Simple and high-resolution method for displacement sensing using self-mixing interferometry

Self-mixing interferometry (SMI) is widely used for vibration, velocity, and displacement measurement applications. Many complex and computationally intensive phase unwrapping algorithms have already been proposed to obtain high-resolution measurements, but there remains a requirement for a high-resolution yet simple method for displacement measurement. In this work, a high-resolution yet simple improved unwrapping method (IUM) is proposed, which addresses the limitations of the previously proposed simple but low-resolution method, consecutive sample-based unwrapping (CSU). IUM shows a remarkable improvement of 49% over CSU. IUM was assessed for a broad range of SMI signals, and results revealed that IUM is capable of processing SMI signals from all three main feedback regimes with an average RMS and peak error of 37.7 nm and 113.3 nm, respectively. Such a high-resolution method with a straightforward processing methodology is a vital step towards real-time independent displacement sensors capable of performing high-resolution measurements.