Optical matrix switch for wavelength-multiplexed signals

Abstract: An optical processing device for converting a wavelength of an optical signal comprises an optical processing unit (11) supplied with an input optical beam carrying thereon one or more optical signals with respective wavelengths that are different from each other, the optical processing unit being further supplied with a control optical beam having a stabilized reference wavelength (λ i ) and selecting the optical signal that has a first wavelength and outputting the same with a second wavelength that is specified by the reference wavelength; and a control unit (12) for controlling the optical processing unit by specifying the first wavelength of the optical beam to be selected.

Description: BACKGROUND OF THE INVENTION The present invention generally relates to optical processing systems and more particularly to a wavelength-synchronized optical processing device that produces an optical signal with a wavelength that is synchronized to a stabilized wavelength of a reference optical beam and various optical information processing systems that use such an optical processing device. With the extensive deployment of optical telecommunication network, studies are made on the optical transmission and reception in the optical exchange systems and optical subscriber systems. Among others, there is a proposal to transmit a plurality of optical signals having different wavelengths on a common optical fiber or optical waveguide in the wavelength multiplex mode. In such a wavelength multiplex transmission of optical signals, it is necessary to superpose the optical signals with sufficient wavelength interval such that a reception side can demultiplex the received optical signal into individual optical signal components with reliability. In such wavelength multiplex systems, it will be easily understood that the change or fluctuation of the oscillation wavelength occurring in the optical signals cause a disastrous effect in the operation of the reception side systems. FIG.1 shows the block diagram of a conventional optical processing system that uses a wavelength converter 1a. Referring to FIG.1, the wavelength converter 1a is supplied with an input optical signal having a wavelength of λ 0 and produces an output optical signal with a wavelength of λ 1 . There, the wavelength converter converts the wavelength of the input optical signal to a second wavelength, and the optical signal having the wavelength λ 1 is divided out from the converted optical signal in response to a reference optical beam given externally with the wavelength λ 1 . More specifically, the output optical signal of the wavelength converter 1a is supplied to an optical divider 2a that divides the incident optical beam into a first output beam corresponding to the output optical signal and a second output beam, and the second output beam is supplied to a wavelength comparator 3a. The wavelength comparator 3a is further supplied with the reference optical beam and produces an electric output indicative of the difference between the wavelength of the output optical signal of the converter 1a and the wavelength λ 1 of the reference optical beam. The output electric signal of the comparator 3a is supplied to a controller 4a that in turn produces a control signal for controlling the operation of the wavelength converter 1a. According to this system, one can convert the wavelength λ 0 of the incident optical signal to the wavelength λ 1 by controlling the converter 1a such that the output of the wavelength comparator 3a becomes zero. The wavelength converter 1a may be formed by using a DFB laser diode that can change the oscillation wavelength by controlling the bias current or temperature. FIG.2 shows another conventional wavelength conversion system wherein an input optical signal having a wavelength λ 0 is supplied to a photoelectric converter 1b that produces an electric output in response to the incident optical signal. The output electric signal is supplied to a clock extraction circuit 2b wherein a clock signal is extracted from the information that is modulated on the input optical signal. The clock extraction circuit further discriminates the logic level of the binary information signal modulated on the input optical beam with a timing given by the clocks, and drives an optical modulator 3b. The optical modulator 3b is thereby supplied with a reference optical beam with the wavelength λl and modulates the same in accordance with the electric output of the clock extraction circuit 2b. As a result, an optical output signal is obtained with the wavelength ; λ1. In any of these conventional optical processing systems, there has been a problem in that the normal operation of the system is not achieved when there is a fluctuation in the wavelength of the input optical beam. It should be noted that, in the telecommunication systems, there is no guarantee that the transmission side uses the stabilized optical source with respect to the oscillation wavelength. Further, such a fluctuation of the wavelength of the optical signal may be caused as a result of the dispersion of optical pulses that occur in the optical fibers. Thus, the optical transmission system is not only required to eliminate the fluctuation of the wavelength of the optical source at the transmission side but is also required to have an ability to adapt to the fluctuation of wavelength and to eliminate the same at the reception side or at any intermediate locations between the transmission side and the reception side. In a prior art, as disclosed in the paper entitled A photonic wavelength-division switching system using tunable LDF by Suzuki et al, World Prosperity through communications, Boston, June 11-14, 1989, vol. 2, pages 722-727, an optical processing device is synchronised to a reference light source and is adapted to convert the wavelength of an input optical signal to a second wavelength. In another prior art, as disclosed in the Japanese patent application JP 01181294, an optical matrix switch uses optical transmission times to convert a wavelength into a predetermined wavelength. SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to provide a novel and useful optical matrix switch comprising wavelength-synchronized optical processing devices, wherein the foregoing problems are eliminated. An object of the present invention is to provide an optical matrix switch for switching a wavelength-multiplexed optical beam carrying thereon a number of optical signals of different wavelengths and comprising optical processing devices each of which being supplied with a reference optical beam having a reference wavelength (λ 1 - λ n ) and being adapted to select an optical signal having a predetermined wavelength pertinent to said device from an input wavelength-multiplexed optical signal and to convert said wavelength of the selected optical signal to a second wavelength that is specified by said reference wavelength, comprising a plurality of first optical transmission lines each supplied with the input wavelength-multiplexed optical signal and transmitting the same, said input wavelength-multiplexed optical signal containing therein a plurality of input optical signals with respective wavelengths (λ 1 ' - λ n ') that are different from each other; a plurality of second optical transmission lines each supplied with an output wavelength-multiplexed optical signal and transmitting the same, said output wavelength-multiplexed optical signal containing therein a plurality of output optical signals with respective wavelengths (λ 1 - λ n ) that are different from each other, each of said second optical transmission lines intersecting with said plurality of first optical transmission lines at respective first type nodes; a first group of the said optical processing devices provided in correspondence to each node, each of said first group optical processing devices further outputting the second wavelength on said second optical transmission line connected to the first type node, the first group optical processing devices that are provided commonly on one of the first optical transmission lines are supplied with a single optical beam; and a reference optical beam generator for producing the reference optical beam (λ 1 - λ n ) and supplying the same to the first group optical processing devices such that the output optical signals outputted on each second optical transmission line have wavelengths (λ 1 - λ n ) that are different from each other. In a preferred embodiment the output wavelength-multiplexed optical signal of each of the plurality of second optical transmission lines is an intermediate wavelength-multiplexed optical signal, and further comprises a plurality of third optical transmission lines, each supplied with an output wavelength multiplexed optical signal and transmitting the same, said output wavelength-multiplexed optical signal containing therein a plurality of output optical signals with respective wavelengths (λ 1 - λ n ) that are different from each other, each of said third optical transmission lines intersecting with said plurality of second optical transmission lines at a respective second type nodes; a plurality of second group of the said optical processing devices provided in correspondence to each second type node, each of said second group optical processing devices being supplied with a reference optical beam having a reference wavelength (λ 1 - λ n ) and selecting an optical signal having a predetermined wavelength pertinent to said device from the intermediate wavelength-multiplexed optical signal for converting said wavelength of the selected optical signal to a third wavelength that is specified by said reference wavelength, each of said second group optical processing devices further outputting the same on said third optical transmission line connected to the second type node, and such that the reference optical beam produced by the reference optical beam generator is independently supplied to the plurality of first and second group optical processing devices such that the optical signals in the intermediate wavelength-multiplexed opticalsignal have the wavelengths that are different from each other and such that the optical signals in the output wavelength-multiplexed optical signal have the wavelengths that are different from each other. In another preferred embodiment, the optical switch is characterized in that: each of said first group optical processing devices comprises a first optical filter filtering out a reference wavelength beam supplied thereto from said reference optical beam generator, a second optical filter filtering out an input optical signal supplied thereto from said plurality of input opticalsignals through one of said plurality of first optical transmission lines, an optical modular modulating said reference wavelength beam according to said input optical signal filtered out by said second optical filter, said optical modulator transmitting an output optical signal along a second optical transmission line connected to said first group optical processing device. Another object of the present invention is to provide an optical information transmission system, comprising the above optical matrix switch characterized in that it further comprises an electro-optic conversion means supplied with a plurality of electric signals for converting the same to optical signals having respective wavelengths that are different from each other; an optical multiplexing means supplied with said plurality of optical signals for merging the same to form a wavelength-multiplexed optical signal that contains therein input optical signals corresponding to the optical signals of the electro-optic conversion means with respective wavelengths that are different from each other, the wavelength-multiplexed optical signal being supplied to each of the plurality of first optical transmission lines; an optical distribution means connected to each of the plurality of third optical transmission lines for receiving the output wavelength-multiplexed optical signal therefrom and distributing the same to a plurality of output ports; a plurality of filtering devices each connected to the output port of the optical distribution means for separating an optical signal that has a predetermined wavelength from the wavelength -multiplexed optical signal outputted at the output port, said predetermined wavelength being determined for each filtering device and a plurality of photodetection devices provided in correspondence to said plurality of filtering devices for detecting the optical signal selected by the filtering device and producing an etectric signal in response to the detection. Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG.1 is a block diagram showing the construction of a conventional wavelength conversion circuit used in an optical transmission system; FIG.2 is a block diagram showing another conventional wavelength conversion circuit; FIG.3 is a block diagram showing the construction of the wavelength-synchronized optical processing device according to a first embodiment of the present invention; FIG.4 is a block diagram showing the construction of a variable filter used in the optical processing device of FIG.3; FIG.5 is a block diagram showing another example of the variable filter of FIG.4; FIG.6 is a block diagram showing still another construction of the variable filter of FIG.4; FIG.7 is a diagram showing the structure of a semiconductor optical device used in the variable filter of FIG.6; FIG.8 is a diagram showing the operational characteristics of the device of FIG.7; FIG.9 is a block diagram showing the construction of the wavelength-synchronized optical processing device according to a second embodiment of the present invention; FIG.10 is a block diagram showing the construction of the wavelength-synchronized optical processing device according to a third embodiment of the present invention; FIG.11 is a block diagram showing the construction of the wavelength-synchronized optical processing device according to a fourth embodiment of the present invention; FIG.12 is a block diagram showing the construction of the wavelength-synchronized optical processing device according to a fifth embodiment of the present invention; FIG. 13 is a block diagram showing the construction of an optical matrix switch according to a sixth embodiment of the present invention that uses the wavelength-synchronized optical processing device; FIG. 14 is a block diagram showing the essential part of the optical matrix switch of FIG.15; FIG. 15 is a block diagram showing the construction of an optical matrix switch according to a seventh embodiment of the present invention; FIG. 16 is a block diagram showing the construction of the optical switching system according to an eighth embodiment of the present invention wherein the wavelength-synchronized optical processing device is used; FIG. 19 is a block diagram showing the construction of the optical transmission system according to a ninth embodiment of the present invention; and FIG. 18 is a block diagram showing the construction of the optical transmission system according to a tenth embodiment of the present invention wherein the wavelength-synchronized optical processing device is used. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.3 shows the general construction of the wavelength-synchronized optical processing device according to a first embodiment of the present invention. The optical processing device of FIG.3 is an optical demultiplexer that selectively recovers an optical signal component from a wavelength-multiplex optical signal modulated on an input optical beam, in response to a reference optical beam that specifies the wavelength of the optical signal to be recovered. Referring to FIG.3, the optical processing device includes an optical processing unit 11 and a control unit 12, wherein the optical processing unit 11 is generally formed from a variable-wavelength band pass filter 13, a photodetector 14 and an optical modulation unit 15. The band pass filter 13 of the optical processing unit 11 is supplied with an incident optical beam and controlled by the control unit 12 such that only the optical signal that has a particular wavelength specified by the control unit 12 is passed through the filter 13. The output optical beam of the filter 13 is supplied to the photodetector 14 wherein the photodetector 14 converts the optical beam to an electric signal. The output electric signal of the photodetector 14 is supplied to the optical modulation unit 15 and the optical modulation unit 15 modulates the reference optical beam in response to the electric output of the photodetector 14. As will be described later in detail, the filter 13 may be formed of a DFB laser amplifier and changes the wavelength of the optical beam passing therethrough in response to a bias current that is controlled below the threshold of laser oscillation. The optical modulation unit 15 may be a Franz-Keldysh effect device or a laser diode of which gain can be changed in response to the output of the photodetector 14. In operation, an input optical beam that carries thereon optical signals having respective wavelengths λ 1 ' - λ n ' in the wavelength-multiplex mode is supplied to the filter 13 that in turn is controlled by the control unit 12 to pass the optical signal having the wavelength λ i ' selectively. Meanwhile, the wavelength of the reference beam is well stabilized by using a stabilized optical source such as a laser diode of which operational temperature and bias current are compensated for with respect to any variation. Thereby, one obtains the output optical signal from the optical modulation unit 15 with the wavelength λ i in correspondence to foregoing original optical signal of the wavelength λ i '. The circuit 11 can be formed as an integrated circuit including the control unit 12. FIG.4 shows the construction of the filter 13 used in the system of FIG.3. Referring to FIG.4, the filter 13 includes a number of filter elements 13 1 - 13 4 respectively passing the optical beams of the wavelengths λ a - λ d , as well as a number of filter elements 13 5 - 13 8 respectively passing the optical beams of the wavelengths λ 1 ' - λ 4 ', wherein the wavelength-multiplexed input optical beam is supplied to each of the filter elements 13 5 - 13 8 parallel with each other. Further, the reference optical beam is supplied parallel to each of the filter elements 13 1 - 13 4 . The output optical beams of the filter elements 13 5 - 13 8 are supplied to corresponding variable transmittance controllers 13 9 - 13 12 each having a transmittance that is controlled in response to the output of the corresponding filter element. Thus, when the reference optical beam is given with the wavelength of λ a , the transmittance of the controller 13 9 is selectively increased and the optical signal having the wavelength λ 1 ' and passed through the filter element 13 5 is selectively outputted as an output optical beam of the filter 13. In the present embodiment, one may employ any of the multi-layered dielectric films, optical waveguides, or the spatial filters that use the diffraction grating, for the filter element 13 5 - 13 9 . Preferably, the wavelengths λ a , λ b , λ c and λ d may be set coincident to the wavelengths λ 1 ', λ 2 ' , λ 3 ' and λ 4 ' such that λ a = λ 1 ', λ b = λ 2 ', λ c = λ 3 ' and λ d = λ 4 ' . This, of course, is not the essential requirement for the operation of the device. FIG.5 shows an example of the variable transmittance controllers 13 9 - 13 12 , wherein the input optical signal from the filter 13 5 - 13 9 is supplied to a laser amplifier 13 23 for amplification by the stimulated emission caused therein in response to the passage of the wavefront of the input optical beam. The operation of the laser amplifier 13 23 is controlled by an electronic control circuit 13 22 that in turn is controlled in response to an electric signal produced by a photodetector 13 21 to which the reference optical beam is supplied. More specifically, the electronic circuit 13 22 produces a bias signal to the laser amplifier 13 23 when there is an incident reference optical beam to the photodetector 13 21 . In response to the bias signal, the laser amplifier 13 23 amplifies the incident input optical signal, while when there is no bias signal, the laser amplifier 13 22 absorbs the input optical signal. For the variable transmittance controllers, one may use, in addition to the foregoing laser amplifier, a Franz-Keldysh effect device or MQW optical modulator that uses the quantum confinement Stark effect. FIG.6 shows another embodiment of the variable-wavelength filter 13 wherein there is provided an optical switch 13 31 that has a first input port A for receiving the reference optical beam and a second input port B for receiving the input optical beam, wherein one of the optical beams at the input port A and the input port B is supplied selectively to a filter device 13 32 of which wavelength is controlled by a controller 13 34 . The optical beam that has passed through the filter device 13 32 is supplied to a second optical switch 13 33 that has a first output port C connected to an output waveguide (not shown) and a second output port D connected to the controller 13 34 . In operation, the first optical switch 13 31 is set at first such that the input port B is selected. Further, the second optical switch 13 33 is set such that the output port D is selected. In this state, the reference optical beam supplied to the input port B is transferred to the controller 13 34 after passing through the filter device 13 32 and the switch 13 33 . Thereby, the controller 13 34 sets the state of the filter device 13 32 such that the transmittance of the optical beam becomes maximum. After such a training of the filter device 13 32 is completed, the state of the optical switches 13 31 and 13 33 switched such that the input optical beam at the port A is outputted at the port C after passing through the filter device 13 32 . Thereby, only the optical signal that has the wavelength coincident to the wavelength of the filter device 13 32 alone appears at the output port C. In other words, the system 13 acts as the variable-wavelength filter that passes the optical signal having a wavelength coincident to the wavelength of the reference optical beam selectively. FIG.7 shows the construction of the filter device 13 32 . Referring to FIG.7, the filter device 13 32 is formed of a DFB laser diode that has an active layer 13 41 and a diffraction grating 13 42 . In operation, the device is biased below the threshold of laser oscillation. Thereby, the incident optical beam causes a stimulated emission in the active layer 13 41 upon passage therethrough. FIG.8 shows the band-pass characteristics of the laser amplifier of FIG.7 for different bias voltages. As can be seen in FIG.8, the peak of the transmittance shifts in response to the bias voltage. By using this effect, one can set the pass-band or pass-wavelength in the filter device by means of the controller 13 34 . According to the construction of FIG.6, one can maintain the stable operational characteristics for the filter 13 as a whole even when there is a change in the operational characteristics of the laser amplifier itself. Obviously, this is due to the feedback control of the laser amplifier 13 32 as described above. For the optical switches 13 31 and 13 33 , one may use the directional coupler and saturable optical absorption switch that changes the transmittance in response to the injection of carriers. . FIG.9 shows a wavelength-synchronized optical processing device according to a second embodiment of the present invention. Referring to FIG.9, the device includes an optical processing unit 11a and a control unit 12a, wherein the optical processing unit 11a uses the photodetector 14 for detecting the input optical beam that has the wavelength of λ i ' similarly to the optical processing unit 11 of the first embodiment. This input optical beam may have the fluctuation in the wavelength λ i '. The output electric signal of the photodetector 14 is supplied to the optical modulator 15 that in turn is supplied with the reference optical beam of the wavelength λ i . Thereby, the optical modulator 15 modulates the reference optical beam with the output electric signal of the photodetector 14, and an output optical beam carrying the optical signal of the original wavelength λ i ' is obtained with a stabilized wavelength of λ i . Further, a control unit 12a is used for controlling the operation of the optical modulator 15. FIG.10 shows a wavelength-synchronized optical processing device according to a third embodiment of the present invention. Referring to FIG.10, the optical processing device is formed of an optical processing unit 11b and a control unit 12b, wherein there is provided a laser diode 16 that is controlled by a controller 12b. There, the laser diode is injected with the reference optical beam of the stabilized wavelength λ i and further with the input optical beam of the wavelength λ i ' for producing an output optical beam carrying thereon the information modulated on the input optical beam, with the wavelength of λ i . Thereby, the laser diode acts as the wavelength converter. Again, the optical signal of the wavelength λ i ' and containing fluctuation is converted to the optical signal of the wavelength λ i that is free from fluctuation. FIG.11 shows a fourth embodiment of the optical processing device according to the present invention. Referring to FIG.11, the optical processing device of the present embodiment has a construction similar to that of FIG.3 except that there is provided a wavelength converter 17 after the optical processing unit 11 for converting the wavelength of the output optical beam from the wavelength λ i to another wavewavelength λ k . By using the optical processing unit 11a or 11b described with reference to FIGS.9 and 10 for the wavelength converter 17, one can obtain the output optical beam with the stabilized wavelength λ k . FIG.12 shows the optical processing device according to a fifth embodiment of the present invention. Referring to the drawing, the optical processing device of the present embodiment has a structure similar to that of FIG.10 except that there is provided a variable-wavelength filter 18 provided for filtering the input optical beam. As shown in FIG.12, the variable-wavelength filter 18 is controlled by the controller 12b and selectively passes one of the optical signals multiplexed on the input optical beam with the wavelengths λ 1 ' - λ n '. In this case, too, any of the desired optical signals that are multiplexed on the input optical beam with the wavelength-multiplex mode is converted to the desired, stabilized wavelength λ i . FIG. 13 shows an optical matrix switch according to a sixth embodiment of the present invention, wherein there are provided a number of optical transmission lines 33 at the input side and a number of optical transmission lines 34 at the output side. On each transmission line 33 of the input side, wavelength-multiplexed optical signals are supplied with wavelengths λ 1 ' - λ n ', while on each transmission line 34 of the output side, wavelength-multiplexed optical signals are carried with wavelengths of λ 1 - λ n . At each intersection of the transmission line 33 and the transmission line 34, there is provided a wavelength-synchronized optical processing device 31 that has a construction of any of the foregoing embodiments of FIGS.3 - 12, and each optical processing system 31 is supplied with the reference optical beam that is produced by a reference optical beam generator 32 with the stabilized wavelengths of λ 1 - λ n . Thereby, the optical processing device 31 causes a transfer of the input optical signal of the selected wavelength from the transmission line 33 of the input side to the optical transmission line 34 of the output side, wherein the optical signal thus transferred has a stabilized wavelength that is specified by the wavelength of the reference optical beam. It should be noted that each optical transmission line 34 carries thereon a number of wavelength multiplexed optical signals produced by a group of the optical processing devices 31 that are connected commonly to a single optical transmission line 33. Particularly, the group of the optical processing devices 31 that are provided commonly on one optical transmission line 33 are supplied with a single reference optical beam commonly, and the wavelength of the reference optical beam is changed in each optical transmission line 33. Thereby, optical signals of different wavelengths are outputted on each optical transmission line 34 of the output side. Further, by changing the combination of the wavelengths of the reference optical beams on the lines 34, one can output any optical signal on any optical transmission line 33 on any desired optical transmission line 34 with any desired wavelength. FIG. 14 shows the details of the optical matrix switch of FIG. 13. Referring to Fig. 14, there is provided an optical divider 35 on the optical transmission line in correspondence to each of the optical processing devices 31 for tapping the wavelength-multiplexed optical signals on the transmission line 33, and the optical signals thus tapped are supplied to the optical processing device 31. The optical processing device 31 selects one of the optical signals on the line 33 and outputs the selected optical signal with the wavelength of the reference optical beam. The output optical beam of the optical processing device 31 in turn is supplied to an optical coupler 36 that is provided on the optical transmission line 34 in correspondence to each of the optical processing device 31. The optical coupler 36 establishes an optical coupling between an optical fiber or waveguide that carries the optical output of the system 31 and the optical fiber or waveguide forming the optical transmission line 34, and the optical beam outputted from the optical processing device 31 is merged or wavelength-multiplexed upon the optical signals on the line 34. It should be noted that such an optical matrix switch can be constructed in the form of optical integrated circuit by forming the optical divider 35 and the optical coupler 36 together with the optical processing device 31 and the reference optical beam generator 32 on a common substrate. FIG. 15 shows an optical matrix switch according to a seventh embodiment of the present invention. Referring to FIG. 15, two optical matrix switches 38 and 39 each having the construction of FIG. 14 are connected in series, wherein the matrix switches 38 and the matrix switches 39 are connected by intermediate optical transmission lines 37 1 - 37 n . These optical transmission lines act as the optical transmission lines at the output side for the optical matrix switch 38 while act simultaneously as the input side optical transmission lines for the optical matrix switch 39. Further, the reference optical beam generator 32 is used commonly for both the optical matrix switch 38 and the optical matrix switch 39, wherein the reference optical beam generator 32 supplies the reference optical beams to the optical matrix 38 and the optical matrix 39 independently. In the typical example of operation, the reference optical beam having the wavelength of λ 1 is supplied to a group of the optical processing devices 31 that are located at the intersections formed between the line 33 1 and the lines 37 1 - 37 n , while the reference optical beam having the wavelength of λ 2 is supplied to another group of the optical processing devices 31 that are located at the intersections formed between the line 33 2 and the lines 37 1 - 37 n. Similarly, the wavelength of the reference optical beam supplied to a group of the optical processing devices 31 that are provided on a common optical transmission line of the input side is changed with respect to the wavelength of the reference optical beam that is supplied to the to another group of the optical processing devices 31 that are provided commonly on another input side optical transmission line. Thereby, the overlapping of the wavelength of the optical signals that are outputted commonly on an output side optical transmission line such as the line 37 1 is positively eliminated. The optical signals thus outputted on the lines 37 1 - 37 n are then switched by the second optical matrix switch 39, wherein the optical switching similar to the one described with reference to the optical matrix switch 38 is achieved. Thereby, output optical signals having respective wavelengths determined by the wavelength of the reference optical beams supplied to the optical matrix switch 39 are obtained at the output optical transmission lines 34 1 - 34 n . The wavelength of these output optical signals is of course stabilized by using the stabilized optical source for the reference optical beam generator 32. FIG. 16 shows an eighth embodiment of the present invention, wherein the present embodiment forms a wavelength converter for converting the wavelength of the optical signals modulated on the input optical beam with the wavelength-multiplex mode and outputting the optical signals thus converted in the wavelength multiplex mode. Referring to FIG. 16, there are provided a number of optical processing devices 41 1 - 41 n each having the construction of any of the wavelength-synchronized optical processing devices described previously, wherein each of the optical processing devices 41 1 - 41 n is supplied with the wavelength-multiplex optical signals from the optical distribution part 44 that in turn is supplied with an input optical beam carrying the wavelength-multiplex signals and distributing the same to the optical processing devices 41 1 - 41 n . Further, the optical processing devices 41 1 - 41 n are controlled by a control unit 43 that selects an optical signal from the wavelength-multiplexed optical signals. When the optical processing unit 11 is used for the optical processing devices 41 1 - 41 n , the control unit 43 controls a variable-wavelength filter similar to the filter 13 of FIG.3. Thereby, the control unit 43 acts as the control unit 12. Further, there is provided a reference optical beam generator 42 that produces the reference optical beam with the wavelengths λ 1 , λ 2 , ..., λ n and supply the same to respective optical processing devices. In response to the reference optical beams thus supplied, the optical processing devices 41 1 - 41 n produce output optical beams in coincidence with respective wavelengths of the reference optical beams. The output optical beams thus produced are added in an optical synthesis unit 45 that produces the an output optical beam on which the optical signals are modulated in the wavelength-multiplex mode. In the system of the present embodiment, it should be noted that one can convert the optical signal of the wavelength λ i to the optical signal having the stabilized wavelength λ j . For example, one can convert the optical signal of the wavelength λ 1 to the optical signal of the wavelength λ n and the optical signal of the wavelength λ 2 to the optical signal of the wavelength λ 1 . FIG. 17 is a block diagram showing the construction of an optical information transmission system wherein an optical matrix switch 61 having the construction of FIG. 13 or FIG. 15 is used. Referring to FIG. 17, there are provided a number of optical transmission terminals 62 1 - 62 m connected to the input side optical transmission lines of the optical matrix switch 61. Further, a number of optical reception terminals 63 1 - 63 m are connected to the output side optical transmission lines of the matrix switch 61. Each optical transmission terminal such as the terminal 62 1 includes an optical transmitter 64 for producing a number of optical signals with respective wavelengths λ 1 - λ n and an optical synthesizing unit 65 supplied with the optical signals for producing a wavelength-multiplexed optical beam from the optical signals. On the other hand, each optical reception terminal such as the terminal 63 1 includes an optical distribution unit 66 supplied with the wavelength-multiplexed optical signals from the optical matrix switch 61 and a variable-wavelength filter 67 for selecting an optical signal of a specific wavelength. Further, there is provided a photodetector 68 in connection with the filter 67 for detecting the optical signal that has passed through the filter 67. By controlling the optical matrix switch 61 in accordance with control information such as the address information, the path and the wavelength of the optical signals are switched in the matrix switch 61. More specifically, one can switch a huge number of channels (number of wavelength multiplex signals X number of transmission lines) simultaneously by using the system of FIG. 17. FIG. 18 shows a thirteenth embodiment of the present invention. Referring to FIG. 18, the system of the present embodiment is also an optical transmission system, wherein there are provided a number of transmission terminals 73 1 - 73 m each supplied with electric signals and producing optical signals in correspondence to the electric signals with respective wavelengths. The output optical signals of the terminals 73 1 - 73 m are supplied to an optical path selector 71 that includes a number of optical synthesis and distribution units 75 as well as 76 provided in correspondence to the transmission terminals 73 1 - 73 m and the reception terminals 74 1 - 74 m . The output optical signals of each transmission terminal are mixed to form a wavelength-multiplexed optical signal. Further these wavelength-multiplexed optical signals are selected by optical processing devices and are distributed further to a number of optical synthesis and distribution units 76 provided in correspondence to the optical reception terminals 74 1 - 74 m . In FIG. 18, the optical processing devices are not illustrated for the sake of clarity of the drawing. There, any combination of the optical signals produced by the optical transmission terminals 73 1 - 73 m is obtained at the output of each optical synthesis and distribution unit 76 in the form of the wavelength-multiplexed optical signals. The optical output thus obtained is then selectively passes through a filter 77 and detected by a photodetector 78. In this case, too, one can switch a large number of connections of which number is given by the product of the number of wavelength-multiplex signals and the number of optical transmission lines or channels, simultaneously. Further, the present invention is not limited to the embodiments described heretofore, but various variations and modifications may be made without departing from the scope of the invention.

Claims: An optical matrix switch for switching a wavelength-multiplexed optical beam carrying thereon a number of optical signals of different wavelengths,and comprising optical processing devices each of which being supplied with a reference optical beam having a reference wavelength (λ 1 - λ n ) and being adapted to select an optical signal having a predetermined wavelength pertinent to said device from an input wavelength-multiplexed optical signal and to convert said wavelength of the selected optical signal to a second wavelength that is specified by said reference wavelength, comprising a plurality of first optical transmission lines (33; 33 1 -33 n ;) each supplied with the input wavelength-multiplexed optical signal and transmitting the same, said input wavelength-multiplexed optical signal containing therein a plurality of input optical signals with respective wavelengths (λ 1 ' - λ n ') that are different from each other; a plurality of second optical transmission lines (34; 37 1 -37 n ) each supplied with an output wavelength-multiplexed optical signal and transmitting the same, said output wavelength-multiplexed optical signal containing therein a plurality of output optical signals with respective wavelengths (λ 1 - λ n ) that are different from each other, each of said second optical transmission lines intersecting with said plurality of first optical transmission lines at respective first type nodes; a first group of the said optical processing devices (31) provided in correspondence to each node, each of said first group optical processing devices further outputting the second wavelength on said second optical transmission line connected to the first type node, the first group optical processing devices that are provided commonly on one of the first optical transmission lines (33) are supplied with a single optical beam; and a reference optical beam generator (32) for producing the reference optical beam (λ 1 - λ n ) and supplying the same to the first group optical processing devices such that the output optical signals outputted on each second optical transmission line have wavelengths (λ 1 - λ n ) that are different from each other. An optical matrix switch according to claim 1, characterized in that : the output wavelength-multiplexed optical signal of each of the plurality of second optical transmission lines (37 1 - 37 n ), is an intermediate wavelength-multiplexed optical signal, the optical matrix further comprises : a plurality of third optical transmission lines (34 1 - 34 n ), each supplied with an output wavelength multiplexed optical signal and transmitting the same, said output wavelength-multiplexed optical signal containing therein a plurality of output optical signals with respective wavelength (λ 1 - λ n ) that are different from each other, each of said third optical transmission lines intersecting with said plurality of second optical transmission lines at a respective second type nodes; a second group of the said optical processing devices (31) provided in correspondence to each second type node, each of said second group optical processing devices being supplied with a reference optical team having a reference wavelength (λ 1 - λ n ) and being adapted to select an optical signal having a predetermined wavelength pertinent to said device from the intermediate wavelength-multiplexed optical signal and convert said viavelength of the selected optical signal to a third wavelength that is specified by said reference wavelength, each of said. second group optical processing devices further outputting the third wavelenght on said third optical transmission line connected to the second type node; and means arranged such that the reference optical beam produced by the reference optical beam generator (32) is independently supplied to the plurality of first and second group optical processing devices such that the optical signals in the intermediate wavelength-multiplexed optical signal have the wavelengths that are different from each other and such that the optical signals in the output wavelength-multiplexed optical signal have the wavelengths that are different from each other. An optical matrix switch according to claim 1, characterized in that : each of said first group optical processing devises comprises a first optical filter (13 1 -13 4 ) filtering out a reference wavelength beam supplied thereto from said reference optical beam generator, a second optical filter (13 5 -13 8 ) filtering out an input optical signal supplied thereto from said plurality of input optical signals through one of said plurality of first optical transmission lines, an optical modulator (13 9 -13 12 ) modulating said reference wavelength beam according to said input optical signal filtered out by said second optical filter, said optical modulator transmitting an output optical signal along a second optical transmission line connected to said first group optical processing device. An optical information transmission system, comprising an optical matrix switch according to claim 2, characterized in that it further comprises: an electro-optic conversion means (64) supplied with a plurality of electric signals for converting the same to optical signals having respective wavelengths that are different from each other; optical multiplexing means (65) supplied with said plurality of optical signals for merging the same to form a wavelength-multiplexed optical signal that contains therein input optical signals corresponding to the optical signals of the electro-optic conversion means with respective wavelengths that are different from each other, the wavelength-multiplexed optical signal being supplied to each of the plurality of first optical transmission lines (33 1 - 33 n ); an optical distribution means (66) connected to each of the plurality of third optical transmission lines(34 1 - 34 n )for receiving the output wavelength-multiplexed optical signal therefrom and distributing the same to a plurality of output ports; a plurality of filtering devices (67) each connected to the output port of the optical distribution means for separating an optical signal that has a predetermined wavelength from the wavelength -multiplexed optical signal outputted at the output port, said predetermined wavelength being determined for each filtering device; and a plurality of photodetection devices (68) provided in correspondence to said plurality of filtering devices for detecting the optical signal selected by the filtering device and producing an electric signal in response to the detection.

Inventors: FUJIMOTO NOBUHIRO, KUROYANAGI SATOSHI, NOBUHARA HIROYUKI, ROKUGAWA HIROYUKI, TANAKA KAZUHIRO, WAKAO KIYOHIDE, FUJIMOTO, NOBUHIRO, KUROYANAGI, SATOSHI, NOBUHARA, HIROYUKI, ROKUGAWA, HIROYUKI, TANAKA, KAZUHIRO, WAKAO, KIYOHIDE, Fujimoto, Nobuhiro, c/o Fujitsu Limited, KUROYANAGI, SATOSHI, C/O FUJITSU LIMITED, Nobuhara, Hiroyuki, c/o Fujitsu Limited, Rokugawa, Hiroyuki, c/o Fujitsu Limited, Tanaka, Kazuhiro, c/o Fujitsu Limited, Wakao, Kiyohide, c/o Fujitsu Limited
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1992
Main classification: H04Q11
IPC codes: H04B10, H04Q11