

Advances in Optics and Photonics 2022, 14 Mode-division and spatial-division optical fiber sensors.
#FILM OVERLAY PLUS#
A Plus Shaped Cavity in Optical Fiber Based Refractive Index Sensor.


With this structured LPG, detection limits of the order of tens of micrograms per liter (10 –11 M) are attained. The specificity of the sensor was validated by performing the same model assay after spiking anti-IgG into human serum. This is the first time that a sol–gel based titania–silica-coated LPG is proposed as an effective and feasible label-free biosensor. The analyte concentration was determined from the wavelength shift at the end of the binding process and from the initial binding rate. After the functionalization of the fiber surface using a methacrylic acid/methacrylate copolymer, an antibody/antigen (IgG/anti-IgG) assay was carried out to assess the performance of sol–gel based titania–silica-coated LPGs as biosensors. Changing both the sol viscosity and the withdrawal speed during the dip-coating made it possible to adjust the thickness of the film overlay, which is a crucial parameter for the sensor performance. The chemical overlay, which increases the refractive index (RI) sensitivity of the sensor, consists of a sol–gel-based titania–silica thin film, deposited along the sensing portion of the fiber by means of the dip-coating technique. An evanescent wave optical fiber biosensor based on titania–silica-coated long period grating (LPG) is presented.
