Contents 1. INTRODUCTION
OPTICAL amplifiers are universally deployed within optical communications networks as a means to boost signal strength and thus maintain an adequate signal to noise ratio. In the case of semiconductor optical amplifiers (SOAs), the use of optical amplifiers requires careful consideration of the network dynamics in order that transients within optical signals may be minimised [1] [2] [4]. Erbium doped fiber amplifiers (EDF As) can operate reliably at high data rates in a multi-wavelength environment, because of their high output saturation powers and slow gain dynamics. However, these same dynamics cause undesirable gain transients when operated in a packet switched or burst mode environments [5]. Gain clamping has been extensively researched and developed as a means of stabilising gain over a wide dynamic range in both semiconductor and fibre based amplifiers [6]–[16]. SOAs have a small form factor and offer the potential for monolithic integration with other functions and their temporal dynamics are better suited for use in switched environments. Furthermore, being fibre based, EDF As have no path to solutions that demand a high degree of integration. While SOAs have been demonstrated as effective amplifier solutions in multi-wavelength long distance transmission applications [1] [2] [4], their operation in this regime requires careful management of signal power levels, such that they maintain operation within their linear region. Gain regulation can be implemented by varying the bias current to SOAs however bias current changes also influence the maximum linear operating power (Psat) of the SOA and hence may be undesirable [15]. This additional degree of management is not desirable, especially in PONs where burst mode signals can operate over a wide dynamic range. Nonetheless the wavelength flexibility of SOAs continues to promote interest in their use in this environment irrespective of the power management issues [13] [14].
