Attenuation, modal, and polarization properties of n < 1, hollow dielectric waveguides

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Abstract
The attenuation coefficients for hollow sapphire and lead-based, oxide glass waveguides are calculated using an approximate formalism from Marcatili and Schmeltzer [Bell Syst. Tech. J. 43, 1783–1809 (1964)]. These results are compared with an exact calculation, and the agreement is found to be excellent for bore diameters greater than 100 μm. Although the hollow lead glass waveguides have measured losses in agreement with theory, the hollow sapphire waveguides have losses greater than those calculated for the lowest-order mode. This excess loss is due to roughness of the inner surface of the sapphire. The hollow dielectric waveguides are also shown to preserve polarization and the single mode as do some of the hollow metallic waveguides.