Optimization of an NALM Mode-Locked All-PM Er:Fiber Laser System

We present an improved design of a nonlinear amplifier loop mirror (NALM) mode-locked Er-fiber laser system with fiber amplifier and compressor contained in all polarization maintaining fiber architecture. Cooperated with a phase shifter in the NALM, the onset behaviors are investigated by optimizing the laser gain and net-cavity dispersion. As a result, the pulsation threshold is remarkably decreased and as short as 10-ms build-up time is achieved. In addition, with a single-stage bidirectional pumped Er-doped fiber amplifier, the self-started seed pulses of 2.6-mW average power, centered at 1576 nm, are nonlinearly compressed to 42-fs duration with single pulse energy of 2.2 nJ. Moreover, by appropriately optimizing the length of cavity gain and fiber in compressor, 28-fs duration with 3-nJ pulse energy is also achieved from a “morning call” pulse with 1567-nm central wavelength.