Optical nonlinearity induced PT-symmetry breaking using photonic metasurfaces and its implications on exceptional points-based optical sensing
Abstract
The complete ramifications of non-Hermitian PT-symmetric systems in classical and non-classical regimes is a matter of intense investigation at present. In condensed-matter physics, the experimental testing of intriguing features exhibited by PT-symmetric systemsis essentially limited by decoherence effects and difficulty in controlling non-Hermiticity of PT-symmetric systems. Photonic configurations provide a pragmatic and flexible ground to explore such intriguing features of PT-symmetric dynamics. Most prominently, the inherent possibility of exciting eigenstates of a PT-symmetric Hamiltonian through an optimum optical gain/loss mechanism is an extremely attractive feature that facilitates the access to various non-Hermitian paradigms. In a more abstract framework, the PT-symmetric systems allow one to explore the dynamics over the entire complex plane; and most interesting situations arise when the potential functions are non-conservative (or complex). This could be achieved without any inherent presence of real loss or gain in the photonic configuration. The process of mode-field interaction (and scattering) in optical systems would suffice to generate complex potential functions and consequently, PT-symmetric manifestations could be explored. From an alternative framework, this idea essentially implies that the virtual loss (or gain) in the photonic system acts as a source for another (sub-) photonic system which exhibits an Hermitian-Hamiltonian led dynamics. It is worth noting that photonic metasurfaces are one of the most versatile and flexible optical architectures that offer extremely wide reconfigurability in terms of effective values of dielectric constants as well as allied optical properties. Through exploring the PT-symmetric manifestations in metasurfaces, system design could be expanded to the entire complex plane spanned by the effective dielectric constant. However, it is important to note that a non-negligible imaginary component of permittivity or permeability is a strong deterrent to the deployment of conventional metasurface/metamaterial based practical devices for #on ground# applications. The present proposal provides a plausible alternative to carry out coherent interactions in all-dielectric (lossless) metasurface based architectures that do not exhibit real (absorption) loss in the mode-field interaction process. Such a system, by virtue of virtual loss, would exhibit PT-symmetric dynamics. Accordingly, the system would host exceptional point(s) (EPs) which would manifest into an abrupt (discontinuous) phase-transition owing to the singularity in the eigenvalue spectrum. The extraordinary dispersive properties of the eigenmodes to develop photonic sensing architectures. An unique feature of the idea presented in this proposal could be understood by noting the fact that the energy lost due to scattering is stored in a reservoir which could be retrieved through coherent optical interactions. This, substantially minimises the decoherence effects and improves the optical SNR for the sensing measurements. The present exploration would provide a plausible alternative method to design metamaterials whose functionalities are not inhibited by the materials loss and thereby, widening the scope of applicability of all-dielectric metamaterials. In order to execute the project, we would be undertaking three primary steps which could be categorized as(i) Fabrication of optimally designed metasurfaces using laser inscription method and electron beam lithography (ii) Experimental measurements involving forward-propagating and backscattered mode coupling features of light scattered from the fabricated metasurface (iii) Comprehensive analysis of experimental results using the dynamical equations derived from the model Hamiltonian describing the non-Hermitian dynamics. Step (ii) mentioned would be extended to develop sensors based on perturbative impact of mode-coupling mechanism from external factors
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 12, 2025
- Source ID
- N629092512016
Entities
People
- Ritwick Das
Organizations
- Indian Institutes of Technology
- Office of Naval Research
- United States Navy