Optical fiber and optical transmission line and optical communication system including such optical fiber

Abstract

Optical fibers to form an optical transmission line suitable for WDM transmission in a wide-spreading wavelength band, having the following characteristics and parameters: a dispersion in absolute value of 0.5 ps/nm/km to 9 ps/nm/km in a wavelength band of 1430 nm to 1625 nm, a dispersion slope in absolute value of 0.04 ps/nm 2 /km or less at a wavelength of 1550 nm, a mode field diameter of 7 μm or less at a wavelength of 1550 nm and a cable cutoff wavelength of less than 1430nm; core 11 surrounded by cladding 7, core 11 being at least two-layered (first layer 1 at the center and second layer 2 surrounding the first layer; relative refractive index of glass layer Δ 1 with reference to the cladding being adjusted to not less than 0.6 but not more than 1.6%, relative refractive index of second layer Δ 2 with reference to the cladding being adjusted to a negative value.

1 . An optical fiber comprising a core and cladding, characterized by: 
 a dispersion “D” of not less than 2 ps/nm/km and not more than 8 ps/nm/km (2≦D≦8) over a wavelength range of 1400 to 1700 nm and,    at least one extreme value of dispersion within said wavelength range.    
   
   
       2 . The optical fiber of  claim 1 , which is further characterized by: 
 a dispersion “D” of not less than −4 ps/nm/km and not more than 4 ps/nm/km (−4≦D≦4) at 1310 nm.    
   
   
       3 . The optical fiber of  claim 1 , which is further characterized by: 
 a cable cutoff wavelength of 1550 nm or shorter.    
   
   
       4 . The optical fiber of  claim 1 , which is further characterized by: 
 a bending loss of 5 dB/m or less in a bending diameter of 20 mm at 1550 nm.    
   
   
       5 . The optical fiber of  claim 1 , which is further characterized by: 
 an effective area (Aeff) of 40 μm 2  or more at 1550 nm.    
   
   
       6 . The optical fiber of  claim 1 , which is further characterized by: 
 a polarization mode dispersion (PMD) of 0.1 ps/√km or less at 1550 nm.    
   
   
       7 . The optical fiber of  claim 1 , which is further characterized by: 
 a dispersion “D” of not less than −2 ps/nm/km and not more than 2 ps/nm/km (−2≦D≦2) at 1310 nm.    
   
   
       8 . The optical fiber of  claim 1 , which is further characterized by: 
 a zero dispersion wavelength of 1350 nm or shorter.    
   
   
       9 . The optical fiber of  claim 1 , further comprising: 
 a plurality of glass layers inside of the cladding having a reference refractive index, wherein    one of two adjacent layers differ in composition from the other,    a first, second, third and fourth layers from the center to outside have relative refractive index differences of Δ 1 , Δ 2 , Δ 3  and Δ 4  from said reference refractive index of said cladding (0), respectively, and satisfy the following condition, Δ 1 >Δ 3 >Δ 4 >0>Δ 2 .    
   
   
       10 . The optical fiber of  claim 9 , wherein: 
 the maximum of said relative refractive index difference of said first layer Δ 1  with said cladding is 0.3 to 0.7%,    α factor of said first layer is 4 or more,    the diameter of said cladding diameter is 124 to 126 μm,    the diameter of said first layer is 7.0 to 10 μm.    
   
   
       11 . The optical fiber of  claim 9 , wherein: 
 said relative refractive index difference of said second layer Δ 2  with said cladding is −0.6 to −0.2%,    a ratio of diameters of said second layer to said first layer is 1.2 to 1.8,    said relative refractive index difference of said third layer Δ 3  with said cladding is 0.25 to 0.5%,    a ratio of diameters of said third layer to said first layer is 1.8 to 2.2,    said relative refractive index difference of said fourth layer Δ 4  with said cladding is 0.05 to 0.2%,    a ratio of diameters of said fourth layer to said first layer is 2.0 to 2.7.    
   
   
       12 . The optical fiber of  claim 1 , 
 wherein    one of any two adjacent layers differ in composition from the other,    a first, second, third, fourth and fifth layers from center to outside have relative refractive index differences, of Δ 1 , Δ 2 , Δ 3 , Δ 4  and Δ 5  with said reference refractive index of said cladding (0), respectively, and satisfy the following condition, Δ 1 >Δ 4 >Δ 5 >0>Δ 3 >Δ 2 .    
   
   
       13 . The optical fiber of  claim 12 , wherein: 
 the maximum of said relative refractive index difference (Δ 1 ) of said first layer with said cladding is 0.3 to 0.7%,    a factor of said first layer is 4 or more,    said cladding diameter is 124 to 126 μm,    the diameter of said first layer is 6.5 to 10 μm.    
   
   
       14 . The optical fiber of  claim 12 , wherein: 
 said relative refractive index difference of said second layer Δ 2  with said cladding is −0.6 to −0.2%,    a ratio of diameters of said second layer to said first layer is 1.2 to 1.8,    said relative refractive index difference of said third layer Δ 3  with said cladding is −0.15 to 0.05%,    a ratio of diameters of said third layer to said first layer is 1.8 to 2.2,    said relative refractive index difference of said fourth layer Δ 4  with said cladding is 0.25 to 0.65%,    a ratio of diameters of said fourth layer to said first layer is 2.0 to 2.7,    said relative refractive index difference of said fifth layer Δ 5  with said cladding is 0.05 to 0.50%,    a ratio of diameters of said fifth layer to said first layer is 2.2 to 3.0.    
   
   
       15 . An optical communications system comprising the optical fibers of  claim 1  and a distributed Raman amplifier for the S-band.  
   
   
       16 . The optical fiber of  claim 12 , which is further characterized by: 
 a dispersion “D” of not less than −4 ps/nm/km and not more than 4 ps/nm/km    (4≦D≦−4) at 1310 nm.    
   
   
       17 . The optical fiber of  claim 12 , which is further characterized by: 
 a cable cutoff wavelength of 1550 nm or shorter.    
   
   
       18 . The optical fiber of  claim 12 , which is further characterized by: 
 a bending loss of 5 dB/m or less in a bending diameter of 20 mm at 1550 nm.    
   
   
       19 . The optical fiber of  claim 12 , which is further characterized by: 
 an effective area (Aeff) of 40 μm 2  or more at 1550 nm.