I will review the properties of phase-sensitive amplifiers based on three- and four-wave mixing in second- and third-order nonlinear media, and the consequences of these properties for information transmission. I will also describe some potential applications of these devices.
Optical parametric amplifiers rely on second-order susceptibility (three-wave mixing) or third-order susceptibility (four-wave mixing) in a nonlinear process where the energy of incoming photons is not changed (elastic scattering). In the latter case, two pump photons are converted to a signal and to an idler photon. Under certain conditions, related to the phase evolution of the waves involved, this conversion can be very efficient, resulting in large amplification of an input signal. As the nonlinear process can be very fast, all-optical applications aside from pure amplification are also possible. If the amplifier is implemented in an optical input-phase-sensitive manner, it is possible to amplify a signal wave without excess noise, i.e., with a noise figure of 0 dB. In this paper, we will provide the fundamental concepts and theory of such amplifiers, with a focus on their implementation in highly nonlinear optical fibers relying on four-wave mixing. We will discuss the distinctions between phase-insensitive and phase-sensitive operation and include several experimental results to illustrate their capability. Different applications of parametric amplifiers are also discussed, including their use in optical communication links.
We theoretically and experimentally analyze the dominant impairment mechanisms affecting the fidelity of optical phase in parametric amplifiers and converters in media characterized by third-order (Kerr) optical nonlinearity. The critical role of narrow-band pump filtering in parametric mixers is quantified with respect to frequency stability of amplified and converted waves. The analysis is generally applicable to all four-photon devices used to generate new frequencies or translate spectral bands.