An experimental analysis of self-Q-switching via stimulated Brillouin scattering in an ytterbium doped fiber laser

摘要

An experimental study of self-Q-switching (SQS) in an ytterbium doped fiber laser (YDFL) arranged using a twin-core GTWave assembly is reported. The main mechanisms that initiate, amplify, and limit SQS pulses in amplitude are revealed to be stimulated Brillouin and Raman scattering (SBS/SRS) and Yb~(3+) amplified spontaneous emission. The parameters featuring SQS oscillation in terms of efficiency and stability of pulsing are found to be intra-cavity loss and feedback strength. An analysis of the YDFL SQS regime's features - pulsing time series, optical and RF spectra, amplitude and timing jitter - is provided for the two experimental situations: (i) when SQS pulsing stochastically intermits with regular active Q-switching pulses, given by the action of an intra-cavity acousto-optical modulator, and (ii) when a pure SQS mode is intentionally implemented in the YDFL without a modulator. The close relationship of the processes involved and SQS parameters in these two circumstances is demonstrated. Giant pulses with durations of 70-80 ns are shown to be generated at threshold intra-cavity powers of around 250 W (SBS threshold) and limited at approximately 2 kW of peak power (SRS threshold). At SBS-SQS, we show that at high values of intra-cavity loss, and thus reduced feedback, the amplitude and timing jitter values can be reduced to 5% and 7%, respectively.