Photonic crystal fibers confine light within a periodic array of elements. We used multiple extrusions of silver halide (AgClxBr1-x) crystalline materials to fabricate photonic crystal fibers, which are transparent in the middle infrared (mid-IR) in the spectral range 2-20 μm. The cores of these fibers consisted of pure silver bromide (AgBr) of refractive index n=2.16, and the cladding area included concentric rings of tens of fiberoptic elements made of pure silver chloride (AgCl), of a lower refractive index n=1.98. Simulations on photonic crystal structures showed that all the fabricated fibers guide a small number of modes. Furthermore, adding rings to such a structure should lower the number of bound modes in the core. We measured the attenuation and the output power distribution of these fibers and carried out spectroscopic measurements in the mid-IR. Good correlation was found between the experimental and the theoretical results. These findings will pave the way for the fabrication of single-mode fibers in the mid-IR range.
Photonic crystal fibers (PCFs) are normally holey fibers, made of silica glass, which is opaque in the mid- and far-infrared spectral range 3-20 μm. We have fabricated novel PCFs by multiple extrusions of silver halide (AgClxBr1-x) crystalline materials, which are highly transparent in this spectral range. These PCFs are composed of two solid materials: the core consists of pure AgBr (n=2.16), and the cladding includes small diameter fiberoptic elements, made of AgCl (n=1.98). These AgCl fiberoptic elements are arranged in two concentric hexagonal rings around the core. This structure gives rise to a cladding region of lower refractive index, thus ensuring total internal reflection. Flexible PCFs of outer diameter 1mm and length of about 1m were fabricated, and their optical properties were measured. Measurements of numerical aperture, laser power transmission and evanescent wave spectroscopy indicated that the PCFs behave like a core-clad structure. There was a good agreement between the results and those obtained by theoretical simulations. Silver halide PCFs would be extremely useful for IR laser power transmission, for IR radiometery and for IR spectroscopy.
Trans-endoscopic Infrared Imaging (IRI) relates the possibility to conduct IRI diagnosis of internal body surfaces under minimal invasiveness. It may also be utilized to control and to optimize the thermal interactions and the potential side effects during Minimally Invasive Surgeries (MIS). However, transferring the thermal images transendoscopically requires the usage of IR imaging bundles, which are neither yet mature nor commercially available. In our setup we have used two basic types of recently-developed imaging bundles: Ag/AgI-coated Hollow Glass Waveguide (HGW) bundles and Silver Halide (AgClBr) core-clad fiber bundles. The optical setup system was consisted of IR optics (e.g. ZnSe lenses, reflective objectives) and a thermal IR camera. We have succeeded to image objects through the bundles, such as various shapes of electrically heated wires, ex-vivo biological phantoms (samples of porcine stomach) and in-vivo phantom models (mice) irradiated by CO2 laser. Measurements were conducted for both - static and dynamic object states.
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