Gamma-shaped long-cavity normal-dispersion mode-locked Er-fiber laser for sub-nanosecond high-energy pulsed generation

Abstract

We propose the design of a novel γ-shaped fiber laser resonator and apply it to build a long-cavity normaldispersion mode-locked Er-fiber laser which features enhanced functionalities for management and optimization of pulsed lasing regimes. We report the generation of sub-nanosecond pulses with the energy of ∼ 0.5 µJ at a kilohertz-scale repetition rate in an all-fiber system based on the new laser design. A combination of special design solutions in the laser, such as polarization instability compensation in the ultra-long arm of the resonator, intra-cavity spectral selection of radiation with a broadband fiber Bragg grating, and polarization selection by means of a tilted refractive index grating, ensures low amplified spontaneous emission (ASE) noise and high stability of the laser system output parameters.

Mode-locked fiber lasers with significant variability of generation regimes

“…They demonstrated the possibility of passive mode locking in long cavities due to saturable absorbers, such as single-wall carbon nanotubes [25,40,41], semiconductor saturable absorber mirrors [42][43][44], and non-linear optical loop mirrors [45]. It was experimentally and theoretically confirmed that passively mode-locked fiber master oscillators give rise to a broad variety of generation regimes in different cavity configurations [46][47][48][49][50][51][52][53], including generation of single and multiple pulses over a cavity round-trip, pulses with various duration, envelope shape, and spectrum width. The results of Refs [30,52] show that in ultra-long lasers, there is high probability of generating double-scale partially coherent pulses, whereas ''normal'' (single-scale) pulses with a smooth temporal optical phase shape and large chirp become difficult to obtain.…”

Compact all-fiber laser delivering conventional and dissipative solitons

“…SESAM1 and SESAM2 have modulation depths of 30% and 9%, respectively, and an identical recovery time of 2 ps. The four-port circulator works as an isolator and incorporates other components into the cavity [25].…”

Square Nanosecond Mode-Locked Laser Based on Nonlinear Amplifying Loop Mirror

“…Nanosecond mode-locking was typically observed in long-cavity fiber lasers [12], wherein nonlinear polarization rotation was responsible for peak-power-clamped ns pulse evolution [23]. The NALM-based ns mode-locking was originated from a mechanism different from nonlinear polarization beating [9].…”