Preparation and characterization of highly thulium- and alumina-doped optical fibers for single-frequency fiber lasers

TL;DR

This paper reports the fabrication and characterization of highly thulium- and alumina-doped optical fibers for efficient single-frequency fiber lasers, demonstrating high pump absorption and stable laser operation.

Contribution

It introduces a modified chemical vapor deposition method to produce fibers with high thulium doping and alumina co-doping, optimizing absorption and laser performance.

Findings

Pump absorption up to 70dB/m at 1611nm

Achieved slope efficiency of 22% at 1944nm

Demonstrated stable single-frequency laser operation

Abstract

Thulium-doped fibers suitable for core-pumped single-frequency lasers were fabricated by the modified chemical vapor deposition (MCVD) method. Refractive index profile, doping profile and spectral absorption was measured. High doping concentration of thulium ions should be achieved to allow for high absorption of light at a pump wavelength while the thulium ions clustering should be avoided to prevent the cooperative upconversion and quenching processes. The fabricated fibers featured pump absorption up to 70dB/m at a pump wavelength of 1611nm. The single-frequency master oscillator with a resonator composed of a pair of fiber Bragg gratings and a thulium-doped fiber was demonstrated with predominantly single ended operation. We achieved a slope efficiency of 22% and a threshold of 22mW at a lasing wavelength of 1944nm.