All-passive phase locking of a compact Er:fiber laser system

A passively phase-locked laser source based on compact femtosecond Er: fiber technology is introduced. The carrier-envelope offset frequency is set to zero via difference frequency generation between a soliton at a wavelength of 2 mu m and a dispersive wave at 860 nm generated in the same highly nonlinear fiber. This process results in a broadband output centered at 1.55 mu m. Subsequently, the 40 MHz pulse train seeds a second Er: fiber amplifier, which boosts the pulse energy up to 8 nJ at a duration of 125 fs. Excellent phase stability is demonstrated via f-to-2f spectral interferometry. (C) 2011 Optical Society of America