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2026

Suspension Waveguide-Enhanced On-Chip Photothermal Gas Sensing

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A team led by Wei Jin at the Hong Kong Polytechnic University, together with teams from Jilin University headed by Chuantao Zheng and from Zhijiang Laboratory under Qingyang Du, has demonstrated a suspended chalcogenide-glass waveguide (ChGW)-enhanced photothermal sensor (PTS) that achieves molecular-gas sensing with sub-parts-per-billion (ppb) sensitivity. The authors employed a CMOS-compatible two-step patterning process to fabricate nanoscale suspended ChGWs with insertion loss as low as 2.6 dB/cm. By developing an equivalent PTS model to guide the optimization of the ChGW’s geometric structure, they achieved a fourfold increase in absorption-induced thermal-source power and a 10.6-fold reduction in effective thermal conductivity, thereby boosting the photothermal phase-modulation efficiency by a factor of 45 compared with non-suspended waveguides. Combined with a high-contrast waveguide-end-face Fabry–Perot interferometer, the authors realized an unprecedented acetylene detection limit of 330 ppb, a wide dynamic range approaching six orders of magnitude, and a rapid response time of less than 1 second. The system as a whole exhibits a noise-equivalent absorption coefficient of 3.8 × 10⁻⁴ cm⁻¹, which, to the authors’ knowledge, sets a new benchmark for photonic-waveguide gas sensors. This work represents a critical advance toward the development of integrated-chip sensor prototypes for high-sensitivity, background-noise-free photonic-sensing applications.

The research findings were published on February 17, 2026, in Light: Science & Applications under the title “Suspended waveguide-enhanced near-infrared photothermal spectroscopy for ppb-level molecular gas sensing on a chalcogenide chip.”