ECE DISTINGUISHED SPEAKER SERIES: Utilizing Geometry and Topology for Designing On-Chip Chiral Photonic Infrastructure
Spin (SAM, intrinsic) and orbital angular momentum (OAM, extrinsic) degrees of freedom (DOF) characterize the chiral nature of light. The interplay between SAM and OAM DOFs has sparked significant interest leading to discovery of new physics in both classical and quantum optics. These findings and their potential applications call for the manipulation of not only individual SAM and OAM scalar states as two separable DOFs, but also the entanglement between photons in both DOFs enabled by non-separable spin-orbit vectorial states, enabling their hyperentanglement that can lead to optical links with a higher channel capacity and enhanced security. To enable this emerging field of quantum hyperentanglement would require development of miniaturized on-chip photonic devices for robust generation, transport and detection of entangled states involving coupled SAM and OAM DOFs. However, this is not an easy task because most materials and devices are not sensitive to optical chirality. The development of on-chip chiral photonic devices requires fundamental investigations and manipulation of momentum space geometry and topology of materials and their coupling to the environment to engineer specific spin-orbit interactions to control and detect the vectorial states of light. We will discuss some recent developments in our laboratory towards the development of on-chip devices that produce different SAM-OAM states and photodetectors utilizing topological semimetals that are uniquely sensitive to SAM-OAM states. The direct transduction of photocurrents mapped to various SAM-OAM coupled states is engineered via nonlocal light-matter interactions that cannot be described within the electric-dipole approximation and requires a theoretical description accounting for the topology of electronic bands and light (OAM states with topological charge). We will also describe our efforts towards assembling topological photonic and polaritonic waveguides that can route signals based on spin (or pseudospin) degree of freedom. Either by protecting or breaking certain symmetries in (meta)materials, prospects of designing new photonic materials and devices will be discussed that can enable the next generation of classical and quantum photonic devices that can encode, manipulate, transmit and sense information encoded in different SAM-OAM modes of light.
Dr. Agarwal is a Professor in the Department of Materials Science & Engineering at University of Pennsylvania