Mid-infrared (MIR) fiber pulsed lasers are of tremendous application interest in eye-safe LIDAR, spectroscopy, chemical detection and medicine. So far, these MIR lasers largely required bulk optical elements, complex free-space light alignment and large footprint, precluding compact all-fiber structure. Here, we proposed and demonstrated an all-fiberized structured gain-switched Ho3+-doped ZBLAN fiber laser operating around 2.9 μm. A home-made 1146 nm Raman fiber pulsed laser was utilized to pump highly concentrated single-cladding Ho3+-doped ZBLAN fiber with different lengths of 2 m or 0.25 m. A home-made MIR fiber mirror and a perpendicular-polished ZBLAN fiber end construct the all-fiberized MIR cavity. Stable gain-switched multiple states with a sub-pulse number tuned from 1 to 8 were observed. The effects of gain fiber length, pump power, pump repetition rate and output coupling ratio on performance of gain-switched pulses were further investigated in detail. The shortest pulse duration of 283 ns was attained with 10 kHz repetition rate. The pulsed laser, centered at 2.92 μm, had a maximum average output power of 54.2 mW and a slope efficiency of 10.12%. It is, to the best of our knowledge, the first time to demonstrate a mid-infrared gain-switched Ho3+:ZBLAN fiber laser with compact all-fiber structure.

Few-mode and multi-core fibers are proposed and demonstrated for contactless vital signs monitoring in this paper. In-line optical fiber interferometers using few-mode and multi-core fibers are designed and offset splicing is utilized for mode excitation. Extinction ratio and insertion loss are analyzed experimentally under different offset distances. The fabricated in-line interferometers are packaged under the mattress to realize contactless vital signs signals collection. By using filtering techniques, both respiration and heartbeat signals can be recovered successfully, and respiration as well as heartbeat ratio are obtained. Mode excitation and interference are theoretically analyzed in few-mode fiber while curvature sensing experiments using multi-core fiber interferometer are performed to verify its excellent performance on vital signs monitoring. The successful demonstration on contactless vital signs monitoring makes few-mode and multi-core fibers promising candidates for healthcare applications.

We report the femtosecond (fs) laser fabrication of biomimetic omnidirectional iridescent metallic surfaces exhibiting efficient diffraction for practically any angle of light incidence. Such diffractive behavior is realized by means of multi-directional low-spatial-frequency, laser-induced periodic surface structures (LSFL) formed upon exploiting the cylindrical symmetry of a cylindrical vector (CV) fs field. We particularly demonstrate that the multi-directional gratings formed on stainless steel surface by a radially polarized fs beam, could mimic the omnidirectional structural coloration properties found in some natural species. Accordingly, the fabricated grating structures can spatially disperse the incident light into individual wavelength with high efficiency, exhibiting structural iridescence at all viewing angles. Analytical calculations using the grating equation reproduced the characteristic variation of the vivid colors observed as a function of incident angle. We envisage that our results will significantly contribute to the development of new photonic and light sensing devices.