Modulation instabilities in birefringent two-core optical fibres

Abstract

Previous studies of the modulation instability (MI) of continuous waves (CWs) in a two-core fibre (TCF) did not consider effects caused by co-propagation of the two polarized modes in a TCF that possesses birefringence, such as cross-phase modulation (XPM), polarization-mode dispersion (PMD) and polarization-dependent coupling (PDC) between the cores. This paper reports an analysis of these effects on the MI by considering a linear-birefringence TCF and a circular-birefringence TCF, which feature different XPM coefficients. The analysis focuses on the MI of the asymmetric CW states in the TCFs, which have no counterparts in single-core fibres. We find that the asymmetric CW state exists when its total power exceeds a threshold (minimum) value, which is sensitive to the value of the XPM coefficient. We consider, in particular, a class of asymmetric CW states that admit analytical solutions. In the anomalous dispersion regime, without taking the PMD and PDC into account, the MI gain spectra of the birefringent TCF, if scaled by the threshold power, are almost identical to those of the zero-birefringence TCF. However, in the normal dispersion regime, the power-scaled MI gain spectra of the birefringent TCFs are distinctly different from their zero-birefringence counterparts, and the difference is particularly significant for the circular-birefringence TCF, which takes a larger XPM coefficient. On the other hand, the PMD and PDC only exert weak effects on the MI gain spectra. We also simulate the nonlinear evolution of the MI of the CW inputs in the TCFs and obtain good agreement with the analytical solutions.

A projection operator approach for computing the dynamics of AS2S3chalcogenide birefringent photonic crystal fiber coupler

“…For further increase in distance, the input signal oscillates between the cores as it propagates. The dynamics of such birefringent nonlinear couplers is described by a set of coupled nonlinear Schrödinger equations (CNLSE) given by [1,24,31] i ∂u…”

Non-Lagrangian approach for coupled complex Ginzburg-Landau systems with higher order-dispersion

“…Among different types of fiber lasers, dual-core ring lasers have been receiving a widespread interest owing to their numerous applications in photonics [13][14][15][16][17][18][19]. Nonlinear directional couplers (NLDC) are one of important components of integrated optical devices and they deliver quite a few lightwave applications including switching (bright and dark) [20][21][22][23][24][25][26][27], logical operations [28,29], ultra-short pulse generation through modulational instability [30][31][32][33][34][35], and amplifiers [36,37]. In particular, Winful and Walton have proven that the asymmetric dual core fibers can act as a passive mode-locking fiber laser provided one of the dual-cores must be doped with rare earth-elements like erbium while the other core must be a passive one [3].…”

Modulational Instability in Linearly Coupled Asymmetric Dual-Core Fibers

“…Moreover, TOD, as usual, has no influence on the MI gain spectrum in NLDC, while self-steepening can significantly shift the dominant MI band at a sufficiently high input power level. In [42], Li et al extended the MI to birefringent fiber couplers by including the cross-phase modulation, polarization mode dispersion, and polarization-dependent coupling. Furthermore, in [43], MI was studied under the combined effects of the intermodal dispersion and saturable nonlinear response.…”