Measurement Of The Semiconductor Laser Linewidth Enhancement Factor In The Low-light Feedback

The measurement of linewidth enhancement factor α is an active research topic, because α is one of characters that differentiate semiconductor lasers from other type lasers. The parameter α relates with many characters of semiconductor, such as linewidth, lineshape, injection-locking range and so on.The laser self-mixing interferometric technology is an exact measure technique. The measure system has very simple and compact set-up and autocollimation capability. The technology is has been studied and applied extensively, and it is mostly applied to geometry sensing measure and laser parameters measure.The parameter a is measured by the laser self-mixing interferometric technology in this paper. The week optical feedback self-mixing system is studied when the external cavity of semiconductor laser suffers a harmonic vibration. The following tasks are accomplished.Firstly, many simulations are completed based on laser self-mixing interferometric system model. We study the relation between the self-mixing signal and the parameters in model, the parameters including linewidth enhancement factor, optical feedback factor, amplitude of the external target with simple harmonic vibration and the initial distance between laser emitting surface and the target. The laws achieved are very significant to establish the perfect model of self-mixing interferometric and explore the new parameters measurement approaches.Secondly, the gradient-based optimization algorithm of measuring a is established after theory analysis and model simulations. New iterate formula is presented and alterable step is introduced when parameters are updating. The simulation results show the algorithm has higher accuracy and better antinoise capability. The relative standard deviation of α is less than 2.55% when SNR is to 20dB. In addition, the validity and accuracy is proved by measured datum, the results show the relative standard deviation of α is less than 5.1%.At last, the algorithm in this paper is contrasted with two congeneric algorithms based on self-mixing interferometric effect. Simulation and experiment datum processing results show the algorithm in this paper is superior to existing congeneric algorithms.