The extraordinary optical transmission (EOT) device holds significant potential in sensing and detection applications due to its exceptional transmittance at specific wavelengths, surpassing traditional optical theory. It also enhances the local light field, boosts nonlinear optical effects, and strengthens light-matter interactions. However, high metal losses limit its transmittance to 10%?20%, while multiple resonance modes caused by different media on the device’s surfaces often split the EOT peak into adjacent transmission peaks. This complicates spectral monitoring and hinders practical applications like biosensing and filtering, which require precise resonance peak identification. To address these challenges, this paper proposes a metal cone-shaped nanohole array structure designed to achieve single-peak EOT resonance with high transmittance and a narrow linewidth, enabling high-sensitivity and high-quality-factor sensing detection.

The proposed metal cone-shaped nanohole array comprises a silica substrate, a gold film, and periodically arranged air holes. A plane wave serves as the excitation light source, incident downward along the z-axis with wavelengths ranging from 1000 nm to 2500 nm. The electric field polarization is defined as 0° along the x-axis and 90° along the y-axis. Simulations are conducted using the finite-difference time-domain (FDTD) method with periodic boundary conditions in the x and y directions and a perfectly matched layer (PML) in the z-direction. The spatial grid step size is set to $\mathrm{\Delta }x=\mathrm{\Delta }y=\mathrm{\Delta }z$=10 nm, and the unit cell period is P_x=P_y=1500 nm. The dielectric constants of gold and silica are derived from Palik’s experimental data. By maintaining constant cone hole volume and base areas, the EOT characteristics are further explored through adjustments to the cone hole shape, light polarization, and lattice arrangement.

By optimizing the taper and depth of the nanopores, multiple resonance modes are effectively suppressed, and transmittance is enhanced by 5?6 times (Fig. 2). Circular or near-circular holes exhibit superior polarization insensitivity (Fig. 3). Adjusting hole shapes and light polarization allows precise control over plasmon excitation positions on the structural surface. For rectangular holes, the EOT resonance peak’s full width at half maximum (FWHM) narrows to 5 nm with a Q factor of 302 when light is polarized along the narrow side (Fig. 4). Transitioning from a square to a hexagonal lattice arrangement increases transmittance by approximately 10% while maintaining linewidth stability, enhancing light-matter interaction (Fig. 5). Sensing performance analysis reveals a sensitivity of 1350 nm/RIU for hexagonally arranged circular holes and a figure of merit (FOM) of 78 with a Q factor of 110 for square lattice rectangular holes (Fig. 6). A comparison with existing metal plasma sensors is provided in Table 2.

This study introduces a metal cone-shaped nanohole array that significantly enhances EOT characteristics. Unlike dielectric-based devices, the metal structure efficiently excites strong surface plasmon polaritons, generating localized electric field enhancement at hole edges to promote light-matter interaction and improve energy transmission. The cone-shaped design effectively suppresses unwanted resonance modes at the metal-silica interface while enhancing those at the metal-air interface, achieving single-peak resonance with high transmittance and a narrow linewidth. Polarization sensitivity varies with nanopore shape, as incident light polarization influences surface plasmon polariton distribution and excitation, leading to polarization-dependent EOT spectra. This enables a minimum FWHM of 5 nm and a maximum Q factor of 302. Hexagonal lattice arrangements enhance transmittance and light-matter interaction due to stronger inter-hole electric field coupling. Sensing performance analysis shows hexagonal lattices outperform square lattices in sensitivity, with circular holes reaching 1350 nm/RIU. Square lattice rectangular holes exhibit higher FOM (78) and Q factor (110). These findings provide valuable theoretical insights and practical design guidelines for advancing high-performance optical sensors.