Enhanced Diffraction Efficiency using Metal Nanoparticle based Grating on Flexible Substrate

We demonstrate a cost-efficient technique to fabricate diffraction gratings using colloidal nanoparticles and capillary-assisted self-assembly process on a flexible substrate. Through experiments, finite difference time-domain simulations (FDTD), and Rigorous Coupled-Wave Analysis (RCWA) we show that the gratings exhibit enhanced diffraction efficiency in the first order when compared to air-polymer gratings.

Our experimental observations match well with simulation results obtained using finite-difference time-domain method and rigorous coupled wave analysis. These nanoparticle-based gratings can be easily transferred from the flexible substrate to any desired surface, for example optical fiber tips, for sensing applications. To understand distribution of power between the zeroth and the first order of diffraction, we use Rigorous Coupled-Wave Analysis (RCWA). We calculate power diffracted into the zeroth order and the first order of a binary air-PDMS grating and a gold-PDMS grating, both with duty cycle of 50%. Here, the gold-PDMS binary grating structure is made of PDMS ridges and the grooves are filled completely with bulk gold and not as nanoparticles as opposed to the FDTD simulation or experiments. We perform the analysis separately for two orthogonal and linear polarizations of the incident electric field: parallel and perpendicular to the grating periodicity. Using Fourier series expansion of the variation of the refractive index and applying appropriate boundary conditions, we find electromagnetic field in all regions. We calculate diffraction efficiency of the zeroth and the first orders in transmission from the ratio of the Poynting vectors of each order and the incident wave. Figure shows that the gold-PDMS grating has lower power in the zeroth order and higher power in the first order in comparison to the air-PDMS grating. These calculations agree with our experimental observations. The details can be found on here https://doi.org/10.1109/IPC53466.2022.9975575 and https://doi.org/10.1364/AO.492232.