Tunable 2 μm Fiber Laser Utilizing a Modified Sagnac Filter Incorporating Cascaded Polarization Maintaining Fibers

A widely tunable 2 μm fiber laser based on a modified Sagnac filter incorporating cascaded polarization maintaining fibers (PMF) is proposed and demonstrated. The modified Sagnac filter consists of two cascaded PMFs which have a 45° angle offset between their fast axes. Two polarization controllers (PCs) are inserted to optimize polarization status in the cavity. The lasing wavelength can be tuned by adjusting axial strain applied on PMFs. A tuning range of more than 40 nm is obtained with free tuning step, ranging from 1859 nm to 1901 nm. The proposed tunable laser is efficient to obtain precise wavelength tunability and wide tuning range.