Swelling-Based Distributed Chemical Sensing with Standard Acrylate Coated Optical Fibers

Abstract

Distributed chemical sensing is demonstrated using standard acrylate coated optical fibers. Swelling of the polymer coating induces strain in the fiber’s silica core provoking a local refractive index change which is detectable all along an optical fiber by advanced distributed sensing techniques. Thermal effects can be discriminated from strain using uncoated fiber segments, leading to more accurate strain readings. The concept has been validated by measuring strain responses of various aqueous and organic solvents and different chain length alkanes and blends thereof. Although demonstrated on a short range of two meters using optical frequency-domain reflectometry, the technique can be applied to many kilometer-long fiber installations. Low-cost and insensitive to corrosion and electromagnetic radiation, along with the possibility to interrogate thousands of independent measurement points along a single optical fiber, this novel technique is likely to find applications in environmental monitoring, food analysis, agriculture, water quality monitoring, or medical diagnostics.

Fabrication of Optical Fibers with Multiple Coatings for Swelling-Based Chemical Sensing

“…After about 10 min, the acrylic coating gradually detached from the fiber; over the entire segment that was exposed to ethanol, the same effect was observed with acetone. Such effect was observed with non-stripped fibers [ 16 ], or the spliced fibers with metal sleeves. Observation of the fiber before and after the exposure under an optical microscope did not reveal any visible difference.…”

“…The coatings were applied sequentially in liquid form and are cured by exposure to ultraviolet light. We demonstrated that coatings on commercially available fibers could be used for chemical sensing [ 16 ]. Here, we investigated methods with which different sensing elements can be realized on the same optical fiber which has multiple sections with different chemistries.…”

“…We have shown that, in the first few minutes, there can be thermal effects due to heating by the enthalpy of mixing. However, they can be excluded when uncoated fiber segments are used to measure the temperature independently [ 16 ]. This preliminary result shows that arrays of differently coated sensors materials can be fabricated and read out, simultaneously.…”

“…Using water-swellable polymers to coat silica fibers and reflectometry approaches, distributed humidity sensors over conventional glass fibers have also been reported [ 8 ]. The coating of the optical fiber can be a specific material that allows for specific chemical sensing [ 14 , 15 , 16 ]. While this approach has been mostly used for point sensors [ 17 ], where several possible coatings for chemical sensing have been investigated [ 17 , 18 , 19 ], we have shown that the approach can be directly applied to distributed sensing approaches [ 16 ].…”

Distributed Fiber Optics Measurements of Rock Deformation and Failure in Triaxial Tests

“…Besides coating stiffness, other physical and chemical interactions of the coating with the host media should be considered. For example, some polymer and acrylate coatings swell in contact with water, and the swelling depends on salt concentration, PH, and presence of other chemical substances (Bai & Seitz, 1994; Janting et al., 2019; Khanikar & Singh, 2021; McCurley & Seitz, 1991; Sedighi et al., 2021; Shakhsher et al., 1994).…”