Numerical modelling of surface plasmons propagation in nanostructured optical waveguides of information and communication networks

Abstract

The study aimed to determine the optimal waveguide configurations in terms of electromagnetic field localisation, propagation length and loss minimisation. The methodology included two- and three-dimensional modelling in the Lumerical Finite-Difference Time-Domain Solutions environment with a spatial resolution of 2 nm, using Perfectly Matched Layer boundary conditions and varying the parameters of the metal layer (Ag, Au, Al), the type of substrate and the waveguide geometry. The source of the disturbance was Gaussian pulses with wavelengths of 1,310 nm and 1,550 nm. The results showed that V-shaped and ribbed waveguides coated with silver or gold provided the best plasmon localisation and minimal losses. The maximum electric field intensity reached 1.78 × 106 V/m in V-shaped waveguides with 100 nm thick gold at a localisation width of less than 100 nm. The ribbed silver structures with a thickness of 60 nm demonstrated good localisation and low losses (0.32 dB/micron). The longest LSPP propagation length (28.3 µm) was found in the Ag/sapphire configuration at neff 1.87-1.91. Monte Carlo simulation (1,000 iterations) showed high resistance of these structures to geometric fluctuations (σ < 0.035 dB/mcm at ± 5%). Experimental verification confirmed a deviation of less than 8%. The data obtained indicate that asymmetric waveguides made of noble metals at the optimum thickness (40-60 nm) provide stable plasmon propagation with minimal losses. The practical significance of the results is determined by the possibility of using the proposed configurations in optical interfaces, photonic integrated circuits and high-speed communication modules developed in nanophotonics laboratories and telecommunications companies.