Fiber-Optic Refractometer Based on an Etched High-Q π-Phase-Shifted Fiber-Bragg-Grating

Authors

Qi Zhang, University of Nebraska-LincolnFollow
Natale J. Ianno, University of Nebraska-LincolnFollow
Ming Han, University of Nebraska-LincolnFollow

Date of this Version

2013

Citation

Sensors 2013, 13, 8827-8834; doi:10.3390/s130708827

Comments

Copyright © 2013, the authors. Licensee MDPI, Basel, Switzerland. Open access, Creative Commons Attribution license 4.0.

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 π 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 x 10⁵, which allows for potentially significantly improved sensitivity over refractometers based on regular fiber Bragg gratings.