Materials science

Refractive index

Optical fiber

Limit (mathematics)

Fiber optic sensor

Wavelength

Frequency synthesizer

Photonic-crystal fiber

Free spectral range

Phase noise

Physics

Multi-mode optical fiber

Mathematics

Optics

Interferometry

Mathematical analysis

Normalized frequency (unit)

Astronomical interferometer

Optical path length

Polarization-maintaining optical fiber

Graded-index fiber

Mach–Zehnder interferometer

Optoelectronics

Dynamic range

Phase-locked loop

Journal of Lightwave Technology

A refractive index (RI) fiber sensor with low detection limit but large dynamic range is proposed and demonstrated using an exposed core microstructured optical fiber. The exposed-core fiber is highly birefringent due to its asymmetry and also supports multimode propagation; thus, can be used simultaneously as a Mach-Zehnder and Sagnac interferometer. The Mach-Zehnder interference is significantly more phase sensitive to RI due to a longer effective path length difference. This leads to a lower detection limit compared to that for the Sagnac interferometer, which has a larger free spectral range that allows the dynamic range of the RI measurement to be extended. By combining these two interferometers, the proposed sensor achieves a detection limit of as low as 6.02 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> refractive index units (RIU) while maintaining a large dynamic range from 1.3320 to 1.3465 RIU. The proposed sensor also has the advantages of biocompatibility, low cost, high stability, small size, ability to operate remotely and to be fabricated.

Optical fiber refractive index sensor with low detection limit and large dynamic range using a hybrid fiber interferometer