Tuning characteristics of fluorescent light source by dye-doped liquid crystal filled hollow fiber
Authors: L&uuml; Yue-Lan  , Yin Xiang-Bao  , Yang Yue  , Liu Yong-Jun  , Yuan Li-Bo  ,   Key Lab of In-fiber Integrated Optics, Ministry Education of China, Harbin Engineering University, Harbin 150001, China;,   College of Science, Heilongjiang University of Science and Technology, Harbin 150022, China
Published: December 2020

The fluorescent fiber light source has been widely used in many areas, such as optical fiber communication and medical imaging, owing to its low cost and wide optical spectrum. The temperature-sensitive refractive index of liquid crystal makes it a suitable filling material used in the fluorescent light source. The existing work has investigated the filling of liquid crystal into the air holes in cladding of photonic crystal fiber. However, the photonic crystal fiber has the disadvantages of complicated craft and high cost. As is well known, the hollow fiber has the advantages of the easy preparation and low cost, but the filling of liquid crystal into the hollow fiber of fluorescent light source is rarely investigated. In this paper, we investigate that a tunable hollow fiber of fluorescent light source is filled with dye doped liquid crystals. The transmission characteristics of the fluorescent light source are theoretically analyzed. The variation in property of the B4400 fluorescent spectrum is numerically discussed with the dye molecule energy level structure theory. The numerical simulation results show that the relative refractive index is dependent on temperature. It first increases linearly with the increase of temperature and then exponentially increases rapidly till clearing point 61.9 C, finally decreases slowly to a saturated value. In order to find an optimum doping concentration, the doping-concentration-dependent fluorescence output intensity is analyzed by using the super continuum spectrum of YAG pump with a wavelength of 1064 nm. The fluorescence light intensities are amplified at three different selective dye doping concentrations, namely 0.2 wt%, 1 wt% and 2 wt% in the experiment, respectively. The highest output is obtained at the 1 wt% doping concentration, which verifies the selective fluorescence amplification property of the fluorescent source. It is also demonstrated that the transmission characteristics and the tunable range of the liquid crystal filled fluorescent light source can be adjusted by modulating the temperature in experiment. And the temperature-dependence of the fluorescence source is experimentally demonstrated by using the 1 wt% doping concentration dye-doped liquid crystal. Using a pulsed YAG pump with a wavelength of 532 nm, tunable characteristics of the fluorescent light source composed of a dye-doped liquid crystal filled hollow fiber, are studied and show that the central wavelength increases from 590 nm to 605 nm and the spectral width broadens from 228 nm to 236 nm with the increase of the temperature. The proposed fluorescent light source can be controlled by adjusting the temperature within limits. These findings will give a guidance for the practical applications of the dye doped liquid crystal based fluorescent light source, and offer a theoretical foundation for the further study of the liquid crystal filled fluorescent fiber light source.