Employing Weak-Field Homodyne Detection for Optical Communications

We investigate the role of weak-field homodyne (WH) measurement for optical communications over a lossy bosonic channel with coherent state encoding. This kind of receiver employs photon-number resolving (PNR) detectors with finite resolution and low-intensity local oscillator. As a figure of merit, we consider the mutual information for both single and double WH detection. At first, we consider a Gaussian input modulation, showing this scheme to be suboptimal with respect to the homodyne and double homodyne capacity, respectively. Thereafter, we investigate the performance of non-Gaussian modulation, by considering a Gamma distribution of the energy of the encoded pulses, and achieve an increase in the information rate with respect to the Gaussian case in all energy regimes. In particular, WH measurement outperforms the Shannon limit for homodyne/double homodyne detection in the photon-starved limit, albeit it does not beat neither the direct detection (DD) limit achieved with Gamma modulation, nor on-off keying (OOK) strategies, e.g. OOK-DD and OOK-Dolinar receiver.