Abstract
In this work, sensitivity to strain and temperature of a sensor relying on modal interferometry in hollow-core photonic crystal fibers is studied. The sensing structure is simply a piece of hollow-core fiber connected in both ends to standard single mode fiber. An interference pattern that is associated to the interference of light that propagates in the hollow core fundamental mode with light that propagates in other modes is observed. The phase of this interference pattern changes with the measurand interaction, which is the basis for considering this structure for sensing. The phase recovery is performed using a white light interferometric technique. Resolutions of +/- 1.4 microepsilon and +/- 0.2 degrees C were achieved for strain and temperature, respectively. It was also found that the fiber structure is not sensitive to curvature.
Highlights
The development of sensors based on hollow-core photonic crystal fibers (HC-PCF) has been a recent and active research topic in the context of fiber optic sensing
When light travels through the single mode fiber and is injected into the HC-PCF the fundamental core mode and other modes are excited
The experimental results indicate its contribution is associated with the decrease of the absolute value of ∆neff .To understand this, we need to consider what happens with the core mode and cladding modes involved in the modal interferometer operation when temperature increases
Summary
The development of sensors based on hollow-core photonic crystal fibers (HC-PCF) has been a recent and active research topic in the context of fiber optic sensing. HC-PCF are made with hundreds of periodically spaced air holes in a silica matrix, typically arranged in a triangular lattice, using the photonic band gap concept to propagate light inside the air-core These fibers are usually multi-mode waveguides supporting, besides the fundamental core mode, higher order core modes, cladding modes and surface modes [5,6]. In a single mode – multimode – single mode fiber structure it was examined the effect of modal interference on the performance of a microbend sensor [7], as well as when considering strain [8,9] and temperature [9,10] measurement Another interesting configuration was based on the series combination of single mode – two modes – single mode fiber sections, which generates a transmission interference pattern with high extinction ratio [11]. The readout of the interferometric phase was achieved combining white light addressing with pseudo-heterodyne signal processing
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