| The liquid crystal laser is a new type of laser that uses the whispering gallery mode,Bragg reflection,or multiple scattering to provide optical resonance by doping fluorescent dyes into the liquid crystal.Liquid crystal laser has the advantages of easy tuning,small size,narrow linewidth and simple manufacturing due to their good response in many aspects such as temperature,electric and magnetic field.Liquid crystal laser has attracted the attention of researchers in many fields.The cholesteric liquid crystal can support multiple optical modes,and these optical modes can be excited by doping fluorescent dyes into the cholesteric liquid crystal and using an external excitation light source.a new type of three-layer Bragg liquid crystal microcavity was designed and the laser emission behavior after laser pumping was analyzed in detail.The microcavity was composed of the dye-doped cholesteric liquid crystal droplet,glycerol,and the hollow glass microsphere.We have observed whispering gallery mode,radial Bragg mode,and Bragg whispering gallery mode in the three-layer cholesteric liquid crystal microspheres with different pitch and liquid crystal refractive index.We also analyzed in detail six laser emission conditions and formation mechanisms and systematically studied the thresholds of different laser emission modes.To solve the problem that the solid-state laser is difficult to tune and the cholesteric liquid crystal droplet laser is unstable,we used the solid-shell dye-doped cholesteric liquid crystal three-layer microspheres manufactured above,and then used a 532 nm pulse laser to bump the above-mentioned three-layer liquid crystal microspheres and the laser behavior was shown as photonic bandgap mode and whispering gallery mode by controlling the refractive index and pitch of the liquid crystal.The effect of temperature and electric field on the emission peak wavelength of photonic bandgap and whispering gallery mode was studied.The above-mentioned cholesteric liquid crystal microspheres exhibited good tunable characteristics.To solve the problem of the difficult and unstable pumping process of liquid crystal lasers,this paper integrated the liquid crystal laser resonator on the end face of the multimode fiber,optimized the way of the liquid crystal laser emission,and studied a new type of fiber micro-tip liquid crystal laser emission method and applied it to high-sensitivity temperature sensing.The structure was based on a fiber probe with a tapered hollow capillary tube,where the probe was welded to the end of a multimode fiber and filled with dye-doped cholesteric liquid crystal and glycerin.The liquid crystal molecules can self-assemble into a periodic dielectric spiral structure under the action of chiral dopants.Therefore,the cholesteric liquid crystal formed a mirrorless Bragg structure microcavity at the fiber end face.When the dye-doped cholesteric liquid crystal was pumped by a 532 nm pulsed laser coupled to the multimode fiber,due to the existence of the multimode coupler,the photonic bandgap mode of the cholesteric liquid crystal was excited and received through the fiber end face at the same time.Therefore,a sharp single peak of the photonic bandgap mode appeared in the laser emission spectrum.This excitation method is stable and simple.By monitoring the wavelength shift of the photonic bandgap mode in the laser emission spectrum to achieved fine temperature sensing,a temperature sensing sensitivity of-9.2 nm/°C,and an ultra-high quality factor of 67.4°C-1were obtained.This high-sensitivity cholesteric liquid crystal fiber tip temperature sensor has the characteristics of small size and identifiable emission spectrum. |
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