Proposal and design of an all-optical encoder for digitising radio-over-fibre transceivers

Abstract

In this paper it is proposed and designed an original all-optical Encoder (o-Encoder) intended, but not exclusively, to be part of future optical digitising radio-over-fibre (o-DRoF) transceiver. It is based on the Semiconductor Laser Amplifier Loop Mirror (SLALOM) configuration exploiting the nonlinearities of a semiconductor optical amplifier (SOA) in cross-switching regime. The proof-of-principle is established using 40-ps RZ control pulses at 2.5 GHz in the C-band. It outputs serially encoded, quantized and amplified optical RZ bits. Computer simulations of the proposed o-Encoder have shown promising results. The proposed device is rather compact, potentially optically integrable and requires much less input optical power (by several orders of magnitude) than other photonic-encoders and can also naturally convert wavelengths in the optical domain.

An all-optical Sampler for digitising Radio-over-Fibre transceivers

“…The o-DRoF-T comprises at least five main optical submodules: (1) optical pulse generator or o-Generator, (2) optical sampler or o-Sampler, (3') and (3'') temporal interleavers or oInterleaver, (4) optical encoder or o-Encoder [20] and (5) optical thresholder or o-Thresholder [8]. The o-Sampler carries out the real-time optical sampling of an input analogue RoF signal and is driven by an optical pulse train that in turn is generated by the o-Generator.…”

“…The o-Sampler carries out the real-time optical sampling of an input analogue RoF signal and is driven by an optical pulse train that in turn is generated by the o-Generator. This pulse train is also used as a reference clock signal by the o-Encoder that optically encodes the sampled signal, thereby accomplishing the photonic ADconversion itself [20]. The o-Thresholder is provided mainly to significantly enhance the contrast between the "0" and "1" optical bits at the output of the o-Encoder and automatically providing amplification [8].…”

“…Therefore, these pulses can be used as the clock signal for the optical sampling and encoding steps. The sub-modules (3') and (3'') essentially multiplies the repetition rate of the clock signal generated by (1) and (2) and is better explained in the reference [20]. …”

“…The optical circuits of the o-Sampler, o-Interleaver, oEncoder [20] and o-Thresholder [8] were designed and simulated using the VPI Transmission Maker TM software. However, in this paper only the results for the o-Sampler are presented.…”

“…The optical circuits of the o-Sampler, o-Encoder [20] and o-Thresholder [8] are based on Sagnac interferometers using fibre-couplers with coupled-ratio equal to 50:50 thus allowing a maximum interference visibility contrast. The SOA is modelled as to be isotropic.…”