Timothy James Kiczenski

Communication: Resolving the vibrational and configurational contributions to thermal expansion in isobaric glass-forming systems

A fundamental understanding of isobaric thermal expansion behavior is critical in all areas of glass science and technology. Current models of glass transition and relaxation behavior implicitly assume that the thermal expansion coefficient of glass-forming systems can be expressed as a sum of vibrational and configurational contributions. However, this assumption is made without rigorous theoretical or experimental justification. Here we present a detailed statistical mechanical analysis resolving the vibrational and configurational contributions to isobaric thermal expansion and show experimental proof of the separability of thermal expansion into vibrational and configurational components for Corning Jade glass.

Laser-written high-contrast waveguides in glass

Laser writing of waveguides in bulk glasses opens the opportunity for creating three-dimensional photonic devices. In order to become practical, the numerical aperture (NA) of these waveguides should be significantly higher than currently achievable of 0.1 - 0.15. One reason is that with higher NAs one can decrease the bending radii of the embedded photonic devices without significant loss penalty and make them compact. Thus, femtosecond-laser-written waveguides in glasses do not allow bending radii smaller than 15 - 20 mm. In order to overcome this limitation, we propose to fabricate waveguides in phase-separable and leachable glass where the index contrast is determined by the difference between the refractive indices of the unprocessed glass and of the leached porous glass. We show that we can achieve the NA = 0.25 prior to optimization. Surface and sub-surface treatment with a nanosecond ultraviolet (UV) laser produces a similar effect with even higher NA = 0.35. Applications may include a range of tightly packed embedded and three-dimensional photonic devices in bulk glass like directional couplers, splitters, interferometers, etc.