We demonstrated, for the first time, micro-ring resonator assisted photothermal spectroscopy measurement of a gas phase sample. The experiment used a telecoms wavelength probe laser that was coupled to a silicon nitride photonic integrated circuit using a fibre array. We excited the photothermal effect in the water vapor above the micro-ring using a 1395 nm diode laser. We measured the 1f and 2f wavelength modulation response versus excitation laser wavelength and verified the power scaling behaviour of the signal.

This work reports on the implementation of a wafer-bonded Fabry–Perot interferometer (FPI) as the transducer of a photothermal spectroscopy system. A near-infrared laser is collimated and propagated through an approximately 1-mm-spaced Fabry-Pérot (FP) cavity to probe the photo-thermal effect induced by the pump beam. The sensor’s metrological figures of merit were evaluated by detecting methane (CH4) gas molecules at various concentrations. For the absorption band centered at 6047 cm⁻¹, a minimum detection limit (MDL) of 42 ppm was achieved with a 1 s integration time, showing that the sensor system has significant potential for the design of compact, stable, and versatile gas detectors with excellent sensitivity. From Allan deviation, we estimate an MDL of 5.1 ppm for an optimum integration time of 100 s.