Fig. 3. Finite difference time domain (FDTD) analysis of the grid structure.

a Measured and FDTD simulated transmittance spectra of structures with different nominal height h₂ (from the black dashed rectangle in Fig. 2a ranging from 1.2 μm to 2.7 μm. 1st and 2nd represent the first and second order resonance dip respectively). Marked positions λ₁ = 490 nm and λ₂ = 710 nm are used for FDTD field analysis in Fig. 3b–e. b, c Cross section view of near-field normalised electric field phase and amplitude for a grid structure (laser power: 30 mW, write speed: 1 mm/s, nominal grid height: h₂ = 2.7 μm) at dip transmittance 490 nm and peak transmittance 710 nm wavelength respectively (|E/E_inc| represents the normalised electric field amplitude). d, e Top view of far-field normalised electric field amplitude for the above grid structure at dip transmittance 490 nm and peak transmittance 710 nm wavelength respectively; the white circle represents collection field for the microscope used in this work (NA = 0.2, CA = 11.5°). f Simulated transmittance spectra for structures with different linewidth w₁ (the colours of the spectrum lines were mapped from the corresponding spectra).