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

In this work a fiber optic interferometric system for differential refractive index measurement is described. The system is based on a white light Mach–Zehnder configuration, with serrodyne phase modulation, used to interrogate two similar non-adiabatic tapered optical fiber sensors in a differential scheme. In this situation the system is able to measure the refractive index independent of temperature. Signal processing with low cost digital instrumentation developed in Labview environment allows a detectable change in refractive index of Δn ≈ 1.46 × 10−6, which is, from the best of our knowledge the highest resolution achieved using a bare fiber taper device for a range of refractive index close to the water index. The results demonstrate the potential of the proposed scheme to operate as a self-referenced chemical and biological sensing platform.