All-fiber mode-locked erbium-doped ring laser based on a highly-nonlinear resonator with a low-noise ultrashort pulse generation

Ultrashort pulse (USP) fiber lasers have found applications in such various fields as frequency metrology and spectroscopy, telecommunication systems, etc. For the last decade, mode-locking (ML) fiber lasers have been under carefully investigations for scientific, medical and industrial applications. Also, USP fiber sources can be treated as an ideal platform to expand future applications due to the complex ML nonlinear dynamics with a presence of high value of group velocity dispersion (GVD) and the third order dispersion in the resonator. For more reliable and robust launching of passive mode-locking based on a nonlinear polarization evolution, we used a highly nonlinear germanosilicate fiber (with germanium oxides concentration in the core similar to 50 mol. %) inside the cavity and we have obtained ultrashort stretched pulses with a high peak power and energy. In this work relative intensity noise and frequency repetition stability is improved by applying isolator-polarizer (ISO-PM) with increased extinction ratio P-ext and by compensation of intracavity group-velocity dispersion from the value beta(2) similar to - 0.021 ps(2) to similar to - 0.0053 ps(2) at 1550 nm. As a result, we have obtained the low-noise stretched pulse generation with duration similar to 180 fs at a repetition rate similar to 11.3 MHz (with signal-to-noise ratio at fundamental frequency similar to 59 dB) with Allan deviation of a pulse repetition frequency for 1 s interval similar to 5,7 * 10(-9) and a relative intensity noise < -101 dBc/Hz.