Abstract

The ability to perform all-optical digital information processing is one of the key requirements for future photonic networks. Recently, the use of semiconductor optical amplifier based all-optical interferometric switches [1] has allowed practical demonstrations of advanced functionality to be demonstrated. These have included a bit-serial regenerative optical memory which is capable of long term storage [2] and has the ability to restore the optical logic level [3]. Here we describe a further advance in all-optical digital functionality with a demonstration of an all-optical pseudorandom bit sequence (PRBS) generator. The all-optical PRBS comprises two coupled regenerative memories [2] which act as a time-of-flight shift register for optical pulses. A digital PRBS can be generated by applying the logical XOR function between the output of the register and a tap point and feeding the logical result back into the start of the register [4]. We use two TOAD all-optical switching gates [5] to create the all-optical PRBS architecture. One TOAD is used for the XOR function and the other acts as a wavelength converter and all-optical regenerator. The PRBS output depends on the number of pulses m in the shift register and the tap position n (n<m). At present, the experimental latency is several hundred bits at a IGHz clock rate and so we use multiples of lower length sequences in order to measure the performance of the design. We have experimentally demonstrated a maximal length 2³¹-1 PRBS ({m,n}={713,552} ≡ 23 x {m,n}={31,24}) and also sub-maximal sequences. The figure below shows a digitally sampled part of the maximal 2³¹-1 PRBS. The apparent amplitude modulation of the pulses is an artefact of the relatively low sampling rate (400Msamples/s). We were only able to record short temporal sequences since the repeat period of the PRBS is ~50s.

© 1998 IEEE