Connection structure for dispersion compensating optical fiber

Abstract

In fusion-splicing a dispersion compensating optical fiber having a negative dispersion slope, with a connection optical fiber having a different near field pattern from that of the dispersion compensating optical fiber, if for the connection optical fiber, one is selected such that a theoretical joint loss in a used wavelength, obtained from an overlap integral of a near field pattern of the dispersion compensating optical fiber after fusion splicing and a near field pattern of the connection optical fiber after fusion splicing is presumed to be 0.3 dB or less, in an unconnected state, a construction enabling connection at a low loss results.

What is claimed is:  
     
         1 . A connection structure for a dispersion compensating optical fiber obtained by fusion-splicing a dispersion compensating optical fiber having a negative dispersion slope with a connection optical fiber having a different near field pattern from that of the dispersion compensating optical fiber, wherein said connection optical fiber has a near field pattern such that a theoretical joint loss in a used wavelength obtained from an overlap integral of a near field pattern of said dispersion compensating optical fiber after fusion splicing and a near field pattern of said connection optical fiber after fusion splicing is 0.3 dB or less, in an unconnected state.  
     
     
         2 . A connection structure for a dispersion compensating optical fiber according to  claim 1 , wherein an effective core area of said connection optical fiber in the unconnected state is larger than that of said dispersion compensating optical fiber in the unconnected state.  
     
     
         3 . A connection structure for a dispersion compensating optical fiber according to  claim 1 , wherein an expansion rate of an effective core area due to heating of said connection optical fiber is smaller than that of an effective core area due to heating of said dispersion compensating optical fiber.  
     
     
         4 . A connection structure for a dispersion compensating optical fiber according to  claim 1 , wherein said dispersion compensating optical fiber is connected to one end of said connection optical fiber, and an other end of said connection optical fiber is connected to a single mode optical fiber having a positive dispersion slope which is compensated by said dispersion compensating optical fiber.  
     
     
         5 . A connection structure for a dispersion compensating optical fiber according to  claim 4 , wherein when an effective core area of said dispersion compensating optical fiber in the unconnected state is designated as A, an effective core area of said connection optical fiber in the unconnected state is designated as B, and an effective core area of said single mode optical fiber in the unconnected state is designated as C, a relation thereof is A<B<C.  
     
     
         6 . A connection structure for a dispersion compensating optical fiber according to  claim 4 , wherein when an expansion rate of an effective core area due to heating of said dispersion compensating optical fiber is designated as D, an expansion rate of an effective core area due to heating of said connection optical fiber is designated as E, and an expansion rate of an effective core area due to heating of said single mode optical fiber is designated as F, a relation thereof is F<E<D.  
     
     
         7 . A connection structure for a dispersion compensating optical fiber according to  claim 4 , wherein an effective core area in a used wavelength of said single mode optical fiber is from 100 to 150 μm 2 .  
     
     
         8 . A connection structure for a dispersion compensating optical fiber according to  claim 4 , wherein an effective core area in a used wavelength of said single mode optical fiber is from 55 to 90 μm 2 .  
     
     
         9 . A connection structure for a dispersion compensating optical fiber according to  claim 1 , wherein said connection optical fiber comprises a core and a cladding provided on a circumference of said core, and fluorine is added to said cladding.  
     
     
         10 . A connection structure for a dispersion compensating optical fiber according to  claim 9 , wherein the addition of the fluorine is at least 0.6% by weight.  
     
     
         11 . A connection structure for a dispersion compensating optical fiber according to  claim 9 , wherein said cladding comprises at least two layers, and an outermost layer of said cladding comprises pure silica.  
     
     
         12 . A connection structure for a dispersion compensating optical fiber according to  claim 1 , wherein said dispersion compensating optical fiber comprises a center core, a side core provided on a circumference of said center core, and a cladding provided on a circumference of said side core, and wherein a refractive index of said center core is higher than that of said cladding, and a refractive index of said side core is lower than that of said cladding.  
     
     
         13 . A connection structure for a dispersion compensating optical fiber according to  claim 12 , wherein an effective core area in a used wavelength of said dispersion compensating optical fiber is 16 μm 2  or larger.  
     
     
         14 . A connection structure for a dispersion compensating optical fiber according to  claim 1 , wherein said dispersion compensating optical fiber comprises a center core, a side core provided on a circumference of said center core, a ring core provided on a circumference of said side core, and a cladding provided on a circumference of said ring core, and wherein a refractive index of said center core and said ring core is respectively higher than that of said cladding, and a refractive index of said side core is lower than that of said cladding.  
     
     
         15 . A connection structure for a dispersion compensating optical fiber according to  claim 14 , wherein an effective core area in a used wavelength of said dispersion compensating optical fiber is 18 μm 2  or larger.  
     
     
         16 . A connection structure for a dispersion compensating optical fiber according to  claim 15 , wherein said dispersion compensating optical fiber has characteristics shown in the following (a-1) to (d-1): 
 (a-1) a chromatic dispersion value in the used wavelength is from −60 to −45 ps/nm/km;    (b-1) a dispersion slope in the used wavelength is from −0.180 to −0.135 ps/nm 2 /km;    (c-1) the effective core area in the used wavelength is from 20 to 26 μm 2 ; and    (d-1) a transmission loss in the used wavelength is 0.35 dB/km or less.    
     
     
         17 . A connection structure for a dispersion compensating optical fiber according to  claim 15 , wherein said dispersion compensating optical fiber has characteristics shown in the following (a-2) to (d-2): 
 (a-2) a chromatic dispersion value in the used wavelength is from −100 to −80 ps/nm/km;    (b-2) a dispersion slope in the used wavelength is from −0.300 to −0.230 ps/nm 2 /km;    (c-2) the effective core area in the used wavelength is from 18 to 24 μm 2 ; and    (d-2) a transmission loss in the used wavelength is 0.40 dB/km or less.    
     
     
         18 . A connection structure for a dispersion compensating optical fiber according to  claim 15 , wherein said dispersion compensating optical fiber has characteristics shown in the following (a-3) to (d-3): 
 (a-3) a chromatic dispersion value in the used wavelength is from −45 to −35 ps/nm/km;    (b-3) a dispersion slope in the used wavelength is from −0.150 to −0.100 ps/nm 2 /km;    (c-3) the effective core area in the used wavelength is from 26 to 35 μm 2 ; and    (d-3) a transmission loss in the used wavelength is 0.25 dB/km or less.    
     
     
         19 . A transmission line having a connection structure for a dispersion compensating optical fiber as disclosed in any one of  claim 1  through  claim 18 .  
     
     
         20 . A dispersion compensator having a connection structure for a dispersion compensating optical fiber as disclosed in any one of  claim 1  through  claim 18 .  
     
     
         21 . A connection method for a dispersion compensating optical fiber for obtaining a connection structure for a dispersion compensating optical fiber as disclosed in any one of  claim 1  through claim  18 .