Patent ID: 8208812

Claim:
An optical relay device that relays a wavelength-multiplexed light in which optical signals with different wavelengths are wavelength-multiplexed, the optical relay device comprising: a total-power measuring unit that measures total power of the wavelength-multiplexed light; a number-of-multiplexed-wavelengths measuring unit that measures number of multiplexed wavelengths in the wavelength-multiplexed light; a variable optical attenuator that attenuates the total power of the wavelength-multiplexed light; a control-target-value setting unit that sets a control target value corresponding to the number of multiplexed wavelengths measured by the number-of-multiplexed-wavelengths measuring unit; a controller that controls the variable optical attenuator based on the control target value; and an optical amplifier that performs an optical amplification with a constant gain regardless of power of the wavelength-multiplexed light, wherein the controller performs feedback control of the variable optical attenuator such that a result of measurement of the total power of the wavelength-multiplexed light meets the control target value, the total-power measuring unit is arranged between the variable optical attenuator and the optical amplifier, the control-target-value setting unit sets the control target value proportional to the number of multiplexed wavelengths, and when there is a change in the number of multiplexed wavelengths, the controller changes the control target value, and sets a time period for measurement of the number of multiplexed wavelengths to a value smaller than a control time constant used when the feedback control of the variable optical attenuator is performed.