Thermal Switching of Lasing Regimes in Heavily Doped Er3+ Fiber Lasers

TL;DR

This paper investigates thermal switching in heavily erbium-doped fiber lasers, demonstrating stable pulsed and continuous regimes and explaining the effect through phonon-assisted up-conversion process weakening at low temperatures.

Contribution

It introduces the observation of thermal switching in erbium-doped fiber lasers and provides a theoretical explanation involving phonon interactions affecting up-conversion.

Findings

Thermal switching from pulsed to CW regime upon cooling to liquid nitrogen temperature.

Stable laser operation achieved with cavities as small as 50 mm.

Theoretical analysis links the effect to weakening of up-conversion due to reduced phonons.

Abstract

A pulsed regime of short-cavity, heavily erbium-doped fiber lasers is of high interest for its possible applications in telecommunications and sensorics. Here, we demonstrate these lasers in two configurations, distributed feedback laser and compare it with a classic Fabry-Perot type laser. We have managed to create lasers that function stably with cavities as small as 50 mm. Pulse properties such as amplitude, frequency and duration, are in a good agreement with our theoretical analysis, which takes into account spontaneous emission. We report the observation of the thermal switching effect, which consists of the pulsing regime changing to CW upon cooling the laser cavities down to the liq-uid nitrogen temperature. We theoretically show that this effect may be explained by weakening of the up-conversion process responsible for the pulsed regime. The slowing of the up-conversion processes is due to the energy mismatch in this process, which is overcome by interaction with phonons. At low temperatures, the number of phonons decreas-es and pulsing switches off.