Universal nonlocal dispersion in optically active materials

Universal nonlocal dispersion in optically active materials. a–c Left panels: optical rotatory power of a α-quartz, b TeO2, and c Te single crystals along their optical axes (z-axis). The black dots represent the measured data, while the solid line shows the fitted results with a coupled-oscillator model. Right panels: measured tunable transmission of Z-cut a 3 mm α-quartz, b 5 mm TeO2, and c 2 mm Te single crystals under linearly polarized input light and an output polarizer rotated at different polarization angles. (d-g) Distinction of the dispersion characteristics in nonlocal optically active crystals and birefringent crystals: d A schematic illustrates the dispersion of refractive indices in standard birefringent crystals. When a linearly polarized light oriented at 45∘ to the crystal’s slow-axis traverses the birefringent medium, it undergoes a transformation through linear, elliptical, and circular polarization states (and then reverses the sequence). This transformation varies in speed with different wavelengths, λ1 and λ2, as depicted on the left and right, respectively. The inset highlights that birefringence microscopically originates from the anisotropic nature of the crystal lattice. e A schematic captures the evolution of polarization states on the Poincaré sphere. Blue and red trajectories correspond to λ1 and λ2 in (d), respectively. In birefringent crystals, these pathways trace the sphere’s meridian. Due to dispersive effects, different wavelengths reach different states along the meridian after traversing the crystal. f A schematic illustrates the nonlocal dispersion in optically active crystals. As linearly polarized light traverses an optically active medium, it retains its linear polarization but experiences a rotation in orientation. For different wavelengths, λ1 and λ2, the rate of polarization rotation per unit length is different. The inset shows that the polarization rotation microscopically arises from the screw symmetry of the lattice. g A schematic represents the evolution of polarization states on the Poincaré sphere. For nonlocal optically active crystals, evolution paths are along the equator. Dispersion causes different wavelengths to reach different states along the equator after traversing the crystal, allowing a linear polarizer to select between these wavelengths effectively.

Recent years have seen significant advancements in exploring novel light-matter interactions such as hyperbolic dispersion within natural crystals. However, current studies have predominantly concentrated on local optical response of materials characterized by a dielectric tensor without spatial dispersion. Here, we investigate the nonlocal response in optically-active crystals with screw symmetries, revealing their lossless, super-dispersive properties compared to traditional optical response functions. We leverage this universal nonlocal dispersion, i.e. the dispersion of optical rotatory power, to explore a novel spectral de-multiplexing scheme compared to conventional gratings, prisms and metasurfaces. We design and demonstrate an ‘Nonlocal-Cam’ - a camera that exploits nonlocal dispersion through sampling of polarized spectral states and the application of computational spectral reconstruction algorithms. The Nonlocal-Cam captures information in both laboratory and outdoor field experiments which is unavailable to traditional intensity cameras - the spectral texture of polarization. Merging the fields of nonlocal electrodynamics and computational imaging, our work paves the way for exploiting nonlocal optics of optically active materials in a variety of applications, from biological microscopy to physics-driven machine vision and remote sensing.

Demonstrations of spectro-polarimetric imaging using the Nonlocal-Cam. a RGB image of the ‘AXION’ imaging target. b–f False color representations of reconstructed spectral frames at 450 nm, 490 nm, 530 nm, 585 nm and 605 nm, respectively. The reconstruction is based on 100 raw imaging frames acquired over a 10-second duration. g Normalized reconstructed spectra (solid) and the corresponding ground-truth (dashed) of four representative pixels (M, N, P, Q) as marked in a. h S0 (intensity) image of a pair of plastic goggles. Inset: normalized S0 spectrum at pixel K. i Degree of linear polarization (DoLP) image of the plastic goggle at 450nm. Inset: DoLP spectrum at pixel K. The DoLP spectrum reveals the wavelength-dependence of the stress-induced birefringence in the goggles unavailable to conventional spectral imagers.

Reference:

Exploiting universal nonlocal dispersion in optically active materials for spectro-polarimetric computational imaging, eLight, 4(1), 1-13, 2024

Wang, X., Van Mechelen, T., Bharadwaj, S., Roknuzzaman, M., Bao, F., Rahman, R., & Jacob, Z.

(See highlight article in Light: Science & Applications)

Quantum Theory of Optical Spin Texture in Chiral Tellurium Lattice, arXiv:2506.21610, 2025

Das P., Bharadwaj S., Mun J., Wang X., Rho J., Jacob Z.