Year: 2009
Miroslav Karásek, DrSc.
Fast signal power transients caused by cross-gain saturation effects constitute a serious limitation in WDM transmission systems and networks with cascades of optical amplifiers. Photonic switching elements in transparent networks, such as reconfigurable optical add drop multiplexers, provide a platform to support greater network flexibility through wavelength rerouting. In such networks the number of optical channels passing through a fiber amplifier may vary. These variations cause power transients in “surviving” channels. Two control schemes have been suggested for suppression of surviving channel power transients in networks based on erbium-doped fibre amplifiers: fast pump power control, and all-optical gain clamping (AOGC).
We have experimentally investigated suppression of surviving channel power transients in an AOGC time-division-multiplexed (TDM)-pumped lumped Raman fiber amplifier ( TDM LRFA). The TDM LRFA consisted of 13 km long dispersion compensating fiber (DCF) counter-directionally pumped by 4 pairs of laser diodes powered from microprocessor controlled pulse generator. Gain clamping was achieved by the introduction of a cavity around the Raman gain medium for the lasing wavelength. Channel addition/removal was simulated by transmitting 19 signals, light of 5 channels was modulated at 10 Gb/s, eight channels was 100% square-wave modulated at 2 kHz. Schematic diagram of the experimental set-up is shown in Fig. 1 [8]. Figure 2 demonstrates the suppression of power transients of channel the 1554.94 nm 10 GE signal: comparison of unclamped and AOGC regime [9].
