Generation and Control of Single and Composite OAM Beams Using Sectorially Spatially Shifted Gratings: Phase Engineering and Plasmonic Wavelength Selectivity

Abstract: A composite orbital angular momentum (OAM) beam is formed by the coaxial superposition of two or more OAM modes. Its field distribution depends on the relative modal weights and phase differences among the constituent modes. Tailoring this distribution therefore requires systematic control over these modal contributions. This work presents a simple grating-based approach with an analytical design procedure for controlling the relative modal weights and phases of composite OAM beams. The first part develops a sectorially spatially shifted grating (S3G) method for generating OAM beams based on the relationship between fractional grating displacement and the corresponding phase shift in the first diffraction order. Numerical simulations and experiments validate the generation of OAM beams with different topological charges. The method is further extended to composite S3G (c-S3G) structures for generating multiple coaxial OAM constituents. Their relative modal weights are tuned by allocating different proportions of grating sectors to the constituent modes. An approximate a priori estimate of the relative modal weights, based on the square of the sector-allocation parameter (β2), is developed and compared with numerical modal-decomposition results. Furthermore, adjusting the relative phase between constituent OAM modes provides an additional means of controlling the composite intensity distribution. The second part explores the potential for spectrally tunable OAM generation using plasmonic S3G structures under broadband illumination. The influence of grating period and surrounding-medium refractive index on the spectral response is examined. Numerical simulations show refractive-index-dependent spectral displacement, while experiments involving dielectric-layer loading reveal a clear colour change in the composite OAM output. Together, these grating-based approaches offer opportunities for tailored structured-light generation and the development of plasmonic structures for spectrally tunable OAM generation.

Title: Generation and Control of Single and Composite OAM Beams Using Sectorially Spatially Shifted Gratings: Phase Engineering and Plasmonic Wavelength Selectivity
Date: November 16, 2026 at 11:00 AM
Venue: ESB 210B
Speaker: Ms. Rajeswari Yerraguntla (EE21D015)
Guide:
Type: PHD seminar