A fiber gas sensor includes a fiber core with first and second refractive
index periodic modulated grating structures having different amplitude
modulation profiles positioned about the fiber core. A fiber cladding is
positioned about the first and second refractive index periodic modulated
grating structures. A sensing layer is positioned about the fiber
cladding of one of the refractive index periodic modulated grating
structures. The sensing layer includes a sensing material made of a
Pd-based alloy, such as nano-PdOx, nano-Pd(x)Au(y)Ni(1-x-y) or
nano-Pd/Au/WOx. The fiber gas sensor provides a measurement of localized,
temperature-corrected gas concentration and composition from a combustion
environment. A reflection-based or a transmission-based sensing system
with an array of one or more fiber gas sensors is also described.