Abstract: An apparatus for drawing a dielectric optical waveguide having minimal attenuation characteristics comprises a double crucible in a closed atmosphere container with glass rod supply means and atmosphere supply means.

Abstract: The attenuation in a dielectric optical waveguide can be reduced by the following techniques:1. Surrounding the double crucible during the drawing operation by a non-oxidizing atmosphere.2. Feeding glass rod into the melt at a slow rate.3. Guiding glass rod into the melt so that movement of the glass rod transverse to the melt surface is inhibited.4. Melting the glass in the double crucible under vacuum.

Abstract: The number of modes propagating as guided modes along a dielectric optical waveguide depends on the refractive index difference between core and cladding materials. By altering this difference the number of modes which are permitted to propagate may be controlled. The effective bandwidth of a dielectric optical waveguide depends on the number of modes transmitted because of group delay dispersion and hence this bandwidth may be controlled by controlling the number of propagating modes. In the case of a liquid cored dielectric optical waveguide, the difference between core and cladding refractive indices and hence the bandwidth may be controlled by controlling the temperature of the dielectric optical waveguide.