Full Control of Fano Spectral Profile with GST-Based Metamaterial

Abstract

Asymmetric line shape in a spectral profile, quantified by the Fano parameter q, is a hallmark feature of Fano resonances. In photonics, this asymmetry captures the Fano physics of coupling localized resonances to the radiative continuum and nourishes many photonic Fano devices. Recent advances have suggested full control of q from negative infinity to positive infinity; here we realize the negative-to-positive q transition in an active and successive manner using Ge 2 Sb 2 Te 5 (GST)-based Fano resonator in the Mid-infrared. The structure consists of two resonating components: an array of dielectric rectangle resonators on dielectric substrate (for localized resonance) and a GST layer (for radiative continuum), coupled by a conductive spacer. With phase transition of GST, the q parameter can be continuously tuned from 5.2 to 0 to −5.6, which directly maps to the wavelength shifts in the GST resonating layer, that is, the modulation in the continuum. Incorporating geometrical optimization, an arbitrary q value is further achieved. Our Fano resonator also demonstrates a unique narrowband switching property based on the q tuning effect at a wavelength of 5 μm. It performs as a strong reflector of reflection intensity R = 0.77 (with Q = 135) for q = −0.2 and switches to a strong absorber with absorption intensity A = 0.94 (with Q = 190) for q = −5.6. This dynamic interplay between radiative continuum and Fano spectral profile in a vast range of q paves the way for new classes of active photonic devices.

A multi-mode super-fano mechanism for enhanced third harmonic generation in silicon metasurfaces

“…The width and spectral position of the individual resonances and thus the Fano-resonance can be easily tuned by varying the elliptical diameters d x and d y . In the special case of highly fine-tuned resonances, the sharp asymmetric resonance feature in the transmission spectrum disappears and a Lorentz resonance profile is formed 25,43 .…”

Generalized Fano resonance theory based on Fabry-Perot cavity

“…Two primary factors influence the asymmetric Fano line shape: (1) the frequency distribution of the discrete state and continuous state [29,30] and (2) the initial phase distributions of the modes [17,[31][32][33]. These factors affect the occurrence of maximum and minimum values within the Fano line shape, which are connected with the asymmetric parameter q [2,34].…”

“…Some relevant work has been reported, which is realized by changing the coupled mode frequencies or interactions between the modes. For example, phase change materials, such as Ge 2 Sb 2 Te 5 (GST), are used to change the frequency of discrete or continuous state by heating or applying a voltage [29,35,36]. Manukumara Manjappa et al regulated the out-of-plane structural asymmetry parameter of the split ring by applying voltage, thereby electrically tuning the Fano resonance [16].…”

Full‐Control and Switching of Optical Fano Resonance by Continuum State Engineering

“…Extensive investigations have been conducted on various metal-based structures as well as all-dielectric metasurfaces, unveiling numerous favorable Fano features, including high Q-factor and tunability. Representative examples involve asymmetric split-ring resonators, [5] nanoclusters, [6][7][8][9][10] photonic crystals, [11,12] gratings, [13][14][15][16][17] and metamaterials. [18][19][20][21] While metasurfaces offer advantageous design freedom, their small feature sizes impose limitations on their practical applicability for large-scale systems.…”

“…[3,22,23] Despite the breakthrough achieved by the film-based optical Fano resonator, the simple geometry has presented challenges in achieving tunability in terms of spectral position, intensity, and spectral line shape. However, design flexibility in Fano resonance is crucial for various optoelectronic applications, [13] such as lasing spacers, [24,25] sensors, [26,27] optical filters, [28] and optical switches. [29] The asymmetric spectral profile is quantified by the well-established Fano relation and Fano parameter (q).…”