A high-sensitivity optical sensor based on a Fabry–Pérot interferometer (FPI) has been demonstrated. The cavity of the FPI is formed by two parallel half-reflective film-coated glass substrates with a distance of 1 mm and works as the sensing area. The interaction between the propagating wave and the analyte gives the sensing signal. High sensitivity of 1149 nm / RIU has been achieved for the wavelength interrogation. The Fabry–Pérot sensor can be made into a large array with multiple microfluidic channels to detect the different types of analytes. It has great potential in biochemical sensing.
Although the cascaded double ring sensor can improve the sensitivity due to the difference between the radii of the reference ring and the sensing ring to produce Vernier effect, a large bandwidth spectrometer or a large tunable range laser is required for the wavelength interrogation. In this paper, the cascaded double ring senor based on silicon on insulator (SOI) with thermo-optical tuning for refractive index sensing is investigated. The peak wavelength shift of the transmission envelope can be converted into the electric power change of the micro-heater. The sensitivity reaches 33.703×103 mW/RIU by fitting Gaussian function to the spectral envelope for the wavelength interrogation with 7.9 nm wavelength measurement range.
In this paper, we compare the sensing sensitivity, the stability and the temperature sensitivity of the micro-ring resonator optical sensor based on silicon waveguide and silicon nitride waveguide. For the silicon waveguide and silicon nitride waveguide single ring, the sensing sensitivities are 1113nm/RIU and 182.64nm/RIU, the resonance wavelength variations are ±12.5pm and ±7.5pm in an hour testing at the ambient temperature and the temperature sensitivities are 0.038nm/K and 0.018nm/K, respectively. . The sensing sensitivity can be improved to 6080.6nm/RIU by cascaded double silicon nitride waveguide rings to produce Vernier effect.
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