Coated long-period fiber gratings as high-sensitivity optochemical sensors

• Published in: Journal of lightwave technology Vol. 24; no. 4; pp. 1776 - 1786
• Main Authors: Cusano, A., Iadicicco, A., Pilla, P., Contessa, L., Campopiano, S., Cutolo, A., Giordano, M., Guerra, G.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-04-2006; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Applied sciences; Chemical sensors; Circuit properties; Cladding; Coatings; Crystalline materials; Crystallization; Electric, optical and optoelectronic circuits; Electronics; Exact sciences and technology; Fiber gratings; Fibers; General equipment and techniques; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Integrated optics. Optical fibers and wave guides; long-period fiber gratings (LPFGs); Nanocomposites; Nanomaterials; Nanoporous materials; Nanostructure; Optical and optoelectronic circuits; Optical fiber sensors; Physics; Probes; R&D; Refractive index; refractive-index sensors; Refractivity; Research & development; Sensors; Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing; Spark plasma sintering; syndiotactic polystyrene (sPS); Temperature sensors; Performance evaluation; Chemical sensors; Measurement sensor; Refraction index; syndiotactic polystyrene (sPS); Nanoporous materials; Selectivity; Chemical sensor; Cladding; Coatings; Grating in fiber; Phase shifter; Coated material; Fiber cladding; High sensitivity; Size effect; refractive-index sensors; High field; long-period fiber gratings (LPFGs); Dip coating; Room temperature
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2006.871128

In this paper, the numerical and the experimental analyses of coated long-period fiber gratings (LPFGs) as a high-sensitivity optochemical sensor are presented. The proposed structure relies on LPFGs coated with nanoscale high refractive index chemical-sensitive overlays. The deposition of overlays with refractive index higher than the cladding one leads to a modification of the cladding-mode distribution. If the overlay features are properly chosen, a strong field enhancement within the overlay occurs, leading to an excellent sensitivity of the cladding-mode distribution to the coating properties. The effects of overlay thickness and cladding-mode order on sensor performances have been numerically and experimentally investigated. In order to provide a high-sensitivity and species-specific optochemical sensor, this mechanism has been proved with nanoscale overlays of syndiotactic polystyrene (sPS) in the nanoporous crystalline /spl delta/ form. The sensitive material has been chosen in light of its selectivity and high sorption properties towards chlorinated and aromatic compounds. Sensor probes were prepared by using dip-coating technique and an adequate procedure to obtain the /spl delta/-form sPS. Experimental demonstration of the sensor capability to perform subparts-per-million detection of chloroform in water at room temperature is also reported.