Patent Publication Number: US-2005141894-A1

Title: Bi-directional add/drop node

Description:
CLAIM OF PRIORITY  
      This application claims priority, pursuant to 35 U.S.C. §119, to that patent application entitled “Bi-directional Add/Drop Node,” filed with the Korean Intellectual Property Office on Dec. 24, 2003 and assigned Serial No. 2003-96661, the contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical communication system, and, in particular, to a bi-directional path-switching network.  
      2. Description of the Related Art  
      Wavelength division multiplexing ring networks can be classified as uni-directional or bi-directional ring networks depending on the direction(s) of traffic transmission. They can further be classified as line-switching ring structures or path-switching ring structures depending on the performance of self-healing modes as a predetermined section of an optical fiber is impaired.  
      A conventional bi-directional path-switching network includes a plurality of nodes connected in a loop formed by a single optical fiber. The conventional bi-directional path-switching network has a simpler structure and a shorter switching time for protection, when compared to other optical network systems. However, in such a bi-directional path-switching network it is necessary to consider an occurrence of signal disturbance or noise caused, for example, by a reflected wave produced by a line problem at the time of bi-directional transmission of respective channels or optical signals.  
       FIG. 1  shows the arrangement of a conventional node  100  according to the prior art in which a plurality of such nodes when joined together, by the optical fiber, the ends of which are shown as fiber  1 ,  101  and fiber  2 ,  102 , forms a bi-directional path-switching network. As shown, conventional node  100  includes a 2×2 interleaver  110 , a waveguide  130  connected to two ports of interleaver  110  in a loop form, and an optical amplifier  120  positioned in the waveguide  130 .  
      Interleaver  110 , as shown, includes four ports referred to as  110 . 1 ,  110 . 2 ,  110 . 3  and  110 . 4 . Among channels inputted from first optical fiber  101  connected to the first port  110 . 1  of the interleaver  110 , odd channels are outputted through the fourth port  110 . 4 , which is positioned diametrically opposite to the first port  110 . 1 . Also, among channels inputted from a second optical fiber  102  connected to the second port  110 . 2 , even channels are outputted through the fourth port  110 . 4 . Thus, interleaver  110  is operable, in this example, to output odd or even channels received from first port  110 . 1  or second port  110 . 2 , respectively, to the waveguide  130  through the fourth port  110 . 4 .  
      Waveguide  130  interconnects the fourth port  110 . 4  and the third port  110 . 3  of the interleaver  110 , thus forming a circulation loop for circulating the odd and even channels inputted from the fourth port  110 . 4  to the third port  110 . 3 . Optical amplifier  120  is positioned in the waveguide  130  and thus, amplifies the odd and even channels circulating through waveguide  130 .  
      The interleaver  110 , outputs from among the odd and even channels received at third port  110 . 3 , odd channels to the second optical fiber  102  through the second port  110 . 2  and the even channels to the first optical fiber  101  through the first port  110 . 1 . In this case first port  110 . 1  is in line with third port  110 . 3  and second port  110 . 2  is diametrically opposite third port  110 . 3 .  
      However, the conventional bi-directional path-switching network has a problem in that when a problem or disturbance is produced or created on an optical fiber line linking a plurality of nodes, a considerable loss in intensity or signal strength of individual channels may occur. Alternatively, a considerable amount of noise may be produced which is reflected to adjacent nodes. Furthermore, it maybe impossible to recognize a problem occurring in the conventional bidirectional path-switching network, and the possible problem in the conventional bi-directional path-switching network may enlarge losses in channel signal strength or increase channel noise.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to provide an add/drop node that can determine whether a problem or disturbance is produced on an optical fiber line by monitoring intensity of input and output channels.  
      In order to accomplish this object, there is provided a bi-directional add/drop node employed in a bi-directional path-switching network including a plurality of bi-directional add/drop nodes linked by an optical fiber in a loop form, the bi-directional add/drop node having a first terminal point and a second terminal point, in which odd channels of channels inputted through the first terminal point are outputted through the second terminal point and even channels of channels inputted through the second terminal point are outputted through the first terminal point, the bi-directional add/drop node comprising a circulation section for circulating even and odd channels in a known direction; a first input-output section located between the circulation section and the first terminal point, for providing the odd channels inputted from the first terminal point to the circulation section through a first input line and providing the even channels inputted from the circulation section to the first terminal point through a first output line, and a second input-output section positioned between the circulation section and the second terminal point for providing the even channels inputted from the second terminal point to the circulation section through a second input line and providing the odd channels inputted from the circulation section to the second terminal point through a second output line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      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:  
       FIG. 1  illustrates a conventional bi-directional add/drop node;  
       FIG. 2  illustrates an exemplary a bidirectional add/drop node according to a first embodiment of the present invention;  
       FIG. 3  illustrates an exemplary bi-directional add/drop node according to a second embodiment of the present invention; and  
       FIG. 4  illustrates an exemplary bidirectional add/drop node according to a third embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Hereinafter, embodiments of 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 make the subject matter of the present invention unclear.  
       FIG. 2  illustrates an exemplary arrangement of a bi-directional add/drop node according to a first embodiment of the present invention. As shown, the add/drop node  200  comprises a circulation section  230  for circulating the odd channels inputted into a first terminal point  201  from fiber  101  and even channels inputted into a second terminal point  202  from fiber  102 , in a predetermined direction, e.g., clockwise, a first input-output section  210  positioned between the circulation section  230  and the first terminal point  201 , and a second input-output section  220  positioned between the circulation section  230  and the second terminal point  202 . In addition, the first and second terminal points  201 ,  202  of the bi-directional add/drop node  200  are linked with one another through other bi-directional add/drop nodes and optical fibers, thus, the odd channels inputted into the first terminal point  201  are outputted to the second terminal point  202  and the even channels inputted into the second terminal point  202  are outputted to the first terminal point  201  as will now be explained in further detail.  
      The first input-output section  210  includes first circulator  213  and a first interleaver  214  and is positioned between the circulation section  230  and the first terminal point  201  so that the odd channels inputted through the first terminal point  201  are outputted to the circulation section  230  through a first input path  211  and the even channels inputted from the circulation section  230  are outputted to the first terminal point  201  through first output path  212 .  
      The first circulator  213  inputs the odd channels, among the channels inputted through the first terminal point  201 , into the first port  214 . 1  of first interleaver  214  through the first input path  211  and outputs the even channels inputted from the first output path  212  to the first terminal point  201 .  
      The first interleaver  214  outputs the odd channels inputted from the first input path  211  to circulation section  230  via third port  214 . 3  and outputs at first port  214 . 1  the even channels inputted from the circulation section  230  at third port  214 . 3  to first output path  212 .  
      The second input-output section  220  includes a second circulator  223  and a second interleaver  224  and is positioned between circulation section  230  and second terminal point  202 , so that even channels received from second terminal point  202  are provided to circulation section  230  through second input path  221  and the odd channels received from circulation section  230  are outputted to the second terminal point  202  of through a second output path  222 .  
      The second input path  221  inputs only the even channels into the second interleaver  221  and the second output path  222  receives only the odd channels from second circulator  223 .  
      The first and second input paths  211 ,  221  and the first and second output paths  212 ,  222  may employ a flat optical waveguide or an optical fiber, in which the first input path  211  is provided with a first tap  21  la for monitoring intensity or signal strength of the odd channels and the second input path  221  is provided with a second tap  221   a  for monitoring the intensity or signal strength of the even channels. Thus, first tap  211   a  may determine the presences of an abnormality in an optical fiber line linked to the first terminal point  201   200  by monitoring the intensity of individual or accumulated odd channels inputted into the first input path  211 , and the second tap  221   a  may determine the presences of an abnormality in an optical fiber line linked to the second terminal point  202  by monitoring the intensity of individual or accumulated even channels inputted into the second input path  221 . In one aspect of the invention, an abnormality may be determined when one or more individual channel intensities or the intensities of accumulated channels are outside predetermined limits or tolerances. In another aspect an abnormality may be determined when a change of intensity exceeds or falls outside predetermined tolerance limits from one sample to another. In another aspect, taps  211   a,    221   a  may monitor signal intensity over a predetermined period of time and may determine an abnormality by changes of intensity from one period or sample, to another period or sample or over several periods.  
      The second circulator  223  outputs the even channels, among the channels inputted from the second terminal point  202  to second input path  221  and outputs the odd channels inputted from the second output path  222  to the second terminal point  202 .  
      The second interleaver  224  provides the even channels received from the second input path  221  at port  224 . 1  to circulation section  230  and outputs the odd channels received from circulation section  230  at port  224 . 3  to second output path  222 , via port  224 . 2 .  
      Circulation section  230  comprises waveguide  234  for circulating the odd and even channels, in a predetermined direction, e.g., as shown, clockwise, a third interleaver  231 , an optical amplifier  233 , and an add/drop multiplexer  232 . Circulation section  230  circulates the odd channels inputted into the first terminal point  201  and the even channels inputted into the second terminal point  202 , in the predetermined clockwise direction and then outputs the odd channels to the second input-output section  220  and the even channels to first input-output section  210 . As one skilled in the art would recognize, waveguide  234  may be an optical waveguide or an optical fiber.  
      The third interleaver  231  provides the even channels and odd channels inputted from the first and second input-output sections  210 ,  220  to the waveguide  234  and outputs the even channels to the first input-output section  210  and the odd channels to the second input-output section  220 .  
      The optical amplifier  233  amplifies the odd and even channels inputted through the waveguide  234  and then provides the amplified signals to the add/drop multiplexer  232 . Add/Drop multiplexer  232  is well-known in the WDM art to remove, i.e., drop, or add predetermined channels or wavelengths to a WDM signal and need not be discussed in detail herein. The WDM signal, including any signals that have been added, is then provided to port  231 . 3  of third interleaver  231  through waveguide  234 .  
      Each of the first to third interleavers  214 ,  224 ,  231  comprises four port, in which the odd channels inputted into each interleaver are outputted through a port positioned diametrically opposite to the port through which the odd channels have been inputted, and the even channels are outputted through a port positioned in line with the port through which the even channels have been inputted. The interleavers of the embodiments to be described later perform the same operations as those described above for the even and odd channels.  
      For example, the even channels inputted into the port  214 . 2  of the first interleaver  214  are outputted to the first port  231 . 1  of the third interleaver  231  through the third port  214 . 2 , which is positioned diametrically opposite to the second port  214 . 2  of the first interleaver  214 . Similarly, the even channels inputted into the third port  231 . 3  of third interleaver  231  are provided to the third port  214 . 3  of first interleaver  214  through first port  231 . 1 , which is positioned in line with the third port  231 . 3  of third interleaver  231 .  
      Although circulator section  230  is shown containing Add/Drop multiplexer  232 , it would be recognized by those skilled in the art that Add/Drop multiplexer  232  is not essential to the operation of the present invention and can be removed without altering the scope of the invention. In such case, circulator section  230  would operate in a manner similar to circulator  130  shown in  FIG. 1 .  
       FIG. 3  shows an arrangement of a bi-directional add/drop node according to a second embodiment of the present invention. As shown, the bi-directional add/drop node  300  comprises circulation section  330  for circulating odd channels inputted through first terminal point  301  and even channels inputted through second terminal point  302 , in a predetermined direction, a first input-output section  310  positioned between circulation section  330  and first terminal point  301 , and second input-output section  320  positioned between circulation section  330  and second terminal point  302 . In addition, similar to the embodiment shown in  FIG. 2 , first and second terminal points  301 ,  302  are in communication through bidirectional add/drop nodes and optical fibers to enable bi-directional add/drop node  300  to, in this exemplary embodiment, output odd channels inputted into the first terminal point  301  through the second terminal point  302  and output even channels inputted into the second terminal point through the first terminal point  301 .  
      The first input-output section  310  includes a first circulator  313  and a first interleaver  314 , which are positioned between circulation section  330  and first terminal point  301  so that odd channels inputted through the first terminal point  301  are provided to circulation section  330  at first node  331 . 1  through first input path  311  and even channels received from circulation section  330  are provided to first terminal point  301  through first output path  312 .  
      First interleaver  313  is positioned between the first terminal point  301  of the add/drop node  300  and the first circulator  314  so that the odd channels inputted from the first terminal point  301  are provided to first circulator  314  through first input path  311  and odd channels inputted from the first circulator  314  through the first input path  312  are outputted to the first terminal point  301 .  
      The first circulator  314  is positioned between first circulation section  330  and first interleaver  313 , whereby the even channels  330  inputted from the circulation section  330  are outputted to the first interleaver  313  through first output path and odd channels inputted from the first interleaver  313  through the first input path are outputted to the circulation section  330 .  
      Second input-output section  320  includes a second circulator  324  and second interleaver  323  and is positioned between circulation section  330  and second terminal point  302 . Thus, second input-output section  320  outputs even channel inputted through the second terminal point  302  to circulation section  330  and outputs odd channels inputted from the circulation section  330  to the second terminal point  302 .  
      Second interleaver  323  is positioned between second circulator  324  and second terminal point  302  so that along with the second circulator  324 , second interleaver  323  forms a second input path  321  for inputting even channels to the circulation section  330  and second output path  322  for outputting odd channels inputted from the circulation section  330  to the second terminal point  302 .  
      The first input path  311  and the second input path  321  are provided with a first tap  311   a  and a second tap  321   a,  respectively, for determining whether odd channels and even channels pass forward and are thus operable for monitoring the presence of abnormality on optical fiber lines linked to the first and second terminal points  301 ,  302 . First and second taps  311   a  and  321   a  operate to determine abnormalities by monitoring signal intensities as previously described and need not be discussed in detail again.  
      The circulation section  300  comprises a waveguide  334  for circulating the odd and even channels clockwise, a third interleaver  331 , an optical amplifier  333 , and an add/drop multiplexer  332  and operates in a manner similar to that discussed with regard to  FIG. 2  and need not be discussed in detail again.  
       FIG. 4  shows an exemplary arrangement of a bidirectional add/drop node according to a third embodiment of the present invention. As shown, the bi-directional add/drop node  400  according to the third embodiment of the present invention comprises a circulation section  430 , and a plurality of input-output sections  410 ,  420 , wherein the bi-directional add/drop node  400  is linked to the first and second terminal points  401 ,  403  through an optical fiber, so that the odd channels inputted into the first terminal point  401  are outputted to the second terminal point  402  and the even channels inputted into the second terminal point  402  are outputted to the first terminal point  401 .  
      The input-output sections  410 ,  420  comprises respective first and second input-output sections  410 ,  420  wherein the first input-output section  410  is positioned between the first terminal point  401  so that the odd channels inputted through the first terminal point  401  are outputted to the second input-output section  420 . Similarly, the second input-output section  420  is positioned between the circulation section  430  and the second terminal point  402  so that the odd channels inputted from first input-output section  410  and even channels inputted through second terminal point  402  are inputted into circulation section  430 .  
      The first input-output section  410  comprises a first interleaver  413 , third interleaver  414 , and first tap  411   a.  Third port  413 . 3  of first interleaver  413  and first port  414 . 1  of third interleaver  414  are connected to one another and form a first output path  412 . In addition, a fourth port  413 . 4  of first interleaver  413  forms a first input path  411  connected to the fourth port  423 . 4  of interleaver  423  of the second input-output section  420 .  
      Interleaver  413  outputs odd channels inputted into the first port  413 . 1  connected to the first terminal point  401  to the first input path  411  through the fourth port  413 . 4  positioned diametrically opposite to first port  413 . 1 , and outputs even channels inputted from circulation section  430  through the first output path  412  to the first terminal point  401  through first port  413 . 1 .  
      Among even and odd channels inputted received from circulation section  430 , third interleaver  414  outputs the even channels to the first port connected to the first output path  412 , and the odd channels to the second output path  422  through the second port  414 . 2  of the third interleaver  414 .  
      The first tap  411 a is positioned in the first input path  411  and determines the presence of abnormality of an optical fiber line linked to the first terminal point  401  of by monitoring the intensity or change of intensity of the odd channels progressing in the first input path  411 , which has been described with regard to  FIG. 2 .  
      The second input-output section  420  comprises a second interleaver  423 , a fourth interleaver  424 , and a second tap  421   a,  and a third port  423 . 3  of the second interleaver  423  and a first port  424 . 1  of the fourth interleaver  424  are connected to each other, thereby forming a second input path  421 . In addition, a fourth port  424 . 4  of the second interleaver  424  forms a second output path  422  connected to the second port  414 . 2  of the third interleaver  414 .  
      In this case, second interleaver  423  outputs even channels inputted into the first port  423 . 1  connected to the second terminal point  421  to the second input path  421  through the third port  423 . 3  positioned in line with the first port  423 . 1 , and outputs the odd channels inputted through the second output path  422  connected to the first input-output section  410  to the second terminal point  402  through the first port  423 . 1 .  
      The fourth interleaver  424  outputs odd channels inputted through the first input path  411 , at port  424 . 2  connected to the first input-output section  410 , i.e., at port  413 . 4 , and outputs even channels inputted from the first port through the first port connected to the second input path  421  to the circulation section  430  through the third port  424 . 3  connected to circulation section  430 .  
      The circulation section  430  comprises a waveguide  433  for interconnecting the third port  424 . 3  of fourth interleaver  424  and the third port  414 . 3  of third interleaver  414 , an optical amplifier  432 , and an add/drop multiplexer  431 , in which the optical amplifier  432  and the add/drop multiplexer  431  are serially connected in the waveguide  433 .  
      The waveguide  433  circulates odd and add channels inputted from the third port  424 . 3  of fourth interleaver  424  and outputs them to the third port  414 . 3  of third interleaver  414 .  
      Amplifier  432  and Add/drop mulitplexer  431  operate as previously described and need not be discussed again. Similarly, taps  411   a  and  421   a  operate a previously described and need not be discussed again.  
      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. For example, the invention has been described with regard to a clockwise progression of odd and even channels of WDM signals. However, it would be with the ability of those skilled in the art to modify the components discussed to provide for counter-clockwise progression of the channels. Furthermore, while the channels are referred to herein as odd and even, one skilled in the art would understand that this reference is made to distinguish channels that are progressing in one direction or the other and not necessarily to a characteristic of the channel or the wavelength. For example, the term “odd channels” is not to be considered to be limited to channels having wavelengths or reference numbers that end in an odd number or “even channels” is not be considered to be limited to channels having wavelengths or reference numbers the end in an even number. Furthermore, the terms “odd” and “even” are not be construed to refer channels that alternate with one another. Hence, the terms “odd channels” and “even channels” may refer to a plurality of adjacent channels or wavelengths. Thus the terms odd and even are merely used to identify one group of channels that are progressing through the network in one direction and another group of channels that are progressing through the network in another direction. Accordingly, the scope of the invention is not to be limited by the above embodiments but by the claims and the equivalents thereof.