Compact deterministic liquid-crystal polarization controller with single-measurement direct control

Polarization controllers (PCs) and their control algorithms are critical for compensating environmental disturbances and maintaining signal fidelity in polarization-sensitive photonic systems. However, existing controllers often involve trade-offs among key performance metrics, while associated control algorithms either converge inefficiently or require multiple state-of-polarization (SOP) measurements. This work presents a compact deterministic liquid-crystal polarization controller (LC-PC) with balanced overall performance, featuring low insertion loss ( < 1 dB), low driving voltage ( < 6 V), and full Poincaré sphere coverage. The device exhibits highly predictable and repeatable polarization modulation characterized by SOP-independent trajectory normal vectors, enabling a single-measurement direct-calculation algorithm using pre-characterized rotation axes and voltage-to-rotation relationships, with degree-level polarization-control accuracy. The combination of this compact deterministic LC-PC and its efficient control scheme provides a practical solution for polarization management in quantum key distribution, optical sensing, and advanced photonic systems.