Sub-100 fs pulses from an all-polarization maintaining Yb-fiber oscillator with anomalous dispersion higher-order-mode fiber

All-integrated modelocked Yb-fiber lasers are very attractive for a wide range of potential applications, including micromachining, spectroscopy, metrology, nonlinear imaging and several clinical applications. The adoption of these lasers beyond laboratory environments is hindered because of the sensitivity of modelocking operation against external perturbations. In non-polarization maintaining (non-PM) fibers, temperature changes, fiber bending and other mechanical perturbations, can influence the birefringence properties of the fibers which can result in degradation of device performance and eventually losing of modelocking. Since environmental instabilities in fiber lasers mainly arise from induced changes in the birefringence of non-PM fibers, the straightforward approach to make the laser robust against them is to use PM fibers with light polarized only along the slow axis [1,2]. A major challenge to develop operational and environmentally stable fiber lasers delivering high fidelity femtosecond pulses at 1 μm wavelength is to realize good higher order dispersion compensation and to manage intracavity nonlinearities.