Optical Nanostructures Laboratory
Recent advances in nanoscience and device nanofabrication have yielded unprecedented control of light from first principles. We can now manipulate the propagation, storage and generation of light, as well as practically prescribe its matter interactions, based on the strong control of dispersion and localization in mesoscopic structures. These unprecedented innovations offer opportunities in theoretical and numerical predictions, precision nanofabrication, and physical measurements. Our focus is at the intersection of optical physics, device optoelectronics, and solid-state science and engineering. Our contributions are in four main themes: nonlinear | ultrafast | quantum | and precision measurements.
Our efforts are enabled by kind support from NSF, DARPA, DoE, DoD, NIH, New York State, Intel, the intelligence community, 3M and others. We concentrate on two regions across the continuum: fundamental breakthroughs in basic optical physics and sciences, and concentrated optoelectronic applications in the industry.
Controlling photons in mesoscopic structures
nonlinear | ultrafast | quantum | precision measurements
The large density of states and inherent phase stability on-chip are promising for a single/bi-photon level and light-matter quantum interactions. For example, we have observed strong exciton - photon coupling in solid-state cavity quantum electrodynamics, including single exciton single photon polariton states in a Fano-like formalism, canonical Jayne-Cummings interactions and Rabi splitting, Purcell dynamics, and Hanbury-Brown and Twiss photon antibunching, spanning from visible to telecommunications infrared wavelengths.
Moreoever, recently our team has observed for the first time the revival of Hong-Ou-Mandel interference -- in frequency and temporal modes -- in a Franson-like scenario for quantum communications. The Hilbert space is further extended by our observations of frequency-time-polarization hyperentanglement and chip-scale 1.55-um Hong-Ou-Mandel interference with bright waverguide-based entangled biphoton states. Entanglement exchange qubit gates have been developed by our team for high-bitrate high-dimensional quantum information processing.
Mesoscopic subwavelength structures afford the strong control of dispersion of localization such as in photonic crystals and nanophotonics. Our recent observations include ultrahigh-Q micro- and nano-scale optical cavities with wavelength and deeply-subwavelength localization, metamaterial superlattices with zero-phase delay and zero-index band gaps, strong disorder localization with ultrahigh-Q modes at the slow-light band edge, diffusive photon transport statistics, and optical analog to electromagnetically induced transparency.
With our cavity photon lifetimes spanning from nanosecond to microseconds and the wavelength-scale modal volumes, such strong field intensities in the cavity permit dramatically-enhanced nonlinear phenomena. Our examples include Fano-type optical bistability in chip-scale resonators, Raman and four-wave mixing, and chip-scale optomechanics such as amplification into stable RF oscillators.
Concurrently we demonstrated graphene optoelectronics for chip-scale signal processing. Graphene, a purely two-dimensional Dirac fermionic structure, has a unique linear and massless dispersion, leading to intense research from condensed matter physics to nanoscale device applications covering electron transport, thermal and mechanical domains. In optical physics and chip-scale optoelectronics, the single graphene monolayer has an optical absorption defined by the fine structure constant, distinctly illustrating the coupling between photons and relativistic electrons. We have examined four-wave mixing, regenerative oscillations, and optical bistability in graphene physics for optical signal processing, supported by ab inito modeling.
We probe the ultrafast carrier-carrier and carrier-phonon scattering in nanostructures such as quantum dots, nanorods and graphene with femtosecond supercontinuum spectroscopy. Through tuning the Fermi level and pump-probe regime, we watch the correlated dynamics different levels such as distinguishing the interband and intraband transitions of graphene, while mapping out the optical and acoustic phonon signatures at hundred femtosecond timescales. Efforts and interests here include multiexciton generation and dynamics, the generation of two electron-hole pairs by single incident photons for next-generation photovoltaics.
Furthermore, the large chi(3) self-phase modulation nonlinearity on-chip, balanced with a large anomalous dispersion in photonic crystals, enables the delicate balance for soliton observations and dynamics. For example, we have observed the ultrafast nonlinear compression to sub-500-fs near-transform-limited soliton pulses while working at pico- to femto-joule regimes and at millimeter lengthscales. Frequency-resolved optical gating observes the phase of these solitons on-chip. Current efforts involve the impact of disorder localization on these ultrafast nonlinear solitons (even at a few pico-joules).
Our team has been developing stabilized and locked ultrahigh-Q mesoscopic cavities for precision measurements. Through Pound-Drever-Hall laser-cavity locks and other techniques, we stabilize lasers to the ultrahigh-Q cavities with rigorous control of noise contributions, comparing with the world's best optical clocks. For long-term stability, the laser and cavities sub-modules are targeted for locking to the cold atom divalent strontium clock transition. The phase stability will be compared against state-of-the-art microwave oscillators.
These precision measurements are also targeted for next-generation sensors with coherent optical readout and excitation, and ultrahigh-bitrate data communication systems and networks.
Left: Schematic of graphene optoelectronics.
Middle top: slow-light four-wave mixing.
Middle bottom: ultrahigh-Q/V slot cavities. Scale bar: 1-um. (inset: |E|^2 field distribution).
Bottom: precision 2D delay-spectrogram.
Left: Schematic of our soliton measurements on-chip.
Right top: measurements of 2D ultrafast pulses.
Right bottom: temporal dynamics at low-pulse energies.
Left: Schematic of our strong coupling single exciton-photon polariton measurements.
Right top: schematic of measurements of two-photon entanglement on-chip.
Right bottom: measurement of Hong-Ou-Mandel interferences.