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

Qi Zhang, Natale J. Ianno, Ming Han

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


We present a compact and highly-sensitive fiber-optic refractometer based on a high-Q π -phase-shifted fiber-Bragg-grating (π FBG) that is chemically etched to the core of the fiber. Due to the π phase-shift, a strong π FBG 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 π FBG 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 π FBG 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 × 105, which allows for potentially significantly improved sensitivity over refractometers based on regular fiber Bragg gratings.

Original languageEnglish (US)
Pages (from-to)8827-8834
Number of pages8
JournalSensors (Switzerland)
Issue number7
StatePublished - Jul 2013


  • Fiber gratings
  • Optical fiber sensors
  • Optical resonators
  • Refractive index

ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry
  • Atomic and Molecular Physics, and Optics
  • Instrumentation
  • Electrical and Electronic Engineering


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