Abstract:

Growing internet traffic and rising data-center energy demands are increasing the need for high-performance, energy-efficient integrated circuits. One promising approach is the integration of silicon-on-insulator electronics with photonic components. Photonic crystal surface-emitting lasers (PCSELs) are strong candidates for compact, coherent on-chip light sources in emerging photonic integrated circuits (PICs).

This talk will highlight our investigations into InP nanowire photonic crystal (PhC) arrays, which have the potential to meet the size requirements for on-chip coherent light sources and passive optical elements in PICs. The InP nanowire PhC arrays were grown by selective area epitaxy (SAE) on InP substrate. One key advantage of the bottom-up SAE approach is that nanowires exhibit atomically smooth crystal facets, unlike in the case of etched membrane structures where surface damage can occur, leading to scattering losses.

To advance the design of nanowire PCSELs, we employed three-dimensional finite-difference time-domain simulations to model the PhC arrays. To reduce the laser threshold, we developed hetero-PCSELs consisting of a small inner lasing array surrounded by an outer non-lasing photonic crystal region. The lasing mode of the inner array lies within the forbidden photonic bandgap of the surrounding array, leading to enhanced optical feedback and reduced lasing threshold. To miniaturize the device footprint, we further explored ultra-compact laser arrays of only several micrometer side-length. Similar to the hetero-PCSELs, these arrays exhibit a reduced lasing threshold compared to large-area PCSELs. The observed threshold reduction is attributed to enhanced optical feedback at the nanowire array-air boundary.

Because of their strong intrinsic birefringence, nanowire PhCs exhibit a highly polarization-dependent reflectance making them well suited for micrometer scale optical elements such as polarizers, analyzers and polarization converting components. Unlike dielectric or plasmonic meta surfaces, which often rely on top-down fabrication, nanowire arrays impose a well-defined polarization state on the diffracted beam, simplifying the design of compact optical elements.

Bio:

Hans-Peter Wagner received his PhD from the University of Regensburg, Germany. After completing his habilitation (Dr. habil.) in 1997 at the University in Regensburg and a post-doctoral appointment at the Technical University of Denmark in Copenhagen, he served as Assistant Professor and interim Associate Professor in the Physics Department at the Chemnitz University of Technology, Germany. He joined the University of Cincinnati in 2001, where he is a full professor. His research focuses on nonlinear optics, ultrafast dynamics, and lasing phenomena in semiconductor materials and devices.