One photon-per-bit receiver using near-noiseless phase-sensitive amplification.

Space communication for deep-space missions, inter-satellite data transfer and Earth monitoring requires high-speed data connectivity. The reach is fundamentally dictated by the available transmission power, the aperture size, and the receiver sensitivity. A transition from radio-frequency links to optical links is now seriously being considered, as this greatly reduces the channel loss caused by diffraction. A widely studied approach uses power-efficient formats along with nanowire-based photon-counting receivers cooled to a few Kelvins operating at speeds below 1 Gb/s. However, to achieve the multi-Gb/s data rates that will be required in the future, systems relying on pre-amplified receivers together with advanced signal generation and processing techniques from fibre communications are also considered. The sensitivity of such systems is largely determined by the noise figure (NF) of the pre-amplifier, which is theoretically 3 dB for almost all amplifiers. Phase-sensitive optical amplifiers (PSAs) with their uniquely low NF of 0 dB promise to provide the best possible sensitivity for Gb/s-rate long-haul free-space links. Here, we demonstrate a novel approach using a PSA-based receiver in a free-space transmission experiment with an unprecedented bit-error-free, black-box sensitivity of 1 photon-per-information-bit (PPB) at an information rate of 10.5 Gb/s. The system adopts a simple modulation format (quadrature-phase-shift keying, QPSK), standard digital signal processing for signal recovery and forward-error correction and is straightforwardly scalable to higher data rates.

Enhanced analog-optical link performance with noiseless phase-sensitive fiber optical parametric amplifiers.

In this paper, we investigate the enhancement of analog optical link performance with noiseless phase-sensitive fiber optical parametric amplifiers. The influence of different noise sources in the link impacts the quality of analog optical signals, especially with low optical signal power, which has not been investigated before. Theoretically, the increase in signal-to-noise ratio and spurious-free dynamic range can be up to ∼6 dB and ∼4 dB, respectively, if the noise figure of optical pre-amplifier drops 3 dB when the received optical power is less than -65 dBm. In addition, experiments based on a 1.3 dB-noise-figure phase-sensitive fiber optical parametric amplifier and conventional optical pre-amplifiers are implemented, and the measured results agree with the theoretical expectations. This illustrates that noiseless phase-sensitive optical amplification may pave the way to long-haul distribution of analog optical signals and find applications in microwave-photonic systems.

Optical injection locking at sub nano-watt powers.

We demonstrate optical injection locking (OIL) at record low injection power of -65 dBm using EDFA-based pre-amplification and an electrical phase locked loop (PLL). Investigating the phase noise characteristics of OIL, we find that at low injection powers the slave laser linewidth and injection ratio strongly influence the phase noise of the locked slave output. By introducing an EDFA pre-amplifier, the minimum locking power for OIL is reduced. Moreover, using this pre-amplifier we find that there exists an optimum injection power into the slave where the output phase noise is minimized and is below the phase noise without EDFA. We evaluate an OIL-based pump recovery in a phase sensitive amplifier (PSA) receiver system aimed at free-space communications.