Abstract:
Disclosed is a node structure of an upgradeable wavelength division multiplexing system that can minimize the expense in implementing, maintaining, and upgrading the system. The node structure includes an interleaver for interleaving a plurality of optical signals received therein into a predetermined number of channels; at least one demultiplexer coupled to one of the output channels for demultiplexing the optical signals received thereto into a prescribed number of channels; at least one multiplexer for multiplexing the respective demultiplexed optical signals from the demultiplexer; and, a deinterleaver for deinterleaving the optical signals outputted from the the multiplexer to be forwarded to the next node.

Description:
CLAIM OF PRIORTY  
         [0001]    This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. Section 119 from an application for “Node Structure of Upgradable Wavelength Division Multiplexing System,” filed earlier in the Korean Industrial Property Office on Dec, 28, 1999 and there duly assigned Ser. No. 99-64110.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an optical communication, and more particularly to a wavelength division multiplexing system that can transmit a plurality of channels through an optical fiber.  
           [0004]    2. Description of the Related Art  
           [0005]    A wavelength division multiplexing (WDM) system provides simultaneous transmission of optical signals with a plurality of different wavelengths via an optical fiber. In the WDM system, the transmission of a large quantity of information at a faster transmission rate is possible by employing an optical fiber as the transmission medium. However, the WDM system has some drawbacks in that the provision of upgrading the transmission capacity to accommodate a growing number of nodes with variable data size.  
           [0006]    [0006]FIG. 1 is a simplified block diagram illustrating the node structure of the WDM system according to a conventional system. As shown in FIG. 1, the mechanism used for upgrading the transmission capacity of the WDM system is achieved by providing a scalable multiplexer  20  and demultiplexer  10  which can accommodate additional channels in the future. Although such a system is initially built with adequate space to add more channel capacity later, it is very costly to install both the multiplexer  20  and the demultiplexer  10  with such a capacity. Moreover, the system is not utilized efficiently in the most instances as most of the extendable capacity is not typically used. Furthermore, it is difficult to predict the optimal size of the multiplexer  20  and the demultiplexer  10  that can be fully utilized in unforeseeable future.  
           [0007]    [0007]FIG. 2 is another simplified block diagram of a prior art illustrating the node structure of the WDM system. As shown in FIG. 2, the mechanism for upgrading the transmission capacity of the WDM system is accomplished by replacing the current multiplexer and demultiplexer with a new multiplexer  40  and demultiplexer  30  with the additional necessary channel capacities. Although this system saves the cost of installing a large system as mentioned in the preceding paragraphs, there are additional costs involved for replacing the old components with the new multiplexer  40  and demultiplexer  30 . Also, it is not economical to replace the old devices whenever a system upgrade is necessary. Moreover, there is a drawback in this type of upgrading method as the service has to be interrupted when replacing the old components.  
           [0008]    [0008]FIG. 3 is a simplified block diagram illustrating the node structure of the WDM system according to anther prior art. As shown in FIG. 3, the mechanism for upgrading the transmission capacity of the WDM system is achieved by adding a pair of multiplexer  80  demultiplexer  70  on each port using an optical strength dividing device, such as optical couplers  50  and  60 . Compared to the previous methods, this method provides a cost saving means to upgrade the transmission capacity as it does not require replacing any components in the existing system. Rather, it merely adds additional components to the existing system by adding the ports  52  and  62 . However, there is still a drawback in that the power loss as a result of dividing the initial power via the optical couplers is increased as more channels are being serviced within the system.  
         SUMMARY OF THE INVENTION  
         [0009]    It is, therefore, an object of the present invention to provide a node structure that is upgradable in the WDN system which can minimize the expense associated with maintaining and upgrading the system in the future.  
           [0010]    Another object of the present invention is to provide a node structure that is upgradable in the WDM system in a simpler manner and prevent power loss associated with the upgrading process.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    The above objects, features, and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings, in which:  
         [0012]    [0012]FIG. 1 is a block diagram illustrating a node structure of the WDM system of a related art;  
         [0013]    [0013]FIG. 2 is a block diagram illustrating a node structure of the WDM system of a related art;  
         [0014]    [0014]FIG. 3 is a block diagram illustrating a node structure of the WDM system of another related art;  
         [0015]    [0015]FIG. 4 is a block diagram illustrating the node structure of the WDM system according to a preferred embodiment of the present invention;  
         [0016]    [0016]FIG. 5 is a block diagram illustrating an interleaver according to the present invention;  
         [0017]    [0017]FIG. 6 is a block diagram illustrating the node structure of the WDM system when the upgrading is not performed according to the present invention; and,  
         [0018]    [0018]FIG. 7 is a block diagram illustrating the node structure of the WDM system when the upgrading is executed according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    In the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments which depart from these specific details. For the purpose of clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.  
         [0020]    [0020]FIG. 4 is a block diagram illustrating the node structure of the WDM system according to a preferred embodiment of the present invention. The major components of node  1  includes an interleaver  100 , a demultiplexer  110 , an upgradable demultiplexer  120 , a multiplexer  210 , an upgradable multiplexer  220 , and a deinterleaver  200 . The interleaver  100  interleaves and outputs each channel signal in a predetermined channel order starting with the lowest wavelength when optical signals with a plurality of channels are multiplexed thereto. The interleaver  100  has at least one output terminal  105  for future upgrading purposes. The upgradeable demultiplexer  120 , which will be added in the future when more capacity is required, will be coupled to the output terminal  105 . The interleaver  100  outputs the interleaved channel through both the presently active output terminals  103  and  105 , if necessary. In response to the optical signals transmitted from the interleaver  100  via the output terminal  103 , the demultiplexer  110  demultiplexes the received optical signals into different channels and then outputs them to the respective input terminal of the multiplexer  210 . Similarly, if more transmission capacity is needed, an additional demultiplexer  120  is provided to demultiplex and output the received optical signals via the output terminal  105 .  
         [0021]    Thereafter, the multiplexer  210  multiplexes the optical signals and outputs the multiplexed signals to the input terminal  203  of the deinterleaver  200 . The deinterleaver  200  deinterleaves the optical signals outputted from the multiplexer  210  and forwards them to the next node. The deinterleaver  200  includes at least one input terminal  205  in the event that more capacity is needed. If the output terminal  205  is connected to the upgradable multiplexer  220 , the deinterleaver  200  deinterleaves the optical signal channels received through the input terminal  205  and then outputs them to the next node via the output terminal  202 . Accordingly, one or more multiplexer  220  is also selectively connected to the input terminal  205  so as to extend the transmission capacity in the future.  
         [0022]    The function of the interleaver according to the present invention will be described with reference to FIG. 5. A 1×4 interleaver  300  having one input terminal  310  and four output terminals  320 ,  322 ,  324 , and  326  is deployed in the present invention. However, it should be noted that a different combination of interleavers with different numbers of output terminals can be used in the present invention. The interleaver  300  is an optical element and serves to place a plurality of optical signals with a constant wavelength interval from many signal sources on one transmission channel and then outputs them in a prescribed order into a plurality of different channels. For example, as shown in FIG. 5, if 32 channels with a constant wavelength interval are inputted through the input terminal  310  of the 1×4 interleaver  300 , channel signals having an order of λ 1 , λ 5 , λ 9 , and λ 13  are outputted through the first output terminal  320  due to the nature of the 1×4 interleaver  300 . Similarly, channel signals having an order of λ 2 , λ 6 , λ 10 , and λ 14  are outputted through the second output terminal  322 ; channel signals having an order of λ 3 , λ 7 , λ 11 , and λ 15  outputted through the third output terminal  324 ; and channel signals having an order of λ 4 , λ 8 , λ 12 , and λ 16  are outputted through the forth output terminal  326 , respectively. Similarly, the deinterleaver functions as the interleaver  300  in a reverse direction, thus the discussion will be omitted.  
         [0023]    The node structure of the WDM system according to the present invention is characterized so that a pair of interleaver  110  and deinterleaver  210  is provided on the sending and receiving ends, respectively. Then, additional pairs of the demultiplexer and multiplexer are subsequently added in the system.  
         [0024]    [0024]FIG. 6 is a simplified block diagram illustrating the node configuration of the WDM system prior to adding extra system capacity. As shown in FIG. 6, the WDM system node includes the demultiplexer  110  and the multiplexer  210  on the output terminal  102  of the interleaver  100  and the input terminal  202  of the deinterleaver  200 , respectively. Accordingly, when the optical signal from multiple sources are inputted through the input terminal  102  of the interleaver  100 , the inputted optical signals are forwarded to the demultiplexer  110  via the output terminal  103  of the interleaver  100 . The optical signals are demultiplexed through different channels by the demultiplexer  110 , then outputted through each output terminal of the demultiplexer  110 . Next, these outputted channels are inputted to the multiplexer  210  to the corresponding input terminal of the multiplexer  210 , and thereafter multiplexed by the multiplexer  210 . The multiplexed signals are forwarded to the deinterleaver  200  through the input terminal  203  and then deinterleaved into one optical fiber transmission by the deinterleaver  200 . Finally, the deinterleaved signals are transferred to the next node through the output terminal  202 .  
         [0025]    [0025]FIG. 7 is a simplified block diagram illustrating the node configuration after additional capacity is added according to the present invention. The optical signal with  4  different signal channels is inputted to the node in FIG. 6, whereas the optical signal with  12  different signal channels is inputted after increasing the channel capacity to accommodate eight more channels in FIG. 7. The WDM system node basically includes the demultiplexer  110  and the multiplexer  210  on the output terminal  103  of the interleaver  100  and the input terminal  203  of the deinterleaver  200 , respectively. Furthermore, the node includes additional pairs of demultiplexer  120   a  and  120   b  and multiplexer  220   a  and  220   b  coupled to the respective output terminals  105   a  and  105   b  of the interleaver  100  and the respective input terminals  205   a  and  205   b  of the deinterleaver  200 .  
         [0026]    Accordingly, as shown in FIG. 7, when the optically multiplexed  12  channels with a constant interval is inputted through the input terminal  102  of the interleaver  100 , the optical signal is interleaved in a predetermined order within the interleaver  100  and then inputted to the demultiplexer  110  and the demultiplexer  210 . Similarly, the inputted optical signal inputted to both the demultiplexer  120   a  and  120   b  are demultiplexed in different channels and outputted to the corresponding multiplexer  220   a  and  220   b  through the respective output terminal of the demultiplexer  120   a  and  120   b.  Thereafter, the demultiplexed optical signals are inputted to the multiplexer  220   a  and  220   b,  then multiplexed by the multiplexer  210 . The multiplexed signals are inputted to the deinterleaver  200  through the respective input terminals  205   a  and  205   b  of the deinterleaver  200 . Finally, the optical signal are deinterleaved into one optical transmission channel by the deinterleaver  200  and then transferred to the next node via the output terminal  202 .  
         [0027]    As described above, the node structure according to the present invention provides an effective way of accommodating additional system capacity, thus eliminating the costly maintenance and upgrading needed in the prior art system. In addition, the present invention upgrades the existing system without the power loss typically involved in the prior art method.  
         [0028]    While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made there in without departing from the spirit and the scope of the invention as defined by the appended claims.