Degree Name

Master of Engineering - Research


School of Electrical, Computer and Telecommunications Engineering


Linewidth enhancement factor, also called α , is a key parameter of a semiconductor laser (SL). This factor determines the characteristic of SL, such as the linewidth, the chirp, the injection lock range in an SL, the response of the SL to external optical feedback. Measurement of α has been attracting many researchers’ attention. Different approaches have been developed for obtaining accurate value of α . Self-mixing Interferometry (SMI) technique is thought as a simple and reliable method used for α measurement. In general, an SMI based sensing system consists of an SL, a lens and an external target. The information of the parameters associated with the system such as α , feedback level factor (denoted as C ) as well as external target are carried in the laser power(called SMI signal) emitted by the SL. The information can be retrieved by applying advanced signal processing on SMI signals.

Regarding α measurement, the existing SMI-based algorithms for measurement of α all have some limitations in terms of measure accuracy, feedback level range and measurement speed. In this thesis, a wavelet-based filtering algorithm is first developed for enhancing the quality of an SMI signal so that the accuracy of α retrieved from the SMI can be improved. Secondly, an improved algorithm is proposed for α measurement under a wide feedback level range up to C = 6 . Finally, a real-time IV measurement system for α is implemented by employing FPGA-based technique. The system is able to provide α value and C value with fast measurement speed and satisfied accuracy.