Femtosecond laser direct writing multilayer chiral waveplates with minimal linear birefringence

Chirality transfer from femtosecond laser direct writing in achiral transparent materials mainly originates from the interplay between anisotropic nanogratings and mechani-cal stress with non-parallel and non-perpendicular (oblique) neutral axes. Yet, the laser fabrication simultaneously induces non-negligible linear birefringence. For precise manipulation of circular polarization properties, as well as to unlock the full functionality, we report here a geometry -inspired multilayer method for direct writing of chiral waveplates with minimal linear birefringence. We perform a theoretical analysis of both circular and linear properties response for different multilayer configurations and achieve strong circular birefringence of up to -2.25 rad with an extinction ratio of circular birefringence to total linear bire-fringence of up to 5.5 dB at 550 nm. Our strategy enables the precise control of circular properties and provides a facile platform for chiral device exploration with almost no linear property existence. (c) 2023 Optica Publishing Group

Automated summary

Chirality transfer from femtosecond laser direct writing in achiral transparent materials is caused by the interplay between anisotropic nanogratings and mechanical stress with non-parallel and non-perpendicular neutral axes. However, laser fabrication also induces significant linear birefringence. To precisely manipulate circular polarization properties and minimize linear birefringence, we propose a geometry-inspired multilayer method for direct writing of chiral waveplates. Theoretical analysis shows that our method achieves strong circular birefringence and provides a facile platform for chiral device exploration with minimal linear property existence.