Sub-200-kHz single soliton generation in a long ring Er-fiber laser with strict polarization control by using twisted fiber

Abstract

In the present work we demonstrate a novel single-soliton ultra-low pulse repetition frequency passively modelocked erbium-doped fiber laser. We mitigate the residual linear birefringence of fiber by fiber twist to achieve a strict control of polarization. For mode-locking the nonlinear polarization rotation (NPR) was used. Special technique was applied to reduce the overdriving of NPR that allows the generation of single soliton in ultra-long cavity. The strict control of polarization yields a stable relation between the polarization state of the pulses propagating in the cavity and the regimes of generation. A 192.12-kHz train of soliton pulses was obtained with pulse duration of 4.7 ps at 1560.1 nm, the average power was 29 μW and the estimated peak power was ̴ 30.8 W with an energy of 150.9 pJ.

Numerical study of polarization evolution governed by linear birefringence, twist-induced circular birefringence and nonlinear birefringence in a single-mode optical fiber

“…In a broad number of optical fiber systems, a uniform twist rate is applied along the fiber, such as fiber Bragg gratings [1][2][3], interferometric schemes [4,5], fiber optic sensors based on induced circular birefringence [6][7][8], optical signal processing devices [9], mode-locked fiber lasers (ML-FL) [10][11][12][13][14] and so on. In most of these physical contexts, the twisted optical fiber is part of a strict polarization control scheme based on birefringence and polarization adjustments, which plays an important role in ensuring predictability and reproducibility of the adjustment process.…”

“…A relevant application of the NPR is the saturable absorber mechanism in a passively ML-FL; in this case, the NPR, together with the birefringence and polarization adjustments, defines the nonlinear transmission characteristic whose tuning allows controlling the pulse generation process, favoring for instance the transition between different emission regimes such as noise-like pulse, soliton crystal [10], or even hybrid regimes (involving the interplay between noise-like pulses, solitons and a continuous wave) [11]. In one approach, polarization control was used to reduce NPR in a long-cavity configuration, making it possible to observe single-soliton emission from cavities even beyond 1 km in length [12,13]. In fact, strict polarization control in twisted passively ML-FLs even allowed complete polarization mapping of all the possible regimes of operation in these sources, making each of them readily accessible through welldefined birefringence adjustments in a clear and repeatable way [10][11][12].…”