Ultra‐Small Birefringence Continuous‐Tuning and Full‐Band Zero‐Order Waveplate Devices

Abstract Waveplates have attracted increasing attention due to their irreplaceable role in polarization optics. For a long time, zero‐order waveplates exhibited ultra‐thin machining and application difficulties because the birefringence of the crystal is not small enough. In this paper, the analysis of polarized directions and birefringence of light in all anisotropy crystals indicates that the birefringence can be adjusted from zero to the intrinsic birefringence value by selecting crystal orientation, which provides a perfect way to obtain ultra‐small birefringence. Therefore, the α‐SiO ₂ , KTiOPO ₄ , and LiInSe ₂ crystals are selected and expected as waveplate crystals in the transmission band from deep ultraviolet to far‐infrared. Zero‐order half and quarter waveplates working at 355, 633, 796, and 2700 nm, whose thicknesses are ≈ 100 times those of the current waveplates, are successfully designed and fabricated based on α‐SiO ₂ and KTiOPO ₄ crystals. Polarization measurement experiments confirmed that the fabricated zero‐order waveplates possess excellent performance for controlling laser polarization states. This research results break the barrier that the thickness and application band of zero‐order waveplates are limited to the material itself, and provide available zero‐order waveplates with millimeter‐level thickness in the full‐wave bands.