Abstract:
A WDM PON includes: a CO for transmitting downstream optical signals; a RN for distributing the downstream optical signals received from the CO; and a SUB for receiving the distributed downstream optical signals. The CO includes: BiDis of a first group for outputting data-modulated downstream optical signals of the first group; BiDis of a second group for outputting data-modulated downstream optical signals of the second group band; a DBLS for outputting downstream light; and an interleaver for generating the downstream injection light of the first and the second groups by spectrum-slicing and deinterleaving the downstream light, providing the downstream injection light of the first group to the BiDis of the first group, and providing the downstream injection light of the second group to the BiDis of the second group.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority to an application entitled “WDM PON With Interleaver,” filed in the Korean Intellectual Property Office on Jun. 23, 2005 and assigned Ser. No. 2005-54510, 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 a Passive Optical Network (PON), and more particularly to a Wavelength Division Multiplexed (WDM) PON using a wavelength-locked optical transceiver.  
         [0004]     2. Description of the Related Art  
         [0005]     A PON corresponds to a communication network in which a Central Office (CO) is connected to a subscriber-side device through an optical fiber for exchange of optical signals. A PON can provide broadcasting information, ultra high speed information, and separate communication services required by each subscriber. A PON has a star structure, connects a CO to a Remote Node (RN), which is installed in an area adjacent to subscribers, through one Feeder Fiber (FF), and connects the RN to subscriber-side devices through a plurality of Distribution Fibers (DFs).  
         [0006]     In a PON, it is important to reduce necessary cost per subscriber in the process of constructing the PON. To achieve this, research into a wavelength-locked optical transceiver, which has a wavelength of injected light and directly outputs modulated optical signals, has been actively conducted. For example, a wavelength-locked optical transceiver may include a Fabry-Perot laser diode, a reflective semiconductor optical amplifier, etc. In order to use such a wavelength-locked optical transceiver, a broadband light source is necessary and important to properly dispose such a broadband light source.  
         [0007]      FIG. 1  is a block diagram illustrating a WDM PON using a conventional wavelength-locked optical transceiver. As shown, the PON  100  includes a CO  110 , a RN  180  connected to the CO  110  through an FF  170 , and a subscriber-side device (SUB)  210  connected to the RN  180  through first to N th  DFs  200 - 1  to  200 -N.  
         [0008]     The CO  110  includes first to N th  Bidirectional optical transceivers (BiDis)  120 - 1  to  120 -N of a first group, a first Wavelength Division Multiplexer (WDM)  130 , a Downstream Broadband Light Source (DBLS)  140 , an Upstream Broadband Light Source (UBLS)  150 , and an optical Coupler (CP)  160 . The RN  180  includes a second WDM  190 . The SUB  210  includes first to N th  BiDis  220 - 1  to  220 -N of a second group.  
         [0009]     Hereinafter, a downstream transmission process in the PON  100  will be described.  
         [0010]     Downstream light output from the DBLS  140  is input to a Multiplexing Port (MP) of the WDM  130  after passing through the CP  160 . The WDM  130  spectrum-slices the input downstream light so as to generate first to N th  downstream injection light, and sequentially inputs the first to the N th  downstream injection light to the first to the N th  BiDos  120 - 1  to  120 -N of the first group in a one-to-one fashion through first to N th  Demultiplexing Ports (DPs). The first to the N th  BiDis  120 - 1  to  120 -N of the first group output first to N th  data-modulated downstream optical signals generated by the first to the N th  input downstream injection light. The WDM  130  multiplexes and outputs the first to the N th  input downstream optical signals, and the multiplexed downstream optical signals are input to the second WDM  190  after passing through the CP  160  and the FF  170 .  
         [0011]     The second WDM  190  demultiplexes the multiplexed downstream optical signals input from the FF  170 , and outputs the demultiplexed downstream optical signals through the first to the N th  DPs. The first to the N th  downstream optical signals output from the second WDM  190  are sequentially input to the first to the N th  BiDis  220 - 1  to  220 -N of the second group in a one-to-one fashion through the first to the N th  DFs  200 - 1  to  200 -N. The first to the N th  BiDis  220 - 1  to  220 -N of the second group convert the first to the N th  input downstream optical signals into electrical signals.  
         [0012]     Hereinafter, an upstream transmission process in the PON  100  will be described.  
         [0013]     Upstream light output from the UBLS  150  is input to the second WDM  190  after passing through the CP  160  and the FF  170 . The second WDM  190  spectrum-slices the upstream light input to an MP so as to generate first to N th  upstream injection light, and sequentially outputs the first to the N th  upstream injection light in a one-to-one fashion through the first to the N th  DPs. The first to the N th  upstream injection light output from the second WDM  190  are sequentially input to the first to the N th  BiDis  220 - 1  to  220 -N of the second group in a one-to-one fashion after passing through the first to the N th  DFs  200 - 1  to  200 -N. The first to the N th  BiDis  220 - 1  to  220 -N of the second group output first to N th  data-modulated upstream optical signals generated by the first to the N th  input upstream injection light.  
         [0014]     The second WDM  190  multiplexes and outputs the first to the N th  input upstream optical signals, and the multiplexed upstream optical signals are input to the WDM  130  after passing through the FF  170  and the CP  160 . The WDM  130  demultiplexes the multiplexed upstream optical signals input to the MP, and sequentially outputs the demultiplexed upstream optical signals the first to the N th  BiDis  120 - 1  to  120 -N of the first group in a one-to-one fashion through the first to the N th  DPs. The first to the N th  BiDis  120 - 1  to  120 -N of the first group convert the first to the N th  input upstream optical signals into electrical signals.  
         [0015]     However, the conventional PON  100  as described above has poor expansibility. That is, in order to accommodate new subscribers, the PON  100  must replace the existing WDMs  130  and  190  with a new WDM having an increased number of DPs corresponding to the number of subscribers. Further, it is necessary to add a new BLS or to replace the existing BLSs  140  and  150  with a new BLS having a wider bandwidth.  
         [0016]     Therefore, it is necessary to provide a PON capable of accommodating many subscribers more economically and efficiently.  
       SUMMARY OF THE INVENTION  
       [0017]     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art and provides additional advantages, by providing a WDM PON capable of accommodating many subscribers more economically and efficiently as compared with the prior art.  
         [0018]     In accordance with one aspect of the present invention, there is provided a Wavelength Division Multiplexed (WDM) Passive Optical Network (PON), which includes: a Central Office (CO) for transmitting downstream optical signals; a Remote Node (RN) for distributing the downstream optical signals received from the CO; and a subscriber-side device (SUB) for receiving the distributed downstream optical signals, wherein the CO includes: Bidirectional optical transceivers (BiDis) of a first group for outputting data-modulated downstream optical signals of the first group generated by downstream injection light of the first group, which belongs to a first wavelength group of a downstream band; BiDis of a second group for outputting data-modulated downstream optical signals of the second group generated by downstream injection light of the second group, which belong to a second wavelength group alternatively disposed with the first wavelength group more than twice within the downstream band; a Downstream Broadband Light Source (DBLS) for outputting downstream light; and an interleaver for generating the downstream injection light of the first and the second groups by spectrum-slicing and deinterleaving the downstream light, providing the downstream injection light of the first group to the BiDis of the first group, and providing the downstream injection light of the second group to the BiDis of the second group. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     The above features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:  
         [0020]      FIG. 1  is a block diagram illustrating a WDM PON using a conventional wavelength-locked optical transceiver;  
         [0021]      FIG. 2  is a block diagram illustrating a WDM PON according to an embodiment of the present invention;  
         [0022]      FIG. 3  is a diagram illustrating downstream and upstream transmission bands used in the PON shown in  FIG. 2 ; and  
         [0023]      FIG. 4  is a diagram illustrating input and output characteristics of the interleaver shown in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0024]     An embodiment of the present invention will be described in detail herein below with reference to the accompanying drawings. For the purposes of clarity and simplicity, a detailed description of known functions and configurations incorporated herein will be omitted as it may obscure the subject matter of the present invention.  
         [0025]      FIG. 2  is a block diagram illustrating a WDM PON according to an embodiment of the present invention, and  FIG. 3  is a diagram illustrating downstream and upstream transmission bands used in the PON.  
         [0026]     As shown, the PON  300  includes a Central Office (CO)  310 , a Remote Node (RN)  410  connected to the CO  310  through an Feeder Fiber (FF)  400 , and a subscriber-side device (SUB)  470  connected to the RN  410  through first to N th  Distribution Fibers (DFs)  450 - 1  to  450 -N.  
         [0027]     In operation, the CO  310  transmits downstream optical signals of a downstream wavelength band (downstream band)  510  to the RN  410  through the FF  400 , and receives upstream optical signals of a upstream wavelength band  520  (upstream band) through the FF  400 . The CO  310  includes first to N th  Bidirectional Optical Transceivers (BiDis)  320 - 1  to  320 -N of a first group, first to N th  BiDis  340 - 1  to  340 -N of a second group, first and second Wavelength Division Multiplexers (WDMs)  330  and  350 , an interleaver (IL)  360 , a Downstream Broadband Light Source (DBLS)  370 , an Upstream Broadband Light Source (UBLS)  380 , and an optical Coupler (CP)  390 .  
         [0028]     The first to the N th  BiDis  320 - 1  to  320 -N of the first group are connected to the first WDM  330 , receive first to N th  downstream injection light of a first group which belong to a first wavelength group of the downstream band  510 , and output first to N th  data-modulated downstream optical signals of the first group generated by the first to the N th  downstream injection light of the first group. The first wavelength group of the downstream band  510  is comprised of downstream wavelengths λ D2 , λ D4 , . . . , λ D(2N)  in even sequences of the downstream band  510 .  
         [0029]     The first to the N th  BiDis  320 - 1  to  320 -N of the first group receive first to N th  upstream optical signals of a first group which belong to a first wavelength group of the upstream band  520 , and convert the first to the N th  upstream optical signals of the first group into electrical signals. The first wavelength group is comprised of upstream wavelengths λ U2 , λ U4 , . . . , λ U(2N)  in even sequences of the upstream band. The N th  BiDi  320 -N receives N th  downstream injection light of a  2 N th  downstream wavelength λ U(2N) , outputs a N th  data-modulated downstream optical signal of the 2N th  downstream wavelength, which is generated by the N th  downstream injection light, and converts the N th  input upstream optical signal of the 2N th  upstream wavelength λ U(2N)  into an electrical signal.  
         [0030]     Each of the BiDis  320 - 1  to  320 -N may include a wavelength-locked optical transceiver such as a Fabry-Perot laser diode and a reflective semiconductor optical amplifier. A Fabry-Perot laser diode has a plurality of oscillation modes, and amplifies and outputs a mode coinciding with the wavelength of input downstream injection light. A reflective semiconductor optical amplifier has a gain curve of a broadband, and amplifies and outputs input downstream injection light.  
         [0031]     The first WDM  330  is disposed so that the first to the N th  BiDis  320 - 1  to  320 -N of the first group are connected to the interleaver  360 . The first WDM  330  has a Multiplexing Port (MP) and first to N th  Demultiplexing Port (DPs). The MP is connected to the interleaver  360 , and the first to the N th  DPs are sequentially connected to the first to the N th  BiDis  320 - 1  to  320 -N of the first group in a one-to-one fashion. The first WDM  330  sequentially outputs the first to the N th  downstream injection light of the first group, which are input to the MP, through the first to the N th  DPs in a one-to-one fashion, multiplexes the first to the N th  downstream optical signals of the first group input to the first to the N th  DPs, outputs the first to the N th  multiplexed downstream optical signals through the MP, demultiplexes the first to the N th  upstream optical signals of the first group input to the MP, and sequentially outputs the first to the N th  demultiplexed upstream optical signals through the first to the N th  DPs in a one-to-one fashion. Herein, the first WDM  330  outputs the N th  downstream injection light and the N th  demultiplexed upstream optical signal through the N th  DP. The first WDM  330  may use a 1×N Arrayed Waveguide Grating (AWG).  
         [0032]     The first to the N th  BiDis  340 - 1  to  340 -N of the second group are connected to the second WDM  350 , receive first to N th  downstream injection light of a second group which belong to a second wavelength group alternatively disposed with the first wavelength group within the downstream band  510 , and output first to N th  data-modulated downstream optical signals of the second group generated by the first to the N th  downstream injection light of the second group.  
         [0033]     The second wavelength group of the downstream band  510  is comprised of downstream wavelengths λ D1 , λ D3 , . . . , λ D(2N−1)  in odd sequences of the downstream band  510 . The first to the N th  BiDis  340 - 1  to  340 -N of the second group receive first to N th  upstream optical signals of a second group which belong to a second wavelength group alternatively disposed with the first wavelength group within the upstream band  520 , and convert the first to the N th  upstream optical signals of the second group into electrical signals.  
         [0034]     The second wavelength group of the upstream band  520  is comprised of upstream wavelengths λ U1 , λ U3 , . . . , λ U(2N−1)  in odd sequences of the upstream band  520 . The N th  BiDi  340 -N receives N th  downstream injection light of a (2N−1) th  downstream wavelength λ U(2N−1) , outputs a N th  data-modulated downstream optical signal of the (2N−1) th  downstream wavelength, which is generated by the N th  downstream injection light, and converts the (2N−1) th  upstream optical signal of the (2N−1) th  upstream wavelength λ U(2N−1)  into an electrical signal. Each of the BiDis  340 - 1  to  340 -N may include a wavelength-locked optical transceiver such as a Fabry-Perot laser diode and a reflective semiconductor optical amplifier.  
         [0035]     The second WDM  350  is disposed so that the first to the N th  BiDis  340 - 1  to  340 -N of the second group are connected to the interleaver  360 . The second WDM  350  has a MP and first to N th  DPs. The MP is connected to the interleaver  360 , and the first to the N th  DPs are sequentially connected to the first to the N th  BiDis  340 - 1  to  340 -N of the second group in a one-to-one fashion. The second WDM  350  sequentially outputs the first to the N th  downstream injection light of the second group, which are input to the MP, through the first to the N th  DPs in a one-to-one fashion, multiplexes the first to the N th  downstream optical signals of the second group input to the first to the N th  DPs, outputs the first to the N th  multiplexed downstream optical signals through the MP, demultiplexes the first to the N th  upstream optical signals of the second group input to the MP, and sequentially outputs the first to the N th  demultiplexed upstream optical signals through the first to the N th  DPs in a one-to-one fashion. Herein, the second WDM  350  outputs the N th  downstream injection light and the N th  demultiplexed upstream optical signal through the N th  DP. The second WDM  350  may use a 1×N AWG.  
         [0036]     The interleaver  360  is disposed so that the first and the second WDMs  330  and  350  are connected to the CP  390 . The interleaver  360  has first to third ports. The first port is connected to the MP of the first WDM  330 , the second port is connected to the CP  390 , and the third port is connected to the MP of the second WDM  350 . The interleaver  360  spectrum-slices and deinterleaves downstream light input to the second port, and then outputs the first to the N th  downstream injection light of the first group through the first port and outputs the first to the N th  downstream injection light of the second group through the third port. The interleaver  360  interleaves both the downstream optical signals of the first group input through the first port and the downstream optical signals of the second group input through the third port, and outputs the interleaved downstream optical signals of the first and the second groups through the second port. Further, the interleaver  360  deinterleaves the upstream optical signals of the first and the second groups input to the second port, and then outputs the upstream optical signals of the first group through the first port and outputs the upstream optical signals of the second group through the third port.  
         [0037]      FIG. 4  is a diagram illustrating input and output characteristics of the interleaver  360 . The interleaver  360  has the first to the third ports as described above. The first port functions as input and output paths of the even wavelengths  620 , the second port functions as input and output paths of the even and odd wavelengths  620  and  610 , and the third port functions as input and output paths of the odd wavelengths  610 . The interleaver  360  deinterleaves optical signals input to the second port, and interleaves optical signals input to the first and the third ports.  
         [0038]     The DBLS  370  is connected to the CP  390 . The DBLS  370  outputs downstream light. The DBLS  370  may use an Erbium Doped Fiber Amplifier (EDFA), etc.  
         [0039]     The UBLS  380  is connected to the CP  390 . The UBLS  380  outputs upstream light. The UBLS  380  may use an EDFA, etc.  
         [0040]     The CP  390  is disposed so that the DBLS  370  is connected to the second port of the interleaver  360 , and the UBLS  380  is connected to the FF  400 . The CP  390  has first to fourth ports. The first port is connected to the second port of the interleaver  360 , the second port is connected to the UBLS  380 , the third port is connected to the FF  400 , and the fourth port is connected to the DBLS  370 . The CP  390  outputs the upstream light, which is input to the second port, through the tnird port, outputs the downstream light, which is input to the fourth port, to the first port, outputs the downstream optical signals of the first and the second groups, which are input to the first port, through the third port, and outputs the upstream optical signals of the first and the second groups, which are input to the third port, through the first port.  
         [0041]     The RN  410  deinterleaves and demultiplexes the downstream optical signals of the first and the second groups input through the FF  400 , and transmits the demultiplexed downstream optical signals to the SUB  470  through the DFs  450 - 1  to  450 -N and  460 - 1  to  460 -N of the first and the second groups. The RN  410  spectrum-slices and deinterleaves the upstream light input through the FF  400  so as to generate the upstream injection light of the first and the second groups, and transmits the upstream injection light to the SUB  470  through the DFs  450 - 1  to  450 -N and  460 - 1  to  460 -N of the first and the second groups. The RN  410  multiplexes and interleaves the upstream optical signals of the first and the second groups input through the DFs  450 - 1  to  450 -N and  460 - 1  to  460 -N of the first and the second groups, and transmits the interleaved upstream optical signals to the CO  310  through the FF  400 . Further, the RN  410  includes an interleaver  420  and first and second WDMs  430  and  440 .  
         [0042]     The interleaver  420  is disposed so that the FF  400  is connected to the first and the second WDMs  430  and  440 . The interleaver  420  has first to third ports. The first port is connected to the first WDM  430 , the second port is connected to the FF  400 , and the third port is connected to the second WDM  440 . The interleaver  420  spectrum-slices and deinterleaves the upstream light input to the second port, and then outputs the first to the N th  upstream injection light of the first group through the first port and outputs the first to the N th  upstream injection light of the second group through the third port. The interleaver  420  interleaves both the downstream optical signals of the first group input through the first port and the downstream optical signals of the second group input through the third port, and outputs the interleaved downstream optical signals of the first and the second groups through the second port. Further, the interleaver  420  deinterleaves the upstream optical signals of the first and the second groups input to the second port, and then outputs the upstream optical signals of the first group through the first port and outputs the upstream optical signals of the second group through the third port.  
         [0043]     The first WDM  430  is disposed so that the first port of the interleaver  420  is connected to the DFs  450 - 1  to  450 -N of the first group. The first WDM  430  has a MP and first to N th  DPs. The MP is connected to the first port of the interleaver  420 , and the first to the N th  DPs are sequentially connected to the DFs  450 - 1  to  450 -N of the first group in a one-to-one fashion. The first WDM  430  demultiplexes the first to the N th  upstream injection light of the first group, which are input to the MP, and sequentially outputs the first to the N th  demultiplexed upstream injection light through the first to the N th  DPs in a one-to-one fashion. The first WDM  430  multiplexes the first to the N th  upstream optical signals of the first group input to the first to the N th  DPs, and outputs the first to the N th  multiplexed upstream optical signals through the MP. The first WDM  430  demultiplexes the first to the N th  downstream optical signals of the first group input to the MP, and sequentially outputs the first to the N th  demultiplexed downstream optical signals through the first to the N th  DPs in a one-to-one fashion. Herein, the first WDM  430  outputs the N th  upstream injection light and the N th  downstream optical signal through the N th  DP. The first WDM  430  may use a 1×N AWG.  
         [0044]     The second WDM  440  is disposed so that the third port of the interleaver  420  is connected to the DFs  460 - 1  to  460 -N of the second group. The second WDM  440  has a MP and first to N th  DPs. The MP is connected to the third port of the interleaver  420 , and the first to the N th  DPs are sequentially connected to the DFs  460 - 1  to  460 -N of the second group in a one-to-one fashion. The second WDM  440  demultiplexes the first to the N th  upstream injection light of the second group, which are input to the MP, and sequentially outputs the first to the N th  demultiplexed upstream injection light through the first to the N th  DPs in a one-to-one fashion. The second WDM  440  multiplexes the first to the N th  upstream optical signals of the second group input to the first to the N th  DPs, and outputs the first to the N th  multiplexed upstream optical signals through the MP. The second WDM  440  demultiplexes the first to the N th  downstream optical signals of the second group input to the MP, and sequentially outputs the first to the N th  demultiplexed downstream optical signals through the first to the N th  DPs in a one-to-one fashion. Herein, the second WDM  440  outputs the N th  upstream injection light and the N th  downstream optical signal through the N th  DP. The second WDM  440  may use a 1×N AWG.  
         [0045]     The SUB  470  transmits the upstream optical signals of the first and the second groups to the RN  410  through the DFs  450 - 1  to  450 -N and  460 - 1  to  460 -N of the first and the second groups, receives the upstream injection light of the first and the second groups through the DFs  450 - 1  to  450 -N and  460 - 1  to  460 -N of the first and the second groups, and receives the downstream optical signals of the first and the second groups through the DFs  450 - 1  to  450 -N and  460 - 1  to  460 -N of the first and the second groups. The SUB  470  includes first to N th  BiDis  480 - 1  to  480 -N of a first group and first to N th  BiDis  490 - 1  to  490 -N of a second group.  
         [0046]     The first to the N th  BiDis  480 - 1  to  480 -N of the first group are sequentially connected to the first to the N th  DFs  450 - 1  to  450 -N of the first group in a one-to-one fashion. The first to the N th  BiDis  480 - 1  to  480 -N of the first group receive the first to the N th  upstream injection light of the first group, output first to N th  data-modulated upstream optical signals of the first group generated by the first to the N th  upstream injection light of the first group, and convert the first to the N th  input downstream optical signals of the first group into electrical signals. The N th  BiDi  480 -N receives N th  upstream injection light of a 2N th  upstream wavelength, outputs a N th  data-modulated upstream optical signal of the 2N th  upstream wavelength, which is generated by the N th  upstream injection light, and converts the N th  input downstream optical signal of the 2N th  downstream wavelength λ U(2N)  into an electrical signal. Each of the BiDis  480 - 1  to  480 -N may include a wavelength-locked optical transceiver such as a Fabry-Perot laser diode and a reflective semiconductor optical amplifier.  
         [0047]     The first to the N th  BiDis  490 - 1  to  490 -N of the second group are sequentially connected to the first to the N th  DFs  460 - 1  to  460 -N of the second group in a one-to-one fashion. The first to the N th  BiDis  490 - 1  to  490 -N of the second group receive the first to the N th  upstream injection light of the second group, output first to N th  data-modulated upstream optical signals of the second group generated by the first to the N th  upstream injection light of the second group, and convert the first to the N th  input downstream optical signals of the second group into electrical signals. The N th  Bidi  490 -N receives N th  upstream injection light of a (2N−1) th  upstream wavelength, outputs a N th  data-modulated upstream optical signal of the (2N−1) th  upstream wavelength, which is generated by the N th  upstream injection light, and converts the N th  input downstream optical signal of the (2N−1) th  downstream wavelength into an electrical signal. Each of the BiDis  490 - 1  to  490 -N may include a wavelength-locked optical transceiver such as a Fabry-Perot laser diode and a reflective semiconductor optical amplifier.  
         [0048]     According to a WDM PON of the present invention as described above, BiDis of first and second groups share one BLS by means of an interleaver, so that it is possible to accommodate many subscribers more economically and efficiently as compared with the prior art.  
         [0049]     That is, according to the prior art, in order to increase the number of subscribers from N to 2N, a BLS must have a wavelength band increased by twice. Therefore, an additional BLS is necessary. However, according to the present invention, since an interleaving scheme is used, a BLS can maintain an initial wavelength band with no change even when the number of subscribers increases from N to 2N. Consequently, N additional BiDis and N existing BiDis can share an existing BLS.  
         [0050]     Although a preferred embodiment of the present invention has been described 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, including the full scope of equivalents thereof.