Numerical Assessment of a Geometry-Aligned Vertical Heat Path for an Au-Loaded Side-Bus Photonic Crystal Nanobeam Sensor

Localized Au loading perturbs the optical response of photonic-crystal sensors and creates a concentrated thermal source. We numerically assess a side-bus silicon-nitride slotted nanobeam with two Au bars and an idealized high-conductivity shunt. Three-dimensional FDTD gives sensitivities of 99.88 and 97.50 nm/RIU for matched Au-loaded and no-Au structures over a general cladding-index sweep of n = 1.000–1.050. The Au-loaded linewidth is 24.28–39.95 nm, with linewidth-derived Q of 16.22–26.49 and figure of merit of 2.50–4.11 RIU−1. A coordinate-registered Au-field weight drives a prescribed-power COMSOL model with explicit thermal contacts. At 1 µW absorbed power and G = 100 MW m−2 K−1, the peak Au temperature rise is 12.68 K, stack peak stress is 31.04 MPa, and maximum displacement is 0.0100 nm. The maximum temperature over both Au bars gives 63.2% and 90% threshold rise times of approximately 1.46 and 8.17 ns relative to the transient on-pulse plateau. The shunt properties are prescribed model assumptions. Thermo-optic feedback, fabrication and experimental validation are not included. Field-overlap diagnostics describe localized redistribution, not independent proof of an SPR/LSPR mode.