Review: Tg - reversible glass door to fabrication of photonic devices and integrated circuits

We review our development of sub-micron hot embossing or imprinting of glasses. We suggest that this is an emerging technology which shows great promise for the fabrication of glass photonic integrated circuits (PICs). The 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, when a glass is heated above T-g, the glass transforms to a supercooled liquid which may be shaped e.g. moulded. Cooling back down through T-g allows the shaping to be retained in the glassy state at room temperature. 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 a reversible door to making photonic devices. This claim is illustrated by reviewing our recent work on hot embossing of inorganic compound glasses to make waveguides. Opportunities and potential pitfalls are highlighted. The background understanding of glass science underpinning the hot embossing methodology is presented.