Long Period Gratings in Random Hole Optical Fibers for Refractive Index Sensing

Ke Wang,Gary Pickrell

doi:10.3390/s110201558

Abstract

We have demonstrated the fabrication of long period gratings in random hole optical fibers. The long period gratings are fabricated by a point-by-point technique using a CO2 laser. The gratings with a periodicity of 450 μm are fabricated and a maximum coupling efficiency of −9.81 dB has been achieved. Sensing of different refractive indices in the surrounding mediums is demonstrated by applying standard liquids with refractive indices from 1.400 to 1.440 to the long period grating.

Highlights

IntroductionRandom hole optical fibers (RHOFs) [1,2], being a new class of photonic crystal fibers (PCFs) [3,4]
Random hole optical fibers (RHOFs) [1,2], being a new class of photonic crystal fibers (PCFs) [3,4]. With their in-vivo generation of thousands of holes randomly distributed in the cladding while being drawn from a glass preform, have significantly reduced the fabrication difficulties compared with ordered-hole PCFs
During the fabrication of the ordered-hole PCFs, especially for the fibers guided by the photonic bandgap effect, any tiny disorder may result in serious degradation of the light guiding ability

Summary

Introduction

Random hole optical fibers (RHOFs) [1,2], being a new class of photonic crystal fibers (PCFs) [3,4]. During the fabrication of the ordered-hole PCFs, especially for the fibers guided by the photonic bandgap effect, any tiny disorder may result in serious degradation of the light guiding ability. Because of their random nature of Sensors 2011, 11 the hole arrangement in the cladding, RHOFs do not suffer the same penalty from the strict ordering requirements in the ordered-hole PCFs, significantly reducing the fabrication difficulties. Glass structure changes and physical deformationin the fiber change the glass volume, densification and fiber core/cladding dimensions, and leading to a change in the effective refractive index too. In order to demonstrate the sensing potentials of the LPGs, wavelength response to the external refractive index has been studied by immerging the LPG into several standard refractive index liquids

Experiment

Findings

Conclusion