Multi-parameter measurement under fiber bending based on directional resonance coupling in photonic crystal fibers

A multi-parameter sensor with enhanced sensitivity based on magnetic fluids infiltrated photonic crystal fiber is proposed. The sensing performances are investigated using the mode coupling theory and finite element method. Four symmetrical defective channels are assembled into the photonic crystal fiber to produce two resonant transmission dips λ_CV and λ_CH in vertical and horizontal directions, respectively. Each dip can be split into two relatively shallow dips (λ_CV1, λ_CV2 or λ_CH1, λ_CH2) when the photonic crystal fiber is bent. Interestingly, the values of (λ_CH2 – λ_CH1) and (λ_CV2 – λ_CV1) are associated with corresponding bend-curvature but almost unaffected by external temperature or magnetic field. On the contrary, the values of (λ_CH2 + λ_CH1)/2 and (λ_CV2 + λ_CV1)/2 are sensitive to temperature or magnetic field regardless of the bending condition. Based on above characteristics and the dependence of the magnetic fluids refractive index on temperature and magnetic field, the proposed sensor can measure not only the bend-curvature and bend-direction, but also the temperature and magnetic field.