Patent ID: 7330303

Claim:
A wavelength division multiplexed optical amplifier comprising: a first-stage optical amplifying unit and a second-stage optical amplifying unit arranged in series with respect to an optical signal, where a first pumping light is supplied to said first-stage optical amplifying unit at an input side of said first-stage optical amplifying unit, a second pumping light is supplied to the first-stage optical amplifying unit at an output side of said first-stage optical amplifying unit, and a third pumping light is supplied to said second-stage optical amplifying unit at an input side of said second-stage optical amplifying unit, a common automatic gain control circuit performing automatic gain control in accordance with the optical signal at the input side of the first-stage optical amplifying unit and the optical signal at an output side of said second-stage optical amplifying unit, producing a first control signal for controlling the first pumping light, and producing a second control signal for commonly controlling both the second pumping light and the third pumping light, and a pumping light distribution function unit receiving the second control signal from said common automatic gain control circuit and, in accordance with the received second control signal, supplying said second pumping light to the first-stage optical amplifying unit at the output side of the first-stage amplifying unit and said third pumping light to the second-stage optical amplifying unit at the input side of the second-stage optical amplifying unit with a predetermined distribution ratio of a:b (a<b) in their levels, which ratio is constant at any level of said first pumping light.