Low-power optical communication: Approaching the quantum limit

by Prof. Konrad Banaszek (Faculty of Physics, University of Warsaw, Poland)

Thursday 12 Feb 2015, 15:00 → 16:00 Europe/Rome

Aula Conversi (Dipartimento di Fisica - Ed. G. Marconi)

We discuss selected strategies to reach the maximum transmission rate, defined by the Holevo bound, of a lossy narrowband optical channel under the constraint of a low fixed average photon number. When direct detection is used at the output, the ultimate capacity can be approached by optimizing pulse position modulation (PPM) encoding with respect to the symbol length. We present an approximate analytical formula for the PPM transmission rate, which quantifies the effects of photon statistics in terms of the g(2) normalized second-order ! intensity correlation function of the light source, and analyse enhancement attainable through the use of sub-Poissonian light. The highly imbalanced instantaneous power distribution in PPM encoding can be remedied by the use of binary phase shift keying (BPSK) employing the recently proposed collective receiver based on Hadamard words. We show that for this encoding, the transmission rate in the presence of phase noise is equivalent to that of PPM with super-Poissonian light statistics, retaining enhanced scaling with mean photon number compared to indvidual detection.