We report a new family of hollow-core photonic crystal fibers with embedded metal wires for sensitive refractive index measurement of fluids. These fibers operate on the principle of resonant coupling of the guided core mode with the surface plasmon mode generated at the surface of metal wires embedded in the photonic crystal structure. A maximum sensitivity of 2151 nm RIU −1 (nanometer per refractive index unit) can be achieved even for refractive index values lower than 1.26. The fiber is simple in design and can be fabricated with a certain modification to the conventional hollow-core photonic band gap fiber manufacturing technique. The proposed design is useful for detecting a small change in refractive index of the sample and may be implemented to estimate the bulk permittivity of the core fluid.

A simple integrated hydrogen sensor using Pd-Au alloy/air based one dimensional photonic crystal with an air defect layer is theoretically modeled. Structural parameters of the photonic crystal are delicately scaled to generate photonic band gap frequencies in a visible spectral regime. An optimized defect thickness permits a localized defect mode operating at a frequency within the photonic band gap region. Hydrogen absorption causes modification in the band gap characteristics due to variation of refractive index and lattice parameters of the alloy. As a result, the transmission peak appeared due to the resonant defect state gets shifted. This peak shifting is utilized to detect sparse amount of hydrogen present in the surrounding environment. A theoretical framework is built to calculate the refractive index profile of hydrogen loaded alloy using density functional theory and Bruggeman's effective medium approximation. The calculated refractive index variation of Pd3Au alloy film due to hydrogen loading is verified experimentally by measuring the reflectance characteristics. Lattice expansion properties of the alloy are studied through X-ray diffraction analyses. The proposed structure shows about 3 nm red shift of the transmission peak for a rise of 1% atomic hydrogen concentration in the alloy.

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Transmission of light in hollow-core photonic crystal fiber (HC-PCF) is traditionally based on the out-of-plane photonic bandgap of the crystal cladding that usually consists of periodically arranged air holes in silica glass. A new kind of wave guidance relying on a special point (Dirac point) of eigenfrequency dispersion plot in high-index glass-based HC-PCF has been reported recently. Pure silica-based HC-PCF is not suitable for this kind of guidance. The existence of the Dirac point in a triangular lattice of air holes surrounded by a germania (GeO 2 )-doped high-index ring in pure silica host has been demonstrated. The addition of the high-index layer provides a control over the density of states around the Dirac point. The operating wavelength can be tuned precisely by controlling the doping concentration and thickness of the doped glass rings. The structure is very simple and can be fabricated through a conventional stack and draw method.