Broken symmetry dielectric resonators for high quality-factor Fano metasurfaces (1607.06469v1)

Abstract: We present a new approach to dielectric metasurface design that relies on a single resonator per unit cell and produces robust, high quality-factor Fano resonances. Our approach utilizes symmetry breaking of highly symmetric resonator geoemetries, such as cubes, to induce couplings between the otherwise orthogonal resonator modes. In particular, we design perturbations that couple "bright" dipole modes to "dark" dipole modes whose radiative decay is suppressed by local field effects in the array. Our approach is widely scalable from the near-infrared to radio frequencies. We first unravel the Fano resonance behavior through numerical simulations of a germanium resonator-based metasurface that achieved a quality-factor of ~1300 at ~10.8 um. Then, we present two experimental demonstrations operating in the near-infrared (~1 um): a silicon-based implementation that achieved a quality-factor of ~350; and a gallium arsenide-based structure that achieves a quality-factor of ~600 - the highest near-infrared quality-factor experimentally demonstrated to date with this kind of metasurfaces. Importantly, large electromagnetic field enhancements appear within the resonators at the Fano resonant frequencies. We envision that combining high-quality factor, high field enhancement resonances with nonlinear and active/gain materials such as gallium arsenide will lead to new classes of active optical devices.

• The paper shows that symmetry breaking in dielectric resonators enables coupling between bright and dark modes, achieving up to ~1300 Q-factor at ~10.8 µm.
• Numerical simulations with germanium-based metasurfaces and experimental tests using silicon and GaAs in the near-infrared confirm the design’s scalability across a wide frequency range.
• The enhanced electromagnetic field confinement from high-Q Fano resonances holds promise for biosensing, tunable filtering, and active optical devices.

High Quality-Factor Fano Resonances in Broken Symmetry Dielectric Metasurfaces

The paper presents a novel approach in the design of dielectric metasurfaces, focusing primarily on achieving high quality-factor (Q-factor) Fano resonances through the utilization of single resonator unit cells. Traditionally, dielectric metasurfaces had been multimodal and exhibited broad spectral resonances. The design proposed in this paper addresses these challenges through the introduction of symmetry-breaking in resonator geometries.

This paper demonstrates that by perturbing highly symmetric structures such as cubes, it is possible to induce coupling between "bright" dipole modes and "dark" dipole modes. These "dark" modes are known for their suppressed radiative decay due to local field effects within the array, enhancing Fano resonance quality. The scalability of the design is evidenced through the wide frequency range it can accommodate, ranging from the near-infrared to radio frequencies.

A series of numerical simulations were performed with germanium-based metasurfaces, where a notable Q-factor of approximately 1300 at a resonance of ~10.8 µm was observed. Experimentally, two implementations were demonstrated in the near-infrared spectrum using silicon and gallium arsenide (GaAs), achieving Q-factors of ~350 and ~600, respectively. These experimental results mark the highest Q-factor achieved within the specified range for metasurfaces of this kind, providing crucial insight into the performance of such structures.

The high electromagnetic field enhancements occurring within these resonators point to numerous vigorous applications. The authors discuss the potential extension to active and nonlinear materials, notably highlighting opportunities within GaAs. The resulting implications could lead to developments in biosensing devices, tunable narrowband filters, and innovations in active optical devices like lasers and modulators.

Theoretical implications of this research suggest substantial impacts on the field of photonics, given the success in controlling spectral resonance with simpler, monolithic geometries. The avoidance of inter-resonator coupling reduces the exacting fabrication tolerances required in previous designs. This is achieved through intra-resonator mode mixing, permitted by the intentional disruption of spatial symmetry, manifesting as a profound leap in unit cell design strategy.

Future research can potentially explore further miniaturization of these devices while maintaining high-Q characteristics, as well as their integration with other advanced materials. There are also prospects for further experimental investigations into even higher ranges of frequency scalability and the incorporation of gain materials to explore lasing and amplifying capabilities.

This paper provides a new perspective on dielectric resonator metasurface design and broadens horizons regarding their practical and academic utility. Ongoing developments will likely enrich the metasurface technology ecosystem and catalyze innovation in photonic devices.