SE521127C2 - Backup systems for optical wavelength division multiplexing communications - Google Patents

Abstract

The optical communication system has two nodes (1) connected by optical fibers (3). Each node has a number of access points (5) to receive or output electrical signals. The received signals are converted by a transmitter (7) into an optical signal. This is converted to a specific wavelength by a transponder (11). The multiple wavelengths are combined (13), transmitted and demultiplexed (15). The separated signals are provided to receivers (9). Each transmitter and receiver is duplicated (7',9'). A spare transponder (21) is available via switches (23,25).

Description

Swedish patent application No. 9602005-2, "Channel protection in data and telecommunication systems", shows an optical fi measured with WDM, in which each node comprises at least one electro-optical backup transmitter and at least one optoelectric backup receiver. A spare wavelength is used by the spare transmitter and receiver. The network is of the bus type with traffic circulating through the node, and in the network the nodes drain WDM channels and / or add WDM channels as required.

SUMMARY OF THE INVENTION It is an object of the invention to provide an optical link with protection, in particular a bidirectional optical link, which forms or is part of an optical network.

It is a further object of the invention to provide an optical link and nodes for use in the node, which have protection, which works for many cases with various faulty components.

It is a further object of the invention to provide nodes in an optical link, which have protection and which can be built up of standard components of a relatively robust type and do not require, for example, tunable lasers.

In a protection device for optical transmitter devices and receiver devices in nodes connected by a bidirectional lark in a WDM network there is a switch, so that when one of the transmitter devices becomes faulty, its input signal is connected to a spare transmitter, so that this transmitter sends the signal over a wavelength not used by the other transmitters. The optical transmitters and receivers in a node of such a bidirectional link may be doubled, so that an optical spare transmitter and an optical spare receiver are arranged as a backup for each regular regular transmitter and each optical regular receiver. Transponders may be connected to receive the signals to be transmitted in an optical carrier which connects the nodes, and they convert the received optical signals into optical signals of wavelengths. The output signals of the transponders are combined in an optical signal combining element or a multiplexer and are transmitted from this / that in the optical beam. In each node there is only one spare transponder arranged as a reserve for the other ordinary transponders. By means of devices comprising optical switches and / or optical couplers, the optical signals from an ordinary optical transmitter or spare optical transmitter can be transmitted to the spare transponder and transmitted therefrom on a wavelength which is different from the wavelengths used by the ordinary transponders.

DESCRIPTION OF THE DRAWINGS The invention will now be described in detail as non-limiting embodiments with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of a bidirectional WDM link without protection, Fig. 2 is a block diagram of a first embodiment of a bidirectional link with protection, Fig. 3 is a block diagram of the same link as the one shown in Fig. 2 but shows the trajectories after a reset which has been caused due to a fault in a transponder, - Figs. 4 - 8 are block diagrams of further different embodiments of a bidirectional link with protection, - Figs. 9 and 10 are block diagrams of 4: 1 hybrid type optical switches, and - Fig. 11 is a block diagram of an optical switch of the "cross-bar" type and of the hybrid type.

DESCRIPTION OF PREFERRED EMBODIMENTS I fi g. 1 shows a bidirectional WDM link without protection. The link comprises two "add-drop" nodes 1, which are connected by means of a carrier 3 for traffic in a first direction and by a carrier for traffic in the opposite direction. channels, each access device 5 comprising a transmitter (TX) 7 and a receiver (Rx) 9. In the general case there are N access devices. optical signal, which is modulated on some wavelength, which may be the same wavelength for all transmitters 7. The optical signal from a transmitter 7 is output to the input of an associated transponder 11, in which the optical signal from the transmitter 7 is received and transmitted on A very well defined wavelength.The output beams from the transponder frames 11 are connected to an optical multiplexer 13, in which the incoming light signals are combined with or superimposed on each other. xom 13, the resulting optical signal is transmitted in an optical carrier 3, which transmits signals from the viewed node 1 to the receiver side of the other node. In the latter, the optical fiber 3 is connected to an optical demultiplexer 15, in which the different wavelengths of the incoming signal are filtered out and transmitted in optical fibers to the respective receivers 9 in an access device 5, the receivers 9 being optoelectric converters. such as suitable FIN diodes.

In the i fi g. 1, the components therein can of course become faulty and stop working as intended. In particular, there may be faults in the access device 5, in the transmitters 7 and the receivers 9, and in the transponders 11, all of which are active optical elements. To provide protection against such errors, a backup channel or backup channel must be provided in the link. This backup channel can then be used, when one of the components becomes faulty. Special devices for switching to this backup channel must also be present and there must also be redundancy in the access device 5.

A bidirectional WDM file with such protection is shown in the block diagram in fi g. 2. In this link the access devices 5 1 + 1 contain optical protection and in the nodes there is 1: 3, generally 1zN, protection of the corresponding three WDM channels in the general case the N WDM channels. Each access device 5 at one end, which is thus arranged on a separate channel, comprises an optical work transmitter or ordinary transmitter 7 and an optical backup transmitter or backup transmitter TX 'or 7', and an optical arc 10. 521 127 4 bit receiver or ordinary receiver 9 and an optical backup or backup receiver Rx 'or 9'.

These spare transmitters 7 'and receivers 9 can be in a working state at all times and are supplied with energy, so that the transmitters 7' always transmit the same signals as the ordinary transmitters 7.

An optical 2x2 cross switch 17 has a first of its two inputs connected to a regular transmitter 7 and its second input connected to the backup transmitter 7 belonging to the pair of regular transmitters and backup transmitters in the other access equipment 5. Similarly, an optical 2x2 cross switch 19 has a of its two outputs connected to a regular receiver 7 and another of its outputs connected to the backup receiver 7 'included in a pair of regular receivers 7 and backup receivers 7' in the same access equipment 5. A cross switch has two inputs and two outputs and can be in either of two states or modes. In straight-ahead mode, which is the ordinary state of the cross-switches considered here, it connects a first input to a first output and a second input to a second output and forms a "parallel" connection or "straight-forward" connection. In the crossing state, which is the state considered here, when the cross-switches receive a control signal, it connects the first input to the second output and the second input to the first output, thereby forming a "crossing" connection.

The WDM equipment in emergency 1 uses a fourth channel for backup, in the general case one (N + 1): th channel. On the transmitter side there is thus a transponder 21 for the backup channel, which has its output also connected to the multiplexer or the optically combining element 13 and works with the regular transponders 11. Each transponder 11, 21 thus transmits on its own special wavelength. In a cross-switch 17 on the transmitter side, the output which in the normal straight-ahead state of the switch is connected to the ordinary transmitter 7 is connected to a regular transponder 11 and its second output, which in the normal straight-ahead position of the drive switch 15 is connected to the spare transmitter. 7 ', is connected to an input of a 4: 1 optical switch 23, this switch being generally designed to select from one of the (NH) inputs to a single output. Thus, in the normal state of the node 1, three inputs of the 4: 1 switch 23 are connected to a single spare transmitter 7 '. There is thus an input to the 4: 1 eagle coupler 23, which is not connected to anything. In the normal operation of the node 1, in which no components are faulty, the 4: 1 switch 23 is in its fourth position, in which it does not receive any signals and does not transmit any signal.

On the receiver side, the demultiplexer 15 is arranged to divide the incoming signal into four individual wavelength bands, in the general case into (NH) individual, different wavelengths or wavelength bands. Three of the outputs of the demultiplexer 15 are connected to the input of the respective cross-switch 19, to its input, which in the normal state of the node 1, in which no components are faulty, is connected to the ordinary receiver 9. The output connection of the demultiplexer 15 , which transmits the wavelength band generated by the backup transponder 21 on the transmitter side, is connected 2 '1' 1 2 7 5 to a 1: 4 optical switch 25, in the general case to a 1: (N + l) switches. Three outputs from this 1: 4 switch 25 are connected to the other of the inputs of the cross-switches 19, to the input of these, which in the normal function of the node 1 is connected to the reserve receiver 9 '. The fourth output of the 1: 4 switch 25 is tennined and thus does not transmit any signal anywhere. This is also the normal position of the 1: 4 switch 25, in which all components on the transmitter side and the receiver side of the nodes 1 operate normally.

Thus, in the normal state, all the cross-switches 17, 19 are in their straight-ahead positions and thus the information-carrying signals are transmitted from the ordinary transmitters 7 to the corresponding ordinary transponder 11, via the optically combining element 13, the beacon 3 and the demultiplexer 15, to the ordinary receiver 9. from the operating backup transmitters 7 'passes to the 4: 1 switch 23 on the transmitter side and is tinned there, since this switch is not in a position to receive any output signal from a transmitter, since it is in the fourth position, in the general case in its (N + 1): th position.

Now, the various cases that may occur when any device in the bidirectional link of Fig. 2 becomes incorrect will be described.

An access transmitter 7 may be faulty. This is detected by transponder 11, which is connected to this faulty transmitter 7 via the corresponding cross-switch 17 and which performs this detection by determining by means of a power detector 27 arranged at its input connection that too little power ("LOP") is present on the input connection. The power detector 27 of the transponder 11 sends a signal to the cross-switch 17, which is connected to the input connection of the transponder. The cross switch 17 then switches from its straight forward state to its crossing state. The output signal from the backup transmitter 7 ', which constantly transmits the same signal as the ordinary transmitter 7 in the same pair of ordinary transmitters and backup transmitters, is now instead directed to the same transponder II via the crossed paths through the cross switch 17, which has changed state to the crossing the situation.

In the event of a fault in an access receiver 9, this condition is detected by a signal processing circuit 29 inside the access equipment 5, which then changes the output signal so that it is emitted from the backup receiver 9 'in the same pair of ordinary receivers and backup receivers, by changing the position of an electrical switch 31. A signal is then sent to the cross-switch 19, which is connected to the input of this pair.

This cross-switch 19 then switches positions from its straight-ahead position to the crossing position and thus directs the light signal from the demultiplexer 15 directly to the functioning backup receiver 9 'in the pair. Even one of the regular transponders may be faulty. This is detected on the receiver side of the demultiplexer 15, more precisely by the fact that there is too little power, which is detected by power measuring devices 33. On the receiver side, the 1: 4 switch 25 and the 4: 1 horn switch 23 are both switched to the position corresponding to the incorrect wavelength channel. . The 1: 4 switch 25 connects its input terminal to the cross-switch 19, which is connected to the receiver 9, which would receive the light signal, which has now disappeared or been lost. The 4: 1 switch 23 correspondingly connects its input connection, which is connected via a cross switch 17 to the transmitter 7, which belongs to the same access equipment 5 as the receiver 9, which would have received the light signal, which has now been reduced, to its output. These cross switches 19 and 17 change position from their straight forward position to the crossing position. The transponder 11 is also switched off for the wavelength band on which no signals are received, and the spare transponder 21 on the same receiver side is activated.

In the transmitting node, too little power is then obtained for the same wavelength band, which is intercepted by its demultiplexer 15, and then the transmitting node is also reconfigured in the same way as the receiving node. For both trajectory directions, the viewed signal now passes from the ordinary transmitter 7, through its associated 2 x 2 cross-switch 17, which is now in the crossing position, to the 4: 1 switch 23 and then the signal is sent to the spare transponder 21 in the transmitting the node, from the backup transponder 21 to the wavelength combining element 13, through a fiber 3 and to the demultiplexer 15 and from the demultiplexer to that of its output terminals, which is connected to the 1: 4 switch 25, to the correct cross-switch 19, which is in its intersecting position and then up to the ordinary receiver 9 for this channel. This case is also shown in Fig. 3.

The node structure shown in Figs. 2 and 3 can be modified in different ways. Thus shown in fi g. 4 shows the same basic node structure, in which the 2x2 cross-switches 17, which are connected to the transmitters 7 and the backup transmitters 7 ', have been omitted. Then the output signal of the ordinary transmitter 7 is directly connected to the input terminal of the respective ordinary transponder 11 and the backup transmitter 9 ', which always transmits the same signals as the ordinary transmitter 7 is directly connected to the respective input of the 4: 1 switch 23.

For a fault in one of the ordinary transmitters 7, the transponder 11, which is connected to the output of this faulty transmitter, detects that there is too little power. Then this transponder 11 is switched off and the spare transponder 21 is activated. Both the 4: 1 and 1: 4 switches 23, 25 switch to the position corresponding to the position of the faulty transmitter. The cross-switch 19, which is connected to the receiver corresponding to the faulty transmitter 7, switches from its straight-ahead position to the crossing position, so that the ordinary receiver 9 now receives a light signal from the 1: 4 switch 25.

In the second node, in which the faulty transmitter 7 is located. It is detected that there is too little power of the demultiplexer 15 by means of the corresponding power monitoring circuit 33 on its output side. Then also here the 4: 1 and 1: 4 switches 23, 25 change position to receive and transmit the wavelength channel corresponding to the channel for which too little power has been detected.

The cross-switch 19, which is connected to the receiver 9, switches from its straight-ahead position to the crossing position, so that the ordinary receiver 9 now receives a light signal from the 1: 4 switch 25. On this page the corresponding regular transponder 1 1 is also switched off and the reserve transponder 21 is activated.

After the conversion is done, traffic for both directions passes from the backup transmitter 7 'to the 4: 1 switch 23, through the backup transponder 21, through the multiplexer 13 and over the fiber link 3, on the receiver side through the demultiplexer 15 to the 1: 4 switch 25 , from the respective output port of this switch to the cross-switch 19, which is in its crossing position, up to the ordinary receiver 9. The cross-switches 19, which are connected to the receivers 9 and 9 ', can also be removed. This case is shown in the image in fi g. 5. An incorrect transmitter 7 is detected in the same way as for the node design according to fi g. 4. The whole rearrangement of the corresponding elements is also the same. Of course, no control signals can be conducted to the cross switches 17, 19 because there are none. Instead, the rearranged light signal will now not arrive at the ordinary receiver 9 but at the backup receiver 9 'in the corresponding pair comprising a regular receiver and a backup receiver.

The advantage of the designs according to fi g. 4 and 5 it is obvious that no cross-switches 17, 19 or at most only one cross-switch 19 are arranged in the path of light from a transmitter 7 to a receiver 9. The disadvantage is that if a transmitter 7 becomes faulty, the spare transponder 21 will be occupied and it will not be possible to use it as a reserve for an ordinary transponder 11.

Another modification, shown in the image in fi g. 6, is to replace the cross switches 15 connected to the transmitters with a standard 2x2 fi carrier switch 35 together with an optical switch 37, the switch being connected between the backup receiver 7 'and the switch 35. The resulting function is the same as use a cross-switch 17. The advantage of this node design is that there is no cross-switch in the path of light after the ordinary transmitter 7. The disadvantage is that the optical power loss for light passing from the transmitter 7 is increased (-3 dB). At this point in the node, this is normally a minor disadvantage.

Another modification is shown in fi g. 7, in which each 2x2 cross-coupler 19, which is directly connected to a pair of receivers 9 and 9 ', is replaced by four 1: 2 50-50% tiber-couplers 39, which are arranged with fixed crossing function and operate by means of power sharing, so that the output signal from the demultiplexer 15 always reaches both the ordinary receiver 9 and the backup receiver 9 'and so that the output signal from the corresponding port of the 1: 4 horn coupler 25 also reaches the two receivers 9, 9' in such a pair simultaneously. For a fault on an ordinary receiver 9, this is detected by the signal detector 29 in the same access equipment 5 and then an automatic change to the backup receiver 9 'occurs by changing the position of the electrical switch 31. No other elements need to be changed. A disadvantage of this structure is an increased optical loss, about -6 dB. The advantage of 15 15 25 25 521 127 8 is that fewer electrical control lines are required in the node.

Another modification is that no spare transmitters 7 'and / or the spare receiver 9' are used, see fi g. 8. Then the corresponding cross switches 17, 19 can be replaced with 1: 2 50/50% optical dividers 47, 49, so that the signal from a transmitter 7 always reaches the correct ordinary transponder 11 and the respective input port of the 4: 1 switch 23 When an ordinary transponder 11 becomes faulty, this is detected as above and the 4: 1 switch 23 is then set to the respective position, so that the backup transponders 21 now forward the traffic. 17,19 and in particular the 1: 4 and 4: 1 switches 23, 25 used in the i fi g. 2 - 8, can be replaced with alternative switches, which are not only made up of optical elements. The reason for the introduction of such alternatives is that in particular large optical switch matrices are not considered reliable. In the i fi g. 9, the receiver 51 is arranged on the input side, which converts the light signals into electrical signals, which are output to an electrical switch 25, which switches the selected incoming electrical signal to the output controlled by electrical control signals on lines 57. The electrical signal is converted to an optical signal of a transmitter 59, which uses a wavelength adapted to the wavelength of the travel transponder, which can thus be omitted. Switch 61 according to fi g. Fig. 9 can thus be used to replace the switch 23 and spare transponder in, for example, Fig. 2.

Another possibility is to use receivers and transmitters connected directly to each other, as shown in the 4: 1 switch 63 in fi g. 10. An incoming light signal is thus received by a receiver 64, in which it is converted into an electrical signal, which is transmitted to an electro-optical transmitter 65. The transmitter 65 is controlled by an electrical signal on a suitable control line 67, and when this is activated, it transmits a light signal using the wavelength of the spare transponder. The outputs of the transmitters are all connected to an optical multiplexer, the output of which is then connected to the optical fiber 3, so that the spare transponder can be omitted. The i fi g. 10 can be used to replace the switch 23 and the spare transponder in, for example, fi g. 2.

A cross switch 71 for use as a switch 17, 19 according to fi g. 2 can be designed as shown in f1g. 11. The two optical input terminals are connected to optoelectric receivers 73, which convert the light signals into electrical signals. The electrical signals are output to an exchange matrix 75, which provides the crossing function / straight-ahead function controlled by a suitable electrical signal on a line 77. The two outputs of the electric cross-switch 75 are connected to the inputs of electro-optical transmitters 79.

Claims (13)

10 15 20 25 30 521 127 9 PATENT REQUIREMENTS A WDM network comprising at least two nodes connected by a bidirectional link, each node comprising at least two pairs of ordinary optical transmitters and ordinary optical receivers, each ordinary optical transmitter receiving electrical signals and converting them into optical signals. and transmits the optical signals to another node and each ordinary optical receiver receives optical signals from another node and converts them into electrical signals, characterized in that each ordinary optical transmitter has a single optical spare transmitter, whereby pair is formed by an ordinary optical transmitter and an optical spare transmitter, the optical spare transmitter and the ordinary optical transmitter in each such pair being arranged to constantly receive the respective electrical signals and to constantly convert them into optical signals and wherein the optical spare transmitter in such a pair pairs are arranged to transmit the optical signals to which they are by spare transmitters n the received electrical signals have been converted, to the second node, if the ordinary optical transmitter in the pair becomes faulty. A WDM network according to claim 1, characterized by a first optical switch, wherein a first optical switch is connected to an ordinary optical transmitter and a spare optical transmitter in a pair for transmitting optical signals from only one of them. 3. A WDM network as claimed in Claim 2, characterized in that each first optical switch is arranged in a first position to connect an ordinary optical transmitter to an ordinary transponder, wherein an ordinary transponder converts received optical signals into transmitted ones. optical signals in a well-defined wavelength band, the wavelength bands for different ordinary transponders in a node being different from each other, the optical signals transmitted by the ordinary transponders in a node being output to an optical multiplexer or an optical combining element combining the signals for transmitting these on an optical transmitter connected to another node, and in another second position of the first optical switch connecting an ordinary transmitter to a spare transmitter, the spare transmitter converting received optical signals into transmitted optical signals in a power definition. nied wavelength band, the wavelength band for the spare transponder being different from the wavelength bands for the ordinary the transponders in the node, the optical signals emitted by spare transponders being delivered to the optical multiplexer or the optically combining element. WDlvI network according to claim 3, characterized in that in the first position of a first optical switch, the optical spare transmitter connected to the first optical switch is connected via the first optical switch to the spare transponder. via also a second switch, the second switch allowing optical signals from a maximum of one optical spare transmitter to reach the spare transponder. 5. A WDM network according to claim 4, characterized in that in the second position of a first optical switch, the ordinary optical transmitter is connected to the first optical switch. , connected via the first optical switch to the spare transponder via also the second switch, the second switch allowing optical signals from at most one ordinary optical transmitter to reach the spare transponder. WDM network according to one of Claims 3 to 5, characterized in that in the second position of a first optical switch, the optical spare transmitter connected to this first switch is connected to a corresponding ordinary transponder. WDM network according to one of Claims 1 to 6, characterized in that each ordinary optical transmitter is connected to an ordinary transponder, an ordinary transponder being arranged for each ordinary optical transmitter, an ordinary transponder being arranged. converting received optical signals into transmitted optical signals in a well-defined wavelength band, the wavelength band of different ordinary transponders in a node being different from each other, the optical signals transmitted by the ordinary transponder frames in a node being output to an optical multiplexer or an optical combining element, which combines the signals to transmit them on an optical fiber connected to another node, and the optical spare transmitters are connected to a spare transponder, the spare transponder converting received optical signals into transmitted optical ones. nals in a well-defined wavelength band, the wavelength band for the spare transponder being separate from the wavelength band one for the ordinary transponders in the node, the optical signals transmitted by the spare transponder being delivered to the optical multiplexer or the optically combining element, the connection of the optical spare ends with the spare transponder being made in such a way that the spare transponder receives at most optical signals, which are transmitted by a maximum of one spare transmitter. WDM network according to one of Claims 1 to 7, characterized in that all ordinary receivers in a node are connected to a single demultiplexer or a single filter and convert received optical signals into electrical signals. WDM network according to one of Claims 1 to 7, characterized in that all ordinary receivers in a node are connected to a single demultiplexer or a single filter and convert received optical signals into electrical signals, a switch being arranged to directing an optical signal from the multiplexer or filter to at most one of the regular receivers, this optical signal having the same wavelength as the wavelength of a spare transponder. 10. A WDM network according to any one of claims 1 to 9, characterized in that each optical ordinary receiver includes a single optical spare receiver, so that an optical spare receiver together with an ordinary optical receiver forms a pair, the optical spare receiver and the ordinary optical receiver in a pair are arranged to convert received optical signals into electrical signals and are connected to output electrical signals to the same output terminal, so that the optical receiver receives electrical signals to the output terminal, if the ordinary optical the receiver cannot emit electrical signals. 11. ll. WDM networks according to claim 10, characterized in that all ordinary receivers in a node are connected to a single demultiplexer or a single filter and convert received optical signals into electrical signals, each spare receiver being connected to the demultiplexer or filter via a switch. , the switch having fl your outputs, each output being connected to an individual receiver among the optical spare receivers and the switch being arranged to forward a signal from the demultiplexer or filter to at most one of the optical spare receivers. A WDM network according to claim 11, characterized in that a signal transmitted from the demultiplexer or filter to one of the optical spare receivers has the same wavelength as the wavelength of a spare transponder. 13. A WDM network according to claim 11, characterized in that a signal transmitted from the multiplexer or filter to one of the optical backup receivers has the same wavelength as the wavelength of the ordinary transmitter in the pair formed by an ordinary transmitter and the regular receiver, together with which the spare receiver is part of a pair.