Dynamic control of polarization and diffraction in tunable Surface-Relief Liquid-Crystal gratings

The precise phase control of light is essential for advancing photonic devices. This study presents electrically tunable liquid–crystal (LC) surface-relief gratings (SRGs) comprising periodic SU-8 photoresist (PR) structures, showcasing notable electro-optical properties. The SRG comprises a periodicity of alternating PR-coated (Region B) and uncoated (Region A) regions. When a DC voltage is applied, Region A exhibits a transmittance shift upon exceeding a threshold voltage, with incomplete recovery when the voltage is reduced. This non-reversible behavior likely stems from ionic migration toward the electrodes, creating an internal electric field. Conversely, Region B acts as an effective shield, stabilizing the electric double layer and minimizing transmittance changes. However, AC stimuli restrict ionic mobility, with higher frequencies leading to increased threshold voltage, particularly in Region B. Analysis of the Stokes parameters further demonstrates that the grating facilitates voltage-controlled tuning of diffraction orders while maintaining polarization stability. By optimizing DC driving schemes, higher diffraction orders can be selectively enhanced, allowing for low-voltage operation and multi-order diffraction, which is crucial for wide-angle holographic displays. These findings lay the groundwork for a robust platform for dynamic light manipulation, paving the way for next-generation tunable photonic systems and advanced display technologies.