Optical two-fibre ring network

The invention relates to a 2-fiber optical ring network for wave multiplex systems with multiple add-drop multiplexer terminals.

Optical networks are often designed as ring networks in order to have a replacement path available in case of disturbances of the regular transmission path. From the article Multiwavelength Survivable Ring Network Architectures, AF Elrefaie, Bellcore, Red Bank, NJ 07701, USA, 0-7803-0950-2 / 93 / $ 3.001993IEEE, page 1245-1251, such ring architectures for a wavelength division multiplexing system are known.

In the ring networks so-called add-drop multiplexers are often provided, which serve for branching and insertion of transmission channels. These functions have so far been realized with electrical signals. In future, however, these functions should take over optically operating coupling fields, which are used in ring structures, which should be realized with little effort and protection circuits (replacement circuits) should have.

A ring network satisfying these conditions is specified in claim 1.

Advantageous developments are described in the subclaims.

The particular advantage of this ring network is that each (a subscriber associated) line assembly is assigned a specific wavelength for both the outgoing signals and for the received signals that are suitable for transmission both in the working channels of the ring network and in the protection Channels is maintained. Switching between undisturbed and protection operation is done via simple optical switching devices. An embodiment of the invention will be described with reference to figures.

Show it:<dl id="dl0001" compact="compact"><dt>FIG. 1</dt><dd>the principle of a ring network according to the invention,</dd><dt>FIG. 2</dt><dd>the transmission paths with a broken optical fiber,</dd><dt>FIG. 3</dt><dd>the transmission paths with two interrupted optical fibers,</dd><dt>FIG. 4</dt><dd>the schematic diagram of a terminal and</dd><dt>FIG. 5</dt><dd>an embodiment of a terminal.</dd></dl>

<b>FIG. 1</b> shows a ring network according to the invention with two optical fibers L1 and L2. The working connections between the terminals are made via a plurality of working channels WW and WE, each of which is assigned to a specific wavelength. For example, the terminal T3 receives data from the terminal T1 via one of the working channels East WE, the data channel Kλ1. For example, the terminal T1 receives over the other part of the ring section via the<img file="EP0969618A2_D0001.tif" />data channel Kλ1 (the same wavelength is used to transmit other data) data from terminal T3, it discouples and can send new data to terminal T2 in the same data channel. This data channel is in each case looped through at the terminals T2 and T4 which are not affected by the data transmission. Accordingly, data is transmitted via working channels West WW in the opposite direction. The terminals are thus interconnected by two unidirectional rings. Each terminal connected to a terminal, eg LE1 and LE31 (there are usually several line terminals are turned on), is thus duplex connected to another line terminal also via one of the two rings. Further channels assigned to a different wavelength in each case provide further terminals via the first optical fiber L1 as well as via the second optical fiber L2. Line terminals to be interconnected.

The working channels WE transmitted via the first optical fiber L1 are a first, eg higher /<img file="EP0969618A2_D0002.tif" />blue transmission band, smaller wavelengths, assigned, while the transmitted via the second optical fiber L2 channels WW have longer wavelengths and a second <img file="EP0969618A2_D0003.tif" />Also, transmission bands are conceivable (but not very useful) in which the individual channels <img file="EP0969618A2_D0004.tif" />Wavy "are nested.

In <b>FIG. 2</b> the second optical fiber L2 is broken between the terminal T1 and the terminal T4. The protection connection (spare connection), which comprises all the channels transmitted on the optical fiber 2, is now switched to the terminal T4 via the first optical fiber L1 and the intact part of the ring. The previously counterclockwise in the west W from the terminal T1 in the red transmission band sent working channels WW are now redirected and as protection channels PE_s fed into the first optical fiber L1 and continue to transmit in the red transmission band but now in a clockwise direction over the intact part of the ring network. Since the red transmission band on the optical fiber L1 was hitherto free, the data additionally now transmitted in the red transmission band does not collide with those of the blue transmission band. The red transmission band is looped through the terminals T2 and T3. For clarity in the illustration, the equivalent circuit in FIG. 2 has been shown only for a channel which transports data for the terminal T4. The remaining channels are fed back into the red transmission band WW via the terminal T4. The indices used to supplement the reference numbers <img file="EP0969618A2_D0005.tif" />s "are used to identify that these signals are sent out as protection signals.

<b>FIG. 3</b> shows the case that both optical fibers L1 and L2 between the terminals T1 and T4 are interrupted (disturbed). The working channels WW and WE, which can no longer be transmitted via this route, will now be redirected and used as protection channels PE_s or PW_s each fed into the other optical fiber and transmitted over the intact part of the ring network, where they are looped through the terminals T2 and T3.

<b>FIG. 4</b> shows a schematic diagram of the terminal T1. It contains two coupling fields CC1 and CC2, which in the undisturbed operating case each have a wavelength multiplex signal, the working channels WW_e or WE_e, and each receive a wavelength multiplexed signal WW_s or WE_s send out (for the received signals is additionally added here as index e, but the signals correspond to the previously provided otherwise with the same reference numerals signals).

The received multiplexed signals are first in line demultiplexers DE and DW in working channels WW_e (or WE_e) and in protection channels PW_e (PE_e), each of which is supplied to an optical panel SFE (SFW). The working channels or protection channels, such as WW_e or PW_e, are fed to a wavelength demultiplexer WDE (WDW) and divided by it into different channels with different wavelengths.

In undisturbed operation, the individual channels are either switched through by the switching networks CC1, CC2 or diverted to line terminals LE1, ..., LEN. In the same way, signals emitted by the line terminals are combined via the switching networks in wavelength multiplexers MW and ME to form wavelength division multiplex signals and transmitted.

The branched signals to be inserted each line terminal are switched through only in a switching matrix.

If, as in FIG. 3, the western terminals of the terminal T1 are disturbed, then the working signals WW to be sent in the direction W via the output OW of the switching matrix CC2 must be present_s via the switching field SFW and the switching field SFE via the output OE of a line multiplexer East ME as protection signals PE_s be coupled into the optical fiber L1.

Due to the disturbance, no signals WE from the direction W can occur_e receive more. However, these receive signals are shown in FIG. 3 from the terminal T4 as a protection signal PW_s emitted and get over the optical fiber L2 via the undisturbed ring segment to a line demultiplexer DE. From there, they are now routed via the SFE and SFW panels to the input IW of the wavelength demultiplexer WDW, where the identical working signals were previously received (the name of the inputs and outputs of the other wavelength demultiplexers and wavelength multiplexers is chosen accordingly). The protection connections are shown in dotted lines.

As can be seen from FIG. 4, in principle the line multiplexers and the wavelength multiplexers or the line demultiplexers and the wavelength demultiplexers can in principle also be combined and the switching fields can be realized as part of the switching matrix.

In <b>FIG. 5</b> essential details of the terminal are shown. About Protection switch PSW1, PSE1 and PSW, PSE (parts of the switching field SFW) can use either the Working outputs W of the line multiplexer DW and DE or the Protection outputs P of the Leitungsmultiplexers DE or DW with the input of the wavelength demultiplexer West WDW or the wavelength demultiplexer East WDE. This allows the receiving side to carry out a protection circuit.

The wavelength demultiplexer West WDW divides the wavelength multiplex signal supplied to it, which, as well as the morning and protection signals, always corresponds to the same (here blue) transmission band, into different channels Kλ1 to Kλ<img file="EP0969618A2_D0006.tif" /> on. Optical switches CSW1 to CSW<img file="EP0969618A2_D0007.tif" /> of the switching matrix CC1 enable the switching of the individual channels to further optical switches CSE1 to CSE<img file="EP0969618A2_D0008.tif" />whose outputs are connected to the wavelength multiplexer East WME and are combined here to form a wavelength multiplex signal to be transmitted. The optical switches CSW1 to CSW<img file="EP0969618A2_D0009.tif" /> of the switching network CC1 instead of switching through the channels Kλ1 to Kλ<img file="EP0969618A2_D0010.tif" /> also their branch (drop function), while the switch CSE1 to CSE<img file="EP0969618A2_D0011.tif" /> the insertion (add function) of corresponding channels or signals from the line end modules LE1 to LE <img file="EP0969618A2_D0012.tif" /> instead of enabling the switching function.

The illustration shows a disturbance of the western lines, so that the wavelength signal demultiplexer WDW the protection signal is supplied.

The output of the wavelength multiplexer East WME is to implement the protection function via protection switch PSE2 and PSW connectable to a protection input of the line multiplexer MW, but this does not correspond to the illustrated fault case.

In the same way, the outputs of the wavelength demultiplexer are East WDE with further switches CSE<img file="EP0969618A2_D0013.tif" />+1 to CSE<img file="EP0969618A2_D0014.tif" /> connected to the switching of the channels Kλ<img file="EP0969618A2_D0015.tif" /><img file="EP0969618A2_D0016.tif" /> to Kλ<img file="EP0969618A2_D0017.tif" /> or serve to their branches (drop function). The insertion or switching is done with other switches CSW<img file="EP0969618A2_D0018.tif" />+<img file="EP0969618A2_D0019.tif" /> to CSW<img file="EP0969618A2_D0020.tif" /> whose outputs are in turn combined by a wavelength multiplexer WMW whose output is connected via a protection switch PSW2 to the line multiplexer West MW or in the illustrated case of interference via this switch and the other protection switch PSE with the line multiplexer ME. With this switch, the protection signal is switched through in unaffected terminals.

In the same way is connected via the protection switch PSE2 either during undisturbed operation the east lines of the output of the wavelength division multiplexer East WME with the Leitungsmultiplexers ME or conduction disorders east of the terminal via the protection switch PSE2 and another Protection switch PSW to the line Multiplexer West MW led.

The positions of the protection switches are shown for interference of both fibers L1 and L2 on the west side. In this case, all connections must be made via the optical fibers connected to the terminal to the east. The wavelength multiplex signal, which is actually to be transmitted in the west, is now connected via the protection switch PSW2 and the protection switch PSE to an input of the line multiplexer East ME and transmitted as a protection signal PE via the first optical fiber L1.

Since the line demultiplexer West DW can not receive a signal, it can only be received via the eastern path via the second optical fiber L2 and supplied as a protection signal via the protection switch PSE1 and PSW to the wavelength demultiplexer West WDW. The protection switches PSE and PSW can also be realized as part of the switching network.

Also, Figure 5 is a functional block diagram. In an implementation, additional but familiar to those skilled components are required.