James Bell You don't know me, but with your quantum work you could benefit from an optical waveguide with a loss of less than 0.01 db/kilometer. and possibly as low as 0.001 db/kilometer. I know you'll think that's impossible, but I know how to design it using low-Si-29 silica, and low-Ge-73 germania. I believe that the typical residual loss of about 0.16 db/km is due almost entirely to Si-29 and Ge-73. Silicon-28 of isotopic purity of 99.995 is already available ("Silicon Kilogram Project"), and Germanium with much less than 0.1% Ge-73 could be made using a gas centrifuge. How would you like to do quantum communications over 5000 kilometers, from New York to London, for instance? You could...