Abstract:
A passive optical network using downstream and upstream optical signals for achieving a two-way communication is provided, wherein the downstream and upstream optical signals have different polarization components and an equal wavelength band.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority to an application entitled “Passive Optical Network,” filed in the Korean Intellectual Property Office on Aug. 20, 2004 and assigned Serial No. 2004-66089, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a wavelength division multiplexing passive optical network(WDM-PON) and, more particularly, to a wavelength division multiplexing passive optical network for realizing a two-way communication.  
         [0004]     2. Description of the Related Art  
         [0005]     The WDM-PON provides an ultra high-speed broadband communication service by classifying specific wavelengths to each subscriber unit. Therefore, the WDM-PON can ensure the secrecy of communication and easily accommodate a new communication line by adding a separate wavelength to a new subscriber. At the same time, the WDM-PON has a disadvantage in that a central office and each optical network unit require both light sources having specific oscillation wavelengths and additional wavelength stabilization circuits for stabilizing the wavelengths of the light sources.  
         [0006]      FIG. 1  is a block diagram illustrating a conventional PON. As shown, the conventional PON includes a central office  110 , a remote node  120 , and a plurality of optical network units  130 . The central office  110  and the remote node  120  are connected to each other through a single optical fiber  101 . The remote node  120  is connected to each of the optical network units  130 , forming a double star structure.  
         [0007]     More specifically, the central office  110  includes a plurality of downstream light sources  111  for generating downstream optical signals λ 1  to λ N , a multiplexing/demultiplexing unit  113  for demultiplexing multiplexed upstream optical signals λ N+1  to λ 2N  and for multiplexing the downstream optical signals, and an upstream light detector  112  for detecting upstream optical signals demultiplexed by the multiplexing/demultiplexing unit  113 .  
         [0008]     The remote node  120  includes a multiplexing/demultiplexing unit  121 , which demultiplexes and outputs the downstream optical signals multiplexed in the central office  110 , to a relevant optical network unit  130 , and further multiplexes and outputs the upstream optical signals inputted from the optical network units  130  to the central office  110 .  
         [0009]     Each optical network unit  130  includes an upstream light source  132  for generating an upstream optical signal and a downstream light detector  131  for detecting a down optical signal demultiplexed in the remote node  120 .  
         [0010]     For a typical two-way communication, the PON uses downstream and upstream optical signals having different wavelength bands from each other. That is, since the central office  110  and the remote node  120  are linked to each other through a single optical fiber, the PON uses downstream and upstream optical signals having different wavelength bands from each other to minimize loss and noise generation due to interference between the upstream and downstream optical signals.  
         [0011]     Meanwhile, when it is necessary to increase the number of lines according to the increase in the number of optical network units, the PON can increase as many lines as necessary by reducing the wavelength interval between the downstream optical signals and the wavelength interval between the upstream optical signals. However, as the wavelength interval are reduced to increase the number of lines in the conventional PON, a higher-price multiplexing/demultiplexing unit is required to stabilize the wavelength bands. Also, it is necessary to include an additional separate stabilizing means for stabilizing the wavelengths in the lines added according to the reduction of the wavelength. Accordingly, the conventional PON has a problem in that the cost of construction of a PON largely increases whenever extra lines are added.  
       SUMMARY OF THE INVENTION  
       [0012]     Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art and provides additional advantages, by providing an economical passive optical network.  
         [0013]     In one aspect of the present invention, there is provided a passive optical network using a downstream optical signal and an upstream optical signal for a two-way communication, wherein the downstream optical signal and the upstream optical signal have different polarization components and an equal wavelength band.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     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:  
         [0015]      FIG. 1  is a block diagram illustrating the construction of a conventional PON;  
         [0016]      FIG. 2  is a block diagram illustrating the construction of a passive optical network according to an embodiment of the present invention; and  
         [0017]      FIG. 3  is a block diagram illustrating the construction of a passive optical network according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]     Hereinafter, embodiments of a passive optical network according to the present invention will be described 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.  
         [0019]      FIG. 2  is a block diagram illustrating the construction of a passive optical network according to a first embodiment of the present invention. As shown, the passive optical network includes a central office  210  for generating wavelength-locked downstream optical signals λ 1  to λ N  and detecting upstream optical signals λ 1  to λ N , a plurality of optical network units  230  for generating upstream optical signals having a polarization component different from the downstream optical signals according to a wavelength locking scheme, and a remote node  220  connected to the central office  210  through a single optical fiber  201 . The upstream optical signals and the downstream optical signals use the same wavelength band and different polarization components.  
         [0020]     The central office  210  includes a plurality of downstream light sources  211  for generating wavelength-locked downstream optical signals, a plurality of upstream light detectors  212  for detecting demultiplexed upstream optical signals, a first multiplexing/demultiplexing unit  213 , a first polarization selective coupler  214 , a broadband light source  215 , and a light coupler  216  located on the single optical fiber  201  to transmit broadband lights to the central office  210  and the remote node  220 .  
         [0021]     The broadband light source  215  generates a light having a wide wavelength band for wavelength-locking lights outputted from each of the optical network units  230  and the downstream light sources  211 , and outputs the light to the first multiplexing/demultiplexing unit  213  and the remote node  220 . The broadband light source  215  includes a semiconductor optical amplifier and a rare-earth element doped optical fiber that can generate amplified spontaneous emission light or incoherent light having a wide wavelength band.  
         [0022]     The first multiplexing/demultiplexing unit  213  multiplexes downstream optical signals generated in the downstream light sources  211  to output the multiplexed downstream optical signals to the remote node  220  and demultiplexes the upstream optical signals to relevant upstream light detectors  212 . In addition, the first multiplexing/demultiplexing unit  213  divides the light generated in the broadband light source  215  into incoherent channels having different wavelengths from each other and then inputs the respective incoherent channels to relevant downstream light sources  211 . Each downstream light source  211  generates a wavelength-locked downstream optical signal using a corresponding incoherent channel. The downstream light sources  211  may include a Fabry-Perot laser and a reflective semiconductor optical amplifier.  
         [0023]     The first polarization selective coupler  214  outputs a demultiplexed upstream optical signal to a relevant upstream light detector  212  and outputs a downstream optical signal generated in a relevant downstream light source  211  to the first multiplexing/demultiplexing unit  213 . The first polarization selective coupler  214  includes a polarization beam splitter capable of splitting and coupling optical signals according to polarization components.  
         [0024]     The remote node  220  includes a second multiplexing/demultiplexing unit  221 , which is connected to the central office  210  through the single optical fiber  201  to demultiplex and output the multiplexed downstream optical signals to the relevant optical network units  230 . It is also configured to multiplex and output upstream optical signals inputted from the optical network units  230  to the central office  210 . The second multiplexing/demultiplexing unit  221  splits the light inputted through the light coupler  216  into incoherent channels having different wavelengths from each other and then outputs each of the incoherent channels to a relevant optical network unit  230 . The single optical fiber  201  includes a polarization-maintaining optical fiber.  
         [0025]     Each of the optical network units  230  includes a downstream light detector  232  for detecting a relevant optical signal demultiplexed in the remote node  220 , an upstream light source  233  for generating a wavelength-locked upstream optical signal, and a second polarization selective coupler  231 . The upstream light source  233  generates a wavelength-locked upstream optical signal by a relevant incoherent channel.  
         [0026]     The second polarization selective coupler  231  outputs a relevant downstream optical signal demultiplexed in the remote node  220  to the downstream light detector  232  and outputs the upstream optical signal generated in the upstream light source  233  to the remote node  220 . The second polarization selective coupler  231  includes a polarization beam splitter.  
         [0027]      FIG. 3  is a block diagram illustrating the construction of a passive optical network according to a second embodiment of the present invention. As shown, the passive optical network includes a central office  310  for generating downstream optical signals and for demultiplexing and detecting multiplexed upstream optical signals, a plurality of optical network units  330  for generating upstream optical signals having a polarization component other than the polarization component of the downstream optical signals and for detecting relevant downstream optical signals having been demultiplexed, and a remote node  320  for intermediating between the central office  310  and the optical network units  330 . The upstream optical signals and downstream optical signals λ 1  to λ N  use the same wavelength band and different polarization components. A single optical fiber  301  for connecting the central office  310  and the remote node  320  includes a polarization-maintaining optical fiber.  
         [0028]     The central office  310  includes a plurality of downstream light sources  311  for generating downstream optical signals, a plurality of upstream light detectors  312  for detecting relevant upstream optical signals having been demultiplexed, a first multiplexing/demultiplexing unit  313 , and a first polarization selective couplers  314 .  
         [0029]     Each of the downstream light source  311  may include a distributed feedback laser, and the downstream and upstream optical signals may have one from among wavelength bands of 1300˜1350 nm, 1450˜1500 nm, and 1520˜1620 nm.  
         [0030]     The first multiplexing/demultiplexing unit  313  multiplexes downstream optical signals generated in the downstream light sources  311  to output the multiplexed downstream optical signals to the remote node  320 , and demultiplexes the upstream optical signals having been multiplexed to output the demultiplexed upstream optical signals to relevant upstream light detectors  312 . The first multiplexing/demultiplexing unit  313  includes an arrayed optical waveguide grating having a plane waveguide.  
         [0031]     Each of the first polarization selective coupler  314  outputs a relevant upstream optical signal having been demultiplexed to a corresponding upstream light detector  312  and outputs a downstream optical signal generated in a relevant downstream light source  311  to the first multiplexing/demultiplexing unit  313 . The first polarization selective coupler  314  may include a polarization beam splitter to input/output downstream and upstream optical signals having different polarization components from each other.  
         [0032]     The remote node  320  includes a second multiplexing/demultiplexing unit  321 . The second multiplexing/demultiplexing unit  321  is connected to the central office  310  through the single optical fiber  301  to demultiplex and output the multiplexed downstream optical signals to the relevant optical network units  330 . It is further configured to multiplex and output upstream optical signals inputted from the optical network units  330  to the central office  310 .  
         [0033]     Each of the optical network units  330  includes a downstream light detector  332  for detecting a relevant downstream optical signal demultiplexed in the remote node  320 , an upstream light source  333  for generating an upstream optical signal, and a second polarization selective coupler  331 .  
         [0034]     The second polarization selective coupler  331  outputs a relevant downstream optical signal demultiplexed in the remote node  320  to the downstream light detector  332  and outputs the upstream optical signal generated in the upstream light source  333  to the remote node  320 . The second polarization selective coupler  331  includes a polarization beam splitter.  
         [0035]     As described above, the passive optical network according to the present invention uses the upstream optical signals and the down optical signals having the same wavelength band and different polarization components, so that it is possible to increase lines at a low cost.  
         [0036]     While the present 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 therein without departing from the spirit and scope of the invention as defined by the appended claims.