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During the last decade, there has been rapid progress in the development of integrated optical circuits, incorporating thin optical waveguides, for the Visible and Near IR (NIR) spectral ranges. In this work we extended the same concept to the Mid-IR (MIR) spectral range 3-30 microns. Towards this goal we developed diffused and strip buried planar waveguides based on silver halide crystals.
Diffused planar waveguides were created by diffusion of Br- ions into crystalline substrates, forming silver chloro-bromide (AgClBr) layers of higher refractive indices and different thickness of 65μm to 600μm. Strip buried planar waveguides were constructed from press-flattened silver chloro-bromide (AgClBr) fibers with different thickness, which were buried into an almost pure substrate. All the waveguides were in a thickness range of 60μm to 170μm. Using CO2 laser we found that the transmission losses at 10.6mm were about 4 to 12dB/cm for the buried waveguides and about 4 to 16dB/cm for the diffused waveguides. We also formed and characterized curved waveguides on AgCl substrate.
By using the planar waveguides as sensing elements for infrared evanescent wave spectroscopy, we were able to detect 1% of glucose or 1% of alcohol in water. In conclusion, we demonstrate the feasibility of using AgClBr waveguides as integrated optical elements in the MIR.
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