Hybrid Fiber Fabry–Perot Interferometer With Improved Refractometric Response

The reflectance of a hybrid fiber Fabry-Perot interferometer modulated by the Fresnel reflection at the fiber tip was used to assess the refractive index (RI) of liquid samples. Notwithstanding the closeness of RI values between samples and fiber core, well-defined interference spectra in Fourier domain were obtained after a robust signal processing algorithm. Then, the analysis of these spectra allowed us to derive a mathematical expression to obtain the RI value of the fiber tip surrounding media. Next, to assess the fiber refractometer measuring capability a series of liquid samples, typically used for RI calibration, with values ranging from 1.3924 to 1.5882 were measured. A standard deviation of 7 × 10
^-4
between the measured and actual RI values was estimated. Finally, the refractometer was used to monitor the RI of a sample, with a high thermo-optic coefficient, while it was heated. The accurate and compact all-fiber refractometer proposed here exhibited immunity to optical power fluctuations and one of the largest dynamic ranges reported. This set of combined features make it very attractive for real-time label-free biosensing applications.