Abstract

The use of fibre-loop memories is being experimented for solving routing contention of data cells in photonic high bit rate ATM switching fabrics.¹ The simplest fiber-loop memory looks like a ring laser consisting of a semiconductor laser amplifier (SOA), a span of fibre introducing a delay of the order of an ATM cell duration (10^–6-sec) and a 50/50 directional coupler (Fig. 1). To compensate for the power tapping at the directional coupler while avoiding the onset of laser oscillations, the SOA is biased above the ring laser threshold only for a limited number of round trips, then the bias current is switched off. The memory is thus driven through the transition from a state ruled by spontaneous emission toward a state above lasing threshold, in which stimulated emission is predominant. Far enough from the beginning of the transition the intensity fluctuations display a maximum.^2,3 The transition is completed after a time depending on the final state intensity.² These features significantly affect the maximum storage time and noise behavior of the memory.

© 1994 IEEE