Theoretical and experimental investigations of metal sulfide dielectric coatings for hollow waveguides

Continuous efforts to develop low-loss flexible waveguides, to transmit mid-IR laser energy for minimally invasive surgical and diagnostic procedures, have been carried out by us and other groups. We have introduced sulfide dielectric films coated over an Ag reflecting layer as another potential solution. The metal sulfides used have high transparency in the IR spectrum, and their thickness can be tailored to minimize the attenuation over a selected wavelength range. The high refractive index contrast of the two metal sulfide materials enables us to produce multilayer hollow waveguides. These waveguide will have low attenuation in both straight and bent conditions, low sensitivity to coupling and to surface roughness, and a broad wavelength range. The lowest loss for a straight guide, measured at 1.55μm for a 1,000-μm-bore Ag/CdS/PbS/CdS hollow glass waveguide (HGW), was 0.06dB/m. This loss is three times less than that measured for a single-layer Ag/CdS-coated HGW at 1.55μm. A theoretical simulation applying the same conditions showed the same pattern with a good potential for improvement.