OPTICAL CHANNEL CROSS CONNECT FOR TELECOMMUNICATION SYSTEMS IN WDM TECHNOLOGY (WAVELENGTH DIVISION MULTIPLEXING) HAVING A DOUBLE SPATIAL SWITCHING STRUCTURE OF OPTICAL FLOWS STRICTLY NOT BLOCKING AND INTERPOSED FUNCTIONAL UNITS OPERATING ON SINGLE CHANNELS

• US 6,542,268 B1
• Filed: 12/28/1999
• Issued: 04/01/2003
• Est. Priority Date: 12/28/1998
• Status: Expired due to Term

• Current Assignee: Siemens Information And Communication Networks, Inc., STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: CNX SPA, STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Rotolo, Salvatore, Brunazzi, Stefano
• Primary Examiner(s): Chan, Jason
• Assistant Examiner(s): KIM, DAVID S
• Application Number:
  US09/472,887
• Time in Patent Office: 1,190 Days
• Field of Search: 359/110, 359/117, 359/119, 359/123, 359/124, 359/125, 359/127, 359/128
• US Class Current: 398/68
• CPC Class Codes: H04J 14/0204 Broadcast and select arrangements, e.g. with an optical splitter at the input before adding or dropping
• CPC Class Codes: H04J 14/021 Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
• CPC Class Codes: H04J 14/0212 using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04J 14/0213 Groups of channels or wave bands arrangements
• CPC Class Codes: H04J 14/0217 Multi-degree architectures, e.g. having a connection degree greater than two
• CPC Class Codes: H04J 14/0283 WDM ring architectures
• CPC Class Codes: H04J 14/0284 WDM mesh architectures
• CPC Class Codes: H04J 14/0286 WDM hierarchical architectures
• CPC Class Codes: H04J 14/0291 Shared protection at the optical multiplex section (1:1, n:m)
• CPC Class Codes: H04J 14/0293 Optical channel protection
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 2011/0009 using wavelength filters
• CPC Class Codes: H04Q 2011/0011 using wavelength conversion
• CPC Class Codes: H04Q 2011/0015 using splitting combining
• CPC Class Codes: H04Q 2011/0016 using wavelength multiplexing or demultiplexing
• CPC Class Codes: H04Q 2011/0024 using space switching
• CPC Class Codes: H04Q 2011/0081 Fault tolerance; Redundancy; Recovery; Reconfigurability

Abstract

An optical cross-connect for the switching of optical channels at variable bit-rate (up to 10 Gbit/s), wavelength division multiplexed on bi-directional optical fibers forming the transmission backbone of a transport network; in particular the cross-connect can be interfaced to fibers crossing the nodes of a ring having large territorial extension, provided with protection fibers. The cross-connect includes a spatial Split & Select input stage of WDM aggregates, followed by a set of channel filters tunable on the whole optical range occupied by the channels, which jointly form a structure strictly not blocking the access to the channels by a set of bridge units whose functionality is selectable on a per-channel basis, such as for instance: transit, drop/insert, regeneration, etc. An output optical spatial Split & Select stage connects in a strictly non-blocking way the single channels from bridge units to optical multiplexers that reconstruct the WDM aggregate on the output fibers. The duplicated architecture of the bridge units for the protection fibers enables the protection of each single local drop/insert channel (FIGS. 9a and 9b).

Claims

1. An optical channel cross-connect, connected to N input fibers and at least a same number of output fibers, being the fibers crossed by relevant signals obtained from the multiplexing of M component channels transmitted at different wavelengths and each input n-th fiber being connected to an n-th input optical splitter having N×

M ways, said N×

M ways being connected to n-th inputs of a set of N×

M input optical selectorsl having N inputs and one output, the outputs of said optical selectors being connected to relevant optical channel filters tunable to any of the M wavelengths of the input signal, said filters being subdivided to form N groups of M filters, and each group of filters sending the M filtered channels towards an output stage including N optical combiners having M inputs and one output, the N outputs of the optical combiners being connected to a same number of optical output fibers, on which M channels are multiplexed, wherein the output stage additionally comprises;

N×

M bridge units whose functionality is selectable on individual basis, each unit being connected downstream a relevant channel filter to receive a signal at any wavelength on which its own functionality is performed;

N×

M output optical splitters having N output ways, each output splitter being connected downstream a relevant bridge unit to receive an optical channel at the wavelength, on which the above mentioned function has been performed, making it available on N ways;

N×

M output optical selectors, having N inputs and one output, to receive N optical channels on N ways and select one to be sent to an input of a said optical combiner included in the output stage;

the connections between said optical output splitters and selectors making available an m-th channel coming from said n-th group of channel filters, to an n-th input of N output optical selectors connected to relevant m-th inputs of said N optical combiners.

2. The optical channel cross-connect, according to claim 1, further comprising a control unit to diagnose internal failure conditions on devices involving single channels, and interruption conditions of at least one of the input or output fibers, in both transmission directions, wherein said control unit controls said input (X_IN) and output (X_OUT) selectors so as to subdivide said N fibers between working fibers, normally operating, and protection fibers, biuniquely associated to the working fibers, which substitute the same in case of failure and to distinguish the bridge units in working bridge units, normally associated to the channels of a working fiber, in absence of failures in said units and/or interruptions of said working fibers, and protection bridge units, which are a duplicate of relevant working bridge units and substituting the same in case of said failure and/or interruption.

3. Optical channel cross-connect according to claim 2, wherein in case of failure of a working bridge unit, or of client equipment connected to the same, or of the connection between them, or of said input selector or of said channel optical filter, associated to the same:

said output optical selector that normally selects the bridge unit that is no longer usable is forced to switch, to select the protection bridge unit in stand-by and associate the protection bridge unit to the output working fiber, thus disconnecting the no longer usable bridge unit;

said input optical selector connected to the bridge unit that is no longer usable, and said input optical selector connected to said corresponding protection bridge unit, are forced to perform a switching, to associate the protection bridge unit to the input working fiber and disconnect the non-usable bridge unit, enabling protection of functionality of the channel, in case of failure of the working bridge unit, and not of the working fibers, preventing the failed unit to interfere on the transmitted signal; and

said tunable filter associated to said corresponding protection bridge unit is tuned on the same wavelength of the filter associated to the corresponding no longer usable working bridge unit, if this condition did not occur yet.

4. The optical channel cross-connect, according to claim 2, wherein in case of failure of an output working fiber, or of failure on an output optical amplifier placed between said output working fiber and a relevant said optical combiner, of a said relevant optical combiner or of a said output selector or of one of the connections among the above mentioned components:

said output optical selectors associated to the interrupted fiber or to the elements where the failure occurred, and said output optical selectors associated to the corresponding protection fiber or to the corresponding protection elements, are individually forced to switch, to select a relevant bridge unit and associate it to the output protection fiber, thus disconnecting the corresponding protection bridge unit, and disconnecting also the relevant working bridge unit from the working output fiber.

5. The optical channel cross-connect according to claim 2, wherein in case of break of an input working fiber, or of failure on an input optical amplifier placed between said input working fiber and a relevant input optical splitter, or of said input optical splitter, or of one of the connections among the above mentioned components:

said input optical selectors connected to said working bridge units, and said input optical selectors connected to said protection bridge units, are individually forced to switch to associate a relevant working bridge unit to the input protection fiber, and disconnects the corresponding protection bridge unit.

6. The optical channel cross-connect according to claim 2, wherein said optical channel cross-connect is included in a node of an optical fiber ring, composed of several nodes and that, in case of failure of one output working fiber, or of failure of an output optical amplifier, or of said optical combiner, or of said output optical selector and simultaneously of unavailability of the relevant protection resources, due to a further break of the corresponding output protection fiber, or to a further failure of one of the relevant output optical amplifiers, or optical combiner, or output optical selector, associated to said output protection fiber:

said output optical selectors associated to an interrupted fiber or to the elements where the failure occurred, and said output optical selectors associated to the output protection fiber on the opposite side with respect to the one where the failure occurred, are individually forced to switch, to select a relevant working bridge unit and associate it to said output protection fiber on the opposite side, thus disconnecting the corresponding protection bridge unit associated to the fiber itself, and disconnects a relevant working or protection bridge unit from the output working or protection fiber on which the failure occurred.

7. The optical channel cross-connect according to claim 2, wherein said optical channel cross-connect is included in a node of an optical fiber ring composed of several nodes and in case of failure of one input working fiber, or of failure of an input optical amplifier, or of a said input optical splitter and simultaneously of unavailability of the relevant protection resources, due to a further break of the corresponding input protection fiber, or to a further failure of one of the relevant input optical amplifiers, or input optical splitter associated to said input protection fiber:

said input optical selectors connected to said working bridge units, which in normal conditions support a connection terminated at the node, and said input

optical selectors connected to protection bridge units associated to protection fiber entering the opposite side with respect to the one where the failure occurred, are individually forced to switch, to associate a relevant working bridge unit to said protection fiber entering the opposite side and disconnects the corresponding protection bridge unit associated to the fiber itself; and

said input optical selectors connected to said working bridge units, which in normal conditions support a connection in transit through the node, and said input optical selectors connected to protection bridge units associated to the protection entering fiber where the failure occurred, are individually forced to switch, to disconnect a relevant working bridge unit from the working or protection fibers at the input side where failures occurred.

8. The optical channel cross-connect according to claim 2, wherein said optical channel cross-connect is included in a node of an optical fiber ring composed of several nodes and in case of joint failure, in a link of the ring not adjacent to the considered node, of a working fiber and of the relevant protection fiber, the configuration of said input and output optical selectors and of the tunable filters, associated to the protection bridge units and to the input and output protection fiber, are arranged to allow the transit of protected channels, through the protection bridge units, in the two transmission directions.

9. The optical channel cross-connect according to claim 2, wherein said optical channel cross-connect is included in a node of an optical fiber ring composed of several nodes and in case of joint failure, in a link of the ring not adjacent to the considered node, of a working fiber and of the relevant protection fiber:

one said input optical selector connected to a working bridge unit that in normal operating conditions locally terminates a channel entering the working fiber and one said input optical selector connected to a protection bridge unit associated to the protection fiber entering the opposite side in respect with that of said working fiber, said protection bridge unit protecting the same channel that must be terminated, are individually forced to switch to associate said working bridge unit to said protection fiber entering the opposite side and disconnects the corresponding protection unit associated to the same protection fiber.

10. Optical channel cross-connect according to claim 2, wherein in case of double failure due to the interruption of an input working fiber and to the failure of a working bridge unit, or of the client equipment connected to the working bridge unit, or of the connection between them, or of said input selector, or of said channel filter associated to the working bridge unit:

said output optical selector that normally selects the bridge unit that is no longer usable, and said output optical selector that normally selects the corresponding protection bridge unit, are forced to switch, to select the protection bridge unit and associate it to the protection output fiber, if this condition did not occur yet, and disconnects the no longer usable bridge unit;

said input optical selector connected to the bridge unit that is no longer usable, and said input optical selector connected to the corresponding protection bridge unit, are forced to switch, to associate the protection bridge unit to the correct input fiber, working or protection, according to the condition upstream, and disconnects the no longer usable bridge unit; and

said tunable filter associated to said corresponding protection bridge unit is tuned on the same wavelength of the filter associated to the corresponding no longer usable working bridge unit, if this condition did not occurred yet.

11. The optical channel cross-connect, according to claim 2, wherein in case of double failure due to the interruption of an input working fiber and to the failure of a working bridge unit, or of the client equipment connected to the working bridge unit, or of the connection between them, or of said input selector, or of said channel filter associated to the working bridge unit:

said input optical selector connected to the bridge unit that is no longer usable, and said input optical selector connected to the corresponding protection bridge unit, are forced to switch in order to associate the input protection fiber to the protection bridge unit, if said condition did not occurred yet, and disconnects the no longer usable bridge unit;

said tunable filter associated to said corresponding protection bridge unit is tuned on the same wavelength of the filter associated to the corresponding no longer usable working bridge unit, if this condition did not occurred yet; and

said output optical selector that normally selects the bridge unit that is no longer usable, and said output optical selector that normally selects the corresponding protection bridge unit, are forced to switch in order to select the protection bridge unit and associate it to the correct output fiber, working or protection, according to the condition downstream, and disconnects the no longer usable bridge unit.

12. The optical channel cross-connect according to claim 1, wherein at least one bridge unit includes:

a first transponder from optical channel to client equipment;

a second transponder from client equipment to optical channel; and

a pair of optical selectors in cascade placed between the transponders, the selectors being individually controlled to connect the client equipment to the optical channel, and vice versa, or to disconnect the client equipment and enable the transit of the optical channel through the bridge unit.

13. The optical channel cross connect according to claim 12, wherein said optical switches have more than two ways, thus improving the flexibility of the cross-connect in optical channel routing.

14. The optical channel cross connect according to claim 1, bridge unit includes:

a receiving stage;

a transmitting stage; and

a pair of electronic selectors in cascade, placed between the receiving and transmitting stages, the selectors being individually controlled to connect a a client equipment to the optical channel, and vice versa, or to disconnect client equipment and enable the transit of the optical channel through the bridge unit.

15. The optical channel cross connect according to claim 1, wherein said bridge unit includes an optical amplifier optimized to operate on single channel.

16. The optical channel cross connect according claim 1, wherein at least one bridge unit includes a transponder from optical channel to optical channel, capable to perform also 3R Regeaneration and wavelength conversion functions.

17. The optical channel cross connect according to claim 1, wherein at least one said bridge unit includes:

a first transponder from optical channel to client equipment, performing the a channel drop function; and

a second transponder from client equipment to optical channel, performing a channel add function.

18. The optical channel cross connect according to claim 1, bridge unit includes an optical amplifier (OFA or SOA) optimized to operate on a single channel and an optical variable attenuator (OVA) placed upstream said amplifier.