Low repetition rate passively mode-locked thulium-doped fiber laser for LIDAR system

Abstract

An all-fiber passively mode-locked thulium-doped fiber (TDF) ring laser with a repetition rate of 736 kHz was demonstrated. This is the lowest repetition rate among those of mode-locked TDF lasers to the best of our knowledge. Numerical calculations to find the best solution for successful mode-locking in a highly lossy oscillator were made based on Haus's master equation with variables such as oscillator loss, small signal gain and modulation depth. Based on the calculation, the laser was configured, where nonlinear polarization rotation (NPR) and two stages of TDF amplifier were properly applied. The overall length of oscillator is about 290 m. The output optical spectrum has a FWHM of 28 nm at 2 μm.