We demonstrate that the strong 4-level Yb emission in a fiber laser can be almost completely suppressed in an Yb all-solid double-clad photonic bandgap fiber, resulting in highly efficient high-power monolithic Yb fiber lasers operating at the 3-level system. We have achieved single-mode continuous wave laser output power of ~151W at ~978nm with an efficiency of 63% with respect to the launched pump power in a practical monolithic fiber laser configuration for the first time. The demonstrated power in this work are setting new records for diffraction-limited double-clad fiber lasers operating at ~978nm.

We experimentally demonstrated compact orange-light passively Q-switched praseodymium (Pr³⁺)-doped all-fiber lasers utilizing two-dimensional (2D) transition-metal dichalcogenides (TMDs, WS₂ and MoS₂) as saturable absorbers (SAs). The filmy TMDs SAs are fabricated by evaporating the composite of TMDs nanosheets and polyvinyl alcohol (PVA), and then inserted into an orange-light Pr³⁺-doped fiber laser cavity, which is designed by coating dielectric mirrors on fiber ends. Stable passively Q-switched orange lasers at 604 nm are successfully achieved. The passive Q-switching generated the short pulse duration of 435 ns and 602 ns, as well as the tunable repetition rate in the range of 67.3 ~132.2 kHz and 50.8 ~118.4 kHz, respectively. This is, to the best of our knowledge, the shortest-wavelength operation of 2D-material-based pulsed fiber lasers.

We evaluated the feasibility of embedding periodically arranged squares with planar and vertical texture into a background with a developable-modulation (DM) type cholesteric liquid crystal (CLC) fingerprint texture by a two-step ultraviolet-induced polymerization method. Checker-patterned optical diffractive elements, which can be seen as a variation of a two-dimensional (2D) barcode, were first realized and the dependence of diffraction behaviors on incident light polarization and applied voltage were investigated. Taking advantage of the natural randomness and uncontrollable variations of a DM-type fingerprint textures, a polymer-stabilized CLC (PSCLC) graphic symbol with a 2D barcode pattern was then implemented with enhanced anti-counterfeiting features that are difficult to falsify or duplicate. The results indicate that the multiplexing of nonuniform DM-type fingerprint gratings, cross-polarized light readout, and unique polarization diffraction characteristics can improve the level of security.

Wavelength-tunable continuous-wave and Q-switching visible Ho ³⁺ -doped all-fiber lasers emitting at green and deep-red wavelengths are successfully demonstrated.

Efficient cladding-pumped three-level Yb fiber lasers are difficult to achieve due to the competing four-level system and necessary high inversions. We demonstrate an efficiency of $\sim 62.7\%$ versus a coupled pump, a record for cladding-pumped fiber lasers with a single-pass pump. 84 W at $\sim 978\mathrm{nm}$ with $\sim 1.12M^2$ was achieved, a record power for flexible fibers. Amplified spontaneous emission was suppressed by $>40\mathrm{dB}$. The efficiency is quantum-limited $\sim 94\%$ versus an absorbed pump. This is made possible by the use of a photo-darkening-free Yb phosphosilicate core and recent progress in single-mode large-core all-solid photonic bandgap fiber designs, which provide the necessary large core-to-cladding ratio and suppression of the four-level system.