A variable-gain optical amplifier for metro WDM networks with mixed span losses: a gain-clamped semiconductor optical amplifier combined with a Raman fiber amplifier

We propose a variable-gain optical amplifier that exhibits excellent performance in metro wavelength-division-multiplexing networks containing mixed span losses. The amplifier consists of a variable-gain Raman fiber amplifier and a gain-clamped semiconductor optical amplifier. Each span of different loss is exactly compensated by adjusting the pump power of a Raman laser diode to have the maximum optical signal-to-noise ratio. Sixteen channels of 10-Gb/s signals were successfully transmitted over 170 km of mixed span losses (total, 87 dB) under dynamic additions/removals situations.