Patent ID: 7379677

Claim:
A wavelength conversion method in which an amplitude-modulated first light having an optical frequency f 1 is received and a second light having a wavelength different from a wavelength of the first light is output, the method comprising the steps of: multiplexing the first light and a reference light, the reference light being a continuous light having a wavelength different from the wavelength of the first light and having an optical frequency f 2 and the first light having larger amplitude than the reference light; propagating the multiplexed first light and reference light through an optical fiber so as to generate a third light having a wavelength different from the wavelength of the first light and an optical frequency f 3 , which is expressed by a formula “f 3 =2f 1 −f 2 ”, by means of a non-linear optical phenomenon; and causing the third light to pass through an optical filter having a pass wavelength range set such that a pulse time width of the third light is 20% or more narrower than a pulse time width of the first light after such passage through said optical filter, thereby obtaining a second light, wherein an absolute value of wavelength dispersion of said optical fiber is not larger than 0.2 ps/nm/km at the wavelength of the first light.