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

We discuss distributed chemical sensing based on the swelling of coatings of optical fibers. Volume changes in the coating induce strain in the fiber's glass core, provoking a local change in the refractive index which is detectable by distributed fiber optical sensing techniques. We describe methods to realize different coatings on a single fiber.

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

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.

Liquid Flow Meter by Fiber-Optic Sensing of Heat Propagation.

Monitoring fluid flow rates is imperative for a variety of industries including biomedical engineering, chemical engineering, the food industry, and the oil and gas industries. We propose a flow meter that, unlike turbine or pressure-based sensors, is not flow intrusive, requires zero maintenance, has low risk of clogging, and is compatible with harsh conditions. Using optical fiber sensing, we monitor the temperature distribution along a fluid conduit.

High-Order Polynomial Fitting Assistance for Fast Double-Peak Finding in Brillouin-Distributed Sensing.

A high-order polynomial fitting method is proposed to accelerate the computation of double-Gaussian fitting in the retrieval of the Brillouin frequency shifts (BFS) in optical fibers showing two local Brillouin peaks. The method is experimentally validated in a distributed Brillouin sensor under different signal-to noise ratios and realistic spectral scenarios. Results verify that a sixth-order polynomial fitting can provide a reliable initial estimation of the dual local BFS values, which can be subsequently used as initial parameters of a nonlinear double-Gaussian fitting.

Mass Flow Monitoring by Distributed Fiber Optical Temperature Sensing.

We developed a novel method to monitor mass flow based on distributed fiber optical temperature sensing. Examination of the temporal and spatial temperature distribution along the entire length of a locally heated fluidic conduit reveals heat flow under forced convection. Our experimental results are in good agreement with two-dimensional finite element analysis that couples fluid dynamic and heat transfer equations.