Optical transmission system having an optical surge suppression function

Abstract

An optical transmission system having an optical surge suppression function comprises operable/auxiliary transmission lines, optical ADM nodes, a regenerative repeating node and optical amplifiers arranged on the operable/auxiliary transmission lines, for amplifying signal light. Each of the ADM nodes comprises an optical demultiplexing/inserting unit for demultiplexing specific signal light from signal light transmitted from the operable or auxiliary transmission lines and inserting specific signal light, and a transmission line switching unit for switching the optical path. The regenerative repeating node comprises optical receiving units for receiving signal light transmitted over the operable or auxiliary transmission lines and optical transmitting units for transmitting signal light by regenerative repeating. The regenerative repeating unit comprises a dummy light output unit for outputting dummy light to the optical transmitting units. A transmission line clock is transmitted to an optical transmitting unit connected to a transmission line in operation out of the operable/auxiliary transmission lines. Light is transmitted in synchronism with a self-oscillating clock from an optical transmitting unit connected to a transmission line out of operation. The dummy light output unit outputs dummy light as a false signal or a continuous signal having a frequency different from the frequency of the transmission clock. Light is always transmitted to the operable/auxiliary transmission lines by carrying out transmission from an optical transmitting unit connected to a transmission line out of operation in synchronism with the self-oscillating clock. Therefore, light is always input into the optical direct amplifiers arranged between the respective nodes. As a result, the occurrence of an optical surge in the optical amplifiers of the optical transmission system is suppressed at the time of switching between the operable/auxiliary transmission lines.

What is claimed is:  
     
         1 . An optical transmission system having an optical surge suppression function comprising: 
 optical amplifiers for amplifying input signal light directly; and    dummy light output means for inputting dummy light different from the signal light into said optical amplifiers.    
     
     
         2 . An optical transmission system having an optical surge suppression function according to    claim 1   , wherein 
 each of said optical amplifiers comprises:    a rare earth element doped optical fiber for amplifying input signal light to output the amplified signal light;    a pumping light source for outputting pumping light;    a first optical wavelength multiplexer for inputting the pumping light to said rare earth element doped optical fiber;    an optical branching device for branching part of the amplified signal light to output the branched signal light; and    pumping light control means for controlling the output of the pumping light based on the output level of the branched light.    
     
     
         3 . An optical transmission system having an optical surge suppression function according to    claim 2   , wherein 
 said dummy light output means comprises:    a dummy light output source for outputting dummy light; and    a second optical wavelength multiplexer for inputting the dummy light into said rare earth element doped optical fiber.    
     
     
         4 . An optical transmission system having an optical surge suppression function according to    claim 3   , wherein 
 the dummy light signal includes a self-oscillating clock.    
     
     
         5 . An optical transmission system having an optical surge suppression function according to    claim 3   , wherein 
 said dummy light output means further comprises:    input light identifying means for identifying whether the input light is dummy light or not; and    clock control means for including a self-oscillating clock in dummy light output from said dummy light output means when the input light is dummy light and for not including a self-oscillating clock in dummy light output from said dummy light output means when the input light is not dummy light.    
     
     
         6 . An optical transmission system having an optical surge suppression function comprising: 
 optical transmission lines including operable transmission lines and auxiliary transmission lines;    ADM nodes, each comprising transmission line switching means for switching optical path between the operable transmission lines and the auxiliary transmission lines;    a regenerative repeating node comprising optical receiving units for receiving signal light transmitted through the operable transmission lines or the auxiliary transmission lines and optical transmitting units for transmitting the signal light by regenerative repeating; and    optical amplifiers, arranged on both the operable transmission lines and the auxiliary transmission lines, for amplifying the signal light, wherein    each of said optical transmitting units comprises dummy light output means for outputting dummy light.    
     
     
         7 . An optical transmission system having an optical surge suppression function according to    claim 6   , wherein 
 said ADM node further comprises optical demultiplexing/inserting means for demultiplexing specific signal light from signal light transmitted through the operable transmission lines or the auxiliary transmission lines and inserting specific signal light.    
     
     
         8 . An optical transmission system having an optical surge suppression function according to    claim 6   , wherein 
 said regenerative repeating node comprises self-oscillating clock sources for transmitting a transmission line clock to an optical transmitting unit connected to a transmission line in operation out of the operable transmission lines or the auxiliary transmission lines and for transmitting dummy light to an optical transmitting unit connected to a transmission line out of operation in synchronism with a self-oscillating clock out of the operable transmission lines or the auxiliary transmission lines.    
     
     
         9 . An optical transmission system having an optical surge suppression function according to    claim 6   , wherein 
 said regenerative repeating node comprises:    input break identifying means for identifying an input break of the signal light input from the operable transmission lines or the auxiliary transmission lines; and    a clock control unit for controlling the switching of a clock so that the signal light is synchronized with a transmission line clock extracted from main signal light when the signal light is identified as the main signal light and with a self-oscillating clock source when the signal light is identified as the dummy light.    
     
     
         10 . An optical transmission system having an optical surge suppression function according to    claim 6   , wherein 
 said optical transmission system having an optical surge suppression function further comprises a center node for transmitting a plurality of signal light having different wavelengths to the operable transmission lines or the auxiliary transmission lines and receiving signal light from the operable transmission lines or the auxiliary transmission lines, and    said optical demultiplexing/inserting means comprises:    a wavelength demultiplexing unit for extracting and demultiplexing signal light having a desired wavelength out of the wavelengths; and    a wavelength multiplexing unit for multiplexing the wavelength of signal light transmitted from said ADM node.    
     
     
         11 . An optical transmission system having an optical surge suppression function according to    claim 10   , wherein 
 said center node, said ADM nodes and said regenerative repeating node are interconnected by said transmission lines in the configuration of a ring.    
     
     
         12 . An optical transmission system having an optical surge suppression function according to    claim 10   , wherein said dummy light output means outputs the dummy light as a false signal having a frequency different from the frequency of the transmission line clock.  
     
     
         13 . An optical transmission system having an optical surge suppression function according to    claim 10   , wherein said dummy light output means outputs the dummy light as a continuous light.  
     
     
         14 . An optical transmission system having an optical surge suppression function comprising: 
 WDM terminal equipment comprising optical transmitting units for transmitting a plurality of signal light having different wavelengths and optical receiving units for receiving a plurality of signal light having different wavelengths;    a plurality of nodes, connected to said WDM terminal equipment through a plurality of transmission lines, for switching the optical path of the signal light having an arbitrary wavelength out of the wavelengths of the signal light input from input ports; and    optical amplifiers arranged between said respective nodes, for amplifying the signal light, wherein    each of said nodes comprises dummy light output means for outputting dummy light to transmit the output dummy light to the transmission lines.    
     
     
         15 . An optical transmission system having an optical surge suppression function according to    claim 14   , wherein 
 each of said nodes comprises a wavelength demultiplexing unit for demultiplexing signal light having a specific wavelength out of the wavelengths of the input signal light and a regenerative repeating unit for carrying out the regenerative repeating of signal light separated by said wavelength demultiplexing unit, and    the dummy light is transmitted to a transmission line between unused nodes at said regenerative repeating unit connected to an unused input port.    
     
     
         16 . An optical transmission system having an optical surge suppression function according to    claim 14   , wherein 
 said dummy light output means outputs the dummy light as a false signal having a frequency different from the frequency of the transmission line clock.    
     
     
         17 . An optical transmission system having an optical surge suppression function according to    claim 16   , wherein 
 said dummy light output means outputs the dummy light as a continuous signal.