

Medical CO2 laser and connector. Inset : Photonic band gap fibers.

High selectivity boolean olfaction using hollow-core wavelength-scalable Bragg fibers
M. Yaman, A. Yildirim, M. Kanik, T. C. Cinkara, M. Bayindir, Analytical Chemistry, volume 84, page 83 (2012).
A new odorant detection scheme, based on infrared absorption of volatile organics inside an optofluidic channel array, is discussed in terms of its selectivity. The sensor unit of the array is a hollow core Bragg fiber that selectively (spectrally) guides an incident continuum radiation. The presence of infrared absorbing molecules in the channel results in the quenching of the otherwise transmitted signal. Each fiber unit in the array is designed and fabricated so that it is sensitive to specific chemical bonds and the bond environment, but at the same time, each fiber is also broadly sensitive to a large number of chemicals due to their infrared absorbance spectra. The cumulative array response data, using an appropriate threshold, enable selective binary sampling of the infrared fingerprint of hundreds of molecules.

Photonic bandgap narrowing in conical hollow core Bragg fibers
F. E. Ozturk, A. Yildirim, M. Kanik, M. Bayindir, Applied Physics Letters, volume 105, page 071102 (2014).
We report the photonic bandgap engineering of Bragg fibers by controlling the thickness profile of the fiber during the thermal drawing. Conical hollow core Bragg fibers were produced by thermal drawing under a rapidly alternating load, which was applied by introducing steep changes to the fiber drawing speed. In conventional cylindrical Bragg fibers, light is guided by omnidirectional reflections from interior dielectric mirrors with a single quarter wave stack period. In conical fibers, the diameter reduction introduced a gradient of the quarter wave stack period along the length of the fiber. Therefore, the light guided within the fiber encountered slightly smaller dielectric layer thicknesses at each reflection, resulting in a progressive blueshift of the reflectance spectrum. As the reflectance spectrum shifts, longer wavelengths of the initial bandgap cease to be omnidirectionally reflected and exit through the cladding, which narrows the photonic bandgap.