Single longitudinal mode narrow linewidth thulium-doped fiber laser based on an eye-shaped dual-ring filter

A single-longitudinal-mode (SLM) thulium-doped fiber laser, based on an eye-shaped passive dual-ring filter, is designed and constructed. The compound cavity consisting of four couplers used to increase the longitudinal mode spacing, its performance numerically analyzed in detail. homemade uniform Bragg grating serves as a wavelength selection device saturable absorber further suppress intense competition laser cavity, ensuring output. experimental results demonstrate output with center 2,049.85 nm optical signal-to-noise ratio 63 dB. Moreover, power fluctuation less than 0.6 dB, 0.03 over continuous measurement period 60 min, demonstrating excellent stability. linewidth measured using unbalanced Michelson interferometer β -separation line method, resulting 11.22 kHz.