Investigation of near and mid infra-red (1.34,1.55 & 8.1μm) laser propagation through the New York city metro area

Low power Mid-IR laser light exhibits much lower attenuation in propagation through the New York metro area when compared to Near-IR wavelengths. Depending on the type of atmospheric extinction we record a reduction of up to 800% in the exponential Beer-Lambert coefficient for Mid-IR light compared to Near-IR, thereby demonstrating the possibility of significantly increased deployable range and SNR of current communication systems by utilizing the Mid-IR spectrum. We present and analyze transmission data from an outdoor collinear, coaxial, multi-wavelength laser test bed comparing 1.31μm, 1.5 5μm and 8μm through outdoor atmospheric fog and rain over a 550 m free space optical link across the Stevens Institute of Technology campus. This is achieved using lasers with average power ranging from 1 mW (Mid-IR QCL) to tens of milliwatts which have been normalized under lock-in detection. We also present corroborating results from an indoor fog experiment simulating various fog types. Here we have also deconstructed Beer's attenuation coefficient and distinguish the contribution of scattering and absorption with a purpose-built polar nephelometer. Using Mie predictions we determine and measure the extent by which a Mid-IR system scatters light less under fog than a traditional Near-IR one, hence accounting for the performance enhancement in the metro-air test bed. We conclude finally that the Kruse-Mie prediction of insignificant Mid-IR-over-Near-IR-gain is strongly in error.