Tg: The Glass Door to Photonic Devices and Integrated Circuits

An emerging technology which shows promise for the fabrication of glass photonic integrated circuits (PICs), is sub-micron-scale embossing or imprinting. This approach makes use of T-g (the glass transition) which gives inorganic compound glasses a key advantage over crystalline materials for fabricating photonic devices and PICs. Thus, on heating the glass above T-g the supercooled liquid temperature regime is accessed which enables shaping, e.g. moulding, to be carried out. Cooling back down through T-g allows the shaping to be retained in the glassy state. In this way, glasses may be shaped from the macro-scale e.g. to make light-refracting lenses down to the nano-scale e.g. for waveguides or photonic crystal arrays for dispersion management. Hence T-g is one door to making photonic devices. This claim will be illustrated by reviewing both the background methodology and our recent work on hot embossing of inorganic compound glasses to make waveguides. Opportunities and potential pitfalls will be highlighted.