Impulsive noise is a major problem that seriously degrades the performance of self-mixing interferometry (SMI). A new method to rectify this issue is proposed. First, an outlier detection approach is employed to detect the data samples corrupted by the impulsive noise, and then the SMI signal waveform is rectified by means of least square (LS) curve fitting. The results show that the proposed method can effectively remove the impulsive noise without introducing distortion to the original waveform and thus lead to improvement in the performance of an SMI system.
The Alpha factor, also known as the linewidth enhancement factor, is one of the fundamental parameters for semiconductor lasers (SLs) as it characterizes many properties of the SLs, such as the responses to the electrical injection and the optical injection. Due to the great importance of alpha factor in research analysis and application design, the high accuracy of the experimental alpha measurement is required. The optical feedback self-mixing interferometry (OFSMI) based method for the alpha measurement is one of the popular approaches in the past twenty years due to its easy implementation and inexpensive, self-aligned experiment set-up. This paper proposes an effective data processing method applied in the frequency-domain based self-mixing approach for alpha factor measurement. The alpha value is estimated from the complex frequency spectrum of the feedback phase signal in an OFSMI system. However, some of the estimated results with large deviations are found in the experimental estimation due to the noises in practice. The work presented in the paper is twofold. Firstly, the errors of alpha estimation are analyzed. Secondly, the algorithm using distance-based outlier removal is proposed for optimizing the estimation results of alpha. The results show that the estimation accuracy of alpha can be achieved to 6.725% and 1.923% for the optical feedback level in the OFSMI system.
As an active research field, the self-mixing interferometry (SMI) based on semiconductor lasers (SLs) is a highly promising and emerging technique for non-contact sensing and parameter measurement of SLs. The basic structure of an SMI system consists of an SL, a lens and an external target. When a portion of reflected light from the target travels back to the laser cavity, a new lasing field is built up leading to both amplitude and phase modulations. The modulated output power is called a self-mixing signal which carries the information of both the target and SL’s feature parameters. Alpha factor, also known as linewidth enhancement factor, is one of the most important SL’s feature parameters. It characterizes the characteristics of SLs, such as the linewidth, the chirp, the injection lock range and the dynamic performances. This paper presents a new method for retrieving alpha factor of SLs by making use of a self-mixing interference (SMI) waveform. According to the well-known Lang-Kobayashi (L-K) theory, the SMI waveform is shaped by multiple parameters, including the alpha, the optical feedback level factor (denoted as C) and other parameters related to the oscillation of the external target. In this work, we build a new equation based on the SMI model derived from the L-K theory, which can be used to calculate the alpha value. In the existing SMI based methods for measuring the alpha factor, the optical feedback level C is limited within a certain narrow range. The proposed method is able to relieve this limitation. The associated simulations and experiments are carried out for verifying the proposed method.