Abstract:
A wavelength division multiplexed self-healing passive optical network using a wavelength injection method. The wavelength division multiplexed self-healing passive optical network includes a central office for coupling modulated multiplexing optical signals and broadband optical signals for an upstream light source. These signals are combined into one signal and transmitted to a plurality of optical network units as a coupled signal through a working main fiber and a protection main fiber. The remote node connects to the central office through the working main fiber and the protection main fiber and to the optical network units through working distribution fibers and protection distribution fibers. The remote node demultiplexes the modulated multiplexing optical signals and the broadband optical signals for an upstream light source. The remote node transmits the demultiplexed signals to the optical network units, which receive the modulated optical signals and the broadband optical signals for an upstream light source, which are transmitted from the remote node and correspond to predetermined optical network units, optically demodulate the modulated optical signals, and modulate upstream optical signals by means of the demultiplexed broadband optical signals for an upstream light source.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority to an application entitled “Wavelength division multiplexed self-healing passive optical network using wavelength injection method,” filed in the Korean Intellectual Property Office on Jan. 9, 2004 and assigned Serial No. 2004-1754, 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 self-healing passive optical network capable of detecting and healing cuts or deterioration of a feeder fiber or distribution fiber, thereby restoring the network by itself.  
         [0004]     2. Description of the Related Art  
         [0005]     A wavelength division multiplexing passive optical network (WDM-PON) can ensure the secrecy of communication and can easily accommodate special communication services required from each subscriber unit. The WDM-PON can enlarge channel capacity by assigning a specific wavelength to each subscriber unit and communicating with each subscriber unit. Also, the WDM-PON can easily increase the number of subscriber units by adding specific wavelengths to be assigned to new subscribers.  
         [0006]     Generally, a WDM-PON uses a double star structure. That is, a central office (CO) and a remote node (RN) installed at an area adjacent to optical network units are connected to each other through one feeder fiber. The remote node and each optical network unit are connected to each other through a separate distribution fiber.  
         [0007]     Multiplexed downstream optical signals are transmitted to the remote node through one feeder fiber. The multiplexed downstream optical signals are demultiplexed by a multiplexer/demultiplexer installed in the remote node and the demultiplexed signals are transmitted to subscriber units through the distribution fibers separately connected to optical network units.  
         [0008]     Upstream signals outputted from the subscriber units are transmitted to the remote node through the distribution fibers separately connected to the optical network units. Then the multiplexer/demultiplexer installed in the remote node multiplexes the upstream signal according to each optical network unit, and transmits the multiplexed signal to the central office.  
         [0009]     In the WDM-PON as described above, when an unexpected error occurs, such as a cut of a feeder fiber or a distribution fiber, a large quantity of transmitted data may be lost even though the error time period is short. For this reason, the error must be quickly detected and corrected.  
         [0010]     Accordingly, it is necessary to develop a self-healing passive optical network (PON) capable of quickly detecting an error, such as a cut of a feeder fiber or a distribution fiber, on an installed optical link and correcting the error by itself.  
         [0011]      FIGS. 1   a  and  1   b  are views of a conventional WDM self-healing ring network.  
         [0012]     Generally, in a WDM optical communication network, a ring network connecting each node in a ring type is mainly used to smoothly cope with an error such as a cut of a transmission optical fiber.  
         [0013]     The aforementioned conventional self-healing ring network connects a central office  100  to a first remote node  200  by means of two strands of optical fiber. Further, the self-healing ring network connects the central office  100  to a second remote node  300  by means of two strands of optical fiber.  
         [0014]     Here, the two strands of optical fiber are a working fiber and a protection fiber. The central office  100  in a normal state transmits optical signals equal to each other, into which several wavelengths (e.g., λ 1 , λ 2 ) of signals are multiplexed, through the two strands of optical fibers. The first remote node  200  or the second remote node  300  drops the optical signals inputted through the two strands of optical fiber to add/drop multiplexers  108  and  109  or add/drop multiplexers  112  and  113  and receives an optical signal having good characteristics from among the inputted optical signals by means of optical switching devices  110  and  111  or optical switching devices  114  and  115 .  
         [0015]     Meanwhile, the first remote node  200  or the second remote node  300  transmits optical signals equal to each other through the two strands of optical fiber. Then, the central office  100  demultiplexes optical signals according to each wavelength, and selects and receives one of two signals by means of optical switching devices  104  and  105 .  
         [0016]      FIG. 1   b  is a view illustrating a case in which an abnormality such as a cut of an optical fiber occurs in a working fiber.  
         [0017]     When an abnormality occurs in the working fiber, the conventional self-healing ring network performs the following self-healing operation.  
         [0018]     If the second remote node  300  cannot receive a second channel λ 2  through the working fiber in a counterclockwise rotation it is assumed that the working fiber between the first remote node  200  and the second remote node  300  is cut., When it is assumed that the working fiber is cut, the second remote node  300  receives the second channel λ 2  transmitted in a clockwise rotation through the protection fiber. Since the first remote node  200  cannot add and transmit a first channel λ 1  through the working fiber in a counterclockwise rotation, the first remote node  200  switches the optical switching device  110  to transmit the first channel λ 1  through the protection fiber in a clockwise rotation.  
         [0019]     The aforementioned conventional self-healing ring network is efficient when a central office and a plurality of remote nodes are spaced away from each other by about several tens of kilometers. However, it is insufficient to introduce the aforementioned ring network structure to a PON which connects a central office to a remote node and connects the remote node to an optical network unit. That is, since a conventional PON has a star structure, a self-healing method having a concept different from a self-healing method in a ring network structure must be developed.  
         [0020]     Furthermore, in the case of a WDM-PON using a wavelength injection method, an upstream/downstream injection light source exists and the directionality of the light source must be considered.  
       SUMMARY OF THE INVENTION  
       [0021]     The present invention has been made to solve the aforementioned problems occurring in the prior art. An object of the present invention is to provide a wavelength division multiplexed self-healing passive optical network capable of detecting a cut of or deterioration of a feeder fiber or a distribution fiber. It is a further object of the present invention to correct an error due to the cut or deterioration by itself in a passive optical network having a star structure.  
         [0022]     In order to accomplish the aforementioned objects, according to one aspect of the present invention, a wavelength division multiplexed self-healing passive optical network is provided using a wavelength injection method. The wavelength division multiplexed self-healing passive optical network may include a central office for coupling modulated multiplexing optical signals and broadband optical signals for an upstream light source. These signals may be combined into one signal and transmitted to a plurality of optical network units as a coupled signal through a working main fiber and a protection main fiber. The remote node may connect to the central office through the working main fiber and the protection main fiber and to the optical network units through working distribution fibers and protection distribution fibers. The remote node may demultiplex the modulated multiplexing optical signals and the broadband optical signals for an upstream light source. The remote node may transmit the demultiplexed signals to the optical network units. The optical network units may receive the modulated optical signals and the broadband optical signals for an upstream light source, which are transmitted from the remote node and correspond to predetermined optical network units, optically demodulate the modulated optical signals, and modulate upstream optical signals by means of the demultiplexed broadband optical signals for an upstream light source. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     The above and other objects, 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:  
         [0024]      FIGS. 1   a  and  1   b  are views of a conventional wavelength division multiplexed self-healing ring network;  
         [0025]      FIG. 2  is a block diagram of a wavelength division multiplexed self-healing passive optical network using a wavelength injection method according to one embodiment of the present invention;  
         [0026]      FIG. 3  shows a wavelength range of a downstream light source and a wavelength range of an upstream light source according to one embodiment of the present invention;  
         [0027]      FIG. 4  is a block diagram illustrating a case in which an abnormality occurs in a working main fiber in a wavelength division multiplexed self-healing passive optical network using a wavelength injection method according to one embodiment of the present invention; and  
         [0028]      FIG. 5  is a block diagram illustrating a case in which an abnormality occurs in a working distribution fiber in a wavelength division multiplexed self-healing passive optical network using a wavelength injection method according to one embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0029]     A preferred embodiment according to the present invention will be described below with reference to the accompanying drawings. Detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention unclear.  
         [0030]      FIG. 2  is a block diagram of a wavelength division multiplexed self-healing passive optical network using a wavelength injection method according to one embodiment of the present invention.  
         [0031]     As shown in  FIG. 2 , the wavelength division multiplexed self-healing passive optical network using the wavelength injection method includes a central office  21 , one strand of working fiber and one strand of protection fiber connecting the central office  21  to a remote node  22 , an N×N multiplexer/demultiplexer (waveguide grating router)  209  located in the remote node  22 , working fibers and protection fibers connecting the remote node  22  to optical network units  23 - 1  to  23 -( n - 1 ), and the optical network units  23 - 1  to  23 -( n - 1 ). The central office  21  includes downstream light sources  204 - 1  to  204 -( n - 1 ), upstream optical receivers  205 - 1  to  205 -( n - 1 ), an N×N multiplexer/demultiplexer (waveguide grating router)  203 , a broadband light source (BLS)  201  for a downstream light source, a broadband light source  207  for an upstream light source, a first and a second circulators  202  and  208  for determining an optical path, and a 2×2 optical coupler  206 . Each of the optical network units  23 - 1  to  23 -( n - 1 ) includes a downstream optical receiver  212 , an upstream light source  213 , a wavelength division multiplexer (WDMC)  211  for dividing/coupling an upstream/downstream signal, and a 1×2 optical switching device  210 .  
         [0032]     Operation of the wavelength division multiplexed self-healing passive optical network using the wavelength injection method will be described with reference to  FIG. 2 .  
         [0033]     First, a downstream signal will be described. A broadband optical signal of the broadband light source  201  for a downstream light source in the central office  21  is inputted into a first terminal of one side of the N×N waveguide grating router  203  through the first circulator  202 , and is then demultiplexed. That is, the optical signal inputted into a first terminal of one side of the N×N waveguide grating router  203  is demultiplexed into (n- 1 ) number of optical signals corresponding to a first through an (n- 1 ) th  terminal on the other side of the N×N waveguide grating router  203 .  
         [0034]     Each of the demultiplexed optical signals as described above is injected into each of the downstream light sources  204 - 1  to  204 -( n - 1 ), assigned with respect to each optical network unit, and is then modulated according to transmission data.  
         [0035]     The modulated optical signals are then inputted into the first through the (n- 1 ) th  terminal of the other side of the N×N waveguide grating router  203 , and are then multiplexed into one optical signal. The multiplexed optical signal is outputted to a first terminal of one side of the N×N waveguide grating router  203 .  
         [0036]     The multiplexed modulation optical signal outputted to a first terminal of one side of the N×N waveguide grating router  203  is sent to the 2×2 optical coupler  206  through the first circulator  202 , is coupled to a broadband optical signal of the broadband light source  207  for upstream light source by the 2×2 optical coupler  206 , and is transmitted to the working main fiber and the protection main fiber.  
         [0037]     The coupled optical signal sent from the central office  21  to the remote node  22  through the working main fiber is inputted into a first terminal of one side of the N×N waveguide grating router  209  located in the remote node  22 . Meanwhile, the coupled optical signal sent from the central office  21  to the remote node  22  through the protection main fiber is inputted to an N th  terminal of the other side of the N×N waveguide grating router  209  located in the remote node  22 . The optical signal transmitted from the central office  21  in this way is demultiplexed by the N×N waveguide grating router  209  and then is transmitted to each of the optical network units  23 - 1  to  23 -( n - 1 ).  
         [0038]     The coupled optical signal sent from the central office  21  to the remote node  22  through the working main fiber is inputted into a first terminal of one side of the N×N waveguide grating router  209  located in the remote node  22 , is demultiplexed into (n- 1 ) number of optical signals corresponding to a first through an (n- 1 ) th  terminal of the other side of the N×N waveguide grating router  209 , and then is transmitted to each of the optical network units  23 - 1  to  23 -( n - 1 ) through the working distribution fiber. The coupled optical signal sent from the central office  21  to the remote node  22  through the protection main fiber is inputted into the N th  terminal of the other side of the N×N waveguide grating router  209  located in the remote node  22 , is demultiplexed into (n- 1 ) number of optical signals corresponding to the second through the N th  terminal of one side of the N×N waveguide grating router  209 , and then is transmitted to each of the optical network units  23 - 1  to  23 -( n - 1 ) through the protection distribution fiber.  
         [0039]     The working distribution fiber and the distribution fiber are connected to each of the optical network units  23 - 1  to  23 -( n - 1 ). For clarity, an operation of the optical network unit  23 - 1  will be described below as an example.  
         [0040]     The optical signals transmitted to the optical network unit  23 - 1  through the working protection fiber and the protection distribution fiber are inputted to two input nodes of the 1×2 optical switching device  210 . Typically, the 1×2 optical switching device  210  is switched to the input node connected to the working distribution fiber. The optical signal inputted through the 1×2 optical switching device  210  is inputted to the wavelength division multiplexer  211 , and then is wavelength division demultiplexed. Then, the modulated optical signal of the coupled signal is inputted into the downstream optical receiver  212  and the broadband optical signal of the broadband light source for upstream light source  207  of the coupled signal is injected into the upstream light source  213 , and they are used for modulation of upstream data of the optical network unit  23 - 1 .  
         [0041]     Next, an upstream signal will be described. When the broadband optical signal of the broadband light source for upstream light source  207  transmitted from the central office  21  is inputted and injected into the upstream light source  213 , the optical network unit  23 - 1  modulates the upstream signal with a preset wavelength.  
         [0042]     The modulated upstream signal passes through the wavelength division multiplexer (WDMC)  211 . Then, the modulated upstream signal is transmitted to the remote node  22  through the working distribution fiber currently connected by the 1×2 optical switching device  210 . In this case, it is assumed that the 1×2 optical switching device  210  is connected to the working distribution fiber.  
         [0043]     An upstream signal of each of the optical network units  23 - 1  to  23 -( n - 1 ) transmitted to the remote node  22  is multiplexed by the N×N waveguide grating router  209  and then is transmitted to the central office  21  through the working main fiber.  
         [0044]     Here, the modulated optical signals transmitted from the optical network units  23 - 1  to  23 -( n - 1 ) to the remote node  22  through the working distribution fiber are inputted into the first through the (N- 1 ) th  terminal of the other side of the N×N waveguide grating router  209  located in the remote node  22 . The inputted optical signals are multiplexed by the N×N waveguide grating router  209  and the multiplexed optical signal is outputted to a first terminal of one side of the N×N waveguide grating router  209 . Then, the multiplexed optical signal is transmitted to the central office  21  through the working main fiber. The modulated upstream signals transmitted from the optical network units  23 - 1  to  23 -( n - 1 ) to the remote node  22  through the protection distribution fiber are inputted into the second through the N th  terminal of one side of the N×N waveguide grating router  209  located in the remote node  22 , are multiplexed by the N×N waveguide grating router  209 , and the multiplexed optical signal is outputted to the N th  terminal of the other side of the N×N waveguide grating router  209 . Then, the multiplexed optical signal is transmitted to the central office  21  through the protection main fiber.  
         [0045]     The upstream signal passing through the 2×2 optical coupler  206  and the second circulator  208  located in the central office  21  is inputted to the N th  terminal of one side of the N×N waveguide grating router  203 , and is demultiplexed into (n- 1 ) number of optical signals corresponding to the second through the N th  terminal of the other side of the N×N waveguide grating router  203 . Then, the demultiplexed signals are inputted into the upstream optical receivers  205 - 1  to  205 -( n - 1 ) according to the optical network units  23 - 1  to  23 -( n - 1 ), and then are converted into electrical signals.  
         [0046]      FIG. 3  is a view showing a wavelength range of a downstream light source and a wavelength range of an upstream light source according to one embodiment of the present invention.  
         [0047]     As shown in  FIG. 3 , the wavelength range  31  of the downstream light source and the wavelength range  32  of the upstream light source according to the present invention are distinguished from each other in the bi-directional wavelength division multiplexed self-healing passive optical network transmitting an upstream signal and a downstream signal simultaneously using one strand of optical fiber. That is, since the waveguide grating routers  203  and  209  used as multiplexers/demultiplexers have a periodic pass characteristic with a free spectral range, an upstream/downstream signal can be multiplexed/demultiplexed simultaneously by means of one of the waveguide grating routers  203  and  209  even though the upstream wavelength range and the downstream wavelength range are distinguished from each other.  
         [0048]      FIG. 4  is a block diagram illustrating a case in which an abnormality occurs in a working main fiber in a wavelength division multiplexed self-healing passive optical network using a wavelength injection method according to one embodiment of the present invention.  
         [0049]     As shown in  FIG. 4 , when an abnormality occurs in the working main fiber in the wavelength division multiplexed self-healing passive optical network using the wavelength injection method according to the present invention, since a downstream transmission signal and a broadband optical signal of a broadband light source for upstream light source transmitted from the central office  21  disappear, the optical signals are not transmitted to the working distribution fiber connected to each of the optical network units  23 - 1  to  23 -( n - 1 ). Accordingly, the state of the 1×2 optical switching device  210  in each of the optical network units  23 - 1  to  23 -( n - 1 ) is switched, thereby enabling communication between the central office  21  and each of the optical network units  23 - 1  to  23 -( n - 1 ) to be performed through the protection main fiber and the protection distribution fiber as shown in  FIG. 4 .  
         [0050]     Each of the optical network units  23 - 1  to  23 -( n - 1 ) informs the central office  21  of the state of the 1×2 optical switching device  210 , and the central office  21  analyzes the state of the 1×2 optical switching device  210 . Therefore, an existence or absence of abnormality of the working main fiber between the central office  21  and the remote node  22  can be checked.  
         [0051]      FIG. 5  is a block diagram illustrating a case in which an abnormality occurs in a working distribution fiber in a wavelength division multiplexed self-healing passive optical network using a wavelength injection method according to one embodiment of the present invention.  
         [0052]     As shown in  FIG. 5 , when an abnormality occurs in the working distribution fiber in the wavelength division multiplexed self-healing passive optical network using the wavelength injection method according to the present invention (the embodiment of the present invention examples a case in which an abnormality occurs in the working distribution fiber connected to the optical network unit  23 - 1 ), since an input of a signal received in the downstream optical receiver  212  disappears, the state of the 1×2 optical switching device  210  in the optical network unit  23 - 1  is switched. Therefore, the optical network unit  23 - 1  receives a downstream signal through the protection distribution fiber. Here, the states of the 1×2 optical switching devices  210  in the remaining optical network units  23 - 2  to  23 -( n - 1 ) are not changed. Further, the central office  21  receives an upstream transmission signal corresponding to the optical network unit  23 - 1  through the protection main fiber, and continuously receives upstream transmission signals corresponding to the remaining optical network units  23 - 2  to  23 -( n - 1 ) through the working main fiber.  
         [0053]     The optical network unit  23 - 1  informs the central office  21  of the state of the 1×2 optical switching device  210 , so that an existence or absence of abnormality of the distribution fiber between the remote node  22  and the optical network unit  23 - 1  can be checked.  
         [0054]     As described above, the present invention provides a wavelength division multiplexed self-healing passive optical network using a wavelength injection method to transmit an upstream signal, a downstream signal, and a broadband optical signal for injection through working fibers and protection fibers, thereby improving efficiency of an optical fiber.  
         [0055]     Further, according to the present invention, a central office and a remote node each use one N×N waveguide grating router, and an abnormality, such as a cut of an optical fiber, is quickly detected by means of a protection fiber connecting the central office to an optical network unit, and the detected abnormality is quickly healed. Therefore, a network can be managed economically and efficiently.  
         [0056]     While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.