On-Chip Chiroptical Sensor based on Directional Deflection of Light: A Stern-Gerlach Integrated Optical Analog

Abstract: Chiroptical techniques for detecting and characterizing the chirality of matter and artificial nanostructures are traditionally based on their interaction with chiral light, typically circularly-polarized fields propagating in free space. More recently, these approaches have been extended to integrated photonic platforms, offering significant practical advantages. However, the generation of chiral guided light is challenging, it requires degeneracy of the fundamental modes of the integrated waveguide, which occurs at a single wavelength and limits broadband characterization. Here, we introduce and simulate numerically a new alternative integrated optical configuration inspired by the Stern-Gerlach experiment, in which a chiral sample is illuminated by a linearly polarized light beam. Such a beam exits from a dielectric waveguide that propagates the fundamental TE mode, thereby eliminating the need for circularly polarized excitation. On this basis, enantio-discrimination is achieved through a spatially resolved scheme using a symmetric arrangement of optical antennas on either side of the propagation axis. Our simulation results suggest that the selective scattering and absorption of the circular polarization component matching the chirality of the sample induces an imbalance of (spin) angular momentum of the optical field, resulting in a transverse deflection of the beam toward the corresponding side. This on-chip platform then provides a direct route to chiroptical functionalities under linearly-polarized illumination, enabling compact implementations of chiral sensing, spectroscopy, optical computing, and communication schemes.