Rare Earth Doped Optical Fibers with Multi-section Core.

The gain bandwidth of a single-mode fiber is limited by the atomic transitions of one rare earth gain element. Here we overcome this long-standing challenge by designing a new single-mode fiber with multi-section core, where each section is doped with different gain element. We theoretically propose and experimentally demonstrate that this configuration provides a gain bandwidth well beyond the capability of conventional design, whereas the inclusion of multiple sections does not compromise single-mode operation or the quality of the transverse modal profile. This new fiber will be beneficial in realizing all fiber laser systems with few-cycle pulse duration or octave tunability.

Developing high energy dissipative soliton fiber lasers at 2 micron.

While the recent discovered new mode-locking mechanism--dissipative soliton--has successfully improved the pulse energy of 1 µm and 1.5 µm fiber lasers to tens of nanojoules, it is still hard to scale the pulse energy at 2 µm due to the anomalous dispersion of the gain fiber. After analyzing the intracavity pulse dynamics, we propose that the gain fiber should be condensed to short lengths in order to generate high energy pulse at 2 µm. Numerical simulation predicts the existence of stable 2 µm dissipative soliton solutions with pulse energy over 10 nJ, comparable to that achieved in the 1 µm and 1.5 µm regimes. Experimental operation confirms the validity of the proposal. These results will advance our understanding of mode-locked fiber lasers at different wavelengths and lay an important step in achieving high energy ultrafast laser pulses from anomalous dispersion gain media.

Compact wearable dual-mode imaging system for real-time fluorescence image-guided surgery.

A wearable all-plastic imaging system for real-time fluorescence image-guided surgery is presented. The compact size of the system is especially suitable for applications in the operating room. The system consists of a dual-mode imaging system, see-through goggle, autofocusing, and auto-contrast tuning modules. The paper will discuss the system design and demonstrate the system performance.

High power tandem-pumped thulium-doped fiber laser.

We propose a cascaded tandem pumping technique and show its high power and high efficient operation in the 2-µm wavelength region, opening up a new way to scale the output power of the 2-µm fiber laser to new levels (e.g. 10 kW). Using a 1942 nm Tm(3+) fiber laser as the pump source with the co- (counter-) propagating configuration, the 2020 nm Tm(3+) fiber laser generates 34.68 W (35.15W) of output power with 84.4% (86.3%) optical-to-optical efficiency and 91.7% (92.4%) slope efficiency, with respect to launched pump power. It provides the highest slope efficiency reported for 2-µm Tm(3+)-doped fiber lasers, and the highest output power for all-fiber tandem-pumped 2-µm fiber oscillators. This system fulfills the complete structure of the proposed cascaded tandem pumping technique in the 2-µm wavelength region (~1900 nm → ~1940 nm → ~2020 nm). Numerical analysis is also carried out to show the power scaling capability and efficiency of the cascaded tandem pumping technique.

Efficient Ho:LuLiF4 laser diode-pumped at 1.15 µm.

We report the first laser operation based on Ho(3+)-doped LuLiF(4) single crystal, which is directly pumped with 1.15-µm laser diode (LD). Based on the numerical model, it is found that the "two-for-one" effect induced by the cross-relaxation plays an important role for the laser efficiency. The maximum continuous wave (CW) output power of 1.4 W is produced with a beam propagation factor of M(2) ~2 at the lasing wavelength of 2.066 µm. The slope efficiency of 29% with respect to absorbed power is obtained.

High-power narrow-bandwidth thulium fiber laser with an all-fiber cavity.

We report diode pumped high power 2-µm Tm(3+) fiber lasers with an all-fiber configuration. The all-fiber configuration is completed by specially designed fiber Bragg gratings with similar structure parameters matched to the gain fiber. The maximum output power is 137 W with an optical-to-optical slope efficiency of 62% with respect to absorbed 793-nm pump power. The laser wavelength is stabilized at ~2019 nm with a spectral linewidth less than 3 nm across all output levels. To the best of our knowledge, this is the highest 2-µm laser output from a single narrow bandwidth all-fiber laser system.