Wavelength-time-space division switching system

Abstract: An optical switching network comprises a plurality of optical splitters coupled respectively to inlet highways for receiving wavelength-time division multiplex (WTDM) signals through the respective inlet highways, each of the multiplex signals comprising a series of WTDM signals each being identified by a unique wavelength and a unique time slot. A like plurality of sets of tunable wavelength filters are provided. The filters of each set are coupled to respective outputs of the splitters for selecting the wavelength of one of the WTDM signals. A like plurality of time-space switches are associated respectively with the sets of the tunable wavelength filters. Each of the time-space switches has input ports and output ports, the input ports of the time-space switch being coupled respectively to outputs of the filters of the associated set for interchanging the time slot of the selected wavelength with another time slot and establishing a path for the selected wavelength between the input ports and the output ports. A like plurality of sets of wavelength switches are provided, the wavelength switch means of each set being coupled to the output ports of an associated one of the time-space switches for interchanging the selected wavelength with another wavelength. A like plurality of optical combiners are provided for coupling the output of the wavelength switches of different sets to a respective one of outlet highways.

Description: The present invention relates generally to switching systems, and more specifically to a wavelength-time division switching system. A time and wavelength division switching system as disclosed in the EP-A-310 058 comprises a splitter for splitting an inlet highway into a plurality of paths which lead to multiple wavelength selectors respectively, multiple optical time switches coupled respectively to the outputs of the wavelength selectors and multiple wavelength converters coupled respectively to the outputs of the time switches. A wavelength-time division multiplex (WTDM) signal is supplied through the inlet highway to the wavelength selectors. Control signals are applied to the wavelength selectors, time switches and wavelength converters to select a wavelength of the WTDM signal on each divided path and interchange time slots of the selected wavelength and finally convert the selected wavelength to a desired wavelength. The optical outputs of the wavelength converters are combined together by a combiner for coupling to an outlet highway. The document "Wavelength-Division and Time-Division Hybrid Switching Networks for Large Line-Capacity Broadband Switching Systems" (Conference Record, IEEE Global Telecommunications Conference 1988, Vol.2) discloses a wavelength-time-division switching network. Since the prior art switching network is only capable of switching optical signals in the wavelength and time domains, it is desired to increase the number of channels that can be switched. It is therefore an object of the present invention to provide a high-capacity optical switching network. According to the present invention, there is provided an optical switching network comprising a plurality of optical splitters coupled respectively to inlet highways for receiving wavelength-time division multiplex (WTDM) signals through the respective inlet highways, each of the multiplex signals comprising a series of WTDM signals each being identified by a unique wavelength and a unique time slot. A plurality of tunable wavelength filters are provided. The filters of each set are coupled to respective outputs of the splitters for selecting the wavelength of one of the WTDM signals. A plurality of time-space switches are associated respectively with the sets of the tunable wavelength filters. Each of the time-space switches has input ports and output ports, the input ports of the time-space switch being coupled respectively to outputs of the filters of the associated set for interchanging the time slot of the selected wavelength with another time slot and establishing a path for the selected wavelength between the input ports and the output ports. A plurality of sets of wavelength switches are provided, the wavelength switch means of each set being coupled to the output ports of an associated one of the time-space switches for interchanging the selected wavelength with another wavelength. A plurality of optical combiners are provided for coupling the output of the wavelength switches of different sets to a respective one of outlet highways. In a preferred embodiment the network further includes a plurality of pre-stages and/or a plurality of post-stages. Each pre-stage comprises a plurality of second optical splitters coupled respectively to the first optical splitters, and a plurality of optical switches each having a plurality of input ports coupled respectively to the second optical splitters and an output port coupled to a corresponding one of the tunable wavelength filters, each of the optical switches selectively coupling an output of the second optical splitters to the associated tunable wavelength filter. Each post-stages comprises a plurality of optical switches each having an input port coupled to a corresponding one of the wavelength converters and a plurality of output ports. Each of the second optical switches couples the output of the corresponding wavelength converter to one of its output ports, and a plurality of second optical combiners each has a plurality of input ports coupled respectively to the output ports of the second optical switches and an output port coupled to a corresponding one of the first optical combiners. The present invention will be described in further detail with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of the multiplexer and demultiplexer of a wavelength-time division switching system according to a first embodiment of the present invention; Fig. 2 is a block diagram of a wavelength-time-space switching network of the present invention; Fig. 3 is a timing diagram associated with the switching network of Fig. 2; and Fig. 4 is a block diagram of a modified time-space-wavelength switching network of the present invention. Referring now to Fig. 1, the wavelength-time-space (WTS) division switching system of this invention is made up of a wavelength-time division multiplexer and a wavelength-time division demultiplexer. The multiplexer comprises a plurality of line interfaces 1 to which electrical signals from lines and trunks are converted to digital signals. Interfaces 1 are divided into "m" groups corresponding respectively to time-division multiplexers 2 1 through 2 m . The digital signals from each group are multiplexed by the associated multiplexer and supplied to a laser 3 i (i = 1, 2, ... m) for emitting light of a particular wavelength unique to the groups of TDM (time-division multiplex) signals. The outputs of lasers 3 are multiplexed into a WTDM (wavelength-time division multiplex) signal by an optical combiner 4 and applied to a waveguide or inlet highway HWY i . Each interface extracts a call processing signal from signals received from the line and supplies it to a network controller. The demultiplexer is made up of an optical splitter 5 for splitting a WTDM signal supplied on an outlet highway HWY o into several optical paths leading respectively to wavelength filters 6 1 through 6 m having wavelength passbands corresponding respectively to the wavelengths light emitted by lasers 3 1 through 3 m . The outputs of wavelength filters 6 1 ∼6 m are converted to electrical signals by optoelectric transducers 7 1 -7 m respectively and applied to time-division demultiplexers 8 1 -8 m so that the WTDM signals of each group are decomposed into electrical signals. For full-duplex operation, the outputs of demultiplexers 8 1 ∼8 m are coupled to the interfaces of the corresponding group. According to the present invention, a plurality of such WTDM multiplexers are provided for connection to multiple inlet highways and a plurality of such WTDM demultiplexers are provided for connection to multiple outlet highways. For simplicity, only two inlet highways and two outlet highways are shown in Fig. 2, and incoming signals from the lines are multiplexed onto two time slots T 1 and T 2 and two wavelengths λ 1 and λ 2 . The WTS switching system comprises a WTDM switching network connected between inlet highways 100, 101 and outlet highways 200, 201, and a network controller 70 to which call processing signals from incoming lines and trunks are supplied through interfaces 1. Inlet highways 100 and 101 are connected to optical splitters 10 and 11, respectively. The optical information signal from a first WTDM multiplexer is coupled through inlet highway 100 and split by splitter 10 into optical waveguides, one leading to a tunable wavelength filter 20 and the other to a tunable wavelength filter 22. Likewise, the optical information signal of a second WTDM multiplexer is coupled through inlet highway 101 and split into two optical waveguides, one extending to a tunable wavelength filter 21 and the other to a tunable wavelength filter 23. Tunable wavelength filters 20-23 are respectively controlled by a wavelength/time slot selection signal which is supplied from network controller 70 on the time slot of a desired signal to select one of the two wavelength components λ 1 and λ 2 . Thus, tunable wavelength filters 20-23 provide a time slot switching function as well as a wavelength switching function. The optical signals from the outputs of tunable wavelength filters 20-23 are converted to corresponding electrical signals by optoelectric transducers 30∼33, respectively. The outputs of O/E transducers 30 and 31 are coupled to respective input ports of a time-space switch 40 and those of O/E transducers 32 and 33 are coupled to respective input ports of a time-space switch 41. Each of the time-space switches is responsive to a time/space switching signal supplied from network controller 70 for switching the time slot of the input signals to a desired time slot on the output port of the switch that leads to a desired outlet highway. Each time-space switch is of memory matrix configuration as described in S. Hayano et al "A Time-Division Broadband Switching Network Using a Frame Synchronization Technique", IEEE Communications Society, IEEE International Conference on Communications, June 12-15, 1988. Wavelength tunable lasers 50 and 51 are coupled to respective output ports of time-space switch 40 and wavelength tunable lasers 52 and 53 are coupled to respective output ports of time-space switch 41. Each of these lasers responds to a wavelength selection signal supplied from network controller 70 by emitting a laser beam of wavelength λ 1 or λ 2 specified by the selection signal. The outputs of wavelength tunable lasers 50 and 51 are coupled by waveguides to first inputs of optical combiners 60 and 61, respectively, and those of wavelength tunable lasers 52 and 53 are coupled to second inputs of optical combiners 60 and 61, respectively. The outputs of combiners 60 and 61 are coupled to outlet highways 200 and 201, respectively. The operation of the system of Fig. 2 will be described with reference to Fig. 3. On inlet highway 100, incoming WTDM signals A and B of wavelength λ 1 are multiplexed on time slots T 1 and T 2 , and WTDM signals C and D of wavelength λ 2 are multiplexed on time slots T 1 and T 2 . Assume that WTDM signals A of successive frames N, N+1, N+2 are to be switched to time slot T 2 and wavelength λ 2 on outlet highway 201, and successive WTDM signals D are to be switched to time slot T 1 and wavelength λ 1 on outlet highway 201. Network controller 70 controls wavelength filter 20 to select wavelength λ 1 and time slot T 1 so that light signals A appearing at the input of wavelength filter 20 are selected during successive frames N, N+1 and N+2 and converted to corresponding electrical signals by O/E transducer 30. Controller 70 then supplies a time/space switching signal to switch 40 to switch the T 1 -time slot of WTDM signals A to T 2 while selecting a path to tunable laser 51. Controller 70 now supplies a wavelength selection signal to laser 51 to cause it to emit light of wavelength λ 2 . Therefore, WTDM signals A of wavelength λ 2 appears on outlet highway 201 as a signal time-division multiplexed on time slot T 2 . In a similar manner, network controller 70 controls wavelength filter 22 to select wavelength λ 2 and time slot T 2 so that WTDM signals D appearing at the input of wavelength filter 22 are selected during successive frames N, N+1 and N+2 and converted to corresponding electrical signals by O/E transducer 32. Controller 70 then supplies a time/space switching signal to switch 41 to switch the T 2 -time slot of signals D to T 1 and select a path to tunable laser 53. Controller 70 now supplies a wavelength selection signal to laser 53 to cause it to emit light of wavelength λ 1 . Therefore, signal D of wavelength λ 1 appears on outlet highway 201 as a signal which is multiplexed on time slot T 1 . If WTDM signals B are to be switched to outlet highway 200, it is seen that controller 70 will supply a λ 1 selection signal to wavelength filter 20 during time slot T 2 , a T 2 -to-T 1 switching signal to switch 40 for switching the signals to time slots T 1 on a path to tunable filter 50, and a λ 1 selection signal to the filter 50. In this way, all signals of each inlet highway are switched to any of the outlet highways. Efficient utilization of the time-space switches and flexibility for network expansion can be achieved by adding optical pre-stages of combination splitter-switch configuration and optical post-stages of combination switch-combiner configuration as shown in Fig. 4. In the illustrated embodiment, two pre-stages 80 and 81 and two post-stages 90 and 91 are provided. Pre-stage 80 comprises splitters 82, 83 and optical switches 84, 85, and pre-stage 81 likewise comprises splitters 86, 87 and optical switches 88, 89. Splitters 82 and 83 are coupled to the respective outputs of splitters 10 and 11 for splitting their incoming optical path into two waveguides leading respectively to optical switches 84 and 85. Similarly, splitters 86 and 87 are coupled to the respective outputs of splitters 10 and 11 for splitting their incoming optical path into two waveguides leading respectively to optical switches 88 and 89. Optical switches 84, 85, 88 and 89 are controlled with a switching signal supplied from network controller 70 to select one of their optical inputs. Post-stage 90 comprises optical switches 92, 93 and combiners 94, 95 and post-stage 91 likewise comprises optical switches 96, 97 and combiners 98, 99. Optical switches 92 and 93 are coupled to the outputs of wavelength tunable lasers 50 and 51, respectively, for switching their optical input to combiner 94 or 95 in response to a switching signal from controller 70. In like manner, optical switches 96 and 97 are coupled to the outputs of wavelength tunable lasers 52 and 53, respectively, for switching their optical input to combiner 98 or 99 in response to a switching signal from controller 70. The outputs of combiners 94 and 98 are coupled to the respective inputs of combiner 60, and those of combiners 95 and 99 are coupled to the respective inputs of combiner 61. By operating switch 84 for coupling the output of splitter 82 to wavelength filter 20 and by operating switch 93 for coupling the output of laser 51 to combiner 95, WTDM signals A can be switched to outlet highway 201 in a manner identical to that described above in connection with the first embodiment of this invention. For switching WTDM signals D to outlet highway 201, switch 88 is operated for coupling the output of splitter 86 to wavelength filter 22 and switch 97 is operated for coupling the output of laser 53 to combiner 99. The foregoing description shows only preferred embodiments of the present invention. Various modifications are apparent to those skilled in the art without departing from the scope of the present invention which is only limited by the appended claims. Therefore, the embodiments shown and described are only illustrative, not restrictive.

Claims: An optical switching network comprising a plurality of optical splitters (10, 11) coupled respectively to inlet highways (100, 101) for receiving wavelength-time-division multiplex (WTDM) signals respectively, a plurality of tunable wavelength filters (20-23) coupled to corresponding outputs of said splitters (10, 11) for selecting one of said WTDM signals to produce a selected time-division (TDM) signal, a plurality of wavelength converters (50-53) for producing an optical signal of wavelength different from the wavelength of the selected TDM signal, a plurality of optical combiners (60, 61) for coupling the output of the wavelength converters (50-53) to a respective one of outlet highways (200, 201), and time-domain switch means (40, 41) connected between outputs of said tunable wavelength filters (20-23) and inputs of said wavelength converters (50-53) for switching the selected TDM signal to a selected time slot, characterized: in that said tunable wavelength filters (20-23) are divided into a plurality of sets corresponding in number to said splitters (10, 11) to receive WTDM signals from the splitters (10, 11), and said wavelength converters (50-53) are divided into a plurality of sets corresponding in number to said optical combiners (60, 61) to supply their output signals to the optical combiners (60, 61), and in that said timedomain switch means (40, 41) comprises a plurality of time-space switches (40, 41) corresponding respectively to the sets of the tunable wavelength filters (20-23) and to the sets of the wavelength converters (50-53), and each time-space switch (40, 41) has input ports and output ports, the input ports being coupled respectively to the outputs of the corresponding set of the tunable wavelength filters (20, 21; 22, 23) and the output ports being coupled respectively to the inputs of the corresponding set of the wavelength converters (50-53), and in that each time-space switch (40, 41) establishes a path to a selected one of said output ports when the selected TDM signal is switched to the selected time slot. An optical switching network as claimed in claim 1, further comprising a plurality of pre-stages (80,81) each comprising: a plurality of second optical splitters (82,83;86,87) coupled respectively to the firstmentioned optical splitters (10,11); and a plurality of optical switches (84,85;88,89) each having a plurality of input ports coupled respectively to the second optical splitters (82,83;86,87) and an output port coupled to a corresponding one of the tunable wavelength filters (20,21;22,23), each of the optical switches (84,85;88,89) selectively coupling an output of the second optical splitters (82,83;86,87) to the associated tunable wavelength filter. An optical switching network as claimed in claim 1 or 2, further comprising a plurality of post-stages each comprising: a plurality of optical switches (92,93;96,97) each having an input port coupled to a corresponding one of the wavelength converters (50,51;52,53) and a plurality of output ports, each of the optical switches (92,93;96,97) coupling the output of the corresponding wavelength converter to one of the output ports thereof; and a plurality of second optical combiners (94,95;98,99) each having a plurality of input ports coupled respectively to the output ports of the optical switches (92,93;96,97) and an output port coupled to a corresponding one of the first-mentioned optical combiners (60,61). An optical switching system incorporating the optical switching network of claim 1,2 or 3, characterized by a plurality of wavelength-time division multiplexers each comprising a plurality of time-division multiplexers (1,2 1 -2 m ,3 1 -3 m ,4) for multiplexing incoming signals onto assigned time slots to produce a plurality of time-division multiplex (TDM) signals and a wavelength-division multiplexer (3 1 -3 m ,4) coupled to the time-division multiplexers (2 1 -2 m ) for multiplexing the TDM signals onto optical carriers of different wavelengths to produce wavelength-time division multiplex (WTDM) signals for coupling to inlet highways (100,101), respectively; and a plurality of wavelength-time division demultiplexers (5,6 1 -6 m ,7 1 -7 m ,8 1 -8 m ) coupled respectively to the outlet highways (200,201), each of the wavelength-time division demultiplexers (5,6 1 -6 m ,7 1 -7 m ,8 1 -8 m ) comprising a wavelength-division demultiplexer (5,6 1 -6 m ) for demultiplexing the signal on the respective outlet highway (200,201) into individual wavelengths, and a plurality of time-division demultiplexers (7 1 -7 m ,8 1 -8 m ) respectively demultiplexing the wavelength-demultiplexed signals into individual time slots.

Inventors: NISHIO MAKOTO, NISHIO, MAKOTO, NISHIO, MAKOTO, C/O NEC CORPORATION
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1991
Main classification: H04Q11
IPC codes: H04Q11, H04B10, H04J4, H04J14, H04Q3