Advanced fiber lasers and related all-fiber devices

Fiber lasers based on rare-earth ions now play an important role in several applications ranging from communications and surgery to spectroscopic sensing because of their efficiency and compactness, and their intrinsic compatibility with single mode communication fibers. As such, there is a strong need to investigate key issues related to the design and fabrication of "rugged" state-of-the-art fiber lasers, and in particular to fabricate versatile high-performance fiber lasers based on "all-fiber" devices, i.e. using only in-fiber devices. This dissertation addresses some of these needs.; One such issue is the polarization property of lasers and amplifiers based on polarization preserving fibers. A dedicated study of the polarization properties of amplifiers and lasers based on rare-earth doped elliptical core fibers has been performed. The results indicate a polarization dependent gain, with a larger gain at the polarization parallel to the major axis of the ellipse. This gain anisotropy is attributed to the differences in the confinement of the two orthogonally polarized fundamental modes of the fiber.; Another issue that has been driven by several medical, sensing, and data storage applications is that of efficient laser transitions in the mid-infrared and visible spectral regions. Such lasers are difficult to achieve in conventional fibers based on silica glass hosts due to their relatively large phonon energies. A fluoride based glass host (ZBLAN) with low phonon energy was chosen to enable green and blue laser transitions using upconversion schemes in erbium and thulium respectively, and realize an efficient mid-infrared transition in erbium. Specifically, the following results have been demonstrated: (1) Green (544 nm) fiber laser with the highest combination of power (50 mW) and efficiency (37%) in Er:ZBLAN; (2) Novel Raman fiber laser-pumped 22 mW blue (490 nm) laser in Tm:ZBLAN; (3) Diode-pumped mid-infrared (2.7 mum) laser with 660 mW output in Er:ZBLAN.; The demonstration of substantial second order nonlinearities (∼1 pm/V) at UNM using thermal-assisted poling in normally symmetry forbidden silica glass has inspired worldwide research efforts aimed at achieving similar nonlinearities in fibers. All-fiber electro-optic devices based on such poled fibers are anticipated to enhance the performance of various lasers, including modelocked and tunable fiber lasers. This dissertation presents the first demonstration of stable, electro-optically tunable fiber Bragg gratings (FBGs) with a tuning range of 20 pm (2.5 GHz), which should enable applications such as reconfigurable add/drop filters and actively modelocked all-fiber lasers. Two key steps in the fabrication of the tunable FBGs viz. the fabrication of thermally stable FBGs, and a novel method for in-situ monitoring of fiber polishing are also demonstrated. Finally, this dissertation discusses issues related to the demonstration of all-fiber electro-optically tunable polarization rotators and their possible impact on future advanced fiber lasers.