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.