Active Nanophotonics.................................................................................................................

Using photons in conjunction with electrons for information processing can open up new possibilities for computing devices operating at the speed limit of the universe. However, optical devices have traditionally been subject to diffraction limits and have remained bulky, limiting their opportunity for dense integration in networks. Metasurfaces are a nanophotonic approach to scaling down the size of optical components by using arrays of subwavelength nanoantennas to control the phase, polarization, and amplitude of light. Our lab is developing highly resonant metasurfaces by making subtle perturbations to periodic structures, breaking translational symmetry and giving rise to high quality factor (high-Q) resonances. We use the resulting enhanced light-matter interactions to realize nanophotonic devices for optical computing, communication, and quantum information applications.

See related research on high-Q metasurfaces with applications in Health here!

Traditional passive metasurfaces are limited to perform a single function by their architecture. However, active control over the spatial propagation of light is needed for applications in spatial computing technologies, such as LiDAR, AR/VR, LiFi, etc. Reconfigurable metasurfaces tackle this by integrating an optically active medium to dynamically change their nanoantenna after fabrication to perform different functions such as tunable beamsteering, beamsplitting, and lensing, among others. By further integrating high-Q resonances into these device designs, we can take advantage of the highly enhanced near-fields to improve the strength of otherwise weak light-matter interactions and the highly sensitive resonant features in the far field to control device performance with high efficiency.

Integrating high-Q resonances into silicon devices, such as a metasurface lens, allows us to efficiently utilize the weak nonlinear Kerr effect inherent to the silicon. Changing the input laser power or temperature the device operates at demonstrates significant shifts of the high-Q resonance, corresponding to modulation of the focal length and intensity and achieving a power-limiting metasurface.

We further design and fabricate electro-optically reconfigurable metasurfaces to completely control the outgoing optical wavefront by applying individual electric biases to constituent nanoantennas. Our highly resonant silicon-on-lithium niobate metasurface design allows us to do this at low voltages and high efficiency, compared to other reconfigurable metasurfaces. Using reconfigurable metasurfaces, we hope to replace large, bulky optical components in spatial light modulation devices with a compact, lightweight nanophotonic platform.

Single photons are promising sources for quantum computation, but the creation and manipulation of single photons is difficult to reliably control. High-Q metasurfaces allow us to control the electric field near the photon source, giving us the ability to enhance emission, decrease decoherence, and control the emitted polarization and phase. Unique to dielectric metasurfaces, we can design electric and magnetic resonances that are tuned to couple strongly with the spin of a particle, in addition to generating the strong light confinement that enhances this interaction. This work enables us to better understand emerging quantum emitters and design new platforms for quantum computation.

Semiconductor excitations - termed excitons - are the primary quasi-particles used in optoelectronic applications such as light-emitting diodes, solar cells, or single-photon sources. Tailoring excitons has so far been limited to the native length scales of excitons of a few nanometers by molecular and atomic engineering of the semiconductor. However, by hybridizing optically-active semiconductor with cavity-confined photons, we can tailor the absorptive and emission properties by accessing a new primary excitation, the exciton-polariton. Our group works towards engineering exciton polaritons via the photonic control inherent to nanophotonic elements such as dielectric metasurfaces and plasmonic gap cavities. Ultimately, our efforts will provide new ways to engineer the optical properties of semiconductors via long-range tuning of photonic effects.

The strong light-matter interactions enabled by high-Q metasurfaces allow us to enhance otherwise weak nonlinear optical processes. These nonlinear effects are particularly powerful for tuning device characteristics with light alone, without requiring additional external components like magnets or modulators.

Interestingly, nonlinearities can be used to violate a fundamental symmetry of energy propagation known as Lorentz Reciprocity. This property, non-reciprocity, is the foundation of the electronic diode and is similarly of fundamental importance to the design and operation of photonic networks. We use spin-polarized nonlinearities to break symmetry and achieve nonreciprocity in nanoscale high-Q metasurfaces. We further exploit the power of geometric symmetry in our metasurfaces to achieve unique device characteristics, such as nonreciprocal beam steering and self-isolated Raman lasing. This work explores multi-functional metasurfaces that interface nonlinear optics with nanoscale manipulation, providing new functionalities in a subwavelength form.