Enhanced-backscattering optical fibers for inline interferometers: applications to biosensing

The interrogation of Rayleigh backscattering in single-mode optical fibers is a key asset for the development of distributed fiber-optic sensors operating in frequency- and time-domain. In order to increase the return signal, fibers with high backscattering have been introduced, exploiting weak random gratings or UV exposure; however the most viable method relies on introducing high doses or nanoparticles directly into the fiber core, which allows reaching scattering increments consistently over 50 dB. In this work, we discuss the use of such fibers for interferometry; exploiting its high backscattering, a short span of enhanced backscattering fiber can act as a random cavity, achieving a semi-stochastic spectrum that can be interrogated with a spectral analyzer. We present some of the recent applications in biosensing, including the detection of poxvirus proteins in wastewater and the detection of retinal biomarkers in tears.