An Optical Fiber Sensor for Remote pH Sensing and Imaging

Abstract

A fiber-optical probe for pH sensing and real-time imaging is successfully fabricated by connecting a polymer imaging fiber and a gradient index (GRIN) lens rod which was modified with a sensing film. By employing an improved metallographic microscope, an optical system is designed to cooperate with the probe. This novel technique has high-quality imaging capabilities for observing remote samples while measuring pH. The linear range of the probe is pH 1.2-3.5. This technique overcomes the difficulty that high-quality images cannot be obtained when directly using conventional imaging bundles for pH sensing and imaging. As preliminary applications, the corrosion behavior of an iron screw and the reaction process of rust were investigated in buffer solutions of pH 2.0 and 2.9, respectively. The experiment demonstrated that the pH values of the analytes' surface were higher than that of buffer solutions due to the chemical reaction. It provides great potential for applications in optical multifunctional detection, especially in chemical sensing and biosensing.

Gradient-Index Materials Based on Thiol–Ene Networks

“…While the GRIN concept was first suggested in the mid-19th century, only in the last few decades have GRIN lenses with large overall index changes (Δ n > 0.04) and depth of gradient ( d > 20 mm) emerged. Control of refractive index gradients over large dimensions (centimeters), in addition to the ability to prepare GRIN lenslet arrays and coatings, is advancing optics for communications, imaging and display systems, sensing, solar concentrators, , and biomedical technologies …”

“…Polymer-based GRIN optics are appealing due to their low density, shatter resistance, flexibility, tunable mechanical properties, and mild synthesis conditions . Gradient-index polymers have been fabricated by a variety of methods including interfacial gel copolymerization, , copolymerization involving immersion, photopolymerization, , and layer-by-layer extrusion into a stack of thin films. − While these approaches have been successful in various geometries, they are process-intensive and require precisely controlled conditions and handling to avoid defects caused by, for example, stress-induced birefringence or phase separation. The development of lightweight materials with improved optical loss characteristics and tunable index of refraction and Abbe number, a measure of a material’s optical dispersion, is critical to expanding the design space of GRIN optics.…”