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The development of new optical materials and metamaterials has seen a natural progression toward both nanoscale geometries and dynamic performance. The development of these materials, such as optical metasurfaces which impart discrete, spatially dependent phase shifts on incident light, often benefits from the measurement of transmitted or reflected phase. Careful measurement of phase typically proves difficult to implement, due to high measurement sensitivity to practically unavoidable environmental sources of noise and drift. To date, no characterization technique has yet emerged as a frontrunner for these applications. This challenge is addressed using a custom‐designed three‐beam Mach–Zehnder interferometer capable of continuously referenced measurement of both phase and transmittance, resulting in a 10× reduction of noise and drift and phase measurement standard deviation over 10 min of 0.56° and over 16 h of 2.8°. High measurement stability provided by this method enables samples to be easily characterized under dynamic conditions. Temperature‐dependent measurements are demonstrated with phase‐change material vanadium dioxide (VO₂), and with wavelength‐dependent measurements of a dielectric Huygens metasurface supporting a characteristic resonant reflection peak. A Fourier‐based signal filtering technique is applied, reducing measurement uncertainty to 0.13° and enabling discernment of monolayer thickness variations in 2D material MoS₂.

A sensing platform is presented that uses dielectric Huygens source metasurfaces to measure refractive index changes in a microfluidic channel with experimentally measured sensitivity of 323 nm RIU⁻¹, a figure of merit (FOM) of 5.4, and a response of 8.2 (820%) change in transmittance per refractive index unit (T/RIU). Changes in the refractive index of liquids flown through the channel are measured by single‐wavelength transmittance measurement, requiring only a simple light source and photodetector, significantly reducing device expense in comparison to state‐of‐the‐art refractive index sensing technologies. A technoeconomic analysis predicts a device costing ≈$2400 that is capable of detecting refractive index changes of the order of 2*10⁻⁸. The metasurfaces utilized are low profile, scalable, and use materials and fabrication processes compatible with CMOS and other technologies making them suitable for device integration. The Huygens metasurface system, characterized by spectrally overlapping electric and magnetic dipole modes, offers a high degree of customizability. Interplay between the two resonances may be controlled via metasurface geometry, leading to tunability of device sensitivity and measurement range. Ultrahigh sensitivity of 350 nm RIU⁻¹with FOM of 219, corresponding to single‐wavelength sensitivity of 360 RIU⁻¹, is demonstrated computationally through use of antisymmetric resonances of a Huygens metasurface illuminated at small incidence angles.

Metasurfaces with dynamic optical performance have the potential to enable a broad range of applications. We computationally investigate the potential of dielectric Huygens metasurfaces, supporting both electric and magnetic dipole resonances, as a candidate platform for dynamic tuning. The asymmetric response of the two dipole resonances to changes in geometric and material parameters, and the potential for separate control of amplitude and phase, is analyzed. A review of dynamic materials, and their promise and limitations for use in dynamic Huygens metasurfaces, is discussed. Vanadium dioxide (${\mathrm{V}\mathrm{O}}_2$) is recognized as a singularly interesting material, due to its variable refractive index and optical absorption in response to several stimuli. Transmitted phase modulation of$\pm <\#comment/>\mathrm{\pi <\#comment/>}$is computationally demonstrated as a function of decaying resonance utilizing only the first 5% of the insulator-metal transition, corresponding to a temperature change of$<<\#comment/>{10}^{\circ <\#comment/>}\mathrm{C}$. As another case study utilizing asymmetric resonance tuning in response to changing incidence angle, phase modulation ($2\mathrm{\pi <\#comment/>}$range for reflected light and$><\#comment/>1.5\mathrm{\pi <\#comment/>}$for transmitted light) and amplitude modulation (from$\mathrm{R}=1$to$\mathrm{T}=1$) are demonstrated using a simple silicon metasurface with varying incident angle within a range of$\sim <\#comment/>{15}^{\circ <\#comment/>}$on two axes. A promising implementation within a micro-electromechanical system (MEMS)-based spatial light modulator, similar to conventional digital micromirror devices, is discussed.