission path other than the transmission path is in a light absorbing state. 9. An optical switching means for selecting a transmission path through which an optical signal should pass, wherein an optical switching means such that the amount of return loss at the time of state setting and at the time of switching operation exceeds the gain of the optical amplification means. The loss compensation optical selector according to claim 2, wherein: 10. The loss-compensating optical selector according to claim 9, wherein an optical switching means for selecting a transmission path through which the optical signal should pass by mechanically displacing an optical medium carrying the optical signal is used. . 11. An automatic protection system for use in an optical network having a plurality of optical transmission lines for avoiding a failure in the optical transmission line, wherein the loss compensation optical selector according to claim 1 is used. Automatic protection system characterized by the following. 12. An optical cross-connect device used for controlling an optical network having a plurality of optical transmission lines, wherein the optical cross-connect device according to claim 1 is used. Connect system. 13. An optical network comprising the loss compensation optical selector according to claim 1.