Hollow-core photonic crystal fiber (HC-PCF) has been proved to be a versatile platform for lab-on-a-fiber applications. By filling the fiber with various gases, liquids or solid materials, the light-matter interaction could be greatly enhanced. Many novel optical phenomena that are unattainable in free-space could be easily identified inside the fiber. Such a platform offers a promising route for creating compact, integrable and biocompatible all-fiber multifunctional optical devices. Here, we review our recent progress in developing a novel HC-PCF coined "hollow-core negative curvature fiber" (NCF) that could provide light guidance at spectral ranges covering from UV, visible, NIR to MIR. These NCFs show attributes of low transmission loss, octave-spanning transmission bandwidth, high damage threshold and single modeness. As a proof-of-concept demonstration for lab-on-a-fiber applications, we filled one of the fibers with ethanol (refractive index 1.36) to form a liquid-core anti-resonant fiber. At a low volume of 1 μL, Raman signal from ethanol was observed at a pump power of 2 mW. Such a high performance NCF opens a window for applications in fiber-enhanced spectroscopy, biochemical sensing and nano-plasmonics.
We report on an ultraviolet-enhanced supercontinuum generation in a uniform photonic crystal fiber pumped by a giant-chirped mode-locked Yb-doped fiber laser. We find experimentally that the initial pluses with giant chirp leads more initial energy transferred to the dispersive waves in visible and ultraviolet wavelength. An extremely wide optical spectrum spanning from 370 nm to beyond 2400 nm with a broad 3 dB spectral bandwidth of 367 nm (from 431 nm to 798 nm) is obtained. Over 36% (350 mW) of the total output power locates in the visible and ultraviolet regime between 370 nm and 850 nm with a maximum spectral power density of 1.6 mW/nm at 550 nm. In addition, a blue-enhanced supercontinuum generation pumped by a giant-chirped SESAM mode-locked ytterbium-doped fiber laser is studied. An extremely wide optical spectrum spanning from 380 nm to 2400 nm with total power of 3 W is obtained.