Photonic Band Gap Fibers

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Interaction between laser and the tissue is realted to properties of the laser such as wavelength, power and pulse times. In addition to the properties of the laser, absoption coeffitient of the tissue, penetration depth and such parameters are important. CO2 lasers are highly demanded in industry for steal cutting welding and high-tech applications because of one can access high laser power with a small spot size with a little cooling requirement. The idea using this laser in medical applications also bring the problem together. How to transmit that high power laser into human body to do operations? Therefore, infrared laser fibers which can easily carry the light make CO2 lasers useable in cancer surgery.

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

A lancet and other cutting tools is dangerous may cause irreversible tissue damages with unrecoverable harms or the death of the patient. When high power CO2 lasers are used, laser beam can easily remove the harmful tissue without damaging the other cells. However, transportation of high power laser light from source to the human body is a limiting problem.
Since, chemotherapy and radiation therapy considered as  very harmful for health cells and as it is still expensive for patients, CO2 laser surgery is one of  the best way for cancer healing. However, carry of such a high power laser light in human body is a limiting problem. It is possible to use CO2 laser much more effective in human body by infrared photonic band gap fibers. In omni directional reflection of infrared laser light in a flexible fiber, it is possible to use this fiber tool as a medical tool to cut or ablate to malignant tissues from the body without damaging other healthy cells.
Bragg fiber can transmit light through the fiber at very narrow band gap. Facilitating this property as a light filter, Bragg fibers has been used as a artificial nose which works at infrared regime. Chemical detecting of gasses possible using Forier transmission infrared spectroscopy (FTIR). Engineering the band-gap of the fibers according the absorption properties of the gasses make it possible to detect their existence chemically by observing the quench in the transmission of the fiber while the analyte was exposed in the hollow core of the fiber. Detection of gasses such as ethanol, methanol acetone and etc. is possible at ppm level. Recently, we developed conical Bragg fiber for a broad band photonic detection of gasses at very low concentrations.

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.

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