Patent Document

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application is a continuation application under 35 U.S.C. § 365(c) of International Application No. PCT/KR2005/001676, filed Jun. 3, 2005 designating the United States. International Application No. PCT/KR2005/00 1676 was published in English as WO2006/129894 A1 on Dec. 7, 2006. This application incorporates herein by reference the International Application PCT/KR2005/001676 including the International Publication No. WO2006/129894 A1 in its entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    The present disclosure generally relates to a wavelength division multiplexing-passive optical network (hereinafter, referred to as “WDM-PON”) system, and more specifically, to a WDM-PON system configured to multiplex and divide laser lights having various wavelengths each having the same intensity in a central office to supply the laser lights to subscribers so that several subscribers share a light source having the same wavelength. 
         [0004]    2. Discussion of the Related Technology 
         [0005]    As the information society is moved into, people are keenly concerned to a WDM-PON configured to connect an optical line directly to a subscriber terminal so as to supply various wideband multimedia services to a plurality of subscribers. The WDM-PON refers to a network configured to connect an interval between an optical line terminal (hereinafter, referred to as “OLT”) and an optical network unit (hereinafter, referred to as “ONU”) with a passive optical device and to transmit optical signals having multiplexed letters/audio/video data into each ONU. The WDM-PON can provide information of large capacity to subscribers with excellent security and performance. 
         [0006]      FIG. 1  is a diagram illustrating a WDM-PON system. 
         [0007]    In the WDM-PON system of  FIG. 1 , when a central office provides a light source (Σλ is ) of a predetermined intensity in different wavelengths for each subscriber, a WDM multiplexer/demultiplexer (hereinafter, referred to as “WDM MD”) located in a remote node of a subscriber demultiplexes wavelengths of light sources in each subscriber and transmits the demultiplexed light source into the ONU. The light source λ is  having the demultiplexed wavelength is modulated by projecting the light into a reflective optical amplifier of the ONU and amplifying or absorbing the light depending on input current of the optical amplifier. A modulated subscriber optical signal λ im  is multiplexed in the WDM MD (Σλ im ) and transmitted into the central office. 
         [0008]    However, in the WDM-PON system, light sources having the same wavelength cannot be used by several subscribers since an optical signal(a downward optical signal) is used to generate a subscriber optical signal(upward optical signal) (λ im ). As a result, a light source between the central office and the ONU and a wavelength of optical signals are different in each subscriber, and a large amount of resources(wavelengths) is required to embody the above-described system in an optical subscriber network to admit a large number of subscribers, thereby requiring great cost. 
         [0009]    The foregoing discussion in this section is to provide general background information, and does not constitute an admission of prior art. 
       SUMMARY 
       [0010]    Various embodiments of the present invention is directed at providing a WDM-PON system configured to multiplex and optical-power-divide light sources with various wavelengths and to provide the multiplexed and divided light sources into subscribers so that several subscribers may share light source having the same wavelength. 
         [0011]    According to an embodiment of the present invention, a wavelength division multiplexing-passive optical network system comprising: a light source provider configured to generate light sources for upward signals , to wavelength-division-multiplex the light sources and to optical-power-divide the multiplexed light source; a plurality of optical line terminals each configured to transmit the divided light source for upward signal into remote node and to convert upward optical signals which the light sources for upward signal are modulated into electric signals when the upward optical signal is received from the remote node; and a plurality of multiplexers/demultiplexers each configured to separate the light sources for upward signal from the optical line terminal in each wavelength and to transmit the separated light sources into optical network units, and to wavelength-division-multiplex the upward optical signals from the optical network units and to transmit the multiplexed upward optical signal into the optical line terminal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]      FIG. 1  is a diagram illustrating a WDM-PON system. 
           [0013]      FIG. 2  is a diagram illustrating a first example according to an embodiment of the present invention, 
           [0014]      FIG. 3  is a diagram illustrating an optical amplifier according to an embodiment of the present invention. 
           [0015]      FIG. 4  is a diagram illustrating a second example according to an embodiment of the present invention. 
           [0016]      FIG. 5  is a diagram illustrating a third example according to an embodiment of the present invention. 
           [0017]      FIG. 6  is a diagram illustrating a fourth example according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0018]    Various embodiments and features of the present invention will be described in detail with reference to the accompanying drawings. 
         [0019]    In an embodiment, a WDM-PON system includes a laser diode (hereinafter, referred to as “LD”), a WDM MD, an optical divider, a photo diode (hereinafter, referred to as “PD”), an optical circulator and an optical amplifier. The WDM-PON system is explained based on the flow of signals.  FIG. 2  is a diagram illustrating a first example according to an embodiment of the present invention. 
         [0020]    According to the first example of the present invention, a WDM MD 1  wavelength-division-multiplexes a light source λ ius  corresponding to a wavelength of an i-subscriber supplied from a LD 1  and light sources for the other subscribers. The light source is supplied from the single mode LD such as a DFB LD (Distributed FeedBack Laser Diode). The light source λ ius  is used for an upward optical signal, which is a source light for generating the upward optical signal, to be transmitted from an ONU 1  into a central office. 
         [0021]    A light source Σλ ius  for upward signal which has been multiplexed in the WDM MD 1  is light-power-divided in a 1×n optical divider  1 , and then supplied into each of OLT 1 ˜OLTn. That is, each of OLT 1 ˜OLTn receive the same wavelength-division-multiplexed and divided light source. Herein, OLTj 1  of the OLTs is exemplified. 
         [0022]    The light source λ ius  for upward signal of each subscriber supplied to the OLTj 1  is transmitted into a WDM MD 3  through an optical circulator OC 1 . The light source Σλ ius  for upward signal is demultiplexed in each subscriber in the WDM MD 3 , and the demultiplexed light source λ ius  is transmitted into the ONU 1  of the subscriber. 
         [0023]    The light source λ ius  for upward signal transmitted into the ONU 1  is transmitted into an optical amplifier  1 , and then modulated into an upward optical signal λ ium  having the same wavelength as that of the light source λ ius  for upward signal. The optical amplifier  1  is a reflection-type semiconductor optical amplifier. 
         [0024]      FIG. 3  is a diagram illustrating the optical amplifier  1  according to an embodiment of the present invention, 
         [0025]    The light source λ ius  projected into an active wave guide path  4  of the optical amplifier  1  through an optical wave guide path  2  is reflected in a high-reflection coating film  6 , and outputted into the optical wave guide path  2  through the active wave guide path  4 . The light source λ ius  is amplified depending on signal current (not shown) inputted into a substrate  8  while moving along the active wave guide path  4 . That is, since the upward optical signal λ ium  copies the signal current, the optical amplifier  1  converts an electric signal into the upward optical signal λ ium  having the same wavelength as that of the light source λ ius  for upward signal. 
         [0026]    The upward optical signal λ ium  generated from the optical amplifier  1  is transmitted into the WDM MD 3  through an optical path where the light source λ ius  for upward signal is transmitted, multiplexed with the upward optical signals of other subscribers by the WDM MD 3 , and then transmitted into the OLTj 1  of the central office. 
         [0027]    The multiplexed upward light signal Σλ ium  is inputted in a 2 nd  port of the OC 1 , and outputted into a 3 rd  port. The outputted upward light signal Σλ ium  is demultiplexed in the WDM MD 2  in each subscriber, projected in the PD 1 , and then converted into an electric signal. 
         [0028]    The above-described first example according to an embodiment of the present invention is characterized in that a single mode laser light source whose wavelength is allotted to each subscriber is multiplexed and divided so that the light source can be shared in several systems, and in that the wavelength of the optical signal transmitted from the ONU is determined by a light source supplied from the central office. The multiplexed light source Σλ ius  for upward signal is shared by a plurality of OLTs (OLT 1 ˜OLTn) so that different subscribers each connected to different OLTs may share light source having the same wavelength. As a result, although the number of subscribers is increased, an additional wavelengths are not required. 
         [0029]      FIG. 4  is a diagram illustrating a second example of the WDM-PON system according to an embodiment of the present invention. The system of  FIG. 4  simultaneously transmits a downward optical signal from the central office into the ONU and an upward optical signal from the ONU into the central office. 
         [0030]    In this embodiment, a WDM MD 4  multiplexes the light source λ ius  corresponding to a wavelength of an i-subscriber supplied from the LD 2  and other light sources of other subscribers. The light source is supplied from the single mode LD such as the DFB LD, and the light source λ ius  is a light source for upward signal transmitted from the ONU 2  into the central office so as to generate an upward optical signal. 
         [0031]    The light source Σλ ius  for upward signal, which is multiplexed in the WDM MD 4  is light-power-divided in a 1×n optical divider  2 , and supplied into each of OLT 1 ˜OLTn. Herein, OLTj 2  of the OLI&#39;s is exemplified. 
         [0032]    The light source Σλ ius  for upward signal of each subscriber supplied to the OLTj 2  is projected into a WDM MD 8  through an optical circulator OC 2 , and multiplexed with a downward optical signal Σλ idm . The WDM MDS multiplexes the light source for upward signal and the downward optical signal. 
         [0033]    The downward optical signal Σλ idm  and the multiplexed light source Σλ ius  for upward signal are transmitted into a WDM MD 9  of a subscriber through an optical path. The light source Σλ ius  is demultiplexed in the WDM MD 9  in each subscriber, and the demultiplexed light sources λ ius  are transmitted into the ONU 2  of the subscriber. Preferably, the light source λ ius  for upward signal and a downward optical signal λ idm  of the i-subscriber are outputted into the same output port. 
         [0034]    The light source λ ius  for upward signal transmitted into the ONU 2  is separated form the downward optical signal λ idm  by a WDM MD 10 , and transmitted into an optical amplifier  3 . The optical amplifier  3  generates the upward optical signal λ ium  as shown in  FIG. 3 . 
         [0035]    The upward optical signal λ ium  generated from the optical amplifier  3  is transmitted into the WDM MD 9  through the WDM MD 10 , multiplexed with upward optical signals of other subscribers by the WDM MD 9 , and transmitted into the OLTj 2  of the central office. 
         [0036]    The multiplexed upward optical signal Σλ ium  is inputted into the 2 nd  port of the optical circulator OC 2  through the WDM MD 8 , and outputted into the 3 rd  port. The upward optical signal Σλ ium  is demultiplexed in a WDM MD 5  in each subscriber, and the demultiplexed upward optical signal λ ium  is projected into the PD 2 , and converted into an electric signal. 
         [0037]    In the second example according to an embodiment of the present invention, a light source λ ids  for downward signal of an i-subscriber is multiplexed in a EM MD 6  with light sources for downward signal of other subscribers. The multiplexed light source Σλ ids  for downward signal is light-power-divided in a 1×n optical divider  3 , and transmitted into a WDM MD 7  through an optical circulator OC 3 . The wavelength of the light source λ ids  for downward signal is determined so that the light source λ ius  for upward signal of the i-subscriber and the downward optical signal λ idm  are demultiplexed into an output port. 
         [0038]    The multiplexed light source Σλ ids  for downward signal is demultiplexed into the light source λ ids  of the i-subscriber in the WDM MD 7 , and the demultiplexed light source λ ids  is transmitted into the optical amplifier  2 . As shown in  FIG. 3 , the optical amplifier  2  generates the downward optical signal λ idm , and transmits it into the WDM MD 7  which multiplexes the downward optical signal λ idm  with downward optical signals of other subscribers. 
         [0039]    The multiplexed downward light signal Σλ idm  is projected into a WDM MD 8  through the optical circulator OC 3 , multiplexed with the light source Σλ ius  for upward signal, and transmitted into the WDM MD 9  of the subscriber. 
         [0040]    The VDM MD 9  demultiplexes the downward optical signal Σλ idm  in each subscriber, and transmits the demultiplexed signal λ idm  into the ONJ 2  of the subscriber. 
         [0041]    The downward optical signal λ idm  transmitted into the ONU 2  is separated from the light source λ ius  for upward signal by a WDM MD 10  in the ONU 2 , transmitted into a PD 3 , and converted into an electric signal. 
         [0042]    As mentioned above, the second example is characterized in that the configuration for transmitting a light source for downward signal and a downward optical signal is further comprised in the first example having the configuration for the light source for upward signal and the upward optical signal. 
         [0043]    While two WDM MDs (WMD MD 5 , WDM MD 7 ) are used for multiplexing and demultiplexing of optical signals and light sources in each subscriber in the OLT in the second example,  FIG. 5  is a diagram illustrating a third example according to an embodiment of the present invention where one WDM MD (WDM MD 14 ) for multiplexing or demultiplexing of optical signals and light sources in each subscriber. In the third example, wavelengths of the light source for downward signal, the downward optical signal, the light source for upward signal and the upward optical signal are determined so that they may be separated into the same port to the same subscriber when they are separated in the WDM MD 14  and the WDM MD 17 . 
         [0044]    In the third example, a WDM MD 11  multiplexes the light source λ ius  corresponding to the wavelength of the i-subscriber supplied from a LD 4  and other light sources of other subscribers. The light sources are supplied from the single mode LD such as a DFB LD. The light source λ ius  is a light source for upward signal transmitted from an ONU 3  into the central office. 
         [0045]    The multiplexed light source Σλ ius  for upward signal in the WDM MD 11  is light-power-divided in a 1×n optical divider  4 , and supplied into each of OLT 1 ˜OLTn. Herein, OLTj 3  of the OLTs is exemplified. 
         [0046]    The light source Σλ ius  for upward signal of each subscriber supplied to the OLTj 3  is projected into a WDM MD 16  through an optical circulator OC 3 , and multiplexed with a downward optical signal Σλ idm . The WDM MD 16  multiplexes the light source for upward signal and the downward optical signal. 
         [0047]    The downward optical signal Σλ idm  and the multiplexed light source Σλ ius  for upward signal are transmitted into a WDM MD 17  of a subscriber through an optical path. The light source Σλ ius  for upward signal is demultiplexed in the WDM MD 17  in each subscriber, and the demultiplexed light source λ ius  is transmitted into the ONU 3  of the subscriber. Preferably, the light source λ ius  for upward signal and a downward optical signal λ idm  of the i-subscriber are outputted into the same output port. 
         [0048]    The light source λ ius  for upward signal transmitted into the ONU 3  is separated form the downward optical signal λ idm  by a WDM MD 18 , and transmitted into an optical amplifier  5 . The optical amplifier  5  generates the upward optical signal λ ium  as shown in  FIG. 3 . 
         [0049]    The upward optical signal λ ium  generated from the optical amplifier  5  is transmitted into the WDM MDI 17  through the WDM MD 18 , multiplexed with upward optical signals of other subscribers by the WDM MD 17 , and transmitted into the OLTj 3  of the central office. 
         [0050]    The multiplexed upward optical signal Σλ ium  is inputted into the 2 nd  port of the optical circulator OC 4  through the WDM MD 16  and outputted into the 3 rd  port. The upward optical signal Σλ idm  is multiplexed with the light source Σλ ids  for downward signal in the WDM MD 15 , and transmitted into the 2 nd  port of the WDM MD 14 . 
         [0051]    The upward optical signal Σλ ium  and the light source Σλ ids  for downward signal are demultiplexed in each subscriber in the WDM MD 14 , and the upward optical signal λ idm  and the light source λ ids  for downward signal of the same subscriber are outputted into the same port (1 st  port). The outputted upward optical signal λ ium  like the light source λ ids  for downward signal in the WDM MD 14  is separated from the light source λ ids  in the WDM MD 13 , transmitted into a PD 4 , and converted into an electric signal. 
         [0052]    In the third example according to an embodiment of the present invention, the light source λ ids  for downward signal supplied from a LD 5  is multiplexed in the WDM MD 12  with other light sources for downward signal of other subscribers, light-power-divided in a 1×n optical divider  5 , and transmitted into the WDM MD  15  through an optical circulator OC 5 . 
         [0053]    The light source Σλ ids  for downward signal is multiplexed with the upward optical signal Σλ ium  by the WDM MD 15 , and then transmitted into the WDM MD 14 . 
         [0054]    The WDM MD 14  outputs the upward optical signal λ ium  and the light source λ ids  or downward signal in each subscriber into the same port (1 st  port). The light source λ ids  for downward signal outputted with the upward optical signal λ ium  in the WDM MD 14  is separated from the upward optical signal λ ium  in the WDM MD 13 , and transmitted into an optical amplifier  4 . The optical amplifier  4  generates the downward optical signal λ idm  as shown in  FIG. 3 . 
         [0055]    The downward optical signal λ idm  generated from the optical amplifier  4  is multiplexed with other downward optical signals of other subscribers in the WDM MD 14 , and transmitted into the WDM MD 16  through the WDM MD 15  and the optical circulator OC 5 . 
         [0056]    The downward optical signal Σλ idm  transmitted into the WDM MD 16  is multiplexed with the light source Σλ ius  for upward signal, and transmitted into the WDM MD 17  of the subscriber through an optical path. 
         [0057]    The WDM MD 17  separates the downward optical signal Σλ idm  and the light source Σλ ius  for upward signal into the same port in each subscriber. The downward optical signal λ idm  separated in each subscriber is transmitted into the ONU 3  with the light source for upward signal, separated from the light source λ ius  for upward signal in the WDM MD 18 , transmitted into a PD 5 , and converted into an electric signal. 
         [0058]    In the third example, the WDM MD 13 , the WDM MD 15 , the WDM MD 16  and the WDM MD 17  multiplex or demultiplex the light source for downward signal or the downward optical signal with the light source for upward signal or the upward optical signal, and the WDM MD 14  and the WDM MD 17  multiplex or demultiplex light sources or optical signals in each subscriber. 
         [0059]      FIG. 6  is a diagram illustrating a fourth example of the WDM-PON system according to an embodiment of the present invention. 
         [0060]    In the fourth example, the light source λ ius  for upward signal supplied from the central office into the ONU is light-power-divided in a 1×n optical divider  6  so that it may be shared in several systems. The DFB LD is used for the light source for upward signal as the single mode LD having a predetermined size. 
         [0061]    The light source λ ius  for upward signal for the i-subscriber which is light-power-divided into 1/n in the 1×n optical divider  6  is multiplexed with the downward optical signal λ idm  in a WDM MD 19 , and transmitted into the i-th port (4 th  port) of bidirectional arrayed waveguide grating (hereinafter, referred to as “BD AWG”). The BD AWG, which is a kind of the WDM MD, multiplexes various wavelengths inputted into different port to output them into one port, or demultiplexes the multiplexed wavelengths inputted into one port to output them into each port. 
         [0062]    The light source λ ius  for upward signal transmitted into the BD AWG is multiplexed with light sources for upward signal of other subscribers. 
         [0063]    The multiplexed light source Σλ ius  for upward signal is transmitted into a WDM MD 20 , separated from the downward optical signal Σλ idm  in the WDM MD 20 , and transmitted into a WDM MD  22  through an optical circulator OC 7 . 
         [0064]    The light source Σλ ius  for upward signal transmitted into the WDM MD 22  is transmitted into the AWG of the subscriber, and demultiplexed in each subscriber, and the demultiplexed light source λ ius  is outputted into the 2 nd  port and transmitted into the ONU. 
         [0065]    The light source λ ius  for upward signal transmitted into the ONU is inputted into the 1 st  port of a WDM MD 24  in the ONU so that it is separated from the downward optical signal λ idm  and outputted into the 2 nd  port. The light source λ ius  for upward signal outputted into the 2 nd  port of the WDM MD 24  is transmitted into an optical amplifier  7 , and converted into the upward optical signal λ ium . 
         [0066]    The upward optical signal λ ium  is inputted into the 2 nd  port of the BD AWG through the WDM MD 24 , multiplexed with other upward signals of other subscribers inputted into other ports, and outputted into the 1 st  port. 
         [0067]    The multiplexed upward optical signal Σλ ium  subscribers is transmitted into the OLT located at the central office, inputted into the 3 rd  port of the BD AWG through the WDM MD 22 , the optical circulator OC 7  and a WDM MD 21  in the OLT, and demultiplexed into each wavelength of each subscriber, and the demultiplexed upward optical signal λ ium  is outputted into the 1 st  port as. 
         [0068]    The upward optical signal λ ium  outputted into the 1 st  port of the BD AWG is transmitted into a PD 6  through a WDM MD 23 , and converted into an electric signal in a PD 6 . The WDM MD 23  multiplexes or demultiplexes the upward optical signal λ ium  and the light source λ ids  for downward signal. 
         [0069]    The light source λ ids  for downward signal supplied from the DFB LD 2  is light-power-divided in a 1×n optical divider  7 , and transmitted into the WDM MD 23 . The WDM MD 23  multiplexes or demultiplexes the upward optical signal λ ium  and the light source λ ids  for downward signal. 
         [0070]    The light source λ ids  for downward signal outputted from the WDM MD 23  is inputted into the 1 st  port of the BD AWG, multiplexed with other light sources for downward signal of other subscribers inputted into other ports, and outputted into the 3 rd  port. 
         [0071]    The multiplexed light source Σλ ids  for downward signal is inputted into the 2 nd  port of the BD AWG through the WDM MD 21 , an optical circulator OC 6  and the WDM MD 20 , and demultiplexed into light sources for each subscriber, and the demultiplexed light source λ ids  for downward signal is outputted into the 4 th  port. 
         [0072]    The light source λ ids  for downward signal of each subscriber outputted into the 4 th  port of the BD AWG is transmitted into the WDM MD 19 . 
         [0073]    The light source λ ids  for downward signal outputted from the WDM MD 19  is converted into the downward optical signal λ idm  in the power amplifier  6  as shown in  FIG. 3 . 
         [0074]    The downward optical signal λ idm  is projected into the WDM MD 19 , multiplexed with the light source λ ius  for upward signal, inputted into the 4 th  port of the BD AWG, multiplexed with other downward optical signals of other subscribers inputted into other ports, and outputted into the 2 nd  port as Σλ idm . 
         [0075]    The multiplexed downward optical signal Σλ idm  is demultiplexed from the light source Σλ ius  for upward signal by the WDM MD 20 , multiplexed with the light source Σλ ius  for upward signal in the WDM MD 22  through the optical circulator OC 6 , transmitted into the BD AWG of the subscriber and demultiplexed in each subscriber, and the demultiplexed downward optical signal λ idm  is outputted into the 2 nd  port, and transmitted into the ONU. 
         [0076]    The downward optical signal λ idm  transmitted into the ONU is inputted into the 1 st  port of the WDM MD 24  in the ONU, separated from the light source λ ius , and outputted into the 3 rd  port. The downward optical signal λ idm  outputted into the 3 rd  port of the WDM MD 24  is transmitted into a PD 7 , and converted into an electric signal. 
         [0077]    In the above-described fourth example, the optical divider is comprised in the rear end of the DFB LD unlike the first through third examples where the WDM MD and the optical divider are sequentially comprised in the rear end of the DFB LD. AS a result, a light source whose wavelength is allotted for a specific subscriber is light-power-divided so that several subscribers may share a single laser. 
         [0078]    As shown in the first through fourth examples, a single mode laser light source having a wavelength allotted to each subscriber is multiplexed by power-dividing the multiplexed light so that several systems may share it. 
         [0079]    As described above, according to an embodiment of the present invention, a single mode laser light source having a wavelength allotted to each subscriber, and light-power-divided so that several systems may share the light source, thereby reducing resources and cost required for constitution of the system. 
         [0080]    Moreover, a wavelength of an optical signal transmitted from an ONU is determined by a light source supplied from a central office so that it is not necessary to administrate the wavelength in the ONU.

Technology Category: 5