Optical Nanostructures Laboratory

 

Recent important advances in subwavelength nanostructures offer extraordinary control over the properties of light. We can now manipulate the propagation, storage, and generation of light, as well as practically prescribe its matter interaction properties based on first-principles. These unprecedented innovations at the nanoscale offer opportunities in theoretical and numerical simulations, device nanofabrication, and physical measurements, focused towards fundamental studies of optics at the nanoscale and photonic applications in the industry.

Our research program involves the themes of photonic crystals, nanophotonics, NEMS/MEMS, and nanofabrication. We have several current projects exploring fundamental optics and derived photonic applications, supported by DARPA, NSF, DOE, 3M, New York State, and the Columbia Nanophotonics Initiative:

 
 

 

 
 

Photonic crystals, nanophotonics, NEMS/MEMS, and nanofabrication

Linear defects in two-dimensional photonic crystals permit discrete localized guided bands (eigenmodes) within the photonic band gap. Dispersion of these guided bands can be tuned to achieve low group velocities, or slow light propagation, in the photonic crystal nanomaterials. Interactions scale as the square of the group velocity reduction, permiting observation of phenomena at significantly lower optical intensities.

(Disorder in right SEM image display due to JPEG compression, not in actual SEM. Scale bar: 1 um.)

Slow-light interactions in photonic band gap nanomaterials

Optical hitless switches and all-state polarization compensators with silicon NEMS

Quantum dot - nanocavity interactions

 

Silicon Photonics: high-density electronic-photonic integrated circuits

Nonlinearities in photonic band gap nanocavities

Ultrahigh Q/V nanocavities in photonic crystals

Insertion of an atom or atom-like particle in a solid-state nanocavity permits a vast range of interesting experiments. In the weak coupling regime, for example, the interactions are governed by the Purcell effect with an enhancement of on-resonance transitions and a suppression of off-resonance transitions. Quantum dots, with their relatively narrow transition width (unlike bulk or quantum-well media), will play a significant role in the pursuit of strongly enhanced spontaneous emission. We are currently pursuing various quantum dot - nanocavity designs and systems, with single photon-counting measurements.

Photonic crystal nanostructures are periodic subwavelength lattices that permit photonic band gaps, frequency spaces where light is forbidden to propagate. Analogous to electronic band gaps in semiconductors, addition of synthetic "defects" -- in this case geometric point defects breaking translational symmetry -- allows localized states to exist with the photonic band gaps. By careful design and guidance from ab initio numerical simulations, we are pushing towards ultrahigh Q/V nanocavities in photonic crystal nanostructures.

(Disorder in right SEM image display due to JPEG compression, not in actual SEM. Scale bar: 1 um.)

Photonic crystal nanocavities permit ultrahigh Q/V ratios, corresponding to long photon lifetimes (high-Q) and high field intensities per photon (subwavelength modal volumes V). Such strong field intensities within the nanocavities permit dramatically enhanced nonlinear phenomena. For example, the optical Kerr chi(3) effect scales as |E|^4, leading to possibilities of ultra-low threshold switches, logic operations and memory elements. Coupled nanocavities and degenerate geometries of such structures are also being investigated, fabricated, and measured.

In collaboration with industrial partners, we are implementing silicon photonics components in high-density high-performance electronic-photonic integrated circuits. The target is to achieve multiple electronic and photonic functionalities on the same silicon chip, fabricated from a CMOS production-grade facility. Core photonic components will be designed, fabricated and measured, along with minimization of optical loss, and demonstration of bandwidth and novel nanophotonic devices. Such high-performance electronic-photonic integrated circuits are designed to serve specific applications.

In our push towards silicon photonics, we are currently developing critical reconfigurable components for high-density electronic-photonic integrated circuits. These components employ the concept of NEMS dielectric proximity perturbation, to dynamically add phase to the propagating wave. In particular, we are investigating:


  • optical hitless switches for switched networks
  • dynamically reconfigurable all-state polarization compensators on-chip

These devices allow ultra-low (nW or less) switching powers, are scalable towards high-density on-chip integration, and compatible with CMOS electronic foundries.

 

 

 

 


Room 134G Mudd Hall, 500 West 120th Street, New York, NY 10027.