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.
Two fiberoptic infrared multi-spectral radiometers were constructed for measurements of the temperature and the emissivity of gray bodies whose temperatures were close to room temperature (40-70°C). In one radiometer, the different spectral regions were obtained by using standard bulk interference filters, and in a second radiometer, the different spectral regions were obtained by using hollow glass waveguides (HGWs) as filters. Using these two radiometers, we carried out temperature and emissivity measurements of three gray bodies which had high emissivity (ε=0.97), medium emissivity (ε=0.71) and low emissivity (ε=0.025). We present the results obtained for these gray bodies and discuss the advantages and disadvantages using each of the radiometers.
A new concept for embedded fiber optic temperature sensor is described. In this sensor the temperature is inferred by analyzing the infrared radiation, which is emitted from the tip of an infrared transmitting optical fiber. The sensor can be adjusted for ambient or high temperature measurements and has a spatial resolution approximately equal to the diameter of the optical fiber. The measurement is immune to changes that can occur along the embedded fiber. Inferring the temperature directly from thermal radiation makes this technique both more accurate and simple relative to other embedded fiber optic temperature sensors. A prototype sensor was constructed by embedding silver halide optical fibers in epoxy and the sensor was used to monitor the temperature of the epoxy. Preliminary results are described which prove the validity of the new technique. Such a sensor can be useful for temperature measurements of smart structures.
A novel infrared (IR) transparent optical fiber coupled to a hand held otoscope and a radiometer was constructed and used to measure the temperatures of the tympanic membrane (TM) and to distinguish between diseased and healthy middle ears. A greater temperature difference between TM readings was found when Acute Otitis Media (AOM) existed in one of the ears examined. This supports the hypothesis that acute inflammation of the middle ear will result in elevated local temperature when measured in such a way that the reading is taken only from the TM without interference of the external canal. The use of an optical fiber enabled temperature measurements of the TM with high spatial resolution eliminating the external ear canal interference. A small patient population was examined and the initial results were statistically significant. In the hands of the primary care physician, this tool would prevent misdiagnosis of AOM preventing indiscriminate use of antibiotics and avoiding complications by early diagnosis.
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