This paper presents an effective integration scheme of nanostructured SnO 2 with the fiber optic platform for chemical sensing applications based on evanescent optical interactions. By using a triblock copolymer as a structure directing agent as the means of nano-structuring, the refractive index of SnO 2 is reduced from >2.0 to 1.46, in accordance with effective medium theory for optimal on-fiber integration. Hightemperature stable fiber Bragg gratings inscribed in D-shaped fibers were used to perform real-time characterization of optical absorption and refractive index modulation of metal oxides in response to NH 3 from the room temperature to 500°C. Measurement results reveals that the redox reaction of the nanostructured metal oxides exposed to a reactive gas NH 3 induces much stronger changes in optical absorption as opposed to changes in the refractive index. Results presented in this paper provide important guidance for fiber optic chemical sensing designs based on metal oxide nanomaterials. ©2014 Optical Society of America References and links1. S. Akbar, P. Dutta, and C. Lee, "High-temperature ceramic gas sensors: a review," Int. J. Appl. Ceram. Tec.3(4), 302-311 (2006). 2. G. Korotcenkov, "Gas response control through structural and chemical modification of metal oxide films: state of the art and approaches," Sens. Actuators B Chem. 107, 209-232 (2005). 3. G. Korotcenkov, "Metal oxides for solid-state gas sensors: What determines our choice?" Mat. Sci. Eng. B Solid.139(1), 1-23 (2007). 4. N. Yamazoe, "Toward innovations of gas sensor technology," Sens. Actuators B Chem. 108, 2-14 (2005). 5. N. Yamazoe, "New approaches for improving semiconductor gas sensors," Sens. Actuators B Chem. 5, 7-19 (1991). 6. A. Ponzoni, E. Comini, I. Concina, M. Ferroni, M. Falasconi, E. Gobbi, V. Sberveglieri, and G. Sberveglieri, "Nanostructured metal oxide gas sensors, a survey of applications carried out at SENSOR Lab, Brescia (Italy) in the security and food quality fields," Sensors 12(12), 17023-17045 (2012). 2813-2826 (1999). 37. S. Shao, M. Dimitrov, N. Guan, and R. Köhn, "Crystalline nanoporous metal oxide thin films by post-synthetic hydrothermal transformation: SnO2 and TiO2," Nanoscale 2(10), 2054-2057 (2010

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In this paper, we are able to fabricate 3D photonic crystals or quasi-crystals through single beam and single optical element based holographic lithography. The reflective optical elements are used to generate multiple side beams with s-polarization and one central beam with circular polarization which in turn are used for interference based holographic lithography without the need of any other bulk optics. These optical elements have been used to fabricate 3D photonic crystals with 4, 5 or 6-fold symmetry. A good agreement has been observed between fabricated holographic structures and simulated interference patterns.

We report the fabrication of both orthorhombic and tetragonal photonic crystal templates using a phase mask technique. Three-dimensional photonic crystal structures were formed by a double exposure of SU8 to three-beam interference patterns generated by a phase mask. Lattice structures and photonic band gap can be controlled by rotational angles of the phase mask between two exposures. Band gap computation predicts that photonic crystal structures with the optimized band gap can be realized when the rotational angle is set between 50° and 70°. A photonic crystal template with 60° phase mask rotation was fabricated, showing improved lattice structures required for the band gap opening.

We demonstrate, for what is believed to be the first time, the design of diamondlike photonic crystals made by holographic lithography based on five-beam interference. All five beams are launched from the same half-space, and the exposure can easily be realized by a single diffractive optical element. The photonic structure can be constructed through the translation of the interference pattern controlled by the phase shift of laser beams. The proposed holographic lithography is capable of creating series photonic crystals with large photonic bandgaps by adjusting the phase and the wave vector of interfering beams.

A distributed sensing capable high temperature D-shaped optical fiber modified with a palladium nanoparticle sensitized mesoporous (∼5 nm) TiO film, is demonstrated. The refractive index of the TiO film was reduced using block copolymer templating in order to realize a mesoporous matrix, accommodating integration with optical fiber. The constructed sensor was analyzed by performing direct transmission loss measurements, and by analyzing the behavior of an integrated fiber Bragg grating. The inscribed grating should reveal whether the refractive index of the composite film experiences changes upon exposure to hydrogen. In addition, with frequency domain reflectometry the distributed sensing potential of the developed sensor for hydrogen concentrations of up to 10% is examined. The results show the possibility of detecting chemical gradients with sub-cm resolution at temperatures greater than 500 °C.

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A new spectroscopic technique is presented, with which environmentalchemistry-induced thermal emissivity changes of thin films are extracted with high isolation through evanescent tunneling. With this method the hydrogen-induced emissivity changes of films of TiO2 , Pd-TiO2 , and Au-TiO2 , with properties of high conductivity, hydrogen chemisorption, and plasmonic activity, are characterized in the UV-vis and NIR wavelength ranges, at 1073 K.