One approach involved polishing aluminum strips down to optical smoothness using them to form a sort of tubular box. Though these were successful at delivering the necessary light, they had the disadvantage of being bulky, relatively difficult to build, and rigid. The vapor is pumped into the tube at a pressure of about 8 Torr for 2 minutes, after which the tube is evacuated for 30 minutes in order to remove any remaining chemical. To coat the inside of a hollow glass tube, researchers used chemical vapor deposition. The tube was first preprocessed with TiCl 4 and then filled with the aluminum compound carried by argon gas.
Deposition takes place as the tube is heated.
This latter point is particularly important for this application because lower temperature deposition also produces smoother coatings. Finally, the aluminum coating was deposited by moving a heater along the length of the tube. The difference was caused by undesirable surface roughness. Using the latter was necessary because light from the ArF laser would turn the oxygen in air into ozone, thus reducing the amount transmitted. As well as measuring the losses in straight waveguides, Tohoku University researchers looked at losses when the waveguide was curved.