Abstract:
An optical cross-connect system is disclosed that use reduces the number of AWGs (Arrayed-Waveguide Grating) as compared to prior art systems so that the hardware complexity is reduced while simultaneously reducing its production costs. The optical cross-connect system includes N×N AWGs for performing multiplexing/demultiplexing functions, an optical circulator for transmitting bidirectional signals via the AWGs, an optical coupler for interconnecting N individual ports of the AWGs, and an optical switching block connected to the optical coupler. One of the optical signals branched from the optical coupler is input to the optical switching block having a corresponding wavelength and distributed to a desired output terminal, and the other one of the optical signals is input to an optical switching block being out of an operable wavelength range and filtered by the optical switching block.

Description:
CLAIM OF PRIORITY  
         [0001]    This application claims priority to an application entitled “OPTICAL CROSS-CONNECT SYSTEM,” filed in the Korean Intellectual Property Office on Oct. 7, 2002 and assigned Serial No. 2002-61010, the contents of which are hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an optical communication system, and more particularly to an optical cross-connect system for demultiplexing/switching wavelength-division-multiplexed optical signal channels received via input optical fibers, performing a wavelength division multiplexing on the optical signal channels, and then outputting the resultant signal to output optical fibers.  
           [0004]    2. Description of the Related Art  
           [0005]    Following the current trend of rapidly growing wavelength division multiplexing techniques using several wavelengths within one optical fiber, it is possible for one optical fiber to transmit a plurality of very high-speed mass storage optical signals. Conventional techniques for fabricating optical components generally use a path setup function, a distribution function (i.e., a switching function) and an add/drop function (i.e., a coupling function) of optical signals that is performed in an optical layer. Given these conventional techniques, an optical communication network on the basis of such wavelength division multiplexing (WDM) techniques can be constructed.  
           [0006]    A wavelength division multiplexing (WDM) optical communication network is typically constructed as a mesh-structure network using an optical cross-connect system. The optical cross-connect system that distributes optical signals according to their wavelengths can be adopted for nodes of such optical communication networks. Optical paths for such optical communication networks are determined by a signal distribution state of the optical cross-connect system. In this case, it is necessary to develop simple and economical optical cross-connect systems to manage efficiently and economically the WDM optical communication network. For definitional purposes, the term ‘distribution’ is used as a generic term encompassing both a routing concept and a switching concept.  
           [0007]    [0007]FIG. 1 is a diagram illustrating a conventional 2×2 optical cross-connect system.  
           [0008]    In FIG. 1, a conventional 2×2 optical cross-connect system  100  have two input terminals and two output terminals includes two 1×N wavelength division demultiplexers  110 . The demultiplexers  110  demultiplex optical signals, where a plurality of wavelengths λ 1 , λ 2 , λ 3 , . . . , λN, received via the input terminals are wavelength-division-multiplexed. The system  100  also includes N optical switches  120  that receive the same wavelengths of signals from the two wavelength division demultiplexers. The optical switches  120  perform a distribution function for distributing the received signals to a desired output port. The output ports provide the signals to two N×1 wavelength division multiplexers  130  that multiplex signals received from the optical switches  120 .  
           [0009]    In 2×2 optical cross-connect system  100 , the wavelength division demultiplexers  110  classify a plurality of multiplexed optical signals received from input terminals according to their wavelengths, and output the classified signals to an appropriate optical switch  120  corresponding to each wavelength. Each of the optical switches  120  receives optical signals of a specified wavelength related to its own operable range from the wavelength division demultiplexers  110 . The optical switches  120  then perform an add/drop operation (i.e., a coupling operation) on the optical signals or passes the optical signals. The resulting signals are distributed to the output ports. Each of the wavelength division multiplexer  130  receives optical signals having different wavelengths from the optical switches  120 , wavelength-division-multiplexes the optical signals, and then outputs them via the output terminals.  
           [0010]    Arrayed-waveguide gratings (AWGs) are typically used as a multiplexer and a demultiplexer, because they have easily extensible optical signal channels, are simply controlled, and have superior degrees of integration. In case of implementing a conventional 2×2 optical cross-connect system, four 1×N AWGs are needed. As can be seen from FIG. 1, the four 1×N AWGs should be controlled to have the same operational characteristics because 2N wavelengths in total are normally multiplexed and demultiplexed.  
           [0011]    Likewise, in the case where N optical signals are transmitted on one fiber, 2M 1×N-AWGs are needed to control an optical cross-connect system having N input optical fibers and N output optical fibers, and N M×M optical switches are also needed. In this case, 2M 1×N-AWGs should be controlled to have the same wavelength transmission characteristics. As will be appreciated, such conventional optical cross-connect systems are complex and incur high production costs due to many requisite components.  
           [0012]    Accordingly, there is a need in the art for improved optical cross-connect systems that use fewer AWG and thereby reducing cost and complexity of the systems.  
         SUMMARY OF THE INVENTION  
         [0013]    One aspect of the present invention is to provide an optical cross-connect system using a minimum number of AWGs so that its hardware complexity is reduced while simultaneously with reducing its production costs.  
           [0014]    In accordance with one embodiment of the present invention, the above and other objects can be accomplished by an optical cross-connect system including M (where M is an even number ≧2) input terminals receiving wavelength-division-multiplexed optical signals and M output terminals receiving wavelength-division-multiplexed optical signals. The optical cross-connect system includes a plurality of wavelength division multiplexers/demultiplexers, each having two one-side ports and N (where N is an integer &gt;0) other-side ports, performing wavelength division multiplexing/demultiplexing functions. The system also includes a plurality of optical circulators, each connected to one-side port of the wavelength division multiplexers/demultiplexers, that output wavelength-division-multiplexed optical signals received via the input terminals to one-side ports of the wavelength division multiplexers/demultiplexers, receive wavelength-division-multiplexed optical signals from one-side ports of the wavelength division multiplexers/demultiplexers, and output the wavelength-division-multiplexed optical signals to the output terminals. The system further includes a plurality of optical couplers, each connected to N other ports of the wavelength division multiplexers/demultiplexers, that branch optical signals of individual wavelengths being wavelength-division-demultiplexed. The optical signals are received from the wavelength division multiplexers/demultiplexers. In addition, the system includes N optical switching blocks for N wavelengths that receiving optical signals branched from the optical couplers according to their wavelengths, switch the optical signals to a desired path, and transmit the switched optical signals to the desired path. One of the optical signals branched from the optical coupler is input to the optical switching block having a corresponding wavelength and distributed to a desired output terminal, and the other one of the optical signals is input to an optical switching block being out of an operable wavelength range and filtered by the optical switching block.  
           [0015]    Preferably, the N optical switching blocks for N wavelengths may respectively include: an optical switch having an M×M matrix structure; and a plurality of optical circulators each connected to M input terminals and M output terminals of the optical switch, for transmitting I/O (Input/Output) bidirectional signals to the optical switch.  
           [0016]    Preferably, the N optical switching blocks for N wavelengths may respectively include: an optical switch having an M×M matrix structure; and a plurality of optical circulators each connected to M input terminals and M output terminals of the optical switch, for transmitting I/O (Input/Output) bidirectional signals to the optical switch. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    The above advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0018]    [0018]FIG. 1 is a diagram illustrating a conventional 2×2 optical cross-connect system;  
         [0019]    [0019]FIG. 2 is a detailed diagram of a 2×2 optical cross-connect system in accordance with a preferred embodiment of the present invention;  
         [0020]    [0020]FIG. 3 is a detailed diagram of an M×M optical cross-connect system in accordance with a preferred embodiment of the present invention; and  
         [0021]    [0021]FIG. 4 is a detailed diagram of an M×M optical switching block in accordance with a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may make the subject matter of the present invention rather unclear.  
         [0023]    [0023]FIG. 2 is a detailed diagram of a 2×2 optical cross-connect system  200  in accordance with a preferred embodiment of the present invention.  
         [0024]    The 2×2 optical cross-connect system  200  have two input terminals and two output terminals. The 2×2 optical cross-connect system  200  also includes two optical circulators  210  and  220 , a single 2×N multiplexer/demultiplexer  230 , N couplers  241 ,  242 ,  243  and  244 , and N optical switching blocks  251 ,  252  and  253 .  
         [0025]    The two optical circulators  210  and  220  each have three terminals. The optical circulators  210  and  220  are adapted to designate optical paths of optical signals and to handle bidirectional signals that are input and output. The first and second optical circulators  210  and  220  respectively receive an N-wavelength division-multiplexed optical signal via first terminals  211  and  221 . The first and second optical circulators  210  and  220  may respectively output the received optical signal to first and second multiplexing ports  231  and  232  of the wavelength division multiplexer/demultiplexer  230 , or may respectively transmit the N-wavelength division-multiplexed optical signal received from the wavelength division multiplexer/demultiplexer  230  to third terminals  213  and  223  via the second terminals  212  and  222 .  
         [0026]    The 2×N wavelength multiplexer/demultiplexer  230  is fabricated as an AWG having two multiplexing ports ( 231  and  232 ) and N demultiplexing ports ( 233  through  236 ). The 2×N wavelength multiplexer/demultiplexer  230  demultiplexes N-wavelength division-multiplexed optical signals received at the multiplexing ports  231  and  232  and then outputs the demultiplexed optical signals to the N demultiplexing ports  233 ,  234 ,  235  and  236 . The 2×N wavelength multiplexer/demultiplexer  230  functions as a wavelength division demultiplexer. The 2×N wavelength multiplexer/demultiplexer  230  also multiplexes optical signals of individual wavelengths received at the N demultiplexing ports  233 ,  234 ,  235  and  236 , and outputs the multiplexed optical signals to the multiplexing ports  231  and  232  each connected to the second terminals  212  and  222  of the first and second optical circulators  210  and  220 . In this regard, the 2×N wavelength multiplexer/demultiplexer  230  functions as a wavelength division multiplexer.  
         [0027]    The N 1×2-couplers  241 ,  242 ,  243  and  244  are respectively connected to, and interconnect, the N demultiplexing ports  233 ,  234 ,  235  and  236  of the 2×N wavelength division multiplexer/demultiplexer  230  The N 1×2-couplers  241 ,  242 ,  243  and  244  also branch the optical signals of individual wavelengths received from the demultiplexing ports  233 ˜ 236  and transmit the branched optical signals to one side port of adjacent couplers. For this operation, the N couplers  241 ˜ 244  are respectively branched into two ports a˜b, and share the ports a˜b with their adjacent couplers.  
         [0028]    The N optical switching blocks  251 ,  252  and  253  are arranged between the branched ports of the N couplers  241 ,  242 ,  243  and  244 . The N optical switching blocks  251 ,  252  and  253  are adapted to pass two signals of individual wavelengths in a signal traveling direction or reflect the two signals in the opposite direction of each signal traveling direction. The optical switching blocks  251 ,  252  and  253  respectively include a pair of wideband pass filters  252 - 1  and an optical mirror  252 - 2 . The wideband pass filters  252 - 1  are connected to each port of the N couplers  241 ,  242 ,  243  and  244 , and pass optical signals of individual wavelengths. The optical mirror  252 - 2  is arranged between one pair of wideband pass filters  252 - 1 , and either passes two signals of individual wavelengths in a signal traveling direction or reflects the two signals in the opposite direction of each signal traveling direction. Also, the optical switching blocks  251 ,  252  and  243  may respectively include a Bragg grating that reflects optical signals of individual wavelengths.  
         [0029]    In operation, the 2×2 optical cross-connect system  200  receives an N-wavelength division-multiplexed optical signal at the first terminal  211  of the first optical circulator  210 . This optical signal is transmitted to the first multiplexing port  231  of 2×N multiplexer/demultiplexer  230  via the second terminal  212 , and is wavelength-division-demultiplexed. The resulting optical signal is then transmitted to the individual ports  233 ,  234 ,  235  and  236 .  
         [0030]    Hereinafter, for the convenience of the description, an optical signal λ 1  from the second terminal  212  will only be described below. After being multiplexed and transmitted to the individual port  233 , the optical signal λ 1  becomes two sub-optical signals by splitting its power via the coupler  241 . The split signals are then transmitted to adjacent ports a˜b. One of the sub-optical signals is transmitted to a second multiplexing port and to adjacent coupler  242  via an optical switching block  251 . This sub-optical signal is then is transmitted to the individual port  234  of the 2×N multiplexer/demultiplexer  230  connected to the coupler  242 . The sub-optical signal is then wavelength-division-multiplexed, and finally it is transmitted to the second multiplexing port  232  of the 2×N multiplexer/demultiplexer  230 . The resulting multiplexed optical signals arc transmitted to the third terminal  223  via the second terminal  222  of the second optical circulator  220 .  
         [0031]    The other sub-optical signal passes an optical switching block  253  and is transmitted to the individual port  236  of the wavelength division multiplexer/demultiplexer  230  via the coupler  244 . However, it is cut off because the individual port  236  is not a port for passing the optical signal λ 1 .  
         [0032]    In this way, an N-wavelength division-multiplexed optical signal received at the first terminal  221  of the second optical circulator  220  is transmitted to the second multiplexing port  232  of 2×N multiplxer/demultiplexer  230  via the second terminal  212 , and is wavelength-division-demultiplexed and then transmitted to the individual ports  233 ,  234 ,  235  and  236 .  
         [0033]    Considering only the optical signal λ 1  from the second terminal  222  for the convenience, the optical signal λ 1  is multiplexed and transmitted to the individual port  234  and becomes two sub-optical signals by splitting its power via the coupler  242 , and is then transmitted to adjacent ports b˜c. One of the sub-optical signal is transmitted to a first multiplexing port is transmitted to the adjacent coupler  241  via the optical switching block  251 . This sub-optical signal is then transmitted to the individual port  233  of the 2×N multiplexer/demultiplexer  230  connected to the coupler  241 , is wavelength-division-multiplexed. The sub-optical signal is finally transmitted to the first multiplexing port  231  of the 2×N multiplexer/demultiplexer  230 . The resulting multiplexed optical signals are transmitted to the third terminal  213  via the second terminal  212  of the second optical circulator  220 .  
         [0034]    The other sub-optical signal passes the optical switching block  252  and is transmitted to the individual port  235  of the wavelength division multiplexer/demultiplexer  230  via the adjacent coupler  243 . However, it is cut off because the individual port  235  is not a port for passing the optical signal λ 1 .  
         [0035]    [0035]FIG. 3 is a detailed diagram of an M×M optical cross-connect system  300  in accordance with another embodiment of the present invention. This diagram illustrates a system configuration for extending the 2×2 optical cross-connect system  200  having two input terminals and two output terminals as shown in FIG. 2 to an M×M optical cross-connect system having M input terminals and M output terminals. For reference, it should be noted that FIG. 3 depicts only a path of an optical signal λ 1 .  
         [0036]    Referring to both FIGS. 2 and 3, the M×M optical cross-connect system  300  includes M/2 2×2 optical cross-connect systems (shown in FIG. 2) each having two optical circulators  210  and  220 , one 2×N multiplexer/demultiplexer  230 , N couplers  241 ˜ 244 , and N optical switching blocks  251 ˜ 253 . In this case, the optical switching blocks are include of N M×M optical switching blocks  351 ,  352  and  353  in such a way that they respectively contain Mwavelength-division-multiplexed input optical signals wherein N wavelengths are division-multiplexed.  
         [0037]    The operation of an N×N optical cross-connect system in accordance with one embodiment of the present invention will hereinafter be described with reference to FIG. 3.  
         [0038]    The optical circulators  301 ,  302 ,  303 ,  304 ,  305 , and  306  transmit N-wavelength division-multiplexed optical signals received at their first terminals to the wavelength division multiplexers/demultiplexers  310 ,  320  and  330  connected to their second terminals.  
         [0039]    The wavelength division multiplexers/demultiplexers  310 ,  320  and  330  separate each signal corresponding to each wavelength from the N-wavelength division-multiplexed optical signal transmitted from the optical circulators  301 ,  302 ,  303 ,  304 ,  305  and  306 , and output the separated signals to 1×2 couplers  311 ,  312 ,  321 ,  322 ,  331  and  332  connected to Nindividual ports.  
         [0040]    The 1×2 couplers  311 ,  312 ,  321 ,  322 ,  331  and  332  branch the optical signals of individual wavelengths received from the wavelength division multiplexers/demultiplexers  310 ,  320  and  330 , and output the branched optical signals to optical switching blocks  351 ,  352  and  353  having individual wavelengths.  
         [0041]    Each of the optical switching blocks  351 ,  352  and  353  receives optical signals of a specified wavelength related to its own operable range from the couplers  311 ,  312 ,  321 ,  322 ,  331  and  332 , and then distributes the result signals to desired output terminals. For this operation, in accordance with another embodiment of the present invention, each of the optical switching blocks  351 ,  352  and  353  are constructed as shown in FIG. 4.  
         [0042]    [0042]FIG. 4 is a detailed diagram of an M×M optical switching block for extending optical cross-connect systems. For the convenience of description, FIG. 4 illustrates only an optical switching block for an optical signal λ 1  in detail.  
         [0043]    Referring to FIG. 4, the M×M optical switching block  351  for the optical signal λ 1  includes one M×M optical switch  470 , a plurality of wideband pass filters  480 ,  481 ,  482 ,  483 ,  484  and  485  respectively connected to input ports Si 1 ˜SiM, and M 3-terminal optical circulators  410 ˜ 460  respectively connected to output ports So 1 ˜SoM of the M×M optical switch  470 . In this case, the M×M optical switching block  351  contains M ports S 1 ˜SM. The ports S 1 ˜SM are respectively connected to the optical circulators  410 ˜ 460  to manage two-way signals which are input and output.  
         [0044]    The 3-terminal optical circulators  410 ˜ 460  receive the same wavelength optical signals transmitted at the M ports S 1 ˜SM of the M×M optical switching block  351  via their first terminals (e.g.,  411 ), and respectively output the received optical signals to the input ports Si 1 ˜SiM of the M×M optical switch  470  via the wideband pass filters  480 ˜ 485  connected to their second terminals (e.g.,  412 ). In addition, the 3-terminal optical circulators  410 ˜ 460  receive optical signals generated from the output ports So 1 ˜SoM at their third terminals (e.g.,  413 ), and output the received optical signals to the ports S 1 ˜SM of the M×M optical switching block  351  connected to their first terminals. This operation is called a two-way signal transmission function. In this case, the wideband pass filter  480 - 485  are adapted to prevent noise in optical signals received at M input terminals of the optical switch, using an optical circulator.  
         [0045]    The M×M optical switch  470  receives the same wavelength optical signals at its own input ports Si 1 ˜SiM via the wideband pass filters  480 ˜ 485  each connected to second terminals of the optical circulators  410 ˜ 460 , distributes the received optical signals to desired output terminals, and then outputs the result signals to third terminals of optical circulators connected to the output ports So 1 ˜SoM of the optical switch  470 .  
         [0046]    The operations of the aforementioned N×N optical cross-connect system will hereinafter be described with reference to a path of an optical signal λ 1 .  
         [0047]    Referring to both FIGS. 3 and 4, M wavelength-division-multiplexed optical signals, where N wavelengths are division-multiplexed, are received at first terminals I 1 ˜IM of the optical circulators  301 ,  302 ,  303 ,  304 ,  305 , and  306  and are transmitted to the wavelength division multiplexers/demultiplexers  310 ,  320  and  330  via second terminals of the optical circulators  301 ˜ 306 . The optical signals are then divided into signals of individual wavelengths by the wavelength division multiplexers/demultiplexers  310 ˜ 330 , and are transmitted to 1×2 couplers  311 ,  312 ,  321 ,  322 ,  331  and  332  connected to N individual ports.  
         [0048]    The optical signal λ 1  is divided into two sub-optical signals by the C1 coupler  341 , the CN+1 coupler  343  and the C(M/2−1)+1 coupler  345 . One of the sub-optical signals is transmitted to the M×M optical switching block  351  for λ 1 , and the other sub-optical signal is transmitted to an M×M optical switching block  353  for λN. The optical signals λ 1  transmitted to the M×M optical switching block  353  for λN is cut off because it is out of an operable range of the optical switching block  353 . On the other hand, the optical signal λ 1  transmitted to each individual port S 1 ˜SM of the M×M optical switching block  351  for λ 1  is transmitted to each input port Si 1 ˜SiM of the optical switch  470  for λ 1  via the wideband pass filter  480  that is connected to the second terminal  412  via each first terminal  411  of the M optical circulators  410 ,  420 ,  430 ,  440 ,  450  and  460 .  
         [0049]    Since the optical signal λ 1  is in the operable range of the optical switch  470  for λ 1 , a λ1&#39;s path is diverted to desired output ports, the optical signal λ 1  is transmitted to output ports So 1 ˜SoM of the optical switch  470 . The transmitted optical signal λ 1  is transmitted to the individual ports S 1 ˜SM of the M×M optical switching block  351  connected to the first terminal via the third terminals (e.g.,  413 ) of optical circulators connected to output ports So 1 ˜SoM of the optical switch  470  and the signal is then transmitted to the individual ports  312 ,  322  and  332  of 2×N multiplexers/demultiplexers  310 ,  320  and  330  via the C2 coupler  342 , the CN+2 coupler  344  and the C(M/2−1)N+2 coupler  346 . The optical signal λ 1  transmitted to the individual ports is wavelength-division-multiplexed. The wavelength-division-multiplexed optical signal λ 1  is then transmitted to the third terminals  02 ,  04  and  0 M via the second terminals of the optical circulators  302 ,  304  and  306  connected to the multiplexing ports of the 2×N multiplexers/demultiplexers  310 ,  320  and  330 .  
         [0050]    In the above manner, the M×M optical cross-connect system according to one embodiment of the present invention divides M N-wavelength division-multiplexed optical signals according to its individual wavelengths, and connects the divided optical signals to an optical switching block of a corresponding wavelength, in such a way that it can divert a signal path toward a desired part and transmit the signals to the desired part.  
         [0051]    As apparent from the above description, in the case of an M×M optical cross-connect system for handing M input optical fibers and M output optical fibers, M/2 2×N-AWGs are needed whereas 2M 1×N-AWGs are needed in the conventional prior art systems. In this manner, the optical cross-connect systems according to the present invention has a simple configuration and low production costs by minimizing the number of requisite components. As a result, the embodiments of the present invention can implement new network node configurations for effectively and economically managing the ever increasing channel capacity demands of optical communication networks.  
         [0052]    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.