Grapefruit photonic crystal fiber sensor for gas sensing application
Abstract. Use of long period gratings (LPGs) formed in grapefruit photonic crystal fiber (PCF) with thin film overlay coated on the inner surface of air holes for gas sensing is demonstrated. The finite element method was used to numerically simulate the grapefruit PCF LPG modal coupling characteristics and resonance spectral response with respect to the refractive index of thin film inside the holey region. A gas analyte induced index variation of the thin film immobilized on the inner surface of the holey region of the fiber can be observed by a shift of the resonance wavelength. As an example, we demonstrate a 2,4 dinitrotoluene (DNT) sensor using grapefruit PCF LPGs. The sensor exhibits a wavelength blue shift of ~820 pm as a result of exposure to DNT vapor with a vapor pressure of 411 ppbv at 25degC, and a sensitivity of 2 pm ppbv 1 can be achieved.