Spinning rate function with higher-order-continuity for robust circular SOP conversion in SQWP

Spun Quarter Wave Plate (SQWP) excels in the conversion of circular state of polarization (SOP) when compared to its conventional counterpart. This is characterized by its low loss, high precision, and thus, its potential applicability in fiber optic systems. Traditionally, to augment the conversion performance of circular SOP, the maximum spinning rate (𝜉max) of the spinning function should be increased. However, this leads to an increase in ellipticity fluctuation (∆𝐸), thereby affecting the outcome stability of the SQWP. To mitigate this issue, this work explores the effect of a high-order continuous spinning rate function on the reduction of ellipticity fluctuations. This exploration is conducted through theoretical research complemented by numerical simulations. A novel high-order continuous spinning rate function is then proposed, which exhibits a ∆𝐸 that is two and three orders of magnitude smaller than those of linear and cosine functions, respectively. The results indicate that the proposed spinning rate functions surpass the conventional linear and cosine functions in terms of both the performance of circular SOP conversion and robustness. The findings from this research are anticipated to provide significant insights and directions for the future advancement and design of SQWP.