Optical switching system

Abstract: An optical switching system receives an optical input signal which is a wavelength-division multiplexed and time-division multiplexed signal. The optical input signal is divided into time-division multiplexed optical signals in different wavelength regions and transferred within an optical data bus (800) after being subjected to a predetermined process including a frequency shift. The optical signals in the different wavelength regions are extracted from the opti­ cal data bus (800) using optical bandpass filters, and multiplexed into an output optical signal which is a wavelength-division multiplexed and time-division multiplexed signal after being subjected to a predetermined process including a frequency shift.

Description: BACKGROUND OF THE INVENTION The present invention generally relates to optical switching systems, and more particularly to an optical switching system used in an optical fiber communication and the like. Various information interchange services such as a video conference system and a high definition television system are being realized using optical information networks such as integrated services digital networks (ISDNs). An optical switching system is used for making these information interchange services. A conventional optical switching system employs a wavelength-division and time-division composite switch as a basic switch of a wavelength-division and time-division composite optical communication path. The wavelength-division and time-division composite switch is capable of arbitrarily interchanging the wavelength and time slot of an input optical signal which is a wavelength-division multiplexed and time-division multiplexed signal. FIG.1 shows a basic structure of the wavelength/time composite switch in an example of the conventional optical switching system. An optical input signal which is applied to a variable branching filter 1 is a wavelength-division multiplexed (wavelengths of λ 1 through λ n ) and time-division multiplexed signal. The variable branching filter 1 branches the input optical signal to k optical T switches 2 for every predetermined wavelength. In addition, the selecting wavelength of the variable branching filter 1 is switched for every time slot of the time-division multiplexed signal component. Outputs of the optical T switches 2 are converted into predetermined wavelengths for every time slot in variable wavelength converting elements 3. Outputs of the variable wavelength converting elements 3 are combined and output as an optical output signal of the wavelength/time composite switch. FIG.2 shows an equivalent circuit of the wavelength/time composite switch shown in FIG.1. As shown in FIG.2, n time division highways of the wavelengths λ 1 through λ n are coupled to k T switches 2' via an nxk S switch 4. Outputs of the T switches 2' are coupled to n time division highways of the wavelengths λ 1 through λ n via a kxn S switch 5. FIG.3 shows a more detailed block diagram of the conventional optical switching system. A variable branching filter 1" branches a reference light in which a light having an accurate wavelength is wavelength-division multiplexed. The wavelength conversion is made by modulating outputs of the variable branching filter 1" in optically controlled optical modulators 3' depending on outputs of optical T switches 2". By switching the selecting wavelengths of the variable branching filter 1" for every time slot, it is possible to also vary the wavelength for every time slot after the wavelength conversion. A wavelength synchronised switching network of essentially this form using wavelength switching, based on a variable wavelength filter and an optically controlled modulator is disclosed in IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS - SOUND TO LIGHT, Seattle, Washington, 7-10 June 1987, vol. 3, pages 1565-1569 (Suzuki et al). This reference also discloses a λ n switching network useful for constructing large-capacity switching systems. EP-A-0 264 119 discloses an optical wavelength-division switching system in which an electric signal is reproduced for each channel from a wavelength division multiplexed optical signal, and the electric signal is then used to modulate a light source (laser diode). The input optical signal which is a wavelength-division multiplexed and time-division multiplexed signal is conventionally subjected to the arbitrary interchange of the wavelength and the time slot in the above described manner. However, the conventional optical switching system is not practical in that it lacks flexibility in the interchange of information contents, collection of required information and the like, and a highly satisfactory service cannot be expected when applied to the information interchange services. SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to provide a novel and useful optical switching system in which the problems described above are eliminated. According to the present invention, there is provided an optical switching system comprising first means for receiving an input optical signal which is a wavelength-division multiplexed and time-division multiplexed signal, said first means including first separating means for separating and outputting a time-division multiplexed signal component of the input optical signal in each of divided wavelengths and second separating means for separating a control information included in the input optical signal, second means coupled to said first means for storing an optical signal output from said first means for every time slot identical to that used for the separation in said first means and for reading out stored optical signals successively in a sequence of predetermined time slots so as to convert wavelengths of the optical signals into predetermined wavelengths based on said control information, third means coupled to said second means for multiplexing wavelengths of optical signals output from said second means into wavelength-division multiplexed optical signals and for delaying a phase of the wavelength-division multiplexed optical signals a predetermined quantity, an optical data bus coupled to said third means for receiving optical signals output from said third means and for transferring the optical signals in a predetermined direction within said optical data bus, fourth means coupled to said optical data bus for extracting optical signals having wavelengths belonging to predetermined wavelength regions from said optical data bus and delaying a phase of the extracted optical signals a predetermined quantity and for converting wavelengths of the extracted optical signals into predetermined wavelengths, and fifth means coupled to said fourth means for multiplexing the wavelengths of the optical signals output from said fourth means so as to output an output optical signal which is a wavelength-division multiplexed and time-division multiplexed signal. Other objects and further features of the present invention will be apparent from the following detailed description given by way of example and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 is a system block diagram showing an example of a conventional optical switching system; FIG.2 is a system circuit diagram showing an equivalent circuit of the conventional optical switching system shown in FIG.1; FIG.3 is a system block diagram showing the conventional optical switching system shown in FIG.1 in more detail; FIG.4 is a system block diagram for generally explaining a first embodiment of an optical switching system according to the present invention; FIG.5 is a system block diagram showing the first embodiment in more detail; FIG.6 shows a data structure of an optical input signal; FIG.7 generally shows an embodiment of a wavelength-division multiplexed signal separator; FIGS.8A through 8C generally show embodiments of a detector; FIG.9 is a system block diagram showing an embodiment of a time slot interchange and frequency shifter used in the first embodiment; FIGS.10A and 10B generally show embodiments of a time-division multiplexed signal separator; FIG.11 generally shows an embodiment of an optical amplifier; FIG.12 generally shows an embodiment of an optically coupled bandpass filter; FIG.13 generallv shows an embodiment of a wavelength multiplexer; and FIGS.14A and 14B respectively are diagrams showing the input optical signal and an output optical signal of the first embodiment. DESCRIPTION OF PREFERRED EMBODIMENTS FIG.4 generally shows a first embodiment of an optical switching system according to the present invention. In FIG.4, wavelength-division multiplexed signal separators 600-1 through 600-n each enter an input optical signal which is a wavelength-division multiplexed and time-division multiplexed signal and separate a time-division multiplexed signal component in each of the divided wavelengths. After separation of the time-division multiplexed signal component, the wavelength-division multiplexed signal separators 600-1 through 600-n each read a control information included in the input optical signal and output an optical signal corresponding to the time-division multiplexed signal component. Optical storage and wavelength converters 730-1 through 730-m are coupled to each of the wavelength-division multiplexed signal separators 600-1 through 600-n and store optical signals output from the wavelength-division multiplexed signal separators 600-1 through 600-n for every time slot identical to that used for the separation in the wavelength-division multiplexed signal separators 600-1 through 600-n. The optical storage and wavelength converters 730-1 through 730-m read out the stored optical signals successively in a sequence of predetermined time slots and convert the wavelengths of the optical signals to predetermined wavelengths based on the control information. Optical multiplexer and delay parts 750-1 through 750-m each multiplex the wavelengths of an output optical signal of the corresponding one of the optical storage and wavelength converters 730-1 through 730-m and output the optical signal after delaying the phase of the optical signal a predetermined quantity. An optical bus 800 enters output optical signals of the optical multiplexer and delay parts 750-1 through 750-m and transfer these optical signals in a predetermined direction in an optical transmission path. In this embodiment, the optical transmission path is a loop-shaped path. Optical delay and wavelength converters 850-1 through 850-m are coupled to the optical bus 800 and each extract an optical signal having wavelengths belonging to a predetermined wavelength region and delay the phase thereof a predetermined quantity so as to convert the wavelengths of the optical signal into predetermined wavelengths. Optical wavelength multiplexers 950-1 through 950-n are each coupled to the optical delay and wavelength converters 850-1 through 850-m and multiplex the wavelengths of the optical signal so as to output an optical output signal which is a wavelength-division multiplexed and time-division multiplexed signal. As a result, the output optical signal is obtained with a space multiplexing factor n, a wavelength multiplexing factor m and a time multiplexing factor m. The optical output signal of the optical switching system has a signal format approximately the same as that of the original optical input signal. In other words, the alignment of the optical wavelength, the center wavelength, the wavelength bandwidth and the like of the input optical signal and the output optical signal of the optical switching system are approximately the same. FIG.5 shows the first embodiment in more detail. An optical input signal which is a wavelength-division multiplexed and time-division multiplexed signal is obtained from a plurality of channels. For the sake of convenience, FIG.5 shows a case where there are two channels. The optical input signal is made up of cells having a fixed length and a header H as shown in FIG.6. The header H contains information such as a wavelength information λ 1 of an optical input signal, a content information A 1 , a wavelength information λ 2 of an optical output signal, an output channel information a 2 , an information quantity ℓ 1 , a priority information ρ, and a time slot information t 2 , and may be described as H(λ 1 , A 1 , λ 2 , a 2 , ℓ 1 , ρ, t 2 , ...). The wavelength information λ 2 includes λ 21 , λ 22 , λ 23 , ... . The output channel information a 2 includes a 21 , a 22 , a 23 , ... , and may be used for making a broadcast. The time slot information t 2 includes t 21 , t 22 , t 23 , ... . For example, the optical input signal received from a first channel CH1 is applied to an optical wavelength-division multiplexed signal separator (frequency divider) 60-1 wherein time-division multiplexed data are separated from the optical input signal in each of the divided wavelengths. Output optical signals of the optical wavelength-division multiplexed signal separator 60-1 are supplied to detectors 65-1 through 65-3 which detect a control information included in the optical signals. This control information is used to control time slot interchange and frequency shifters 70-1 through 70-3. The optical wavelength-division multiplexed signal separator 60-1 has a structure shown in FIG.7. The optical wavelength-division multiplexed signal separator 60-1 has an optical fiber 60-11, ring optical resonators 60-121 through 60-12n respectively having center optical frequency f i (i=1, 2, ..., n and n=3 in this embodiment), and optical fibers 60-131 through 60-13n. Each ring optical resonator 60-12i is optically coupled to the optical fiber 60-11 and the corresponding optical fiber 60-13i. Each of the detectors 65-1 through 65-3 have a structure shown in FIG.8A, 8B or 8C. In FIG.8A, the detector 65-1 has optical couplers 65-11 and 65-12, an optical local oscillator 65-13, an optical delay circuit 65-14, and a photodetector 65-15. The optical signal from the optical wavelength-division multiplexed signal separator 60-1 is output via the optical delay circuit 65-14. On the other hand, the control information is extracted by the optical local oscillator 65-12 and is output from the photodetector 65-15 in the form of an electrical signal. In FIG.8B, the detector 65-1 has an optical coupler 65-21, an optical delay circuit 65-22, a photodetector 65-23, a local oscillator 65-24, and electrical tuners 65-251 through 65-25n. The optical signal from the optical wavelength-division multiplexed signal separator 60-1 is output via the optical coupler 65-21 and the optical delay circuit 65-14. On the other hand, a portion of the optical signal (for example, 1/10 the optical power) is branched by the optical coupler 65-21 and supplied to the photodetector 65-23. The electrical tuners 65-251 through 65-25n respectively detect the modulation frequency of the header of the optical signal responsive to an output of the local oscillator 65-24 and output control information CI 1 through CI n . In FIG.8C, the detector 65-1 has an optical coupler 65-31, an optical amplifier 65-32, an FM/AM converter 65-33, a photodetector 65-34, and electrical filters 65-351 through 54-35n having mutually different passbands. The optical signal from the optical wavelength-division multiplexed signal separator 60-1 is output via the optical coupler 65-31. On the other hand, the optical signal is branched by the optical coupler 65-31 and is supplied to the FM/AM converter 65-33 via the optical amplifier 65-32. For example, a known semiconductor optical amplifier may be used as the optical amplifier 65-32. For example, the FM/AM converter 65-33 comprises a known etalon element which passes an optical signal having a predetermined wavelength. Thus it is possible to convert a frequency modulated (FM) optical signal into an amplitude modulated (AM) optical signal. The output optical signal of the FM/AM converter 65-33 is converted into an electrical signal in the photodetector 65-34, and the electrical signal is supplied to the electrical filters 65-351 through 65-35n which respectively output control information CI 1 through CI n . Output optical signals of the detectors 65-1 through 65-3 are supplied to the corresponding time slot interchange and frequency shifters 70-1 through 70-3. Each of the time slot interchange and frequency shifters 70-1 through 70-3 have a structure shown in FIG.9. The time slot interchange and frequency shifter comprises a time-division multiplexed signal separator 72, optical gate memories 73-1 through 73-100, optical frequency shifters 74-1 through 74-100, a wavelength multiplexer 75, and an optical delay circuit 76. In the embodiment shown in FIG.9, the time-division multiplexed signal separator 72 separates 100 time-division multiplexed signals from the output optical signal of one of the detectors 65-1 through 65-3. An output optical signal or optical packet of the time-division multiplexed signal separator 72 is successively supplied and stored in the optical gate memories 73-1 through 73-100 in this sequence during mutually different time slots. The optical data stored in the optical gate memories 73-1 through 73-100 are read out based on the control information described above and supplied to the corresponding optical frequency shifters 74-1 through 74-100 which convert the wavelengths of the input optical signals into mutually different wavelengths. Output optical signals of the optical frequency shifters 74-1 through 74-100 are supplied to the wavelength multiplexer 75 wherein a wavelength multiplexing takes place. A wavelength-division multiplexed optical signal output from the wavelength multiplexer 75 is supplied to the optical delay circuit 76 which compensates for a phase error caused by different input positions of the optical signals to the optical bus 80. An output optical signal of the optical delay circuit 76 is supplied to the optical bus 80 via a corresponding one of optical couplers 77-1 through 77-3. Hence, the optical signal from the optical delay circuit 76 is transferred in a predetermined direction in the optical bus 80. The time-division multiplexed signal separator 72 has a structure shown in FIGS.10A and 10B. In FIG.10A, the time-division multiplexed signal separator 72 has an optical amplifier 721 and a star branch part 722. The optical amplifier 721 includes a semitransparent mirror 723 which receives a light for optical pumping, and Er doped fiber 724, and an optical filter 725. In FIG.10B, the time-division multiplexed signal separator 72 has optical fibers 725 and electrodes 726 provided on a chip 727. The output optical signal of the time-division multiplexed signal separator 72 is controlled responsive to a control signal applied to the electrodes 726. A known optical memory may be used for the optical gate memories 73-1 through 73-100. For example, it is possible to employ an all optical flip-flop proposed by Odagawa et al., "All Optical Flip-Flop Operation of Bistable Laser Diode", Extended Abstracts of the 20th (1988 International) Conference on Solid State Devices and Materials, The Japan Society of Applied Physics. Each of the optical couplers 77-1 through 77-3 have a structure shown in FIG.11. In FIG.11, the optical coupler 77-1 has an optical fiber 77-10 which is optically coupled to the optical data bus 80 at a portion 77-11. One end of the optical fiber 77-10 is connected to an absorbing part 77-12 which absorbs the optical signal transferred within the optical fiber 77-10. In addition, a known optical frequency shifter may be used for the optical frequency shifters 74-1 through 74-100. For example, it is possible to employ a wavelength conversion element proposed in Kuno et al., "Study on the Wavelength-Switching Devices Using Bistable DFB Lasers", National Conference of Semiconductor/Materials Group of Electronics and Information Communication Society, 1987 or a wavelength conversion element proposed in Kondo et al., "A Tunable Optical-Wavelength Conversion Laser with TM-Polarized Light Input", National Conference of Electronics and Information Communication Society, Fall 1988. Returning now to the description of FIG.5, optically coupled bandpass filters 81-1 through 81-3 each output an optical signal which is obtained from the optical bus 80 and has a wavelength in a vicinity of a center wavelength thereof, that is, a wavelength within a predetermined wavelength range. Optical signals output from the optically coupled bandpass filters 81-1 through 81-3 are supplied to corresponding optical delay circuits 85-1 through 85-3 wherein a phase error compensation similar to that described above takes place. A known optical delay element may be used for the optical delay circuits 85-1 through 85-3. Optical signals output from the optical delay circuits 85-1 through 85-3 are supplied to corresponding optical frequency shifters 90-1 through 90-3 wherein the wavelengths of the optical signals are returned to the original wavelengths. Optical signals output from the optical frequency shifters 90-1 through 90-3 are supplied to a wavelength multiplexer 95-1 which multiplexes the wavelengths of the optical signals, and an output optical signal of the wavelength multiplexer 95-1 is transferred to an optical fiber (not shown), for example. Each of the optically coupled bandpass filters 81-1 through 81-3 have a structure shown in FIG.12. In FIG.12, the optically coupled bandpass filter 81-1 has a ring optical resonator 81-10 and an optical fiber 81-11. The ring optical resonator 81-10 is optically coupled to the optical data bus 80 and the optical fiber 81-11. The optical fiber 81-11 transfers the passed optical signal to the corresponding optical delay circuit 81-1. The wavelength multiplexer 95-1 has a construction shown in FIG.13. The wavelength multiplexer 95-1 has optical fibers 95-11 through 95-1n, ring optical resonators 95-21 through 95-2n respectively having center optical frequency f i (i=1, 2, ..., n and n=3 in this embodiment), and an optical fiber 95-3. Each optical resonator 95-2i is optically coupled to the corresponding optical fiber 95-1i and the optical fiber 95-3. The optical input signal received from a second channel CH2 is processed similarly to the optical input signal received from the first channel CH1. For this reason, a description of an optical wavelength-division multiplexed signal separator 60-2, detectors 66-1 through 66-3, time slot interchange and frequency shifters 71-1 through 71-3, optical couplers 78-1 through 78-3, optically coupled bandpass filters 82-1 through 82-3, optical delay circuits 86-1 through 86-3, optical frequency shifters 91-1 through 91-3, and a wavelength multiplexer 95-2 will be omitted. FIGS.14A and 14B respectively show the input optical signal and the output optical signal of the first embodiment. In FIG.14A, signals S1, S2 and S3 are time-division multiplexed to a wavelength λ 1 of the input optical signal, signals S1', S2' and S3' are time-division multiplexed to a wavelength λ 2 of the input optical signal, and signals S1", S2" and S3" are time-division multiplexed to a wavelength λ 3 of the input optical signal. In FIG.14B, signals S2, S1' and S3' are time-division multiplexed to the wavelength λ 1 of the input optical signal, signals S1', S2" are time-division multiplexed to the wavelength λ 2 of the input optical signal, and signals S1", S2' and S3 are time-division multiplexed to the wavelength λ 3 of the input optical signal. When it is assumed that the optical input signal received by the optical switching system shown in FIG.5 has a multiplexing factor (a, b, c), where a denotes a number of input optical fibers, b denotes a number of optical frequencies which are multiplexed and c denotes a time-division multiplexing factor, the optical output signal of the optical switching system has the same multiplexing factor (a, b, c). In other words, in FIG.5, the optical input signal to the optical switching system is divided into b optical frequencies in each of the optical wavelength-division multiplexed signal separators 60-1 through 60-a, where a=2 and b=3 in FIG.5. The b optical frequencies from the optical wavelength-division multiplexed signal separator 60-1, for example, are supplied to the corresponding b detectors 65-1 through 65-b wherein a routing information is extracted. The routing information includes the number a of output optical fibers of the optical switching system, the number b of optical frequencies output from the optical switching system and a time-division slot address (time slot number) c at the time of output. When the routing information is extracted in the detectors 65-1through 65-b, the optical signal is stored in the optical gate memories 73-1 through 73-c (c=100 in FIG.9) of the control time slot interchange and frequency shifters 70-1 through 70-b for the time c which is in conformance with the time slot number c, and the stored optical signals are read out in the sequence of the time slot number c. The optical signals stored in the optical gate memories 73-1 through 73-c may be read out at the same time, but no problems are introduced thereby. This is because the optical frequencies of the optical signal are all converted in the c optical frequency shifters 74-1 through 74-c shown in FIG.9 so as to carry out a routing in conformance with the extracted routing information. The optical frequency shifters 74-1 through 74-c are optical frequency converters. The optical frequencies are converted as shown in the following Table 1. In the Table 1, a subscript "111" means that the 111th optical frequency (which is an optical frequency only used within the optical switching system) is assigned to the optical signal and a=1, b=1 and c=1 in this case. A subscript "112" is adjacent to the 111th optical frequency and only the value of c differs by "1". In other words, the number of optical fibers and the optical frequencies at the time of output are the same as those at the time of input, but the time slot number c increases by "1". The routing information is included in a portion of the header H shown in FIG.6. In other words, the header H includes the routing information of the above Table 1. The header H additionally includes an information instructing a broadcasting of the same information, a priority of the information, the size (length) of the information and the like. For example, when the header H includes the information instructing the broadcasting of the same information, the optical gate memory 73-1 for example is not only opened during one time slot but is opened during a number of time slots to send the information a plurality of times to output a plurality of optical signals (a', b', c'), (a", b", c"), (a, b, c), ... . In other words, the same information is transferred for the number a' of optical fibers, the number b' of optical frequencies and the time slot number c. In the case of the information having a high priority, it is for example possible to give priority to the information over other information by assigning a small number to a portion of the number "abc". In the described embodiment, the optical data bus has the loop shape. However, it is not essential that the optical data bus has the loop shape. According to the disclosed embodiment, the rules of frequency conversion are as follows. For the sake of convenience, an optical packet routing information within the header H is denoted by (a, b, c), and it is assumed that an optical packet signal having a frequency X is converted into an optical packet signal having a frequency "abc". Here, a denotes a number of output optical fibers (number of output highways), b denotes an output optical frequency (output highway freqency), and c denotes an output time slot (output highway time slot). The optical frequencies of all the optical packet signals are converted depending on the optical packet routing information (a, b, c), and the converted optical frequencies are sequentially arranged depending on the values of "abc" as shown in the following Table 2. This Table 2 shows the optical packet arrangement in the optical data bus. the same output highway signals (packets) have the same first digit as "a##" in the optical data bus (800 and 80, for example). The group is named the a-group as shown in the Table 2. In the a-group, the packets of the same output highway frequency have the same first two digits as "ab#" and this group is named the b-group. The reference signs in the claims are intended for better understanding and shall not limit the claims.

Claims: An optical switching system comprising: first means (600-1 - 600-n) for receiving an input optical signal which is a wavelength-division multiplexed and time-division multiplexed signal, said first means including first separating means for separating and outputting a time-division multiplexed signal component of the input optical signal in each of divided wavelengths and second separating means for separating a control information included in the input optical signal; second means (730-1 - 730-m) coupled to said first means for storing an optical signal output from said first means for every time slot identical to that used for the separation in said first means and for reading out stored optical signals successively in a sequence of predetermined time slots so as to convert wavelengths of the optical signals into predetermined wavelengths based on said control information; third means (750-1 - 750-m) coupled to said second means for multiplexing wavelengths of optical signals output from said second means into wavelength-division multiplexed optical signals and for delaying a phase of the wavelength-division multiplexed optical signals a predetermined quantity; an optical data bus (800) coupled to said third means for receiving optical signals output from said third means and for transferring the optical signals in a predetermined direction within said optical data bus; fourth means (850-1 - 850-m) coupled to said optical data bus for extracting optical signals having wavelengths belonging to predetermined wavelength regions from said optical data bus and delaying a phase of the extracted optical signals a predetermined quantity and for converting wavelengths of the extracted optical signals into predetermined wavelengths; and fifth means (950-1 - 950-n) coupled to said fourth means for multiplexing the wavelengths of the optical signals output from said fourth means so as to output an output optical signal which is a wavelength-division multiplexed and time-division multiplexed signal. The optical switching system as claimed in claim 1, characterized in that said first separating means of said first means (600-1 - 600-n) comprises a frequency divider (60-1, 60-2) and said second separating means of said first means comprises a detector (65-1 - 65-3, 66-1 - 66-3) for detecting the control information included in the input optical signal and for outputting the input optical signal. The optical switching system as claimed in claim 1 or 2, characterized in that said second means (730-1 - 730-m) comprises for each optical signal output from said first means (600-1 - 600-n) a time-division multiplexed signal separator (72) for separating time-division multiplexed optical signals from the optical signal output from said first means, optical memories (73-1 - 73-100) for storing the time-division multiplexed optical signals or optical packet output from said time-division multiplexed signal separator during mutually different time slots, and a frequency shifter (74-1 - 74-100) for converting into the predetermined wavelengths the wavelengths of the optical signals which are read out from said optical memories based on said control information. The optical switching system as claimed in any of claims 1 to 3, characterized in that said third means (750-1 - 750-m) comprises a wavelength multiplexer (75) for multiplexing the optical signals output from said second means (730-1 - 730-m) into a wavelength-division multiplexed optical signal, and an optical delay circuit (76) for delaying the phase of the wavelength-division multiplexed optical signal the predetermined quantity. The optical switching system as claimed in claim 4, characterized in that said third means (750-1 - 750-m) further comprises for each wavelength-division multiplexed optical signal output from said optical delay circuit (76) an optical coupler (77-1 - 77-3, 78-1 - 78-3) for optically coupling said optical delay circuit to said optical data bus (800). The optical switching system as claimed in any of claims 1 to 5, characterized in that said optical data bus (800) comprises a loop shaped optical fiber. The optical switching system as claimed in any of claims 1 to 6, characterized in that said fourth means (850-1 - 850-m) comprises an optical bandpass filter (81-1 - 81-3, 82-1 - 82-3) for extracting the optical signals having the wavelengths belonging to the predetermined wavelength regions from said optical data bus (800). The optical switching system as claimed in claim 7, characterized in that said fourth means (850-1 - 850-m) further comprises an optical delay circuit (85-1 - 85-3, 86-1 - 86-3) for delaying the phase of the extracted optical signals the predetermined quantity, and a frequency shifter (90-1 - 90-3, 91-1 - 91-3) for converting the wavelengths of the extracted optical signals output from said optical delay circuit into the predetermined wavelengths. The optical switching system as claimed in any of claims 1 to 8, characterized in that said control information contains at least an information selected from a group including a wavelength information of the optical input signal, a content information, a wavelength information of the optical output signal, an output channel information, an information quantity, a priority information, and a time slot information. The optical switching system as claimed in any of claims 1 to 9, characterized in that said input optical signal is made up of cells having a fixed length and a header which includes a routing information, said routing information comprising a number a of output optical fibers which are coupled to an output side of said fifth means, an optical frequency b and an output time slot c. The optical switching system as claimed in claim 10, characterised in that said second means (730-1 - 730-m) are arranged to convert the wavelengths of all the stored optical signals depending on values of the routing information (a,b,c). The optical switching system as claimed in claim 11, characterised in that said second means (730-1 - 730-m) are arranged to convert optical frequencies of all the stored optical signals to predetermined wavelengths based on the central information. The optical switching system as claimed in any of claims 1 to 12, characterised in that said first to fifth means are arranged to process optical signals by an all-optical processing.

Inventors: MASUDA SHIGEFUMI, MASUDA, SHIGEFUMI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1989
Main classification: H04Q11
IPC codes: H04Q11, H04Q3, H04M3, H04B10