Chemical sensing by differential thermal analysis with a digitally controlled fiber optic interferometer

Abstract

In this work the implementation of an optical fiber interferometric system for differential thermal analysis enabling the identification of chemical species is described. The system is based on a white light Mach-Zehnder configuration using pseudo-heterodyne demodulation to interrogate two identical fiber Bragg gratings (FBG) in a differential scheme. System performance is compared using either standard hardware or low cost virtual instrumentation for operation control and signal processing. The operation with the virtual system enabled temperature measurements with a ±0.023 °C resolution nearly matching the performance of the standard hardware. The system ability to discriminate chemical species by differential thermal analysis was demonstrated. Mixed samples of acetone and methanol could be successfully identified, indicating the suitability of the system for high precision measurements using low cost instrumentation.

High resolution temperature independent refractive index measurement using differential white light interferometry

“…Using appropriate setting of the path imbalances of each of the interferometers the phase difference between the two signals depends only on the modulation imposed by the parameter of interest, thereby reducing also the effects of cross-sensitivity, indissociable of these systems. Differential WLI system have been employed to measure temperature [22,23], liquid refractive index [24,25], air refractive index [26] and for fuel conformity analysis [27].…”