Qingmei Sui

TiO_2 nanoparticle thin film-coated optical fiber Fabry-Perot sensor

In this paper, a novel TiO(2) nanoparticle thin film coated optical fiber Fabry-Perot (F-P) sensor had been developed for refractive index (RI) sensing by monitoring the shifts of the fringe contrast in the reflectance spectra. Using in situ liquid phase deposition approach, the TiO(2) nanoparticle thin film could be formed on the fiber surface in a controlled fashion. The optical properties of as-prepared F-P sensors were investigated both theoretically and experimentally. The results indicated that the RI sensitivity of F-P sensors could be effectively improved after the deposition of nanoparticle thin-films. It was about 69.38 dB/RIU, which was 2.6 times higher than that of uncoated one. The linear RI measurement range was also extended from 1.333~1.457 to 1.333~1.8423. More importantly, its optical properties exhibited the unique temperature-independent performance. Therefore, owing to these special optical properties, the TiO(2) nanoparticle thin film coated F-P sensors have great potentials in medical diagnostics, food quality testing, environmental monitoring, biohazard detection and homeland security, even at elevated temperature.

Optical Response of Fiber-Optic Fabry-Perot Refractive-Index Tip Sensor Coated With Polyelectrolyte Multilayer Ultra-Thin Films

The polyelectrolyte multilayer (PEM) thin film-coated Fabry-Perot (F-P) optical fiber tip sensors had been developed for in situ refractive index (RI) measurement. Using the simple layer-by-layer (LBL) approach, the sensor surfaces had been successfully coated with PEM thin films of poly(diallyldimethyl- ammonium choloride)/poly(styrenesulfonate sodium salt) (PDDA/PSS)n (n is number of bilayers). Their optical response to the changes of external RI had been investigated and evaluated. The results demonstrated that after coated with PEM thin films, the inflection point of as-formed F-P tip sensor would shift from 1.457 to 1.4623 but its RI sensitivity was slightly reduced from 39 dB/RI to 25 dB/RI. In addition, their fringe contrast exhibited the unique temperature-independent performance. Therefore, owing to these special optical properties, simple operation and easy miniaturization, these novel PEM thin film coated F-P tip sensors have great potential in the detection and sensing of chemical and biological molecules, even at elevated temperature.

Acoustic emission source localization technique based on least squares support vector machine by using FBG sensors

An intelligent acoustic emission (AE) source localization technique by using fiber Bragg grating (FBG) sensors was investigated. Four FBGs sensing network was established for detecting the AE signal. And power intensity demodulation method was initialized employing narrow-band tunable laser. The intelligent AE source localization method was proposed based on wavelet transform, cross-correlation analysis, and least squares support vector machines (LS-SVM). LS-SVM modal’s input is signal time difference and output is AE source position. The location experiments were carried out on a 500 mm × 500 mm × 2 mm aluminum alloy plate. The results showed that the AE source position abscissa and ordinate localization errors are all less than 10 mm. The maximum and average localization errors are 8.65 and 6.78 mm, respectively. The research results provided a novel method for AE source localization by using FBG sensors.