Concept and implementation of the birefringence-managed normal-dispersion fiber laser. (a) Coupling manner at the interface between SMF and PMF (left) and laser operations at different polarization orientations (right). The and components of pulses along two principal axes of PMF rely on the input polarization orientation as well as and components in SMF, following the relation depicted in the coordinate system. When or 0 (bottom right) and (top right), DS and BMS operations are achieved, respectively, in which the spectrum and chirp (pulse) are denoted by a solid (dot) curve. (b) Comparison of BMS and DS in the same fiber laser from aspects of frequency chirp, harmonic order, pulse duration, bandwidth, pulse energy, and self-starting threshold. (c) Sketch of the BMS fiber laser and measurement system. LD: laser diode; WDM: wavelength division multiplexer; EDF: erbium-doped fiber; OC: optical coupler; PI-ISO: polarization insensitive isolator; CNT-SA: carbon nanotube saturable absorber; ET-PC: electrically tunable polarization controller; ED: ET-PC driver; PC: personal computer; DCF: dispersion compensating fiber; PD: photodetector; PBS: polarizing beam splitter; OSA: optical spectrum analyzer; OSC: oscilloscope; AC: autocorrelator; FROG: frequency-resolved optical gating; RFA: radio frequency analyzer.