Photonic integrated circuits (PICs), the optical analog of microelectronic circuits, are key to the next major advancement in communication, sensing, information, display, and other technologies. They offer several advantages compared to discrete systems including smaller size, lower power consumption, better performance and reliability through simplification of component coupling and packaging processes, and lower cost through batch fabrication. The methods currently employed for fabricating PICs are suitable for planar geometries, whereas achieving a high density of device elements requires fabrication of 3D systems that are particularly important for optical computing, optical communication and new forms of high density optical memory. A major hurdle toward this goal is the difficulty of fabrication and integration of transparent, multifunctional micro-optical elements, which must be crystals of low symmetry rather than glass that is inherently passive. A multinational team led by researchers at Lehigh University recently demonstrated the proof-of-principle for fabricating 3D single crystal architecture in glass (SCAG) using a femtosecond (fs) laser. The present research is extending this method further for specifically realizing the concept of "principal state transmission" recently introduced by Corning, Inc. It promises to increase the transmission bandwidth of an optical fiber by an order of magnitude, thereby facilitating the next breakthrough in optical communication. In parallel, the project is training two graduate students in application-driven research through collaboration with Corning, Inc., engaging a few undergraduate students and introducing K-12 students to the emerging field of laser fabrication of new structures and devices.
TECHNICAL DETAILS: Nonlinear absorption of fs laser radiation allows heating a glass deep inside, at the focal point of the otherwise transmitting beam. This feature and controlled translation of the beam have been exploited in a viable method for fabricating ferroelectric SCAG in a congruently crystallizing lanthanum borogermanate model composition. However, the glass to crystal transformation becomes increasingly complex for compositions of practical interest, where the two phases have different compositions. Therefore, this GOALI collaboration between Lehigh University and Corning, Inc. is focusing on the fundamental understanding of fs laser-induced crystal growth process in continuously evolving composition, and applying this knowledge to fabricate SCAG of shape and size suitable for prototypic devices. Through continuous feedback and interactions between the teams, a correlation is being developed between the fabrication process parameters, structure of SCAG and optical performance. These results are helping to develop a predictive model that will provide guidelines for making lower optical loss SCAGs in complex compositions suitable for use in devices.
