Self-mixing interferometry (SMI) is an attractive sensing scheme that typically relies on mono-modal operation of an employed laser diode. However, change in laser modality can occur due to change in operating conditions. So, detection of occurrence of multi-modality in SMI signals is necessary to avoid erroneous metric measurements. Typically, processing of multi-modal SMI signals is a difficult task due to the diverse and complex nature of such signals. However, the proposed techniques can significantly ease this task by identifying the modal state of SMI signals with 100% success rate so that interferometric fringes can be correctly interpreted for metric sensing applications.