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.

I. Introduction

Span lengths typically differ and the span losses may change due to upgrading and reconfiguration of systems in metro wavelength-division-multiplexing (WDM) networks. The resulting unequal span losses, as well as the transient changes in gain due to channel add–drops, can make system design difficult if appropriate optical amplifiers are not used [1], [2].