Research On Single-frequency Narrow Linewidth Laser Based On Whispering Gallery Mode Cavity And Self-injection Locking

With the development of laser technology,semiconductor lasers have been widely used in different fields,such as atomic clocks,high-resolution spectroscopy,quantum information science,high-resolution optical sensing,light detection and ranging,etc.However,the intrinsic linewidth is limited by the size and quality factor of the laser resonator,usually in the megahertz range,and can no longer support the optimization of the relevant applications.Therefore,how to effectively compress the linewidth of semiconductor lasers has always been one of the continuous research directions in the field of lasers.The external cavity semiconductor laser based on self-injection locking has the advantages of simple structure,narrow spectral linewidth and wide tuning range,and self-injection locking does not require any electronic devices,which is convenient for packaging,can improve thermal stability,and reduce the effect of noise on frequency.It has received more and more attention and research from researchers.The whispering gallery mode(WGM)microcavity has the characteristics of high quality factor,small size,easy integration,etc.,and in the transmission window of the microcavity material,it is suitable for any laser of different wavelengths such as ultraviolet light,visible light,infrared light.It is an ideal optical component as an external cavity resonator for narrow linewidth lasers.With the continuous improvement of micromachining technology,the research of WGM microcavity with more types and higher quality factor has also made breakthroughs,which further improves the application of microcavity.As a kind of WGM microcavity,the microrod cavity has the characteristics of high quality factor and easy processing,and has been applied in different optical fields.Based on the microrod cavity,this thesis has done the following related work on the realization of narrow linewidth lasers:1.The formation of the WGM and the distribution of the electromagnetic field in the WGM microcavity are analyzed from the perspectives of geometric optics and electromagnetic field theory,respectively.The electromagnetic field distribution of the microrod cavity is simulated by COMSOL.2.The coupling platform of the tapered optical fiber and the microrod cavity was built,and the Q value of the microrod cavity is calculated by measuring the time-domain transmission spectrum,which is about 1.23×10~6.The coupling of the microrod cavity and the prism is modeled,and the changes of the optical field in the three media of prism,air and microrod cavity are analyzed,and the influence of the incident angle and the coupling distance on the coupling efficiency,which can provide guidance for the optimal adjustment of narrow linewidth lasers.3.A single-frequency narrow linewidth laser system based on WGM microrod cavity and self-injection locking is designed and built,and a time-delayed self-heterodyne linewidth measurement system is built.By optimizing and adjusting the prism in coupling,the microrod cavity and the prism are efficiently coupled to excite WGM,and the optical feedback is generated by resonant Rayleigh scattering in the WGM microrod cavity,which achieves 20 times the linewidth compression of the DFB laser diode.The DFB laser diode linewidth was compressed from 2.5 MHz to 127 KHz.