Towards ultrasensitive optical links enabled by low-noise phase-sensitive amplifiers

In principle, optical phase-sensitive amplifiers are known to be capable of realizing noiseless amplification, as well as improving the signal-to-noise-ratio of optical links by 3 dB compared to conventional, phase-insensitively amplified links. However, current state-of-the-art phase-sensitive amplifiers are still far from being practical, lacking, for example, significant noise performance improvement, broadband gain and modulation-format transparency. Here, we demonstrate experimentally, for the first time, an optical-fibre-based non-degenerate phase-sensitive amplifier link consisting of a phase-insensitive parametric copier followed by a phase-sensitive amplifier that provides broadband amplification, signal modulation-format independence, and nearly 6 dB link noise-figure improvement over conventional, erbium-doped fibre amplifier-based links. The PSA has a record-low 1.1 dB noise figure, and can be extended to work with multiple wavelength channels with modest system complexity. This concept can also be realized in other materials with third-order nonlinearities, and is useful in any attenuation-limited optical link.