Patent ID: 7212334

Claim:
An optical signal-to-noise ratio improving device comprising: one or more optical signal-to-noise ratio improving sections; a dividing device that divides an input optical signal into a first component and a second component orthogonal to the first component, the first component being supplied to one of the optical signal-to-noise ratio improving sections at a predetermined polarization angle, the second component being supplied to another one of the optical signal-to-noise ratio improving sections at a predetermined polarization angle; a combination device that combines output light from the one optical signal-to-noise ratio improving section and output light from the other one optical signal-to-noise ratio improving section; an optical clock regeneration unit that regenerates an optical clock from the input optical signal; and a wavelength conversion unit that is supplied with the input optical signal and the regenerated optical clock, and generates an output optical signal having a predetermined polarization state and including an intensity-modulated signal of the input optical signal at the wavelength of the regenerated optical clock, the optical signal output from the wavelength conversion unit being supplied to the one optical signal-to-noise ratio improving section and the other one optical signal-to-noise ratio improving section.