Research On Linewidth And Phase Noise Characteristics Of A Narrow Linewidth External Cavity Diode Laser

Light source with low noise and narrow linewidth is widely used in optical communication and high precision sensing.The noise and coherence of light source directly affect the communication and measurement accuracy.The narrow linewidth laser with external cavity has become an ideal light source by increasing the cavity length and introducing the optical feedback of external cavity to effectively achieve the noise suppression and linewidth compression.Based on the principle of optical frequency selection in external cavity and the basic model of traditional external cavity diode laser,this paper introduced a new type of external cavity semi-conductor laser with the optical frequency selection structure using etalon.The linewidth and phase noise characteristics of laser were analyzed,based on which an optimization method of noise performance was proposed.The main contents of the thesis are as follows:(1)The basic working principle of the external cavity semi-conductor laser of the structure was illustrated by combining theory with experiment.The single longitudinal mode could be selected successfully with the aid of the optical frequency selection structure using etalon and filter.The side-to-side suppression ratio of lasing could be up to around 80 d B,and the output power could reach more than 10 m W.(2)A linewidth measurement system was built by means of beat frequency testing through delayed self-heterodyne.The beat frequency signal of the laser was measured.Then the phase noise and frequency noise characteristics were tested by a noise tester.The beat frequency spectrum and noise power spectral density were obtained,based on which the coherence and noise indices were analyzed.(3)The accuracy improvement of the etalon in external cavity was proved to be effective in optimizing the output characteristics of the laser by contrast experiment.With this method,the phase noise could be further suppressed by improving the accuracy of the etalon,and the Lorentz linewidth could be further reduced from 5?10 kHz to less than 1 kHz.