NOISE CHARACTERISTICS OF NONLINEAR SEMICONDUCTOR OPTICAL AMPLIFIERS IN THE GAUSSIAN LIMIT

This paper addresses noise properties of nonlinear semiconductor optic al amplifiers, From a basic point of view, noise properties of nonline ar optical amplifiers are sufficiently different from those of linear amplifiers to warrant detailed modeling which has not been formulated previously, From a practical point of view, nonlinear semiconductor op tical amplifiers are important for future all-optical signal-processin g applications which may involve the operation of these devices in a s aturated regime, Nonlinear amplifiers are also common in systems opera ting near 1300 nm and in integrated booster amplifiers. Under nonlinea r operating conditions, amplifier noise contains a narrow-band contrib ution that comes about due to the nonlinear coupling of noise and gain , The more conventional broadband spontaneous noise also changes as th e inversion factor becomes power-dependent and varies along the amplif ier axis, We analyze noise in nonlinear amplifiers in the Gaussian lim it (meaning, for fields consisting of large photon numbers) for CW or NRZ modulated signals and separately for short pulses, We consider the case of a single input as well as configurations of multi-input signa ls interacting via four-wave mixing, Using a specific detection system for the calculations of electronic Signal-to-noise ratios, we demonst rate a reduction in the narrow-band electronic noise due to saturation in the single input case, We also demonstrate a vast advantage of usi ng short pulses in four-wave-mixing applications.