RESUMO
For the first time, to our knowledge, an all-solid transverse Anderson localizing optical fiber laser is demonstrated. A combination of the molten core and stack-and-draw fiber fabrication techniques is used to produce a 112 µm core diameter fiber that is a random array of Yb-doped high index and passive low index regions. A localized channel first assists in the guidance of amplified spontaneous emission before stimulating laser action, which occurs in the same channel via mixed Anderson localization and step index wave-guiding. Threshold behavior and lasing are monitored with changing output power slopes, beam profiling, spectral content, fluorescence clamping, and temporal intensity. The average output power is stable, while the laser wavelength hops between 1066 and 1088 nm. Lasing is highly directional along the fiber axis.
RESUMO
The focus of this study was the development of a second generation of fiber lasers internally cooled by anti-Stokes fluorescence. The laser consisted of a length of a single-mode fiber spliced to fiber Bragg gratings to form the optical resonator. The fiber was single-moded at the pump (1040â nm) and signal (1064â nm) wavelengths. Its core was heavily doped with Yb, in the initial form of CaF2 nanoparticles, and co-doped with Al to reduce quenching and improve the cooling efficiency. After optimizing the fiber length (4.1â m) and output-coupler reflectivity (3.3%), the fiber laser exhibited a threshold of 160â mW, an optical efficiency of 56.8%, and a radiation-balanced output power (no net heat generation) of 192â mW. On all three metrics, this performance is significantly better than the only previously reported radiation-balanced fiber laser, which is even more meaningful given that the small size of the single-mode fiber core (7.8-µm diameter). At the maximum output power (â¼2â W), the average fiber temperature was still barely above room temperature (428â mK). This work demonstrates that with anti-Stokes pumping, it is possible to induce significant gain and energy storage in a small-core Yb-doped fiber while keeping the fiber cool.
RESUMO
Recent progress in the fabrication of Yb-doped silicate fibers with low concentration quenching and low background absorption loss has led to the demonstration of anti-Stokes-fluorescence cooling in several aluminosilicate compositions. This breakthrough is critical to combat deleterious thermal effects due to the quantum defect in fiber lasers and amplifiers. Since cooling efficiencies remain low (1-2.7%), it is paramount to engineer compositions that improve this metric. We report a silica fiber with a core glass heavily doped with aluminum and phosphorus that sets, to our knowledge, a few new records. This few-mode fiber (16-µm core) was cooled in air by -0.25â K from room temperature with â¼0.5â W of 1040-nm power. The measured cooling efficiency is 3.3% at low pump power and 2.8% at the power that produced maximum cooling. The critical quenching concentration inferred from the measured dependence of cooling on pump power and careful calibration of the pump absorption and saturation is 79â wt.%. The inferred background absorption loss is 15â dB/km. Together with the fiber's average Yb concentration of 4.2â wt.%, these metrics rank among the best reported in a silica glass.
RESUMO
An all-glass optical fiber capable of two distinct methods of optical thermometry is described. Specifically, a silica-clad, barium fluorosilicate glass core fiber, when pumped in the infrared, exhibits visibly intense green defect luminescence whose intensity and upper-state lifetime are strong functions of temperature. Intensity-based optical thermometry over the range from 25°C to 130°C is demonstrated, while a lifetime-based temperature sensitivity is shown from 25°C to 100°C. Time-domain measurements yield a relative sensitivity of 2.85% K -1 at 373 K (100°C). A proof-of-concept distributed sensor system using a commercial digital single-lens reflex camera is presented, resulting in a measured maximum relative sensitivity of 1.13% K -1 at 368 K (95°C). The sensing system described herein stands as a new blueprint for defect-based luminescence thermometry that takes advantage of pre-existing and relatively inexpensive optical components, and allows for the use of standard cameras or simply direct human observation.