Nonlinear optical fiber, nonlinear optical device, and optical signal processing apparatus

Abstract

A core includes a center core region, a core layer that is formed around the center core region and that has a refractive index lower than that of the center core layer, and at least one buffer core layer that is formed between the center core region and the core layer and that has a refractive index lower than that of the center core region and higher than that of the core layer. A cladding is formed around the core layer and that has a refractive index lower than that of the center core region and higher than that of the core layer. An effective core area at a wavelength of 1550 nm is equal to or smaller than 18 μm 2 .

1 . A nonlinear optical fiber comprising:
 a core including
 a center core region, 
 a core layer that is formed around the center core region and that has a refractive index lower than a refractive index of the center core layer, and 
 at least one buffer core layer that is formed between the center core region and the core layer and that has a refractive index lower than the refractive index of the center core region and higher than the refractive index of the core layer; and 
   a cladding that is formed around the core layer and that has a refractive index lower than the refractive index of the center core region and higher than the refractive index of the core layer, wherein   an effective core area at a wavelength of 1550 nanometers is equal to or smaller than 18 μm 2 .   
   
   
       2 . The nonlinear optical fiber according to  claim 1 , wherein the core further includes an additional core layer that is formed between the core layer and the cladding and that has a refractive index higher than the refractive index of the cladding. 
   
   
       3 . The nonlinear optical fiber according to  claim 1 , wherein a ratio of an outer diameter of the buffer core layer to a diameter of the center core region is equal to or larger than 1.2 and equal to or smaller than 2.0. 
   
   
       4 . The nonlinear optical fiber according to  claim 1 , wherein a relative refractive index difference between the center core region and the cladding is equal to or larger than 1.8%. 
   
   
       5 . The nonlinear optical fiber according to  claim 1 , wherein a ratio of an outer diameter of the core layer to a diameter of the center core region is equal to or larger than 2.5. 
   
   
       6 . The nonlinear optical fiber according to  claim 1 , wherein a relative refractive index difference between the core layer and the cladding is equal to or larger than −1.2% and equal to or smaller than −0.2%. 
   
   
       7 . The nonlinear optical fiber according to  claim 1 , wherein a relative refractive index difference between the buffer core layer and the cladding is equal to or larger than 0.1% and equal to or smaller than 0.6%. 
   
   
       8 . The nonlinear optical fiber according to  claim 1 , wherein a variation range of wavelength dispersion in a longitudinal direction at the wavelength of 1550 nanometers is equal to or smaller than 1 ps/nm/km per a length of 1 kilometer. 
   
   
       9 . The nonlinear optical fiber according to  claim 1 , wherein a variation range of zero dispersion wavelength in a longitudinal direction is equal to or smaller than 30 nanometers per a length of 1 kilometer. 
   
   
       10 . The nonlinear optical fiber according to  claim 1 , wherein an absolute value of wavelength dispersion at the wavelength of 1550 nanometers is equal to or smaller than 5 ps/nm/km. 
   
   
       11 . The nonlinear optical fiber according to  claim 10 , wherein an absolute value of wavelength dispersion at the wavelength of 1550 nanometers is equal to or smaller than 1 ps/nm/km. 
   
   
       12 . The nonlinear optical fiber according to  claim 10 , wherein a variation of the wavelength dispersion at the wavelength of 1550 nanometers when an outer diameter of the core layer is changed by 1% is equal to or smaller than 0.7 ps/nm/km in a range where the absolute value of the wavelength dispersion at the wavelength of 1550 nanometers is equal to or smaller than 5 ps/nm/km. 
   
   
       13 . The nonlinear optical fiber according to  claim 1 , wherein
 an absolute value of wavelength dispersion slope at the wavelength of 1550 nanometers is equal to or larger than 0.02 ps/nm 2 /km and equal to or smaller than 0.06 ps/nm 2 /km, a nonlinear coefficient at the wavelength of 1550 nanometers is equal to or larger than 40×10  −10 /W,   a cutoff wavelength is shorter than 1500 nanometers, and   a polarization mode dispersion at the wavelength of 1550 nanometers is equal to or smaller than 0.2 ps/km 1/2 .   
   
   
       14 . The nonlinear optical fiber according to  claim 1 , wherein a transmission loss at the wavelength of 1550 nanometers is equal to or smaller than 1.5 dB/km. 
   
   
       15 . The nonlinear optical fiber according to  claim 1 , further comprising a stress applying member provided on both sides of the cladding sandwiching the core. 
   
   
       16 . The nonlinear optical fiber according to  claim 1 , wherein a polarization crosstalk at the wavelength of 1550 nanometers is equal to or smaller than −20 decibels per a length of 100 meters. 
   
   
       17 . The nonlinear optical fiber according to  claim 1 , wherein an outer diameter of the cladding is equal to or smaller than 100 micrometers. 
   
   
       18 . The nonlinear optical fiber according to  claim 1 , further comprising a coating formed around the cladding, wherein
 an outer diameter of the coating is equal to or smaller than 150 micrometers.   
   
   
       19 . A nonlinear optical device comprising:
 an optical input unit that inputs a light;   an optical output unit that outputs a light; and   a nonlinear optical fiber provided between the optical input unit and the optical output unit, wherein   the nonlinear optical fiber includes
 a core including
 a center core region, 
 a core layer that is formed around the center core region and that has a refractive index lower than a refractive index of the center core layer, and 
 at least one buffer core layer that is formed between the center core region and the core layer and that has a refractive index lower than the refractive index of the center core region and higher than the refractive index of the core layer, and 
 
 a cladding that is formed around the core layer and that has a refractive index lower than the refractive index of the center core region and higher than the refractive index of the core layer, 
   an effective core area at a wavelength of 1550 nanometers is equal to or smaller than 18 μm 2 , and   the nonlinear optical fiber causes a nonlinear optical phenomenon to be generated by the light input from the optical input unit and outputting a light obtained by the nonlinear optical phenomenon to the optical output unit.   
   
   
       20 . An optical signal processing apparatus comprising:
 an optical signal input unit that inputs an optical signal;   an optical signal processing unit that includes a nonlinear optical fiber, and performs a signal processing of the optical signal input from the optical signal input unit by using a nonlinear optical phenomenon generated in the nonlinear optical fiber; and   an optical signal output unit that outputs the optical signal that is signal processed, wherein   the nonlinear optical fiber includes
 a core including
 a center core region, 
 a core layer that is formed around the center core region and that has a refractive index lower than a refractive index of the center core layer, and 
 at least one buffer core layer that is formed between the center core region and the core layer and that has a refractive index lower than the refractive index of the center core region and higher than the refractive index of the core layer, and 
 
 a cladding that is formed around the core layer and that has a refractive index lower than the refractive index of the center core region and higher than the refractive index of the core layer, and 
   an effective core area at a wavelength of 1550 nanometers is equal to or smaller than 18 μm 2 .