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We detect trace gases at parts-per-billion levels using evanescent-field absorption spectroscopy in silicon nitride microring resonators coated with a functionalized sorbent polymer. An analysis of the microring resonance line shapes enables a measurement of the differential absorption spectra for a number of vapor-phase analytes. The spectra are obtained at the near-infrared overtone of OH-stretch resonance, which provides information about the toxicity of the analyte vapor.

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Photonic integrated circuits have enabled progressively active functionality in compact devices with the potential for large-scale integration. To date the lowest loss photonic circuits are achieved with silica or silicon nitride-based platforms. However, these materials generally lack reconfigurability. In this work we present a platform for achieving active functionality in any dielectric waveguide via large-scale opto-electro-mechanical tuning of the effective refractive index (Δn_eff≈0.01-0.1) and phase (Δϕ>2π). A suspended microbridge weakly interacts with the evanescent field of a low-mode confinement waveguide to tune the effective refractive index and phase with minimal loss. Metal-coated bridges enable electrostatic actuation to displace the microbridge to dynamically tune n_EFF. In a second implementation we place a non-metallized dielectric microbridge in a gradient electric field to achieve actuation and tuning. Both approaches are broadband, universally applicable to any waveguide, and pave the way for adding active functionality to many passive optical materials.

Abstract