Evanescent wave optical-fiber sensing (temperature, relative humidity, and ph sensors)

Abstract

Sensitive and versatile evanescent wave-sensing systems featuring polished optical fiber-based sensor designs with low-cost light sources have been developed for temperature, relative humidity, and pH measurements. The work herein contained describes the fabrication of three types of sensors based on standard silica, single-mode fibers previously subjected to a lateral polishing of the cladding. Temperature sensing through oils whose refractive index varied linearly with temperature showed applicability with up to 5 dB/ C for a 5 range. Polyvinyl alcohol films on the fibers showed almost 10-dB linear variation from 70% to 90% relative humidity. Sol-gel trapped dyes as thin films on the polished surface were capable of performing 15-dB output variation (although not linearly) for pH ranging from 2 to 11.

Current status of micro- and nano-structured optical fiber sensors

“…Numerous reports have appeared on the fabrication of and applications of the D-shape fiber [82][83][84][85][86]. Gaston et al have devised temperature, relative humidity (RH), and pH sensors by using side-polished single mode fibers [83].…”

Optical pH sensor based on polyaniline sol-gel film immobilized with bromothymol blue and phenol red

“…However, this electrochemical device have several problems including the need to have constant re-calibration [4] because it does not give a reproducible electromagnetic field over longer periods of times. Recently, optical pH sensor most widely used because immunity to Immunity to Electromagnetic Interference (EMI), good flexibility, small sensing volume and electrically passive operation [5][6][7][8][9].…”

High-sensitivity optical humidity sensor based on a thin dielectric waveguide

“…In principle, optical sensors can be more advantageous than their electrical counterpart as they are less sensitive to electromagnetic interference. Particularly, optical methods based on evanescent waves (EW) were shown to be useful to probe the effects of relative humidity (RH) in thin films deposited on silica [10][11][12][13] and plastic [14] optical fibers. Planar waveguides (WGs) also constitute good tools to generate a probe EWand are employed in techniques using surface plasmon resonance (SPR) [15] and dielectric thin films WGs [16], which are versatile and accurate devices for refractive index (RI) measurements.…”