Research On Scattering-Assisted Fiber-Type Microcavity Laser

Fiber-type microcavity laser is a novel style of laser based on optical fluidic technology,which is filled with gain and scattering medium in microlevel fiber structure(such as capillary).According to different resonance mechanisms,fiber-type microcavity lasers can be divided into two categories,namely,disordered style lasers and Whispering Gallery Mode(WGM)lasers.Fiber-type WGM laser has attracted wide attention in many fields such as imaging,sensing and detection due to its simple structure,low cost,small mode volume,high quality factor and good tunability.Liquid Crystal(LC),as a weak scattering medium,has both birefringence characteristics and anisotropy,good temperature/electric field response ability,and can be well integrated with various dyes to form a gain medium,providing an excellent environment of light and matter interaction for the implementation of adjustable and controllable microcavity laser.Therefore,this thesis focuses on the laser characteristics and tuning performance of the fiber-type WGM laser filled with LC solution.The concrete details of the thesis are as follows:Firstly,two kinds of microcavity lasers with different mechanisms,namely refractive-guided microcavity laser and gain-guided microcavity laser,are realized by filling the capillary tubes with LC solution doped with laser dye or laser dye solution.The experiments and simulations show that the Free Spectral Range(FSR)of the refractiveguided microcavity laser is about 0.94 nm,while the spectra of the gain guided laser are randomly distributed and dynamically changed.This is because the high refractive index of LC molecules in refractive index guided lasers,and the weak scattering of LC molecules plays an active role in laser generation(that is,the laser works under the scattering assisted mechanism of LC molecules).In order to verify the accuracy of the experimental results and avoid the chance,lasers filled with different laser dyes are made and their laser properties are analyzed and compared.Secondly,due to the good response ability of LC molecule of scattering medium to temperature and voltage,the resonant wavelength tuning of WGM laser is realized by temperature/voltage regulation in this thesis.The results indicate that the resonant wavelength of WGM laser presents an opposite tuning rule under the action of voltage and temperature,that is,as the temperature increases or the voltage decreases,the output spectra will blue shift,and the vice versa will cause the red shift,and the maximum value of central wavelength shift is about 5.3 nm.In addition,the stability of voltage and temperature regulation is further explored.Through comparison,it can be seen that the fiber-type WGM laser has good stability and repeatability under voltage control,which is attributed to the fact that compared with temperature regulation,voltage regulation has less influence on the stability of dye molecules.Finally,on the basis of the stability of voltage regulation,a new type of laser tuned by zonal voltage in free space mode is developed in this thesis.The laser can realize spectrum broadening,reconstruction and programming through voltage regulation of zones,laying an infarctate foundatin for the research of spectral programmable soft material laser.