Abstract:
An optical gate based optical space division switch for switching optical signals inputted through arbitrary input ports to a desired output port with no internal collision. The optical space division switch comprises a first splitting section for splitting the optical signals inputted through the input ports, a first amplification section for selectively amplifying output optical signals from the first splitting section, a second splitting section for splitting output optical signals from the first amplification section, a second amplification section for selectively amplifying output optical signals from the second splitting section, a coupling section for coupling output optical signals from the second amplification section, and a third amplification section for amplifying an output optical signal from the coupling section and transferring the amplified optical signal to the output port. According to the present invention, optical gates are connected in a two-stage manner to cross-couple optical signals. Therefore, the optical signals are transferred only to a desired output port, thereby reducing the number of their crosstalk components and so significantly improving a signal-to-noise ratio.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to optical gate based optical space division switches, and more particularly to an optical space division switch in which optical gates are connected in a two-stage manner to cross-couple optical signals, so that optical signals inputted through arbitrary input ports can be switched to a desired output port with no internal collision. 
     2. Description of the Prior Art 
     Generally, optical gate based optical space division switches function to switch optical signals inputted through arbitrary input ports to a desired output port in response to optical gates being turned on or off. 
     A 4×4 optical gate based optical space division switch has been proposed by Gustavsson et al., and it is shown in FIG. 1 herein (see: “Monolithically integrated 4×4 InGaAs/InP laser amplifier gate switch arrays”, Electronic Letters, vol.28, no.24, pp.2223-2225, Nov. 1992). 
     As shown in FIG. 1, the 4×4 optical gate based optical space division switch comprises an optical gate  110  with four optical amplifiers  111  based on semiconductor devices, and 1×4 optical splitters  121 - 124  having their input terminals connected respectively to output terminals of the optical gate  110 . Optical gates  131 - 134  each includes four optical amplifiers  111  based on semiconductor devices and has its input terminals connected respectively to output terminals of a corresponding one of the 1×4 optical splitters  121 - 124 . The conventional optical space division switch further comprises 4×1 optical couplers  141 - 144  each having its input terminals connected respectively to corresponding ones of output terminals of the optical gates  131 - 134 . An optical gate  150  includes four optical amplifiers  111  based on semiconductor devices, and has its input terminals connected respectively to output terminals of the 4×1 optical couplers  141 - 144 . 
     Noticeably, the input optical gate  110  and the output optical gate  150  are always maintained at their ON state. For this reason, the input and output optical gates  110  and  150  are not operated as optical gates for selectively transferring optical signals, but only as optical amplifiers for compensating for signal loss by optical components. 
     The operation of the conventional 4×4 optical gate based optical space division switch with the above-mentioned construction will hereinafter be described. 
     First, the four optical amplifiers in the input optical gate  110  amplify optical signals inputted through input ports IP 1 -IP 4  and transfer the amplified optical signals to the 1×4 optical splitters  121 - 124 , respectively. 
     Each of the 1×4 optical splitters  121 - 124  splits a corresponding one of the output optical signals from the optical gate  110  into four optical signals and transfers the split optical signals to a corresponding one of the optical gates  131 - 134 . 
     The four optical amplifiers in each of the optical gates  131 - 134  amplify the output optical signals from a corresponding one of the 1×4 optical splitters  121 - 124  and transfer the amplified optical signals to the 4×1 optical couplers  141 - 144 , respectively. At this time, the optical gates  131 - 134  are turned on or off to selectively transfer the output optical signals from the 1×4 optical splitters  121 - 124  to the 4×1 optical couplers  141 - 144 . 
     Each of the 4×1 optical couplers  141 - 144  couples the four output optical signals from the optical gates  131 - 134  into one optical signal, which is then transferred to the output optical gate  150 . 
     The four optical amplifiers in the output optical gate  150  amplify the output optical signals from the 4×1 optical couplers  141 - 144  and transfer the amplified optical signals externally through output ports OP 1 -OP 4 , respectively. 
     However, the above-mentioned conventional optical sspace divisionswitch has a disadvantage in that, even if the optical gates  131 - 134  are turned off, they often transfer partially the optical signals due to their imperfect ON/OFF characteristic. Such crosstalk components degrade the performance of other signals. 
     SUMMARY OF THE INVENTION 
     Therefore, the present invention has been made in view of the above problem, and it is an object of the present invention to provide an optical gate based optical space division switch which is capable of switching optical signals inputted through arbitrary input ports to a desired output port with no internal collision. The transfer of the input optical signals is blocked by double gating so that they can hardly be transferred to undesired output ports. Hence, the input optical signals can be transferred only to a desired output port, resulting in a significant reduction in the number of their crosstalk components. 
     In accordance with one aspect of the present invention, there is provided an optical gate based optical space division switch for switching optical signals inputted through arbitrary input ports to a desired output port with no internal collision, comprising first splitting means for splitting the optical signals inputted through the input ports; first amplification means for selectively amplifying output optical signals from the first splitting means; second splitting means for splitting output optical signals from the first amplification means; second amplification means for selectively amplifying output optical signals from the second splitting means; coupling means for coupling output optical signals from the second amplification means; and third amplification means for amplifying an output optical signal from the coupling means and transferring the amplified optical signal to the output port. 
     In accordance with another aspect of the present invention, there is provided an optical gate based optical space division switch for switching optical signals inputted through arbitrary input ports to a desired output port with no internal collision, comprising first amplification means for amplifying the optical signals inputted through the input ports; signal splitting means for splitting output optical signals from the first amplification means; second amplification means for selectively amplifying output optical signals from the signal splitting means; first coupling means for coupling output optical signals from the second amplification means; third amplification means for selectively amplifying output optical signals from the first coupling means; and second coupling means for coupling output optical signals from the third amplification means and transferring the coupled result to the output port. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a block diagram of a conventional 4×4 optical gate based optical space division switch; 
     FIG. 2 is a block diagram of an optical gate based optical space division switch in accordance with an embodiment of the present invention; 
     FIG. 3 is a block diagram of an optical gate based optical space division switch in accordance with an alternative embodiment of the present invention; and 
     FIG. 4 is a view showing the comparison between characteristics of the conventional optical space division switch in FIG.  1  and optical space division switch of the present invention in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 2, there is shown in block form an M×N optical gate based optical space division switch in accordance with an embodiment of the present invention. As shown in this drawing, the M×N optical gate based optical space division switch comprises 1×n optical splitters  211 - 21 M having their input terminals connected respectively to M input ports IP 1 -IPM. Optical gates  221 - 22 M each includes n (where, n=N ½ ) optical amplifiers  22 AP 1 - 22 APn having their input terminals connected respectively to output terminals of a corresponding one of the 1×n optical splitters  211 - 21 M. Optical splitter blocks  231 - 23 M each includes n 1×n optical splitters  230 D 1 - 230 Dn having their input terminals connected respectively to output terminals of a corresponding one of the optical gates  221 - 22 M. Optical gates  241 - 24 M each includes n×n optical amplifiers  24 AP 1 - 24 AP(n×n) each having its input terminal connected to a corresponding one of output terminals of the 1×n optical splitters  230 D 1 - 230 Dn in a corresponding one of the optical splitter blocks  231 - 23 M. The optical space division switch further comprises M×1 optical couplers  251 - 25 N each having its input terminals connected respectively to corresponding ones of output terminals of the optical gates  241 - 24 M. An optical gate  260  includes N optical amplifiers  26 AP 1 - 26 APN having their input terminals connected respectively to output terminals of the M×1 optical couplers  251 - 25 N and their output terminals connected respectively to N output ports OP 1 -OPN. 
     Noticeably, the optical amplifiers  26 AP 1 - 26 APN in the optical gate  260  are always maintained at their ON state to compensate for a loss in output optical signals. 
     The operation of the M×N optical gate based optical space division switch with the above-mentioned construction in accordance with the embodiment of the present invention will hereinafter be described in detail. 
     First, each of the 1×n optical splitters  211 - 21 M splits one optical signal incident upon a corresponding one of the input ports IP 1 -IPM into n optical signals and transfers the split n optical signals respectively to the n optical amplifiers  22 AP 1 - 22 APn in a corresponding one of the optical gates  221 - 22 M. 
     In each of the optical gates  221 - 22 M, one of the n optical amplifiers  22 AP 1 - 22 APn, connected toward a selected output port, is turned on and the others are turned off. The turned-on optical amplifier amplifies a corresponding one of the optical signals transferred by the associated 1×n optical splitter and transfers the amplified optical signal to a corresponding one of the optical splitter blocks  231 - 23 M. 
     The output optical signal from the turned-on amplifier in each of the optical gates  221 - 22 M is split into n optical signals by the associated 1×n optical splitter in a corresponding one of the optical splitter blocks  231 - 23 M and transferred to a corresponding one of the optical gates  241 - 24 M. 
     In each of the optical gates  241 - 24 M, one of the n×n optical amplifiers  24 AP 1 - 24 AP(n×n), connected toward the selected output port, is turned on and the others are turned off. The turned-on optical amplifier amplifies a corresponding one of the optical signals transferred by the associated 1×n optical splitter in a corresponding one of the optical splitter blocks  231 - 23 M and transfers the amplified optical signal to a corresponding one of the M×1 optical couplers  251 - 25 N, connected toward the selected output port. 
     Then, the M×1 optical coupler connected toward the selected output port couples the M optical signals from the turned-on optical amplifiers in the optical gates  241 - 24 M into one optical signal and transfers the coupled optical signal to a corresponding one of the optical amplifiers  26 AP 1 - 26 APN in the optical gate  260 , connected to the selected output port. 
     The optical amplifiers  26 AP 1 - 26 APN in the optical gate  260  are always maintained at their ON state. As a result, the optical amplifier connected to the selected output port amplifies the output optical signal from the M×1 optical coupler and transfers the amplified optical signal to the selected output port. 
     In this manner, the optical signals incident upon the input ports are passed sequentially through the first optical gates  221 - 22 M and the second optical gates  241 - 24 M and then transferred to the selected output port. But, the incident optical signals are hardly transferred to non-selected output ports by the first optical gates  221 - 22 M and the second optical gates  241 - 24 M. Therefore, the number of crosstalk components of the input optical signals is reduced by M ½ −1, resulting in an improvement in signal-to-noise ratio. 
     With reference to FIG. 3, there is shown in block form an M×N optical gate based optical space division switch in accordance with an alternative embodiment of the present invention. As shown in this drawing, the M×N optical gate based optical space division switch comprises an optical gate  310  which includes M optical amplifiers  31 AP 1 - 31 APM having their input terminals connected respectively to M input ports IP 1 -IPM. The optical space division switch further comprises 1×N optical splitters  321 - 32 M having their input terminals connected respectively to output terminals of the optical amplifiers  31 AP 1 - 31 APM in the optical gate  310 . Optical gates  331 - 33 N each includes m×m optical amplifiers  33 AP 1 - 33 AP(m×m) having their input terminals connected respectively to corresponding ones of output terminals of the 1×N optical splitters  321 - 32 M. Optical coupler blocks  341 - 34 N each includes m (where, M=M ½ ) m×1 optical couplers  340 C 1 - 340 Cm having their input terminals connected respectively to output terminals of a corresponding one of the optical gates  331 - 33 N. Optical gates  351 - 35 N each includes m optical amplifiers  35 AP 1 - 35 APm having their input terminals connected respectively to output terminals of the m×1 optical couplers  340 C 1 - 340 Cm in a corresponding one of the optical coupler blocks  341 - 34 N. The optical space division switch further comprises m×1 optical couplers  361 - 36 N each having its input terminals connected respectively to output terminals of the optical amplifiers  35 AP 1 - 35 APm in a corresponding one of the optical gates  351 - 35 N and its output terminal connected to a corresponding one of N output ports OP 1 -OPN. 
     Noticeably, the optical amplifiers  31 AP 1 - 31 APM in the optical gate  310  are always maintained at their ON state to compensate for a loss in input optical signals. 
     The operation of the M×N optical gate based optical space division switch with the above-mentioned construction in accordance with the second embodiment of the present invention will hereinafter be described in detail. 
     First, the optical amplifiers  31 AP 1 - 31 APM in the optical gate  310  amplify optical signals incident upon the input ports IP 1 -IPM and transfer the amplified optical signals to the 1×N optical splitters  321 - 32 M, respectively. 
     Each of the 1×N optical splitters  321 - 32 M splits the output optical signal from a corresponding one of the optical amplifiers  31 AP 1 - 31 APM in the optical gate  310  into N optical signals and transfers the split N optical signals respectively to corresponding ones of the m×m optical amplifiers  33 AP 1 - 33 AP(m×m) in the optical gates  331 - 33 N. 
     One of the optical gates  331 - 33 N, connected toward a selected output port, is turned on and the others are turned off. As a result, the m×m optical amplifiers  33 AP 1 - 33 AP(m×m) in the turned-on optical gate amplify the optical signals transferred by the 1×N optical splitters  321 - 32 M and transfer the amplified optical signals to a corresponding one of the optical coupler blocks  341 - 34 N, respectively. 
     The m optical signals transferred by the optical amplifiers in the turned-on optical gate are coupled into one optical signal by the associated m×1 optical coupler in a corresponding one of the optical coupler blocks  341 - 34 N and then transferred to a corresponding one of the optical gates  351 - 35 N. 
     One of the optical gates  351 - 35 N, connected toward the selected output port, is turned on and the others are turned off. As a result, the optical amplifiers  35 AP 1 - 35 APm in the turned-on optical gate amplify the optical signals transferred by the m×1 optical couplers  340 C 1 - 340 Cm in the associated optical coupler block and transfer the amplified optical signals to a corresponding one of the m×1 optical couplers  361 - 36 N, connected to the selected output port, respectively. 
     Then, the m×1 optical coupler connected to the selected output port couples the m optical signals from the optical amplifiers  35 AP 1 - 35 APm in the turned-on optical gate into one optical signal and transfers the coupled optical signal to the selected output port. 
     As stated previously, the optical signals incident upon the input ports are passed sequentially through the first optical gates  331 - 33 N and the second optical gates  351 - 35 N and then transferred to the selected output port. But, the incident optical signals are hardly transferred to nonselected output ports by the first optical gates  331 - 33 N and the second optical gates  351 - 35 N. Therefore, the number of crosstalk components of the input optical signals is reduced by M ½ −1, resulting in an improvement in signal-to-noise ratio. 
     FIG. 4 shows the comparison between characteristics of the conventional optical space division switch in FIG.  1  and optical space division switch of the present invention in FIG.  2 . In this drawing, the comparison is made especially with respect to the number of optical gates required in construction and the number of crosstalk components. 
     In FIG. 4, the characteristic of the conventional optical space division switch in FIG. 1 is indicated by solid lines and the characteristic of the present optical space division switch in FIG. 2 is indicated by dotted lines. 
     It can be seen from FIG. 4 that, for an M×N optical space division switch fabric, the present optical space division switch in FIG. 2 requires a number of optical gates about 17% more than that in the conventional optical space division switch in FIG.  1 . However, the number of crosstalk components in the present optical space division switch in FIG. 2 is significantly reduced as compared with that in the conventional optical space division switch in FIG.  1 . 
     As apparent from the above description, according to the present invention, optical gates are connected in a two-stage manner to cross-couple optical signals, so that the optical signals can hardly be transferred to undesired output ports. Therefore, the optical signals are transferred only to a desired output port, thereby reducing the number of their crosstalk components and so significantly improving a signal-to-noise ratio. 
     Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.