Study on a sodium-based broadband SPR dual-parameter sensor tuned with Ta2O5 thin films

Abstract Bandwidth is an important factor affecting the sensitivity of the sensor, and broadening the bandwidth can improve the sensitivity of the sensor. Figure of merit (FOM) is closely related to sensitivity and full width at half maximum (FWHM). High sensitivity and low FWHM sensor with high FOM and detection accuracy. Na has low intrinsic loss compared with Au or Ag, and Na film-based SPR sensor has narrower FWHM, better sensing performance than Au or Ag in the near infrared region, and wider bandwidth, which are the key factors for the sensor to have high precision and high sensitivity. Ta2O5 can make resonance peak redshift, broaden the bandwidth and improve the sensitivity of cascade two-parameter sensors. Combining the advantages of Na and Ta2O5, this paper proposes a surface plasmonic resonance (SPR) photonic crystal fiber (PCF) sensor based on Na/Ta2O5 composite film, which has high sensitivity and FOM. Two polishing surfaces were introduced into the cladding by polishing, and the two polishing surfaces were coated with Na/Ta2O5 and Na/Ta2O5/polydimethylsiloxane (PDMS) to measure the refractive index (RI) and temperature simultaneously. Based on the finite element method, the SPR optical fiber sensor is numerically studied and its structure is optimized. Under optimal geometry and film thickness. The maximum sensitivity of RI (1.30-1.41) is 12100 nm/RIU, the maximum FOM is 1313.24 RIU-1. The maximum sensitivity of temperature (0-40 ℃) is 16 nm/℃, and the maximum FOM is 0.68 RIU-1. The change of structural parameters of the sensor does not affect the performance, which reduces the difficulty of manufacturing. This study provides the choice of non-precious metal composite film to improve the bandwidth and sensitivity of dual-parameter SPR sensor, expands the application of non-precious metal in biochemical and environmental detection fields.