Generation of Perfectly Achromatic Optical Vortices Using a Compensated Tandem Twisted Nematic Cell

Abstract

The generation of white optical vortices is currently constrained by intrinsic trade-offs between spectral bandwidth, conversion efficiency, and temporal pulse integrity in conventional diffractive and geometric-phase approaches. In this work, we theoretically investigate a compensated tandem crossed twisted nematic (TN) liquid crystal architecture that overcomes these fundamental limitations. By developing a rigorous Jones matrix model and defining specific figures of merit for chromatic fidelity, we analyze the impact of manufacturing imperfections and non-adiabatic waveguiding (deviations from the Mauguin regime) on the device performance. We propose and evaluate three distinct compensation strategies, ranging from optimized passive designs for specific manufacturing tolerances to a robust active compensation scheme utilizing a tunable retarder. Our analysis demonstrates that the active approach effectively nullifies parasitic amplitude modulation, enabling the generation of perfectly achromatic vortices with high phase purity across an arbitrary bandwidth. This establishes the compensated tandem TN cell as a superior and versatile platform for high-fidelity white-light singular optics.