Optical network with distributed sub-band rejections

The present invention generally relates to optical transmission systems and is particularly relevant to optical networks with dispersed subband rejections.

Telecommunications systems, cable television systems and data communication networks utilize optical networks to carry large amounts of information between remote locations. In optical networks, optical fibers transmit information in the form of optical signals. Optical fibers are composed of thin glass wires that can transmit signals over long distances with very low loss.

Optical networks often use wavelength division multiplexing (WDM) or high-density wavelength division multiplexing (DWDM) schemes to increase transmission capacity. In WDM and DWDM networks, many optical channels are transmitted at different wavelengths on each fiber. Network capacity is a quantity based on the number of wavelengths, the number of channels, or the size of channels in each fiber and band.

<p> An object of the present invention is to provide an optical network having a distributed subband prohibition unit, a node and a method in the optical network.</p>

<p> A node for an optical network is connected to a first transmission element that is connected to an optical ring and functions to carry traffic in the first direction, and is connected to the optical ring to carry traffic in another second direction. Includes a working second transmission element. Each of the first and second transmission elements includes an optical splitter element that functions to separate the ingress signal into an intermediate signal and a drop signal. The filter within each node functions to block at least the first subband of the network from among the intermediate signals in order to generate a passing signal that includes multiple distinct subbands of the network. Each node contains an additional element that functions to add at least the first subband local traffic to the passing signal for transmission over the network.</p>

<p> A technical advantage of the present invention includes providing an optical ring network with distributed subband prohibitions. In certain embodiments, separate subbands of the network are open at each node. As a result, an open ring network that can flexibly set the channel interval within the subband is provided. The network does not need to be physically open at any single point, and therefore Unidirectional Path-Switched Ring (UPSR) protection switching is supported.</p><p> Other advantages of certain embodiments may include optical interconnection capabilities with tunable bandpass filters. By preparing a simple, low-loss, and low-cost optical network, the channel spacing within the subband may be flexibly set. The node configuration may allow the broadcast of traffic, resulting in a negligible passband narrowing within the subband. Ring interfaces may be avoided due to low node loss (4 dB) and low loss variation. Also, no equalization of channel power is required.</p>

It will be appreciated that the various aspects of the invention may or may not include all or part of the technical advantages described above. In addition, other technical advantages of the present invention will become apparent to those skilled in the art from the drawings, description and claims below.

For a more complete understanding of the present invention and its advantages, the following description of the accompanying drawings will be referred to. In the figure, similar numbers represent similar elements.

FIG. 1 shows an optical network 10 according to an embodiment of the present invention. In this embodiment, the network 10 is an optical ring network in which a large number of optical channels are propagated at different wavelengths through the same path. The network 10 may be wavelength division multiplexing (WDM), high density wavelength division multiplexing (DWDM) or any other suitable multi-channel network. The network 10 may be used in a short-distance metropolitan network, a long-distance intercity network or any other suitable network, or may be used in a combination of a plurality of networks.

As described in detail below, network 10 is a ring network having subband prohibitions distributed around the ring. As used herein, "subband" means a portion of a network band consisting of a subset of the channels of a network. In certain embodiments, the entire bandwidth of the network may be divided into multiple subbands of equal or different bandwidth. In the subband of one embodiment, each node is assigned to a subband to which it adds its local traffic. Also, the node screens or blocks ingress traffic in that band, and that ingress traffic has already circulated through the ring. Therefore, each node controls channel interference in the network by both adding and removing traffic in the subband.

Referring to FIG. 1, the network 10 includes a plurality of nodes 12 and an optical ring 26, the optical ring consisting of a first optical fiber 14 and a second optical fiber 16. Optical information signals are transmitted in different directions on fibers 14 and 16 to provide fault tolerance. Therefore, both of the nodes send traffic to and receive traffic from each of the adjacent nodes. As used herein, "each" means every single one in at least one subset of the identified matter. The optical ring 26 may be composed of two unidirectional optical fibers or one bidirectional optical fiber as shown in the figure. Optical signals have at least one attribute for encoding into audio, video, textual, real-time, non-real-time and / or other suitable data. Modulation may be based on phase shift keying (PSK), intensity modulation (IM) and other suitable methods.

In the illustrated example, the traffic in the first fiber 14 propagates clockwise. The traffic in the second fiber 16 propagates counterclockwise. Node 12 operates to add and remove traffic to and from ring 26. At each node 12, traffic received from the local client is added to ring 26, and traffic destined for the local client is dropped (removed). Traffic may be added to the transmission signal by inserting a traffic channel or combining the signal of the channel, and at least a part of the transmission signal is transmitted on both or one of the fibers 14, 16. Traffic may be removed from ring 26 by making it available for transmission to local clients. Therefore, the traffic may be removed and may continue to be patrolled on the fibers 14 and / or 16.

In one embodiment, node 12 may further multiplex to append data from the client to ring 26 and operate to separate the data channel from ring 26. Node 12 may also perform light-to-electricity or electrical-to-light conversion for signals received and transmitted from the client.

Signal information such as wavelength, power and quality parameters may be monitored within node 12 and / or by a central control system. Therefore, the node 12 may provide a circuit protection function when a line disconnection occurs on both or one of the fibers 14 and 15. In one embodiment, optical surveillance channels (OSCs) may be used by nodes to communicate with each other and with the control system. In another embodiment, the network 10 may be a unidirectional routing ring (UPSR) network, with a lower bit error rate (BER) and as described further below with reference to FIG. / Or the switch is toggled to forward local client traffic from the higher power label direction (clockwise or counterclockwise).

FIG. 2 shows the details of the node 12 according to the embodiment of the present invention. In the illustrated example, at node 12, traffic is passively stripped from ring 26 by a passive splitter. "Passive" in this situation means that it is done without power, electricity and / or moving parts. Therefore, active devices use power, electrical or moving parts to perform their functions. In certain embodiments, the traffic is passively or otherwise ringed by splitting within the transmission ring and / or separating part of the signal within the ring, without multiplexing / separating. May be removed from 26. The filter acts to block the specified (assigned) subbands for the network and allow the remaining subbands to pass. Local traffic may be attached to ring 26 within the specified subband. Traffic may be added passively or otherwise.

With reference to FIG. 2, node 12 is composed of a first or counterclockwise transmission element 30, a second or clockwise transmission element 32, a composite element 36 and a distribution element 34. Transmission elements 30, 32 add traffic to ring 26, drop traffic from ring 26, remove previously transmitted traffic, and / or perform other interactions with the ring with respect to node 12. The synthetic element 36 passively or otherwise generates a local additional signal. The distribution element 34 passively or otherwise distributes the drop signal (removal signal) to individual signals in order to restore local drop traffic. In certain embodiments, each of the transmission, coupling and distribution elements 30, 32, 36, 34 may be implemented as separate cards, interconnected through the backplane of the card shelf at node 12. May be good. Further, the functions of the elements themselves may be distributed across a plurality of individual cards. In this way, node 12 is a modular and upgradeable format that provides a pay-as-you-grow architecture that pays for enhancements.

Each of the transmission elements 30, 32 is connected to or otherwise connected to the corresponding fiber 14 or 16 to add traffic to the ring 26 and remove the traffic from the ring 26. Each of the transmission elements 30, 32 has an optical splitter element 44, which operates to split the ingress signal into an intermediate signal and an elimination signal, and a plurality of separate components for the network, blocking the subband designated for the network from the intermediate signal. It has a filter 44 that operates to generate a pass signal that includes a subband and an additional element that operates to add local traffic in the assigned subband to the pass signal for transmission within the network. In the illustrated example, the filter 44 also functions as an additional element. In other embodiments (eg, in the examples shown in FIGS. 7A, 7B), the additional elements are separate elements. The additional elements may consist of filters, couplers or other suitable devices that add traffic to the optical network. The devices may be coupled directly, indirectly, or by other suitable connections or associations. In the illustrated example, the elements of node 12 and the devices in the elements are connected by fiber optic connections, but in other embodiments, plane wave guide circuits and / or free space optics are partially or wholly realized. You may.

Each of the optical splitter elements (splitter 42) may consist of a fiber optic coupler or other optical splitter that couples and / or splits the optical signal. The splitter 42 provides flexible channel spacing functionality, which means that there are no restrictions on channel spacing in the main streamline. As used herein, an optical splitter or optical coupler couples or generates an optical signal synthesized on the basis of two or more optical signals without multiplexing and demultiplexes them. Instead, any device may operate to passively divide or divide an optical signal into individual optical signals or based on the optical signal. The individual signals may be the same or similar in terms of frequency, form and / or content. For example, the individual signals may be content-same and have the same or substantially the same power, may be content-same but have substantially different powers, and may or may not have slightly different content. You may. In one embodiment, the splitter 42 may split the signal into two replicas with substantially equal power. The coupler may have a orientation greater than 55 dB. The wavelength dependence of insertion loss may be less than about 0.5 dB over 100 nm. The insertion loss of the 50/50 coupler may be less than about 3.5 dB.

The filter 44, described in detail below with reference to FIGS. 3A, 3B, operates to block traffic in the specified subband and allow the rest of the traffic to pass. As used herein, reject may mean terminating or removing a traffic stream. Filter 44 may append local traffic within the specified subband. The filter 44 may be optically passive, which does not require traffic multiplexing and / or separation.

In one embodiment, each of the transmission elements 30, 32 includes an amplifier 40. The amplifier 40 may be an erbium-doped fiber amplifier (EDFA) capable of receiving and amplifying an optical signal or other suitable amplification. The output of the amplifier may be, for example, 17 dBm. The section loss (section loss) of the clockwise fiber 14 may be different from the section loss of the counterclockwise fiber 16, and the amplifier 40 has an automatic level control (ALC) function with a wide dynamic range of inputs. You may use it. Therefore, the amplifier 40 is equipped not only with automatic gain control (AGC) to achieve gain flatness with respect to input power fluctuations, but also with a variable optical attenuator (VOA) to achieve ALC functionality. It's okay. In certain embodiments, one or more nodes 12 in network 10 include an amplified spontaneous emission (ASE) filter (not shown) coupled to amplifier 40, which may cause unwanted spontaneous emission from the amplifier in network 10. The increase in noise may be suppressed. The ASE filter is further described below in connection with FIGS. 7 and 9.

During operation of the transmission element, the amplifier 40 receives an ingress transmission signal from the connected fiber 14 or 16 and amplifies that signal. The amplified signal is transmitted to the optical coupler 42. The optical coupler 42 separates the amplified signal from the fiber 14 or 16 into an intermediate signal and a local drop signal. Filter 44 blocks the specified subband of the network from the intermediate signal to generate a pass signal and adds the local traffic of that specified subband to the pass signal for transmission on the fibers 14 and 16. The local drop signal is transmitted to the distribution element 36 for processing. Thus, for example, traffic is passively removed from ring 26 at node 12.

The distribution element 34 may consist of a drop splitter 50 that receives a dropped (dropped) signal from the fiber 14 or 16. The splitter 50 may consist of one fiber optic ingress lead and a plurality of fiber optic drop leads. The drop lead may be connected to the switch 52, the switch may allow UPSR protection switching, and one or more filters 54 may be connected to one or more optical receivers 56.

In certain embodiments, switch 52 is initially configured to forward local client traffic from the direction (clockwise or counterclockwise) corresponding to the lower bit error rate (BER). The threshold is set so that the switch remains in the default state unless the BER exceeds the threshold. Other threshold levels may be set for the power level. When the BER exceeds the BER threshold, or the power exceeds the power threshold, the switch selects the other signal. Commands related to the switch may be transmitted by the connection unit 57. As a result, simple and rapid protection can be locally controlled.

The composite element 36 may consist of a coupler 60, which receives traffic from a plurality of fiber optic additional leads, which leads to one or more additional optical transmitters 62 associated with a local client or other source. May be done. The composite element 36 further consists of two fiber optic ingress leads, the ingress leads being provided to the amplifier 40. In other embodiments, the amplifier 40 may be omitted. The amplifier 40 may consist of EDFA or other suitable amplifier. Therefore, a copy of the same traffic is forwarded through the bandpass filter 44 to each of the transmission elements 30 and 32 and added to the ring 26 in both clockwise and counterclockwise directions.

FIG. 3A is a block diagram showing the operation of the filter 44 of the node of FIG. 2 according to an embodiment of the present invention. The filters 44 may consist of thin films, fixed filters, tunable filters or other suitable filters, each filter 44 being connected from a single filter or in series, in parallel or in different forms. It may consist of a filter of. In the illustrated example, the filter 44 is a single bandpass filter.

As shown in FIG. 3A, the bandpass filter 44 operates to receive an optical signal 80 carrying traffic in multiple subbands. Each subband may or may not carry one or more traffic. The traffic channel may flexibly take up space within the subband. Bandwidth filter 44 blocks the specified subband 86 from signal 80 and passes the remaining subband 82 of the network. The blocked traffic is previously transmitted traffic and is removed to prevent re-patrolling and channel interference. Traffic that has passed may be blocked by another node in network 10. Local traffic within the specified subband 86 may be attached to signal 80.

FIG. 3B is a diagram showing a state of passage and addition / removal in the filter 44 illustrated in FIG. 3A according to an embodiment of the present invention. As described with respect to FIG. 3A, the pass filter 44 transmits through the selected subband 82 and blocks one or more selected subbands 86 from the signal 80. In the illustrated example, the passing subband 82 consists of subbands A and B, which subband consists of multiple channels on the low end side of the C band spectrum. In the illustrated example, subband A contains four 2.5 Gb / s channels, one 10 Gb / s channel, and one 40 Gb / s channel (represented by thin, medium, and thick arrows, respectively). , Subband B contains one 10 Gb / s channel and seven 2.5 Gb / s channels. The transit subchannel 82 is also composed of subband D, which is on the upper end side of the C band spectrum and contains four 2.5 Gb / s channels and four 10 Gb / s channels. The blocked subband C contains two 10 Gb / s channels and two 40 Gb / s channels within the same central range of the C band spectrum. Although Figure 3B depicts an exemplary channel spacing; the channel spacing is flexible, i.e. there are no restrictions on the channel spacing within the subband. The bandwidth of the network may consist of other suitable bands, or the bandwidth may be divided into multiple subbands with different subbandwidths, and the subbands to which the blocked subbands are added. It will be understood that it may be composed of different subbands.

In certain embodiments, some bands that do not carry traffic are provided between adjacent subbands to avoid interference. In the illustrated example, the interval 90 constitutes a guard band of 200 GHz between adjacent subbands. Traffic signals are not assigned to guard bands and try to minimize signal loss and / or interference.

FIG. 4 is a block diagram showing an exemplary band propagation path for the optical ring of FIG. 1 according to an embodiment of the present invention. In the example shown in FIG. 4, each of the nodes 12 blocks the traffic from the ring 26 for the specified subband, adds new traffic to the ring 26 with the specified subband, and each node Block the subbands specified by you. For the sake of brevity, only the fiber 14 of the ring 26 is drawn. It will be appreciated that there is also a clockwise path on the fiber 16 that corresponds to the path shown in FIG.

With reference to FIG. 4, traffic is added to subband A at node 22, propagates around fiber 14, and is removed (blocked) from fiber 14 at node 22. In this way, channel interference is avoided. Similarly, subband B is blocked and added at node 24, subband C is blocked and added at node 18, and subband D is blocked and added at node 20. In certain embodiments, subbands A, B, C and D include subbands across the C-band spectrum, with each subband within the C-band assigned to one of nodes 18, 20, 22, 24.

FIG. 5 shows an exemplary band propagation path in the optical ring of FIG. 1 according to an embodiment of the present invention. For convenience of reference, the details of the add / remove node 12 are shown in a superordinate concept.

With reference to FIG. 5, the optical paths 200 and 202 represent the same stream of traffic added to the network from the outgoing node 18 in the bands selected in the counterclockwise and clockwise directions (node 18 band), respectively. In the illustrated example, the intended destination node for the node 18 band is node 22. In normal mode of operation, each of the optical paths 200,203 starts at node 18 and ends there to avoid channel interference. As mentioned above, each node adds and removes traffic in the specified subband, the optical path may be terminated by blocking by filter 44, and the filter blocks all traffic in the assigned subband. .. Although Figure 5 shows node 22 as the destination node, it should be noted that node 18 also reaches the drop nodes of nodes 20, 24, 18. Therefore, the network has a broadcast function. As described below with reference to FIG. 6, the broadcast of node 18 in both clockwise and counterclockwise directions provides protection in the event of line disconnection or other failure.

FIG. 6 is a block diagram showing a protection function related to the propagation path of FIG. 5 at the time of line disconnection or other failure according to the embodiment of the present invention. In the example shown in FIG. 6, as described above, the optical paths 200 and 202 represent the same stream of traffic added to the network from the outgoing node 18 in the counterclockwise and clockwise directions, respectively.

In the illustrated example, disconnection 250 prevents the node 18 band from reaching its destination node 22 through the optical path 202. According to the protection switching protocol, node 22 responds by detecting a BER that exceeds the BER threshold for clockwise traffic (counterclockwise traffic still remains below the BER threshold due to disconnection). ), Switch 54 from receiving clockwise (fiber 14) traffic to receiving counterclockwise (fiber 16) traffic. After repairing the disconnection, the network may return to the pre-protection switching state as shown in FIG. 5 or remain switched.

FIG. 7A is a block diagram showing details of add / remove nodes according to another embodiment of the present invention. In certain embodiments, one or more elements shown within node 300 of FIG. 7A may be used in place of the elements shown within node 12 of FIG.

Node 300 is composed of a composite element 36 and a distribution element 34, as described with reference to FIG. However, node 300 has transmission elements 330,332 instead of transmission elements 30, 32, each of which is composed of a filter 304 between a drop coupler 42 and an additional element consisting of an additional coupler 302. Similarly, like the drop coupler 42, the add-up coupler 302 is passive and has the flexibility to set the channel spacing. Filter 304 blocks one or more bands from the connected fibers 14 or 16 to prevent channel interference. The filter 304 may consist of a tunable bandpass filter or other suitable filter. Although filter 304 blocks traffic within the specified subband as described above with reference to filter 44; in the embodiment shown in FIG. 8, filter 304 does not have to add traffic to the network. .. Instead, local traffic is added through add-on coupler 302. The configuration of transmission elements 330,332 shares the route within the network in non-UPSR mode, allowing traffic outside the specified subband to be added by the add-on coupler 302, as shown below, with reference to FIG. Increase overall network capacity as described in detail.

The amplifier 344 may be an erbium-doped fiber amplifier (EDFA) or other suitable amplifier capable of receiving and amplifying optical signals. Node 300 includes an amplified spontaneous emission (ASE) blocking filter 346 connected to amplifier 344 to prevent unwanted spontaneous emission due to ASE along the ring and increased noise due to amplification of network 10. For example, a typical EDFA has a gain band of 35 nm between 1530 nm and 1565 nm. The network may block ASE patrol for any portion of the overall gain band (1530-1565 nm), even if the number of nodes in the ring is relatively small (eg, 3 nodes). Thus, in a particular embodiment, each ring has one ASE blocking filter 346 within at least one node of the ring. In certain embodiments, the ASE blocking filter 346 may be included within a one-node transmission element of a multi-node network. In certain embodiments, the ASE blocking filter 346 may screen or block noise in unused subbands of the network's bandwidth. If additional nodes are added to the network, additional subbands may be used to carry the traffic, and the ASE blocking filter 346 selectively reduces the subbands it screens and its It may be adapted to accommodate additional subbands of such traffic. As described below with reference to FIG. 9, the ASE blocking filter 346 may consist of a set of multiple bandpass filters, allowing network scalability to add additional nodes. ..

FIG. 7B is a block diagram showing the details of the addition / removal nodes according to still another embodiment of the present invention. The add / remove node 350 is composed of a distribution element 334, a composite element 336, and a transmission element 352,354. The transmission elements 352 and 354 are additionally composed of the drop coupler 42 and the addition coupler 302, respectively, similarly to the transmission elements 330 and 332 of FIG. 7A.<u style="single">element</u>Consists of a filter 304 between and. A 2x2 switch 356 is provided between the amplifier 344 and the drop coupler 42 to operate the transmission element and thus at the node 350 to open the optical ring. In certain embodiments, the 2x2 switch 356 may be opened in the event of failure of the ASE blocking filter 346 to prevent the ASE blocking filter 346 from blocking ASE patrols for unused subbands. For example, if the ASE blocking filter 346 in the transmission element 352 fails, the 2x2 switch in the transmission elements 352,354 is opened to effectively form a fiber break within that segment. In the UPSR protection regime, the optical path is protected under such effective fiber cutting conditions.

The distribution element 334 may consist of a drop splitter 50 that receives a signal dropped from the fiber 14 or 16. Like node 12, the splitter 50 may consist of a splitter with one fiber optic ingress lead and a plurality of fiber optic drop leads. However, one splitter 50 in node 300 is coupled to filter 308, that filter is connected to optical receiver 310, one splitter is connected to filter 312, and that filter is connected to filter 314. Similarly, the composite element 336 may be composed of a coupler 316 connected to the transmitter 320 and a coupler 318 connected to the transmitter 322. Thus, 1 + 1 protection and network redundancy are provided for both distribution and synthesis elements.

The UPSR protection method may be supported by the redundancy of the receiver 62. In certain embodiments, the receiver 62 may receive the same subband traffic from both clockwise and counterclockwise directions to simultaneously perform BER monitoring. In this embodiment, if the BER of the working traffic exceeds the BER threshold even slightly, the receiver associated with the lower BER may continue to receive the traffic.

FIG. 8A is a block diagram showing an exemplary band propagation path in an optical ring according to another embodiment of the present invention. In the embodiment shown in FIG. 8, the network capacity is increased as a whole by sharing the route.

In FIG. 8A, nodes 18, 20, 22, 24 are composed of nodes 300 as described with reference to FIG. As mentioned above with reference to FIG. 4, subband B is blocked and any subband may be added at node 24, subband C is blocked and added at node 18, and subband D is Blocked and added at node 20. However, for the sake of brevity, only the optical path of subband A is shown in FIG.

Working traffic is added at node 22 in subband A only in the clockwise direction, propagates around fiber 14, and is eliminated from fiber 14 at node 22 as described above with reference to FIG. .. However, the node configuration in FIG. 8 also allows route sharing by allowing additional subband A traffic to be added to fiber 16 at node 20. Such additional traffic may be referred to as Protection Channel Access (PCA) traffic. Both working and PCA subband A traffic are blocked at node 22 for both fibers 14 and 16 to avoid channel interference.

FIG. 8B is a block diagram showing a transmission / reception redundancy function unit at the addition / removal node according to another embodiment of the present invention. The transmit redundancy element shown in FIG. 8B may be added to the composite element of FIGS. 2,7A, or may be appropriately used in the present invention in other ways. Similarly, the receive redundancy function shown in FIG. 8B may be added to the distribution element 36 of FIGS. 2,7A, or may be appropriately used in the present invention in other ways. The redundant 1x2 switch 362 and redundant transmitters 366,368 provide redundancy for the traffic added to the clockwise and counterclockwise rings. Similarly, the redundant filter 370, redundant receivers 372,374 and 1x2 switch 362 provide redundant means for receiving traffic from the clockwise and counterclockwise rings. In certain embodiments, redundancy may be given 1 + 1 protection or N: 1 protection.

FIG. 9 is a block diagram showing an example of a band transmission line in an optical ring according to another embodiment of the present invention. Similar to the ring described with reference to FIGS. 1 and 4, the network 380 is composed of multiple nodes 382,384,386,388 within the optical ring, which is composed of a clockwise optical fiber 390 and a counterclockwise optical fiber. Will be done. For simplicity, counterclockwise fibers are not shown. Similar to the example shown in Figure 4, each node 382,384,386,388 blocks traffic from the specified subband of traffic from the ring, appends new traffic to the ring in the specified subband, and each node. Blocks another designated subband. Traffic is added in subband 382 within subband G, propagates around fiber 390, and is removed from fiber 390 at node 382. Similarly, subband H is excluded and added at node 384, subband E is excluded and added at node 386, and subband F is excluded and added at node 388.

Unlike the nodes described above, nodes 382,384,386,388 have additional subband filters that act to block and add additional subbands (subband Z). In the illustrated example, subband Z is blocked and added at each of nodes 382,384,386,388. Therefore, channels within the common subband Z are added and dropped at each node. Dropped channels in subband Z can be reinserted into the ring or terminated at all nodes. When terminated, these drop channels in subband Z can be shared by other traffic within other nodes. In this way, the overall capacity of the network may be increased.

10A-C show the details and operation of the ASE blocking filter according to an embodiment of the present invention. FIG. 10A is a block diagram showing a reconfigurable ASE blocking filter 400 according to an embodiment of the present invention. In certain embodiments, the ASE blocking filter 346 may have a plurality of sets of filters 400 to allow the network to be expandable so that additional nodes and additional subbands carry traffic. In other embodiments, it will be appreciated that the ASE blocking filter 346 may consist of one or more filters connected in series, in parallel, or in another form.

The filter group 400 may be composed of a plurality of individual bandpass filters 404. The individual filters 404,406 may be provided to pass selected subbands (which may consist of one or more frequencies) and block other subbands. Switch 402 may be provided to terminate traffic corresponding to a particular filter 404,406. The filter 404 operates to separate (demultiplex) subbands, the filter 406 operates to multiplex (multiplex) subbands, and in the illustrated embodiment, the bandpass filters 404,406 operate to subband AH. Corresponds to.

For cascaded filters 400, both transmission and reflection of each subband are used. For example, if the ASE input consists of all subbands (A, B, ..., H), then subbands B through H are screened by the filter 404 associated with subband A and subband A Passes there. In a particular embodiment, the spectral power (mW / Hz) of the light in subband A in the reflected light is 1/10000 of the spectral power of the passing subbands (B, C, D, ..., H). , The spectral power of the blocked subbands (B, C, D, ..., H) in the transmitted light is 1/100 of the spectral power of subband A. When the switch 202 corresponding to subband A is in the "on" or "passing" position, the spectral power of the blocked subbands (B, C, D, ..., H) is the passing sub. It is 1/10000 of the spectral power of band A.

The subbands (B, C, D, ..., H) blocked by the subband A filter 404 enter the filter 404 corresponding to subband B. The sub-band reflected by the sub-band B filter 404 contains only sub-bands C, D, E, F, G, and H. In the final filter 404, the light of the subband H enters the subband filter H404 and passes through the subband filter H406. Since the power loss due to reflection is so small, the amount of loss for each subband (the loss due to the two subband filters (404,406) and the loss due to the switch 402) is substantially equal. Therefore, the wavelength (or subband) -dependent loss of multiplex light at the output is small.

The second filter 406 is provided to further select the passing light. For example, subband B light (if the corresponding switch 202 is "passed" on) passes through subband B filter 406 and is mixed with passed and reflected subband A light, thereby subband A and Multiplex B. As mentioned above, by controlling switch 202, the ASE blocking filter changes its band on the basis of the subband.

If additional nodes and / or subbands are added to the network, the additional switch 402 may be closed to allow the additional subbands to pass through. For example, as shown in FIG. 10B, a four node network may carry four subbands A, B, C, D. The filter group 400 may be provided to block non-subbands A, B, C, D and reduce or eliminate noise in other unused subbands. As shown in Figure 10C, when an additional subband E is added, the additional switch 402 corresponding to the additional subband is closed and the additional bandpass corresponding to that additional node. Filters 404,406 may be allowed to pass traffic corresponding to these bands.

FIG. 11 is a flowchart showing a method of transmitting traffic in an optical network according to an embodiment of the present invention. As mentioned above, the traffic is carried within the optical ring network, and each node is assigned a subband of the network to which it adds a channel. The subband may include any number of traffic channels as appropriate. Traffic may be forwarded in the first and second directions on the optical ring.

The flow begins at step 500 and at each of the nodes connected to the ring, the transmitted signal consisting of ingress traffic is passively split into a drop signal and an intermediate signal. In step 502, a bandpass or other suitable filter blocks one or more subband channels from the intermediate signal in order to generate a pass signal.

Proceeding to step 504, traffic is added to the pass signal. The traffic may be added to the subband by a bandpass filter or may be added by an optical coupler.

FIG. 12 is a flowchart showing a method of inserting an additional node into an optical network according to an embodiment of the present invention. The method of FIG. 12 may be used in an embodiment as shown in FIG. 8 (an example in which route sharing is used for protection channel access (PCA) traffic).

The flow begins at step 1000 and PCA traffic is removed from the network by stopping PCA traffic transmission or otherwise. Proceeding to step 1002, all working channels are switched to the counterclockwise ring. In step 1004, the clockwise fiber into which the new node is inserted is cut, and the new node is inserted into the network and connected to the clockwise fiber. Proceeding to step 1006, the clockwise ASE blocking filter associated with the new node is switched "on" or in the pass position.

Proceeding to step 1008, all working channels are switched clockwise. In step 1010, the counterclockwise fiber into which the new node is inserted is cut and the new node is connected to the counterclockwise fiber. In step 1012, the counterclockwise ASE blocking filter corresponding to the new node is toggled to the on position. Finally, at step 1014, the network is prepared as shown in FIG. 8 or properly prepared for route sharing so that PCA traffic may be terminated at the network.

In the embodiments of the present invention in which UPSR protection switching is used, the method of FIG. 12 will not be used. Instead, inserting a new node involves separating the optical ring at a point on the ring where the new node is inserted, and connecting the new node to a clockwise or counterclockwise fiber optic. Switch 52 automatically protects any traffic, which is interrupted by the temporary opening of the ring by switching to the signal associated with the lowest BER. In a particular embodiment, as described with reference to FIGS. 10A-10C, switching the subband filter corresponding to the new node to the on position enables transmission of the new subband corresponding to the new node. As such, the ASE blocking filter 344 may be provided.

Although the present invention has been described above with some examples, various modifications and modifications will be suggested to those skilled in the art. The present invention is intended to include such changes and modifications within the scope of the appended claims.

<figref num="1">It is a block diagram which shows the optical ring network by one Example of this invention.</figref><figref num="2">It is a detailed block diagram of the addition / removal node of FIG. 1 according to one embodiment of the present invention.</figref><figref num="3A">It is a block diagram which shows the operation of the bandpass filter of the node of FIG. 2 by one Example of this invention.</figref><figref num="3B">It is a figure which shows the subband about the addition, removal and passage function of FIG. 3A by one Example of this invention.</figref><figref num="4">FIG. 3 is a block diagram showing an exemplary propagation path for the network subband of FIG. 1 according to an embodiment of the present invention.</figref><figref num="5">It is a block diagram which shows the exemplary band propagation path in the optical ring of FIG.</figref><figref num="6">It is a block diagram which shows the protection function about the propagation path of FIG. 5 by one Example of this invention.</figref><figref num="7A">It is a block diagram which shows the detail of the addition / removal node by another Example of this invention.</figref><figref num="7B">It is a block diagram which shows the detail of the addition / removal node by still another Example of this invention.</figref><figref num="8A">FIG. 3 is a block diagram showing an exemplary propagation path of subbands in the network of FIG. 1 provided at the node of FIG. 7A or 7B according to another embodiment of the present invention.</figref><figref num="8B">It is a block diagram which shows the redundant function part in the addition removal node by still another Example of this invention.</figref><figref num="9">It is a block diagram which shows the example of the transmission path of the subband in the network of FIG. 1 by still another Example of this invention.</figref><figref num="10">It is a figure which shows the detail and operation of the amplified spontaneous emission (ASE) filter by one Example of this invention.</figref><figref num="11">It is a flowchart which shows the traffic management method in the optical network by one Example of this invention.</figref><figref num="12">It is a flowchart which shows the method of inserting a new node into an optical network by one Example of this invention.</figref>