Abstract:
A wavelength division multiplexed passive optical network (WDM PON) is disclosed. In one aspect, WDM-PON comprises a central office comprising a plurality of semiconductor optical amplifiers each adapted to output an optical signal modulated in accordance with data inputted thereto, and a wavelength division multiplexer adapted to multiplex the optical signals outputted from the semiconductor optical amplifiers, and a remote node connected to the central office via a main optical fiber, adapted to distribute the optical signals received, on to corresponding distribution optical fibers connected thereto, and a plurality of optical network units connected to the remote node via corresponding distribution optical fibers, the optical network units receiving from the remote node the optical signals associated therewith. In another aspect of the invention, the central office further comprises an amplifier for amplifying the multiplexed signal.

Description:
CLAIM of PRIORITY  
       [0001]     This application claims priority, pursuant to  35  USC § 119, to that patent application entitled “WAVELENGTH DIVISION MULTIPLEXED PASSIVE OPTICAL NETWORK” filed in the Korean Intellectual Property Office on Jan. 20, 2004 and assigned Serial No. 2004-4183, 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 network, and more particularly to a wavelength division multiplexed passive optical network.  
         [0004]     2. Description of the Related Art  
         [0005]     A wavelength division multiplexed (WDM) passive optical network (PON) can provide ultrahigh-speed broadband communication services by assigning specific wavelengths to respective subscribers. Accordingly, such a WDM PON ensures communication security, while being capable of easily accommodating a separate communication service required by a subscriber. The service is also easily expandable to accommodate user communication needs. Also, the WDM PON allows addition of a particular wavelength to be assigned to a new subscriber, so that it is possible to easily achieve an increase in the number of subscribers. In spite of such advantages, however, the WDM PON additionally requires, for a central office (CO) thereof and each optical network unit (ONU) thereof, light sources with a known oscillation wavelength, and wavelength stabilizing circuits adapted to stabilize the wavelength of the light sources. As a result, a heavy burden is imposed on the network and the subscriber&#39;s equipment.  
         [0006]     WDM PONs have been proposed that use as a WDM light source either a distributed feedback (DFB) laser, a DFB laser array, a multi-frequency laser (MFL), a picosecond pulse light source, or the like. Recently, research has been conducted to use as an economical WDM light source either a spectrum-sliced light source requiring no wavelength selectivity and wavelength stability, a mode-locked Fabry-Perot laser with incoherent light, or a wavelength-seeded reflective semiconductor optical amplifier.  
         [0007]      FIG. 1  is a schematic diagram illustrating a conventional WDM PON  100  and conventional means of obtaining stable wavelengths. The PON  100  includes a central office (CO)  110 , a remote node (RN)  170  connected to the central office  110  via a main optical fiber (MF)  160 , and a plurality of optical network units (ONUs), ONU 1  to ONU n    200 - 1  to  200 - n , connected to the remote node  170  via n distribution optical fibers (DFs), DF 1  to DF n ,  190 - 1  to  190 - n , respectively. Hereinafter, the plurality of optical network units and the number of distribution optical fibers are referred to with regard to the conventional notation of arbitrary numbering “n”. However, while the number “n” is shown with regard to both the number of ONU and the number of DF and ports, one skilled in the art would recognize that the number of ONU and number of DF need not be the same. For example, the number of DF may be significantly greater than the number of ONU to allow for the incorporation of additional ONU at a future time.  
         [0008]     The central office  110  includes “n” Fabry-Perot laser diodes (FP-LDs), FP-LD 1  to FP-LD n ,  120 - 1  to  120 - n , a first wavelength division multiplexer, WDM 1 ,  130 , a broadband light source (BLS)  140 , and a circulator (CIR)  150 .  
         [0009]     The “n” FP-LDs  120 - 1  to  120 - n  output “n” optical signals as they are wavelength-locked by “n” different wavelengths, respectively. For example, the FP-LD n    120 - n  outputs an n-th optical signal as it is wavelength-locked by the n-th wavelength.  
         [0010]     In this illustrated example, WDM 1   130  includes a multiplexing port MP, and “n” de-multiplexing ports DP 1  to DP n . The multiplexing port MP of the WDM 1   130  is connected to the circulator  150 , whereas the “n” de-multiplexing ports DP 1  to DP n  of the WDM 1   130  are connected to corresponding FP-LD n    120 - 1  to FP-LD n    120 - n . The WDM 1   130  de-multiplexes a broadband optical signal inputted to the multiplexing port MP, and outputs de-multiplexed optical signals at the “n” de-multiplexing ports DP 1  to DP n . The WDM 1   130  also multiplexes “n” optical signals inputted on corresponding de-multiplexing ports DP 1  to DP n  and outputs the multiplexed optical signals at the multiplexing port MP.  
         [0011]     Broadband light source  140  is connected to the circulator  150 , and is adapted to output broadband incoherent light.  
         [0012]     Circulator  150  includes three ports wherein the first port is connected to the broadband light source  140 , the second port is connected to the multiplexing port MP of the WDM 1   130 , and the third port is connected to the main optical fiber  160 . The circulator  150  outputs a broadband light, inputted to the first port to the second port, while outputting “n” optical signals, inputted to the second port to the third port.  
         [0013]     The remote node  170  includes a second wavelength division multiplexer, WDM 2 ,  180 . The WDM 2   180  includes a multiplexing port MP, and “n” de-multiplexing ports DP 1  to DP n . The multiplexing port of the WDM 2   180  is connected to the main optical fiber (MF)  160 , whereas the “n” de-multiplexing ports DP 1  to DP n  of the WDM 2   180  are connected to the “n” distribution optical fibers (DFs), DF 1  to DF n ,  190 - 1  to  190 - n , respectively. For example, the n-th de-multiplexing port DP n  of the WDM 2   180  is connected to the n-th distribution optical fiber, DF n ,  190 - n . The WDM 2   180  de-multiplexes “n” optical signals inputted to the multiplexing port MP, and outputs the demultiplexed “n” optical signals to corresponding demultiplexing ports DP 1  to DP n .  
         [0014]     The “n” ONUs, ONU 1    200 - 1  to ONU n    200 - n , are connected to corresponding distribution optical fibers  190 - 1  to  190 - n . For example, the ONU n    200 - n  is connected to the n-th distribution optical fiber  190 - n . Each ONU detects an optical signal received from the associated distribution optical fiber in the form of an electrical signal. For example, the ONU n    200 - n  detects an optical signal received from the n-th distribution optical fiber  190 - n , in the form of an electrical signal.  
         [0015]     As m entioned above, the conventional PON  100  additionally uses the broadband light source  140  used to wavelength-locked or wavelength-injected light source. The use of the broadband light source increases the cost of the conventional PON  100 , and makes conventional PONs uneconomical. For this reason, the WDM PON has not been practically used. Therefore, it is necessary to develop an WDM light source in order to develop an economical WDM PON. Furthermore, where a bi-directional single transmitter/receiver module is used to secure a competitive cost, it is also necessary to take into consideration bands of input and output wavelengths.  
       SUMMARY OF THE INVENTION  
       [0016]     Therefore, the present invention has been made in view of the above mentioned problem involved with the related art, and an object of the invention is to provide a WDM PON which can be implemented without using a broadband light source.  
         [0017]     In accordance with the present invention, this object is accomplished by providing a wavelength division multiplexed passive optical network (WDM PON) comprising a central office including a plurality of semiconductor optical amplifiers each adapted to output an optical signal modulated in accordance with data inputted thereto in association therewith, and a wavelength division multiplexer adapted to multiplex the optical signals respectively outputted from the semiconductor optical amplifiers, a remote node connected to the central office via a main optical fiber adapted to distribute the optical signals received to distribution optical fibers connected thereto, and a plurality of optical network units connected to the remote node via corresponding distribution optical fibers, the optical network units receiving, from the remote node, the optical signals associated therewith. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]     The above objects and advantages of the present invention will become more apparent by describing, in detail, embodiments with reference to the attached drawings in which:  
         [0019]      FIG. 1  is a schematic diagram illustrating a conventional WDM PON;  
         [0020]      FIG. 2  is a schematic diagram illustrating a configuration of a WDM PON according to a first embodiment of the present invention;  
         [0021]      FIG. 3  is a schematic diagram illustrating a configuration of a WDM PON according to a second embodiment of the present invention; and  
         [0022]      FIG. 4  is a schematic diagram illustrating a configuration of a WDM PON according to a third embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]     Embodiments of the present invention will now be described in detail with reference to the annexed drawings. For the purpose of clarity, a detailed description of known functions and configurations incorporated herein will be omitted when it may obscure the subject matter of the present invention.  
         [0024]      FIG. 2  illustrates a configuration of a WDM PON according to a first embodiment of the present invention. In this illustrative embodiment, the PON,  300 , includes a central office (CO)  310 , a remote node (RN)  350  connected to the central office  310  via a main optical fiber (MF)  340 , and a plurality of optical network units (ONUs), ONU 1  to ONU n ,  380 - 1  to  380 - n , connected to the remote node  350  via a plurality of distribution optical fibers (DFs), DF 1  to DF n ,  370 - 1  to  370 - n , respectively.  
         [0025]     The central office  110  includes n semiconductor optical amplifiers (SOAs), SOA, to SOAN,  320 - 1  to  320 - n , and a first wavelength division multiplexer, WDM 1 ,  330 .  
         [0026]     The SOA 1    320 - 1  to SOA n    320 - n  output “n” optical signals, respectively. For example, the SOA n    320 - n  outputs an n-th optical signal modulated by associated data inputted thereto. Each of the SOA 1    320 - 1  to SOA n    320 - n  may comprise a transmissive SOA requiring no wavelength selectivity and wavelength stability, a gain-clamped SOA (GC-SOA), or a reflective SOA (RSOA).  
         [0027]     The WDM 1   330  includes a multiplexing port MP, and “n” de-multiplexing ports DP 1  to DP n . The multiplexing port MP of the WDM 1   330  is connected to the main optical fiber  340 , whereas the “n” de-multiplexing ports DP 1  to DP n  of the WDM 1   330  are connected to the SOA 1    320 - 1  to SOA n    320 - n , respectively. The WDM 1   330  multiplexes “n” optical signals inputted to the “n” de-multiplexing ports DP 1  to DP n  and, outputs the multiplexed optical signal at the multiplexing port MP. In one aspect, the WDM 1   330  may comprise an arrayed waveguide grating (AWG).  
         [0028]     The remote node  350  includes a second wavelength division multiplexer, WDM 2 ,  360 . The WDM 2   360  has a multiplexing port MP, and “n” de-multiplexing ports DP 1  to DP n . The multiplexing port of the WDM 2   360  is connected to the main optical fiber (MF)  340 , wherein the “n” de-multiplexing ports DP 1  to DP n  of the WDM 2   360  are connected to corresponding distribution optical fibers (DFs), DF 1  to DF n ,  370 - 1  to  370 - n . For example, the n-th de-multiplexing port DP n  of the WDM 2   360  is connected to the n-th distribution optical fiber, DF n ,  370 - n . The WDM 2   360  de-multiplexes “n” optical signals inputted to the multiplexing port MP, and outputs the demultiplexed optical signals to the corresponding de-multiplexing ports DP 1  to DP n . In one aspect, the WDM 2   360  may comprise an AWG.  
         [0029]     The “n” ONUs, ONU 1  to ONU n ,  380 - 1  to  380 - n , are connected to corresponding distribution optical fibers, DF 1  to DF n ,  370 - 1  to  370 - n . For example, the ONUN  380 - n  is connected to the n-th distribution optical fiber, DF n ,  370 - n . Each ONU detects an optical signal received from the associated distribution optical fiber, in the form of an electrical signal. For example, the ONU n    380 - n  detects an optical signal received from the n-th distribution optical fiber, DF n ,  190 - n , in the form of an electrical signal.  
         [0030]      FIG. 3  illustrates a configuration of a WDM PON  400  according to a second embodiment of the present invention. The PON  400 , has the same configuration as that shown in  FIG. 2 , with the addition of an optical amplifier  440  to the transmitter configuration shown in  FIG. 2 . Accordingly, the following description will be given of a configuration associated with the added optical amplifier.  
         [0031]     In this illustrative embodiment, the optical amplifier (AMP)  440  in  FIG. 3  is connected between a multiplexing port MP of a WDM 1   430  and a main optical fiber (MF)  450 . The optical amplifier  440  may comprise a transmissive SOA, a GC-SOA, or an RSOA.  
         [0032]     Operation of the PON  400  will now be described. As discussed with regard to  FIG. 2 , “n” optical signals respectively outputted from the SOA 1    420 - 1  to SOA n    420 - n  are inputted to the WDM 1   430 . The WDM 1   430  receives the “n” optical signals at respective de-multiplexing ports DP 1  to DP n  and multiplexes the received “n” optical signals. The multiplex signal available at the multiplexing port MP is inputted to optical amplifier  440 . The optical amplifier  440  receives the multiplexed “n” optical signals from the WDM 1   430 , and amplifies each of the “n” optical signals. The amplified “n” optical signals are then inputted fiber  450  and provided to a WDM 2   470 , which is included in a remote node (RN)  460 .  
         [0033]     The WDM 2   470  receives the multiplexed “n” optical signals at a multiplexing port MP and, de-multiplexes the received multiplexed optical signal into individual “n” optical signals. The de-multiplexed “n” optical signals are outputted to respective de-multiplexing ports DP 1  to DP n . The de-multiplexed “n” optical signals are provided to corresponding ONUs, ONU 1  to ONU n ,  490 - 1  to  490 - n , via an associated distribution optical fibers, DF 1  to DF n ,  480 - 1  to  480 - n . Each of the ONU 1    490 - 1  to ONU n    490 - n  detect the optical signal inputted thereto, in the form of electrical signals.  
         [0034]      FIG. 4  illustrates a configuration of a WDM PON  500  according to a third embodiment of the present invention. The PON,  500  includes a central office (CO)  510 , a remote node (RN)  590  connected to the central office  510  via a main optical fiber (MF)  580 , and “n” optical network units (ONUs), ONU 1  to ONU n ,  620 - 1  to  620 - n , connected to the remote node  590  via corresponding distribution optical fibers (DFs), DF 1  to DF n ,  610 - 1  to  610 - n.    
         [0035]     The central office  110  includes “n” transceivers, TRX 1  to TRX n ,  520 - 1  to  520 - n , a first wavelength division multiplexer, WDM 1 ,  530 , first and second circulators, CIR 1  and CIR 2 ,  540  and  560 , and first and second optical amplifiers, AMP 1  and AMP 2 ,  550  and  570 .  
         [0036]     The TRX 1    520 - 1  to TRX n    520 - n  transmit “n” downstream optical signals while receiving “n” upstream optical signals, respectively. For example, the TRX n    520 - n  outputs an n-th downstream optical signal, and receives an n-th upstream optical signal. In order to generate a downstream optical signal modulated by associated data inputted thereto, each of the TRX 1    520 - 1  to TRX n    520 - n  may comprise a transmissive SOA requiring no wavelength selectivity and wavelength stability, a GC-SOA, or an RSOA.  
         [0037]     The WDM 1   530  has a multiplexing port MP, and “n” de-multiplexing ports DP 1  to DP n . The multiplexing port MP of the WDM 1   530  is connected to the first circulator  540 , whereas the “n” de-multiplexing ports DP 1  to DP n  of the WDM 1   530  are connected to the TRX 1    520 - 1  to TRX n    520 - n , respectively. The WDM 1   530  multiplexes downstream optical signals inputted to the “n” de-multiplexing ports DP 1  to DP n  and outputs a multiplexed downstream optical signals composed of the “n” inputted signals at the multiplexing port MP. The WDM 1   530  also de-multiplexes an upstream optical signal, composed of “n” optical signal, inputted to the multiplexing port MP, and outputs de-multiplexed upstream optical signals to the corresponding de-multiplexing ports DP 1  to DP n , respectively. The WDM 1   530  may comprise an AWG.  
         [0038]     The first circulator  540  has three ports, wherein the first port is connected to the multiplexing port MP of the WDM 1   530 , the second port is connected to the first optical amplifier  550 , and the third port is connected to the second optical amplifier  570 . The first circulator  540  outputs, to the second port, the multiplexed downstream optical signal inputted to the first port, and outputs, to the first port, a multiplexed upstream optical signal inputted to the third port.  
         [0039]     The second circulator  560  includes three ports, wherein the first port is connected to the main optical fiber  580 , the second port is connected to the second optical amplifier  570 , and the third port connected to the first optical amplifier  550 . The second circulator  550  outputs, to the second port, the multiplexed upstream optical signal inputted to the first port, while outputting, to the first port, the multiplexed downstream optical signal inputted to the third port.  
         [0040]     The first optical amplifier  550  connects the second port of the first circulator  540  to the third port of the second circulator  560 . The first optical amplifier  550  amplifies the multiplexed downstream optical signal received from the first circulator  540 , and outputs the amplified downstream optical signal to the second circulator  560 . Each of the first and second optical amplifiers  550  and  570  may comprise a transmissive SOA, a GC-SOA, or an RSOA.  
         [0041]     The second optical amplifier  570  connects the second port of the second circulator  560  to the third port of the first circulator  540 . The second optical amplifier  570  amplifies the multiplexed upstream optical signal received from the second circulator  560 , and outputs the amplified multiplexed upstream optical signal to the first circulator  540 .  
         [0042]     The remote node  590  includes a second wavelength division multiplexer, WDM 2 ,  600 . The WDM 2   600  has a multiplexing port MP, and n de-multiplexing ports DP 1  to DP n . The multiplexing port of the WDM 2   600  is connected to the main optical fiber (MF)  580 , whereas the n d-multiplexing ports DP 1  to DP n  of the WDM 2   600  are connected to the n distribution optical fibers (DFs), DF 1  to DF n ,  610 - 1  to  610 - n . For example, the n-th de-multiplexing port DP n  of the WDM 2   600  is connected to the n-th distribution optical fiber, DF n ,  610 - n . The WDM 2   600  de-multiplexes the provided multiplexed signal into “n” downstream optical signals, and outputs the de-multiplexed “n” optical signals to corresponding de-multiplexing ports DP 1  to DP n . The WDM 2   600  also multiplexes “n” upstream optical signals inputted to the “n” de-multiplexing ports DP, to DPn, and outputs the multiplexed upstream optical signal to the multiplexing port MP thereof. The WDM 2   600  may comprise an AWG.  
         [0043]     ONUs, ONU 1  to ONU n ,  620 - 1  to  620 - n , are connected to the corresponding distribution optical fibers, DF 1  to DF n ,  610 - 1  to  610 - n , respectively. For example, the ONU n    620 - n  is connected to the n-th distribution optical fiber, DF n ,  610 - n . Each ONU detects a downstream optical signal received from the associated distribution optical fiber, in the form of an electrical signal. For example, the ONU n    620 - n  detects a downstream optical signal received from the n-th distribution optical fiber, DF n ,  610 - n , in the form of an electrical signal. Each ONU also generates an upstream optical signal, and transmits the generated upstream optical signal to the associated distribution optical fiber. For example, the ONU n    620 - n  generates an upstream optical signal, and transmits the generated upstream optical signal to the n-th distribution optical fiber, DF n ,  610 - n.    
         [0044]     As apparent from the above description, the WDM PON of the present invention can be implemented, using only a transmissive SOA, a GC-SOA, or an RSOA, without using a broadband light source.  
         [0045]     While this invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment, but, on the contrary, it is intended to cover various modifications within the spirit and scope of the appended claims.