An optical displacement transducer with system-intrinsic linearity achieved by a laser diode

Abstract

High-fidelity state tracking with minimal latency and compact hardware is essential for advanced vehicle suspension control systems. Self-mixing interferometry (SMI) based sensing, distinguished by its compact form factor and rapid response, represents a promising solution for such applications. However, the practical integration of SMI into high-bandwidth control loops is currently hindered by the significant computational burden associated with reconstructing physical quantities from periodic interference fringes. To address this limitation, we propose an intrinsic linear displacement/vibration transducer by operating an SMI system within a designated feedback window. This specific operating mode yields a direct, monotonic conversion of mechanical excursion into optical intensity. The theoretical boundaries of the operational window for linear transduction are derived, and a closed-form governing equation for detection sensitivity is established. Experimental characterization demonstrates robust linearity of the proposed transducer. This hardware-level linearization eliminates the need for signal demodulation and other auxiliary signal-processing steps, thereby enabling instantaneous and embedded sensing suitable for real-time vehicle vibration and suspension control.