Phase-sensitive seeded modulation instability in passive fiber resonators

Modulation instability is one of the most ubiquitous phenomena in physics. Here we investigate the phase-sensitive properties of modulation instability with harmonic seeding in passive fiber resonators. Theoretical investigations based on the Lugiato−Lefever equation with time dependent pump and a three-wave truncation show that the dynamics of the system is sensitive to the relative phase between input signal, idler, and pump waves. The modulation instability gain can even vanish for a peculiar value of the initial relative phase. An advanced multi-heterodyne measurement technique had been developed to record the real time evolution, round-trip to round-trip, of the power and phase of the output cavity field to confirm these theoretical predictions.

Output Pulse Characteristics of a Mamyshev Fiber Oscillator

The dependence of the output pulse characteristics of a Mamyshev fiber oscillator on cavity parameters is investigated in detail. We analyze the change in pulse spectrum bandwidth, pulse duration, dechirped pulse duration and chirp with the change in fiber group velocity dispersion, fiber nonlinearity, gain, and filters by putting forward a numerical model. In particular, as one of the most important components, the effect of filters bandwidth and the central wavelength interval between them is discussed. The passive fibers are classified into two kinds according to their locations in the cavity, which are the one before the gain fiber and the one after the gain fiber. Numerical simulation results show that a wide spectrum can be obtained by increasing the nonlinearity of the second passive fiber, while the change in nonlinearity of the first passive fiber has a weak effect on spectrum broadening. A wide spectrum could also be obtained by increasing the nonlinearity or the small-signal gain coefficient of the gain fiber. A Yb-doped Mamyshev fiber oscillator is demonstrated. The results show the increase in pump power, which agrees reasonably well with the numerical simulation results.

Анализ эффективности методов защиты от атак активного оптического зондирования на волоконные системы квантового распределения ключей в спектральном диапазоне 1260-1650 nm

In this paper, the results of research of spectral features of several passive fiber optic components are presented. There are spectra of isolators, circulators, spectral filters, and WDM, that are used in quantum key distribution (QKD) systems, and contribute to the protection of these systems against active optical probing attacks. We also provide an estimate of the degree of isolation required to protect the QKD system from Trojan-horse attacks. Based on the isolation requirements and measurement data we analyzed the efficiency of the QKD system protection through the use passive isolating components. As an example, we have shown the achievement of the required isolation level (150 dB) in the considered spectral range in the system presented in the article.