Fiber Bragg Grating Dynamic Sensing Through a Dispersive Spectrometer

In the field of shock physics and energetic materials, Fiber Bragg Gratings (FBGs) are used to measure shock velocity, detonation velocity and shock pressure levels. They are also used to measure strain in structures loaded with explosive effects. FBG sensors are known to be light, small, immune electromagnetic environments and have fast response compared to electrical sensors. To use one or more gratings along a fiber, a high-resolution spectrometer with a high sampling rate has been developed. This dynamic spectrometer employs time-multiplexing by wavelength-to-time conversion using dispersion. It provides a complete view of the spectra evolution at a rate of 100 MHz. Thus, complex phenomena can be observed. In this paper, the interrogation technique is presented in more detail, and experimental results are discussed. The experiments presented are a low-pressure shock velocity measurement in epoxy, a deflagration-to-detonation transition in a porous energetic material, a Shock-to-Detonation Transition in a dense energetic material, a tentative-to-measure pressure level in epoxy from an FBG made in a sapphire fiber and multi-point strain measurements up to eight FBGs. The advantages and limits are discussed for each type of experiment.