On the basis of computing models of stimulated Brillouin scattering (SBS), the optical limiting response characteristics in SBS process are investigated theorctieally. Dependence of limiting parameter ——residual energy on pump parameters (input power density, pulse duration), medium parameters (gain, phonon life time) and configuration parameters (focusing length, cell length) are analyzed. Response characteristics of SBS limiting are given by studying the variation of delay time, residual peak power and residual energy. Ideal response system can be obtained by choosing a medium with larger gain and shorter phonon life time. But the vesidual energy could not be got rid of by choosing SBS medium parameters only. In experiment, we obtained flat-roofed optical limiting pulse shapes in SBS process using dye absorption.

Based on the numerical models of stimulated Brillouin scattering(SBS) limiting, the influence of seed pulse duration, induced time and seed power on transmitted pulse shape in SBS optical limiting process is theoretically investigated. By seeding a Stokes pulse into the SBS optical limiting system, the SBS induced by this seeded Stokes pulse can reshape the transmitted limited pulse profile. By choosing suitable physical parameters, the best limited temporal profile can be obtained. The theoretical simulation shows that limited pulse shape can be controlled. When seed pulse duration is chosen as five times the length of the pump pulse duration and the delay time is just the same as the pump pulse duration, the limited pulse shape levels off, and the higher the seed power is, the lower the limited power steps. Optical limiting of pulse-shape can be controlled by introducing a seed to a stimulated Brillouin scattering cell.

Adopting noise initiation mode of stimulated Brillion scattering (SBS), the influence of focal length on optical limiting power and energy is numerically simulated. It shows that the characteristic of limiting power and energy are controlled by focal length. When focal length is moderate, say 15cm, the limiting energy is lowest. When focal length is short, say 5cm, the characteristic of limiting power is close to ideal. In experiment, focusing 8ns, 1064nm, 16mJ pulses into CCl4 medium, the variation of limiting power and energy versus focal length is investigated. The experimental results are in good agreement with the conclusions predicted by the simulations.

The dye doped liquid crystal filling tunable laser has been widely adopted in many areas, such as optical communication, sensor and medical imaging with a low cost. The temperature-sensitive refractive indice of liquid crystal makes it a filling material suitable for being used in the capillary. The existing studies have introduced the liquid crystal filled with capillary, which has the complicated craft and big cost. As is well known, the capillary has the advantages of the easy preparation and low cost, but the liquid crystal filled capillary based dye doped liquid crystal filling tunable laser is rarely studied. Dye-doped cholesteric liquid crystal (CLC) based tunable laser has many advantages such as small-size, low-threshold, high-efficiency, wide-tunability with wavelength varying from ultraviolet to infrared. So It shows great promise in applications of single-chip experiment, biological identification and sensor. To develop high-efficiency dye-doped CLC tunable lasers for different potential applications, it is crucial to explore their emission performances in three laser emission modes:distributed feedback (DFB), whispering gallery modes (WGMs) and random laser (RL). We theoretically propose and experimentally demonstrate the characteristics of laser emission based on dye-doped CLC in capillary tubes which are treated with the photo-alignment PI films. Firstly, we prepare capillary tubes filled with dye-doped CLC with three inner diameters of 100 m, 200 m and 300 m. By using a double-frequency Nd:YAG 532 nm laser as a pump source, the emission spectra, energy thresholds and temperature dependent tunabilities in the cases with and without PI films are analyzed, respectively. It is clearly shown that dye-doped CLC in the capillary with the PI films generate DFB-mode lasing and WGMs lasing. Experimental results show that the capillaries with thinner-inner diameters and PI films have lower emission threshold energies than without PI films, the former threshold can be reduced to as low as 4.5 J mm-2. Meanwhile, with temperature increasing, the DFB wavelength is blue-shifted, resulting in a central wavelength tuning range of 5.9 nm. Then high performance WGM with an FSR of 1.05 nm is created when the temperature is increased up to as high as 43 ℃. It can be found that the laser emission with photo-alignment PI films shows an optimum RL mode with less laser emission peaks than the laser emission without photo-alignment PI films. In this work we propose and demonstrate that a capillary based dye-doped CLC tunable laser with photo-alignment PI films can easily work with three emissions:DFB-mode, WGMs or RL by changing optical field and the applied temperature. The above research results provide valuable clues and methods to develop high-quality dye-doped CLC based tunable laser, filter, optical switch and sensor.

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.