Dispersion-compensating module

Abstract

The present invention relates to a dispersion-compensating module having a structure which compensates for the dispersion of an optical transmission line in a 1.55-μm wavelength band and adjusts loss fluctuations among signal wavelengths in the 1.55-μm wavelength band into an appropriate range. The dispersion-compensating module comprises a structure adapted to be installed in an already installed optical fiber transmission line, and has a loss slope with a polarity opposite to that of the optical fiber transmission line in the 1.55-μm wavelength band. One application of the dispersion-compensating module comprises a dispersion-compensating optical fiber as a dispersion-compensating device, and an optical fiber doped with a transition metal element as a loss-equalizing device. By the above configuration, the loss fluctuations among individual signal wavelengths in the whole transmission line including the dispersion-compensating module can be adjusted by the loss-equalizing device in the dispersion-compensating module so as to fall within an appropriate range.

What is claimed is:  
     
         1 . A dispersion-compensating module to be installed at a predetermined position on an optical transmission line having a predetermined length, said dispersion-compensating module having a positive loss slope in a 1.55 μm wavelength band and constituting a part of said optical transmission line, said dispersion-compensating module comprising: 
 a dispersion-compensating device for compensating for the dispersion of said optical transmission line in the 1.55-μm wavelength band; and  
 a loss-equalizing device for adjusting the total loss slope of said optical transmission line including said dispersion-compensating module such that a loss deviation between individual signal wavelengths in the 1.55-μm wavelength band caused by propagation in said optical transmission line and dispersion-compensating device falls within an appropriate range.  
 
     
     
         2 . A dispersion-compensating module according to  claim 1 , wherein said optical transmission line is a single-mode optical fiber having a zero-dispersion wavelength in a 1.3-μm wavelength band, and 
 wherein the loss slope (dB/m) of said loss-equalizing device is set such that the total loss slope (dB/m) of said dispersion-compensating module becomes greater than 0 but not greater than 0.000175×L+α where L is the length of said single-mode optical fiber, and a is the absolute value of a permissible manufacturing error.  
 
     
     
         3 . A dispersion-compensating module according to  claim 1 , wherein said loss-equalizing device includes an optical fiber comprising a core region doped with a transition metal element, and a cladding region disposed at an outer periphery of said core region; said optical fiber securing a single mode in the 1.55-μm wavelength band.  
     
     
         4 . A dispersion-compensating module according to  claim 1 , wherein said loss-equalizing device includes an optical fiber formed with a long-period grating in which a propagation mode and a radiation mode are coupled to each other.  
     
     
         5 . A dispersion-compensating module according to  claim 1 , wherein said dispersion-compensating device has, as said loss-equalizing device, a long-period grating in which a propagation mode and a radiation mode are coupled to each other.  
     
     
         6 . A dispersion-compensating module according to  claim 1 , wherein said loss-equalizing device includes a fused portion obtained by fusion-splicing respective end portions of a pair of optical fibers.  
     
     
         7 . A dispersion-compensating module according to  claim 6 , wherein respective optical axes of said pair of optical fibers are shifted from each other in said fused portion.  
     
     
         8 . A dispersion-compensating module according to  claim 6 , wherein respective core regions of said pair of optical fibers are bent in said fused portion.  
     
     
         9 . A dispersion-compensating module according to  claim 6 , wherein said pair of optical fibers have respective core regions each having an outside diameter expanding toward said fused portion.  
     
     
         10 . A dispersion-compensating module according to  claim 1 , wherein said loss-equalizing device includes a fiber coupler.  
     
     
         11 . A dispersion-compensating module according to  claim 1 , wherein said loss-equalizing device includes an optical fiber bent at one or more parts thereof.