Patent Publication Number: US-2007116463-A1

Title: Bi-directional optical cross coupler

Description:
CLAIM OF PRIORITY  
      This application claims priority under 35 U.S.C. § 119 to an application entitled “Bi-directional Optical Cross Coupler,” filed in the Korean Intellectual Property Office on Nov. 21, 2005 and assigned Serial No. 2005-111249, the contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to a wavelength division multiplexing (WDM) optical communication network, and in particular, to a metro access WDM optical communication network including an optical cross coupler for cross-connecting two different communication networks.  
      2. Description of the Related Art  
      A conventional optical cross coupler includes a plurality of passive components and wavelength selectors for exchanging optical signals by connecting different wavelength division multiplexing (WDM) optical communication networks to each other. The conventional optical cross coupler can include circulators for routing optical signals, an optical splitter, and wavelength selectors, such as an optical fiber grid, for selecting a wavelength.  
      An example of the conventional optical cross coupler is disclosed in U.S. Pat. No. 6,288,812 (Sep. 11, 2001) invented by Gary et al. entitled, “Bidirectional WDM Optical Communication Network with Optical Bridge between Bidirectional Optical Waveguides.” Briefly, the optical cross coupler disclosed in U.S. Pat. No. 6,288,812 includes 16 circulators and 6 wavelength selectors, and it can transmit/receive optical signals having a total of four different wavelengths by connecting two different optical communication networks to each other.  
      However, since the conventional optical cross coupler uses circulators and wavelength selectors in which an optical loss is high, an optical loss of more than 8 dB per transmission/reception channel occurs. In addition, since the conventional optical cross coupler includes a plurality of components, the cost is high.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to substantially solve at least the above problems and/or disadvantages and to provide at least the advantages below. Accordingly, an object of the present invention is to provide an economical optical cross coupler composed of a fewer number of components for minimizing an optical loss.  
      According to one aspect of the present invention, there is provided an optical cross coupler for connecting more than two different optical communication networks to each other which includes: first to fourth circulators, each circulator comprising first to fourth ports, the first port coupled to a relevant communication network; a first line coupling the second port of the first circulator and the fourth port of the second circulator; a second line coupling the fourth port of the first circulator and the second port of the second circulator; a third line coupling the second port of the third circulator and the fourth port of the fourth circulator; a fourth line coupling the fourth port of the third circulator and the second port of the fourth circulator; a fifth line coupling the third port of the first circulator and the third port of the fourth circulator; and a sixth line coupling the third port of the second circulator and the third port of the third circulator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a configuration of an optical cross coupler according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Embodiments of the present invention will be described herein below with reference to the accompanying drawings. For the purposes of clarity and simplicity, well-known functions or constructions are not described in detail as they would obscure the invention in unnecessary detail.  
       FIG. 1  is a configuration of an optical cross coupler  100  according to an embodiment of the present invention. As shown, the optical cross coupler  100  is configured for connecting more than two different optical communication networks to each other and includes first to fourth circulators  111 ,  112 ,  113 , and  114 , first to sixth optical lines  121 ,  122 ,  123 ,  124 ,  125 , and  126 , and first and second wavelength selectors  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b ,  134   a , and  134   b  disposed in the first to fourth lines  121 ,  122 ,  123 , and  124 .  
      Each of the first to fourth circulators  111 ,  112 ,  113 , and  114  includes first to fourth ports, wherein the first and second circulators  111  and  112  are located on a first network and the third and fourth circulators  113  and  114  are located on a second network. The first network transmits and receives a first optical signal, which is composed of first and third channels λ 1  and λ 3 , and a second optical signal, which is composed of second and fourth channels λ 2  and λ 4 , and the second network transmits and receives a third optical signal, which is composed of fifth and seventh channels λ 5  and λ 7 , and a fourth optical signal, which is composed of sixth and eighth channels λ 6  and λ 8 .  
      The second port of the first circulator  111  and the fourth port of the second circulator  112  are connected to each other by the first line  121  in which the first wavelength selectors  131   a  and  132   a  for respectively reflecting the first channel λ 1  and the fifth channel λ 5  are arranged in series. That is, the first optical signal input through the first port of the first circulator  111  is output through the second port of the first circulator  111 , and the first channel λ 1  of the first optical signal output through the second port of the first circulator  111  is reflected to the second port of the first circulator  111  by the first wavelength selector  131   a  and output through the third port of the first circulator  111 . The third port of the first circulator  111  is connected to the third port of the fourth circulator  114  by the fifth line  125 , thus, the first channel λ 1  is input to the fourth circulator  114 . The third channel λ 3  passes through the first wavelength selectors  131   a  and  132   a  located in the first line  121  and is output through the first port of the second circulator  112 .  
      The fourth port of the first circulator  111  and the second port of the second circulator  112  are connected to each other by the second line  122  in which the second wavelength selectors  133   a  and  134   a  for respectively reflecting the second channel λ 2  and the sixth channel λ 6  are arranged in series. That is, the second optical signal input through the first port of the second circulator  112  is output through the second port of the second circulator  112 , and the second channel λ 2  of the second optical signal output through the second port of the second circulator  112  is reflected to the second port of the second circulator  112  by the second wavelength selector  133   a  and output through the third port of the second circulator  112 . The third port of the second circulator  112  is connected to the third port of the third circulator  113  by the sixth line  126 , and thus, the second channel λ 2  is input to the third circulator  113 . The fourth channel λ 4  passes through the first wavelength selectors  133   a  and  134   a  located in the second line  122  and is output through the first port of the first circulator  111 .  
      The second port of the third circulator  113  and the fourth port of the fourth circulator  114  are connected to each other by the third line  123  in which the first wavelength selectors  131   b  and  132   b  for respectively reflecting the first channel λ 1  and the fifth channel λ 5  are arranged in series. The fourth port of the third circulator  113  and the second port of the fourth circulator  114  are connected to each other by the fourth line  124  in which the second wavelength selectors  133   b  and  134   b  for respectively reflecting the second channel λ 2  and the sixth channel λ 6  are arranged in series.  
      The third circulator  113  outputs the third optical signal, which is input through the first port, to the fourth circulator  114  through the third line  123 , and the fifth channel λ 5  of the output third optical signal is reflected to the second port of the third circulator  113  by the first wavelength selector  132   b . The fifth channel λ 5  reflected to the second port of the third circulator  113  is input to the third port of the second circulator  112  through the sixth line  126  and output through the fourth port of the second circulator  112 . The fifth channel λ 5  output through the fourth port of the second circulator  112  is reflected by the first wavelength selector  132   a  and output to the first network through the first port of the second circulator  112 . The second channel λ 2  input to the third port of the third circulator  113  through the sixth line  126  is output through the fourth port of the third circulator  113 , reflected by the second wavelength selector  133   b , and output to the second network through the first port of the third circulator  113 . The seventh channel λ 7  passes through the first wavelength selectors  131   b  and  132   b  located in the third line  123  and is output through the first port of the fourth circulator  114 .  
      The fourth circulator  114  outputs the fourth optical signal, which is input through the first port, to the third circulator  113  through the fourth line  124 , and the sixth channel λ 6  of the output fourth optical signal is reflected to the second port of the fourth circulator  114  by the second wavelength selector  134   b . The sixth channel λ 6  reflected to the second port of the fourth circulator  114  is input to the third port of the first circulator  111  through the fifth line  125  and output through the fourth port of the first circulator  111 . The sixth channel λ 6  output through the fourth port of the first circulator  111  is reflected to the fourth port of the first circulator  111  by the second wavelength selector  134   a  and output to the first network through the first port of the first circulator  111 . The eighth channel λ 8  passes through the second wavelength selectors  133   b  and  134   b  located in the fourth line  124  and is output through the first port of the third circulator  113 .  
      The fourth circulator  114  outputs the first channel λ 1 , which is input through the fifth line  125 , through the fourth port thereof. The first channel λ 1  output through the fourth port of the fourth circulator  114  is reflected to the fourth port of the fourth circulator  114  by the first wavelength selector  131   b  and output to the second network through the first port of the fourth circulator  114 .  
      The number of the first and second wavelength selectors  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b ,  134   a , and  134   b  can be more than two according to the number of channels to be crossed to another network and be variously arranged according to wavelengths of the channels to be crossed. Bragg gratings can be used for the first and second wavelength selectors  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b ,  134   a , and  134   b . That is, the first wavelength selectors  131   a ,  131   b ,  132   a , and  132   b  and the second wavelength selectors  133   a ,  133   b ,  134   a , and  134   b  can be implemented by connecting at least two Bragg gratings, which can selectively reflect light having different wavelengths, in series in each line.  
      However, as in the embodiment of the present invention, the arrangement of the wavelength selectors  131   a ,  131   b ,  132   a ,  132   b ,  133   a ,  133   b ,  134   a , and  134   b  can be implemented by configuring the first wavelength selectors  131   a ,  131   b ,  132   a , and  132   b  located in the first and third lines  121  and  123  to reflect channels having the same wavelengths and configuring the second wavelength selectors  133   a ,  133   b ,  134   a , and  134   b  to reflect channels having the same wavelengths.  
      As described above, according to the embodiment of the present invention, an optical cross coupler can cross-connect a plurality of channels to different networks while minimizing the number of optical components. Thus, effective network cross coupling can be achieved with low cost.  
      While the invention has been shown and described with reference to a certain preferred embodiment 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.