Ultralow Noise, Broadband Phase-Sensitive Optical Amplifiers, and Their Applications

Frequency nondegenerate phase-sensitive amplifiers (PSAs) have the potential to realize broadband and noiseless amplification. However, the rigorous requirement of phase- and wavelength-locking of the input waves has significantly hampered their progress. In this paper, we review recent research on this type of optical amplifier. This work is based on a copier-PSA scheme, which consists of a parametric phase-insensitive copier followed by one or more PSAs. Broadband gain and noise performance of a fiber-based nondegenerate PSA has been characterized, both theoretically and experimentally. A record-low 1.1 dB noise figure was measured at >;26 dB gain, and a clear phase dependent gain was observed. Moreover, potential applications including phase noise squeezing and ultralow noise, multichannel and modulation-format-transparent linear amplification with up to 6 dB link noise figure advantage over conventional EDFA-amplified links have been experimentally demonstrated. The prospects and practical challenges of this intriguing amplification technology are also discussed.

I. Introduction

Optical amplifiers are key devices used in a wide range of applications such as optical communications, photon detection, optical processing, and laser physics to compensate passive loss, increase power level or enhance receiver sensitivity. To date all commercialized optical amplifiers are phase-insensitive [1]–[4], which amplify the two orthogonal quadratures of the input signal equally. This type of optical amplifier is characterized by the well-known 3 dB quantum-limited noise figure (NF) [5] and will thus degrade the output signal-to-noise ratio (SNR) by adding excess noise.