All-fiber 1.55 µm erbium-doped distributed-feedback laser with single-polarization, single-frequency output by femtosecond laser line-by-line direct-writing

Abstract

We report an all-fiber single-polarization, single-frequency distributed-feedback (DFB) laser by a novel femtosecond laser line-by-line (LbL) direct-writing method. The phase-shifted fiber Bragg grating with a length of 26 mm is written in a single-mode non-polarization-maintaining (PM) Er-doped silica fiber. Single-polarization, single-frequency 1.55 µm laser oscillation is observed in the all-fiber DFB cavity configuration, with a pump threshold of 16 mW. The maximum laser output power from one port of the laser approaches 3.9 mW, and the slope efficiency of the DFB laser is 0.7% under the pump power of 640 mW. The FWHM (Full Width at Half Maximum) linewidth of the DFB fiber laser output is measured to be <1 kHz. High polarization extinction ratio of >30 dB has been observed by measuring the powers in the two orthogonal polarization directions of the DFB laser output. Single polarization mode laser oscillation has been verified. It is promising to use the femtosecond LbL writing method to achieve high-performance all-fiber single-polarization, single-frequency DFB fiber laser sources without relying on PM fiber elements.