To input in a wavelength transformation circuit after signal light reaches predetermined strength.
When signal light with wavelength λ and continuous light Pcw-in with wavelength λ' are input, an XPM type wavelength transformation circuit 101 outputs wavelength transformation signal light Pout with wavelength λ', but when the strength of the signal light is changed, an action of the optimum wavelength transformation cannot be carried out. Accordingly, the strength of transmitted signal light Ps-in is controlled to the predetermined constant strength with a signal light strength control circuit 101, and equalized signal light Ps-eq reached the predetermined strength is sent to the XPM type wavelength transformation circuit 101. Accordingly, even if the strength of signal light Ps-in is changed, because the strength of the equalized signal light Ps-eq is constant, the XPM type wavelength transformation circuit 101 can carry out an action of the optimum wavelength transformation without changing the action point of the wavelength transformation.
SATOU RIEKO
SUZUKI YASUHIRO
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