Patent ID: 7061670

Claim:
An optical fiber amplifier comprising: an optical amplifying section for amplifying an inputted optical signal; a sampling section including: a tap coupler configured for shunting and outputting part of an optical signal inputted from said sampling section to form said optical signal; a circulator which comprises first to third ports, the first port configured for inputting the shunted optical signal, the second port configured for outputting the shunted optical signal, the third port configured for outputting first and second test lights inputted from the second port; first and second reflective gratings configured for obtaining the first test light and the second test light from said shunted optical signal; optical detectors configured for detecting a first test light belonging to a short wavelength band adjacent to a signal wavelength band from the shunted optical signal and a second test light belonging to a long wavelength band adjacent to the signal wavelength band from the shunted optical signal; a wavelength division multiplexing coupler configured for separating the first and second test lights from each other; an input power control circuit configured for comparing powers of the first and second test lights with each other and outputting a control signal for controlling an input power of the optical signal inputted to said optical amplifying section according to the power differential of the first and second test lights; an output power control circuit for configured deriving an output power of said optical amplifying section from the power of the optical signal shunted at the sampling section and controlling the optical amplifying section so that the output power of the optical amplifying section is controlled to a desired value; and a variable attenuator configured for controlling the power of the optical signal inputted to the optical amplifying section according to the control signal.