Abstract
Regular and cascaded long period gratings (LPG, C-LPG) of periods ranging from 460 to 590 μm were inscribed in an endlessly single mode photonic crystal fiber (PCF) using CO2 laser for sensing measurements of helium, argon and acetylene. High index sensitivities in excess of 1700 nm/RIU were achieved in both grating schemes with a period of 460 μm. The sharp interference fringes in the transmission spectrum of C-PCF-LPG afforded not only greatly enhanced sensing resolution, but also accuracy when the phase-shift of the fringe pattern is determined through spectral processing. Comparative numerical and experimental studies indicated LP01 to LP03 mode coupling as the principal coupling step for both PCF-LPG and C-PCF-LPG with emergence of multimode coupling at shorter grating periods or longer resonance wavelengths.
Original language | English |
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Pages (from-to) | 20951-20961 |
Number of pages | 11 |
Journal | Optics Express |
Volume | 20 |
Issue number | 19 |
DOIs | |
State | Published - 10 Sep 2012 |