This chapter addresses simple optical fiber sensors based on modal interference in multimode optical fibers: their working principles, potential applications, and challenges for industrial sensor realizations. Different sensor structures and approaches to sensing have been. Multimode fibers (MMF) are promising candidates to increase the data rate while reducing the space required for optical fiber networks. This can be overcome by measuring the transmission matrix. In this work, we present an alternative fiber-optic vibration sensing strategy that harnesses a multimodal architecture combining speckle and polarization interrogation. This review summarizes recent progress and emerging trends in multiparameter optical fiber sensing, emphasizing techniques that enable the simultaneous measurement of temperature, strain, acoustic waves, pressure, and other environmental quantities within a single sensing network.