Patent ID: 7391560

Claim:
A multistage optical amplifier comprising: a plurality of optical amplifiers in a multistage connection, wherein a first pumping light of a former-stage optical amplifier is incident from a direction of an input signal and a second pumping light of a latter-stage optical amplifier is incident from a reverse direction of the input signal; probe light sources inputting probe lights disposed at both ends of a wavelength range of a main signal to each of said plurality of optical amplifiers, wherein probe lights of the former-stage optical amplifier are incident from a direction of an input signal and probe lights of the latter-stage optical amplifier are incident from a reverse direction of the input signal; and a common control section commonly controlling pumping light powers of said plurality of optical amplifiers, wherein said common control section includes: tilt detection means for detecting amounts of tilt of each of said plurality of optical amplifiers; and tilt cancellation means for controlling the pumping light powers of said plurality of optical amplifiers so that the amounts of tilt of each of the optical amplifiers detected by said tilt detection means cancel each other, wherein said tilt detection means detects the amounts of tilt of each of said optical amplifiers from the difference of output level between said probe lights disposed at both ends of a wavelength range of a main signal, and said tilt cancellation means achieves flat gain-wavelength characteristics of the multistage optical amplifier by canceling the amounts of tilt of each of said optical amplifiers.