title: Fiber-optic refractometer based on an etched high-Q π-phase-shifted fiber-Bragg-grating.
abstract: We present a compact and highly-sensitive fiber-optic refractometer based on a high-Q π-phase-shifted fiber-Bragg-grating (πFBG) that is chemically etched to the core of the fiber. Due to the p phase-shift, a strong πFBG forms a high-Q optical resonator and the reflection spectrum features an extremely narrow notch that can be used for highly sensitivity refractive index measurement. The etched πFBG demonstrated here has a diameter of ~9.3 μm and a length of only 7 mm, leading to a refractive index responsivity of 2.9 nm/RIU (RIU: refractive index unit) at an ambient refractive index of 1.318. The reflection spectrum of the etched πFBG features an extremely narrow notch with a linewidth of only 2.1 pm in water centered at ~1,550 nm, corresponding to a Q-factor of 7.4 × 10(5), which allows for potentially significantly improved sensitivity over refractometers based on regular fiber Bragg gratings.
authors.affiliation: Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA. qzhang@huskers.unl.edu
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.forename: Natale J
authors.initials: NJ
authors.lastname: Ianno
authors.forename: Ming
authors.initials: M
authors.lastname: Han
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D005336:Fiber Optic Technology / Q000295:instrumentation*; D012031:Refractometry / Q000295:instrumentation*; D014159:Transducers