In the optical communication field, for expansion of a transmission capacity and flexible use of a network, there have been demands for a wavelength conversion technique for freely converting a carrier light frequency (wavelength) of signal light. The wavelength conversion technique is realized using optical to electrical and electrical to optical signal conversion, an optical vector modulator, a nonlinear optical medium, or the like.
The optical to electrical and electrical to optical signal conversion is wavelength conversion performed by converting an optical signal into an electrical signal, performing wavelength conversion on the electrical signal, and regenerating the electrical signal to the optical signal. It is possible to generate an optical signal having a desired wavelength via the optical to electrical and electrical to optical signal conversion. However, an electric circuit corresponding to a modulation format of the optical signal may be requested. Power consumption increases when the capacity of the optical signal to be converted increases. The light vector converter has a limit in a conversion band. Conversion into different wavelength grids is difficult.
On the other hand, in wavelength conversion performed using a nonlinear optical effect, processing not depending on a modulation format is possible. There is no limit in a frequency band that may be converted. It is possible to perform wavelength conversion of optical signals in a wide frequency band.
Examples of related art are described in Japanese Laid-open Patent Publication Nos. 2008-76752 and 4-136823.
However, in the wavelength conversion performed using the nonlinear optical effect, when conversion efficiency is low, the quality of an optical signal after conversion is deteriorated and a transmission distance decreases. On the other hand, it is conceivable to increase the intensity of control light made incident on a nonlinear optical medium to increase the conversion efficiency.
However, when the intensity of the optical signal input to the nonlinear optical medium is large, induced Brillouin scattering occurs. As a result, signal quality is deteriorated.