A tunable demodulation system for fiber Bragg grating sensors utilizing photonic crystal fiber loop mirrors (PC-FLM) in a ratiometric scheme is presented in this paper. The characterization of the demodulation system in two schemes is presented, a single loop PC-FLM and a two loop PC-FLM scheme. For the two loop scheme the length of the photonic crystal fiber must be optimized to achieve opposite slopes for a fixed wavelength range. A comparison of the performance of the system with a single fiber loop mirror and two fiber loop mirrors in a ratiometric scheme is also presented in this paper. The proposed system can be used as a tunable demodulation system to allow it to interrogate FBGs with different peak wavelengths. A tunable wavelength demodulation system is demonstrated with a single loop PC-FLM, with a wavelength range of 4 nm, a tuning range of 2 nm and a wavelength resolution of 2 pm. © 2009 SPIE.