A redesigned photonic chip that “floats” its waveguide in air has pushed gas detection into the parts-per-billion range – an important step toward compact, high-performance chemical sensors.
The device replaces the conventional solid substrate beneath a chalcogenide glass waveguide with air. This seemingly simple change dramatically improves performance: more light leaks into the surrounding gas, while reduced heat dissipation amplifies the photothermal signal used for detection. The result is a 45-fold increase in sensing efficiency compared with traditional designs.
Using photothermal spectroscopy, the chip detected acetylene at concentrations as low as 330 ppb, with a noise-equivalent absorption of 3.8 × 10⁻⁷ cm⁻¹ – setting a new benchmark for on-chip photonic gas sensors. Despite its sensitivity, the device remains compact (1.2 cm long) and delivers results in under a second.
Because the platform operates in the near-infrared – compatible with existing telecom technologies – and the material supports mid-infrared light, the approach could be extended to a wide range of gases, from pollutants to disease biomarkers. The researchers envision integrated “sensor-on-a-chip” systems for environmental monitoring, industrial safety, and wearable health diagnostics.
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