Presented is a quantum model describing noise generation and system accumulation from both optical amplification and nonlinearity, leading to the definition of information-capacity limits in long-haul WDM transmission.
We analyze the information-capacity limitations of the optical communication channel, as determined by noise accumulation from optical amplification and nonlinear wave-mixing. We review the concepts of signal-to-noise ratio and entropy for binary-coded and continuous communications, leading to a definition of ultimate capacity for the optically-amplified channel. A unified quantum model, describing both amplification and nonlinearity limitations, makes possible to determine the power transmission window within which the channel capacity can be maximized.
Y-00 quantum stream cipher is a signal-level encryption technique that prevents signal interception in optical fiber communications. Security of the Y-00 cipher depends on the signal power, and thus the cipher system has a tradeoff between the security and signal quality. This letter reports theoretical analysis of Nyquist wavelength-division multiplexed transmission of phase-shift keying Y-00 cipher over a nonlinear fiber channel. A tradeoff formula between reach and signal security is derived utilizing the Gaussian noise model. Numerical study shows that the PSK Y-00 cipher achieves high-capacity ultra-long-haul transmission with a countermeasure against interception.
This tutorial reviews the Holevo capacity limit as a universal tool to analyze the ultimate transmission rates in a variety of optical communication scenarios, ranging from conventional optically amplified fiber links to free-space communication with power-limited optical signals. The canonical additive white Gaussian noise model is used to describe the propagation of the optical signal. The Holevo limit exceeds substantially the standard Shannon limit when the power spectral density of noise acquired in the course of propagation is small compared to the energy of a single photon at the carrier frequency per unit time-bandwidth area. General results are illustrated with a discussion of efficient communication strategies in the photon-starved regime.