Low-contrast one-dimensional photonic crystals for optical chirality enhancement

Chirality, defined as the lack of a symmetry plane, is a common phenomenon found both at the macro and nanoscales. This geometrical property, which is essential in many biochemical processes, is found in all biomolecules. As a result, the study and separation of chiral compounds has recently acquired prominence in the pharmaceutical industry. Chiroptical analysis approaches enable versatile and low-cost structural characterization, but their poor sensitivity precludes smaller scale integration. We overcome these obstacles by creating one-dimensional photonic crystals capable of generating large optical chirality at their surfaces [1], [2], [3]. Nevertheless, the intrinsic anisotropy of these structures represents a disadvantage when attempting to precisely control the polarization state of the surface wave [4]. We show that low-contrast one-dimensional photonic crystals successfully address this issue, and allow for a better control of the surface wave polarization, along with broadband, large area optical chirality enhancement in relevant spectral ranges. These results represent a step towards the integration of chiroptical methods with microfluidic techniques, augmenting the widely used lab-on-chip techniques with additional capabilities.