The present invention is generally directed to a photonic bad gap fiber and/or fiber preform with a central structured region comprising a first non-silica based glass and a jacket comprising a second non-silica based glass surrounding the central structured region, where the Littleton softening temperature of the second glass is at least one but no more than ten degrees Celsius lower than the Littleton softening temperature of the first glass, or where the base ten logarithm of the glass viscosity in poise of the second glass is at least 0.01 but no more than 2 lower than the base ten logarithm of the glass viscosity in poise of the first glass at a fiber draw temperature. Also disclosed is a method of making a photonic bad gap fiber and/or fiber preform.

Embodiments of the present disclosure are directed to infrared optical lightguides or fibers formed with molten halide material (e.g., silver halide), which can provide low loss broadband transmission of wavelengths from approximately 0.5 microns to approximately 25 microns, and methods for forming such lightguides or other optical devices based on solidifying halide melts. In some embodiments, surfaces of a retaining element may be passivated (e.g., using a silver ion exchange process) before the molten halide material is deposited into the retaining element. In some embodiments, the molten halide material may be solidified in a microgravity environment.