Reconfigurable Subwavelength Hole-Disk Array

Updated 23 October 2025

The paper demonstrates that precise alignment between subwavelength holes and disks significantly enhances light coupling through surface plasmon polaritons, enabling tunable electromagnetic resonances.
Mechanical and electronic reconfiguration methods allow high-contrast modulation and precise control of resonance spectra from terahertz to visible frequencies.
Resonance engineering via circuit modeling and nonlinear dynamics underpins practical applications such as beam steering, ultrafast switching, and super-resolution imaging.

A reconfigurable subwavelength metallic hole coupled disk array consists of a dual-layer or hybrid metasurface architecture in which a periodic lattice of subwavelength holes in a metallic membrane is aligned atop a correspondingly periodic array of metallic disks. The close proximity and central alignment between each hole and disk strongly enhance light coupling and support tunable and/or switchable electromagnetic resonances mediated by surface plasmon polaritons (SPPs) and mode hybridizations. Devices of this class enable active control over light transmission, switching, filtering, beam steering, and spatial localization at terahertz, infrared, or visible frequencies, depending on the geometric scale. Recent advances demonstrate both electronically and mechanically reconfigurable arrays with high contrast ratios and broad bandwidths, and ongoing research centers on maximizing functionality via careful resonance engineering, circuit modeling, and integration of active elements.

1. Resonant Transmission Mechanisms

Transmission enhancement in subwavelength metallic hole arrays is enabled primarily by SPP-assisted diffraction phenomena. In a periodic metal film perforated with subwavelength holes and aligned over metallic disks, electromagnetic waves couple efficiently to SPPs propagating at the metal-dielectric interfaces. The key momentum-matching condition governing SPP excitation is

$k_{sp} = k_\parallel \pm i G_x \pm j G_y,$

where $k_{sp}$ is the SPP wavevector, $k_\parallel$ is the in-plane wavevector of the incident light, and $G_x, G_y$ are the reciprocal lattice vectors. The dispersion relation for SPPs at a flat interface is

$k_{sp} = \frac{\omega}{c} \sqrt{\frac{\varepsilon_m \varepsilon_d}{\varepsilon_m + \varepsilon_d}},$

where $\varepsilon_m$ and $\varepsilon_d$ denote the metal and dielectric permittivities.

When the hole array is precisely aligned with the disk array, near-field coupling is significantly enhanced: each disk collects incident electromagnetic energy and funnels it through the corresponding hole, boosting the local field and supporting extraordinary optical transmission (EOT) or spoof plasmon resonances in the THz regime (Zarei, 20 Oct 2025). The resonance spectra feature peaks whose position and width are governed by the lattice periodicity, hole/disk size, metal thickness, and dielectric environment (0708.1532).

2. Reconfigurability via Mechanical or Electronic Control

Reconfigurability in these arrays is achieved through mechanical displacement, electronic modulation, or integration of tunable circuit elements.

Mechanical switching: In broadband terahertz switches, a MEMS actuator adjusts the vertical spacing between the metallic membrane and the disk substrate by several microns. At the optimal separation (e.g., 2 μm), strong coupling supports high transmission (ON state); when the membrane contacts the disks (OFF state), transmission is suppressed by over 89 dB at the resonance frequency (942 GHz), representing high-contrast modulation (Zarei, 20 Oct 2025). The process is inherently polarization-insensitive due to the array’s fourfold symmetry.
Electronic modulation: In Schottky-diode-configured arrays, a reverse bias expands the depletion region at the metal-semiconductor interface, reducing free carrier absorption and sharpening the plasmonic resonance, thus modulating the transmitted intensity. For example, electronic switching in GaAs-based devices yields a modulation depth up to 52% by adjusting the bias between 0 and 16 V (0804.2942).

Control schemes can be extended to higher optical frequencies by shrinking hole dimensions or incorporating varactors, PIN diodes, or MEMS on individual disks for local impedance tuning (Chen et al., 2017, Li et al., 11 Apr 2024).

3. Resonance Engineering and Coupling Effects

Fine control over resonance wavelengths is governed by near-field electromagnetic coupling, sometimes involving anti-parallel dipole image effects in metal-dielectric-metal (MDM) nanodisk arrays. Thickness variation of the metal nanodisk ( $t_d$ ) allows precise bidirectional tuning of plasmonic resonances according to an exponential plasmon ruler relationship: $\lambda_{res,2} = \lambda_{off} + a\exp(-t_d/\tau)$ Record blueshift responses (up to 457.82 nm for a 5–10 nm thickness change) have been achieved in MDM architectures, greatly surpassing previous tunability ranges (Sarker et al., 16 Oct 2025). Thinner disks couple more strongly to their image dipoles in the underlying mirror, yielding blueshifts as the coupling weakens with increasing $t_d$ ; thicker disks yield redshifts via increased charge storage.

Arrays supporting strong mode hybridization—such as coupling anapole states in dielectric nanodisks to SPPs at the metal surface—exhibit avoided crossings and large vacuum Rabi splitting (129 meV), accessible via FDTD simulation and coupled oscillator models (Ravishankar et al., 2021). These hybrid modes enable on-chip photonic and cavity QED platforms with tunable responses.

In dual-slit resonator arrays, close spacing (on order of slit width $\varepsilon$ ) induces two resonance groups:

broad resonances ( $\text{Im}\,k^{(1)} = O(\varepsilon)$ ), and
narrow resonances ( $\text{Im}\,k^{(2)} = O(K\varepsilon^2)$ ), whose interference causes Fano-type transmission anomalies—an asymmetric peak-dip line shape exploitable for filtering and switching (Lin et al., 2019).

4. Circuit and Coupling Models

Analytical circuit models for subwavelength aperture/disk arrays are based on transmission-line equivalence: the structure is partitioned into regions (above, in, and below the hole), with each region expanded in modal series. The generalized circuit equation involves admittance contributions from dominant and higher-order modes: $Y_0^1\frac{1-R}{1+R} = Y_0^2(\text{C}_0 \text{B}_0/\text{D}_0 \text{A}_0) + \sum'[\ldots]$ where terms encapsulate modal overlap and spatial profiles at the aperture openings (Pasdari-Kia et al., 2022). Multi-mode treatment is essential for accuracy, especially in thin structures. Field profiles for square/circular apertures are specified with closed-form approximations (see Section 3 of (Pasdari-Kia et al., 2022)), which directly enter the circuit model’s coupling coefficients.

Reconfigurability is modeled via lumped circuit loads or tuning circuits attached to each scatterer/disk. Circuit-based transfer function matrices formally connect the transmitter, array, and receiver through detailed mutual impedance matrices, now available in closed-form using exponential integral functions (Renzo et al., 2022). This framework is central for design and optimization in reconfigurable metasurfaces, RIS, and advanced electromagnetic front-ends.

5. Nonlinear and Solitonic Effects

Arrays of metallic disks or holes embedded in nonlinear media host discrete nonlinear phenomena. Plasmonic lattice solitons (PLSs) arise when local Kerr nonlinearity compensates for discrete diffraction, yielding tightly confined nonlinear modes controllable by input phase and power (Ye et al., 2010). Arrays with cubic nonlinearity support bistable responses and plasmonic kinks—switching waves linking distinct polarization states. These kinks propagate with tunable velocity, allowing dynamic reconfiguration of localized high or low intensity domains for ultrafast switching and signal processing (Noskov et al., 2012).

Such nonlinear and bistable effects can be incorporated in reconfigurable subwavelength hole coupled disk arrays to enable all-optical switching, ultrafast logic, and compact photonic routing.

6. Wave Manipulation, Imaging, and Aperiodic Architectures

Active and aperiodic metasurface design enables manipulation of wavefronts with flexibility beyond Floquet-theorem constraints. In arrays where each scatterer or disk is independently loaded with a programmable impedance,

$Z \cdot I = U,$

the vector of induced currents can be tailored optimally (for beam splitting, focusing, superabsorption, or superdirectivity) (Li et al., 11 Apr 2024). Control over phase and amplitude at the subwavelength disk level enables dynamic steering, adaptive beam patterns, and focusing below the diffraction limit.

For super-resolution imaging, subwavelength hole arrays generate resonant illumination patterns with neighbor spacing $\ell < \lambda/2$ , supporting transmission peaks at

$k_m = m\pi/\ell + O(\ell)$

The resultant spatial oscillations encode high spatial frequency information into the far-field data, allowing reconstruction with resolution $\sim \ell/2$ , robust against noise and relaxed with respect to probe-sample distance (Lin et al., 2020).

THz detector arrays fabricated on GaAs substrates, featuring reconfigurable optical probe spots via SLM phase modulation, achieve subwavelength imaging with 30 μm spot size and 100 μm element gaps. These arrays offer dynamic, rapid scanning for advanced imaging modalities, with direct comparisons showing improved flexibility relative to static disk/hole arrays (Nallappan et al., 2017).

7. Applications, Limitations, and Outlook

Reconfigurable subwavelength metallic hole coupled disk arrays are being implemented for a wide range of applications:

Terahertz switches: Polarization-insensitive devices with contrast up to 89.4 dB at 942 GHz and bandwidths of 288 GHz, suitable for wireless communications, real-time imaging, and coded aperture systems. Their operational frequency and bandwidth can be scaled by tuning geometric parameters and spacer thickness (Zarei, 20 Oct 2025). Formulas such as $\omega_{\text{res}} \propto 2\pi c/P$ (resonant frequency versus periodicity) and transmission $T(\omega,d) \propto e^{-\alpha d}$ (coupling vs interlayer spacing) summarize key dependencies.
Sensing: Resonance engineering enables ultrasensitive detection; the bidirectional plasmonic tuning in MDM arrays is particularly valuable for biosensors and chemical sensors due to the enhanced sensitivity of resonance wavelength to nanoscale changes (Sarker et al., 16 Oct 2025).
Optical communications: Fully reconfigurable hole/disk arrays are candidate platforms for integrated photonic switches, modulators, and filters with capabilities extending into the visible and infrared (Ravishankar et al., 2021).
Imaging and signal processing: Aperiodic metasurfaces and dynamic probe arrays offer superdirective, superabsorptive, and superresolution imaging, with programmable spatial filtering via local element control (Li et al., 11 Apr 2024, Lin et al., 2020).

Challenges include precise microfabrication for alignment, reliability of mechanical actuation (e.g., MEMS cycle wear), loss management, and miniaturization for higher frequency operation. Circuit modeling, mutual impedance analysis, and nonlinear effects are critical for further functional integration and optimization.

In summary, reconfigurable subwavelength metallic hole coupled disk arrays represent a powerful approach for actively manipulating electromagnetic waves with high spatial resolution, tunable resonance spectra, and wide-ranging application potential. Their operation is fundamentally grounded in SPP-assisted diffraction, strong near-field coupling, advanced circuit and nonlinear modeling, and flexible active/adaptive architectures. Their ongoing development continues to advance frontiers in sensing, telecommunication, imaging, and integrated photonic systems.