How does angle of incidence effect the polarisation control in metamaterials?
Supervisor: Rebecca Craig
School: Engineering
Description:
Control of electromagnetic polarisation is central to both established and emerging photonic technologies. In quantum communication, the BB84 protocol depends on preparing and measuring non-orthogonal polarisation states to ensure a secure key exchange. In advanced imaging, structured and vector beams use spatially varying polarisation to improve contrast and allow edge detection. Across these applications, precise manipulation of polarisation is a fundamental requirement.
Metamaterials have allowed compact and highly tailored polarisation control through subwavelength structuring, supporting applications in integrated photonics, structured light generation, and polarisation-sensitive imaging. These devices are often optimised for specific input states, and retuning them usually requires structural redesign and fabrication. Their complexity and cost can therefore limit scalability and adaptability. This proposal investigates an alternative approach based on naturally anisotropic crystals exhibiting hyperbolic dispersion, such as calcite. In these materials, infrared-active phonon resonances cause the main parts of the dielectric tensor to have opposite signs within certain spectral regions, leading to an indefinite permittivity response. This hyperbolic behaviour supports unusual optical phenomena including negative refraction, surface polaritons, and cross-polarisation conversion.
When incident radiation includes both transverse electric TE and transverse magnetic TM components, each one interacts differently with the ordinary and extraordinary dielectric tensor elements. The difference in phase accumulation changes the relative phase between orthogonal field components, which alters the overall polarisation state. This study focuses on systematically characterising reflection-driven interactions to show that hyperbolic anisotropic crystals can serve as a simple and adaptable platform for tunable polarisation control. This approach aims to connect traditional birefringent optics with nanostructured metamaterials.
This project will investigate the effects of the angle of incidence on the resulting polarisation after reflection from the metamaterial. To start, we will investigate and construct a compact sensor for the infrared wave detection. The sensors typically used for this work are expensive and bulky, making rotational measurement prohibitive. However, there is promise in the use of thermal sensors in place of pyroelectric sensors typically used. Then we can take reflection measurements using calcite that can be compared to simulated data. These measurements are key to understanding the full capabilities of the calcite and its role in the control of electromagnetic polarisation.