Gigahertz free-space electro-optic modulators based on Mie resonances

Abstract

Electro-optic modulators from non-linear χ(2) materials are essential for sensing, metrology and telecommunications because they link the optical domain with the microwave domain. At present, most geometries are suited for fiber applications. In contrast, architectures that modulate directly free-space light at gigahertz (GHz) speeds have remained very challenging, despite their dire need for active free-space optics, in diffractive computing or for optoelectronic feedback to free-space emitters. They are typically bulky or suffer from much reduced interaction lengths. Here, we employ an ultrathin array of sub-wavelength Mie resonators that support quasi bound states in the continuum (BIC) as a key mechanism to demonstrate electro-optic modulation of free-space light with high efficiency at GHz speeds. Our geometry relies on hybrid silicon-organic nanostructures that feature low loss (Q = 550 at λres = 1594 nm) while being integrated with GHz-compatible coplanar waveguides. We maximize the electro-optic effect by using high-performance electro-optic molecules (whose electro-optic tensor we engineer in-device to exploit r33 = 100 pm/V) and by nanoscale optimization of the optical modes. We demonstrate both DC tuning and high speed modulation up to 5 GHz (fEO,-3 dB = 3 GHz) and shift the resonant frequency of the quasi-BIC by Δλres =11 nm, surpassing its linewidth. We contrast the properties of quasi-BIC modulators by studying also guided mode resonances that we tune by Δλres=20 nm. Our approach showcases the potential for ultrathin GHz-speed free-space electro-optic modulators.

Tunable Metasurface Using Thin-Film Lithium Niobate in the Telecom Regime

“…The experimental results correspond very well to the numerical simulations and the analytic prediction. Recent works on EO optical tuning, including tunable polymers and organic layers such as JRD1:PMMA , on metasurfaces, exhibit a high spectral shift of Δλ = 11 nm but use a higher applied voltage, which yields merely , half of the spectral shift we achieved in our device. Nevertheless, these works have presented materials with higher EO coefficients above r 33 = 100 pm/V compared to LiNbO r 13 = 10.12 pm/V we used.…”

“…By doing so, the applied electric field will be higher for a given applied voltage, and consequently, a larger spectral shift per volt is expected. An additional option to reduce the modulation voltage is using materials with a higher EO coefficient, as mentioned above. − …”

Space and Time Modulations of Light with Metasurfaces: Recent Progress and Future Prospects

“…Another example of active spectral tuning of q-BIC states is realized using silicon resonators covered by a polymer with dispersed EO-molecules (active JRD1/PMMA layer). 105 It employs second-order nonlinear materials exhibiting a linear EO effect as a surrounding for meta-atoms supporting high-quality factor resonances designed by symmetry breaking. Each unit cell consists of two ellipses that are rotated with respect to the vertical axis, as shown in Figure 3b (right).…”

Nano-electromechanical spatial light modulator enabled by asymmetric resonant dielectric metasurfaces

“…Achieving similar spatial resolution but with an active metasurface would enable high-speed and high-resolution SLMs in a compact footprint 10 . Many seminal works have been proposed in the context of the active metasurfaces, using various active materials or mechanisms such as transparent conducting oxides 1 , 11 , 12 , liquid crystals 13 , electro-optic materials 14 – 17 , phase-change materials 18 , 2D materials 19 – 22 , electromechanical systems 23 – 28 , and semiconductors 29 . The active plasmonic metasurfaces based on transparent conducting oxides 1 , 11 , 12 have successfully achieved complex modulation.…”