Optical trapping, also sometimes called "optical tweezers", is a relatively old field that has found many scientific and practical applications in its simiplest form, wherein a relatively powerful laser beam is focused into a solution containing suspended particles (eg. micron sized styrene beads that may be functionalized for selective attachment to strands of DNA), in order to localize, or trap individual particles at the laser's beam waist, which can be easily maneuvered in 3 dimensions. The strength of the optical trapping force is related to the gradient of the intensity of the light, and the polarizability of the particle. Since the laser beam waist is limited to dimensions on the order of the laser's emission wavelength, the only way to increase the force for a given size particle is to increase the laser power. The need to use relatively high laser powers limits the size and nature of objects that can be trapped. One of our current research thrusts uses photonic crystal microcavities formed in silicon wafers, in order to boost the intensity and gradient of the intensity of a relatively low power laser so that particles as small as just 10 nm can be optically trapped using no more power than is available from a laser pointer.
For more, check out: Optical Trapping
|Superconducting Single Photon Detector|
Ultimately there is much interest in achieving a sufficiently strong light-matter interaction to enable a single photon to induce a change in a single electronic transition within some material that is large enough to reliably influence another single photon. This is the domain of quantum optics, where information can be manipulated using individual photons (quantum information processing). Work in this domain requires the ability to detect and generate single photons with high efficiency in the absence of large background (spurious) events. Another of our active projects again involves the use of microcavities, but now to enable high efficiency absorption of single infrared photons within a tiny superconducting wire with cross sectional area 8 nm x 35 nm.
For more, check out: Single Photon Detectors
Silicon-on-Insulator Photonic Circuits
|Silicon-on-Insulator Photonic Circuit|
Most of our current research projects involve silicon optical microcavities. This is due to the very rapidly evolving technology surrounding silicon-on-insulator (SOI) photonic circuits. While other material systems (glasses, III-V semiconductors such as GaAs or InP, diamond, etc.) can also be used to miniaturize optical components and integrate them in planar optical "chips", SOI has the advantage of building directly on the massive infrastructure and know-how associated with the silicon microelectronics industry, and in particular, offers the ability to directly integrate sophisticated microelectronic circuitry with the relatively new and rapidly evolving photonic circuitry. While very high quality single photon emitters have been demonstrated in III-V semiconductors, using epitaxially grown quantum dots, the indirect bandgaps of silicon has so far called for different approaches to realizing high quality single photon sources compatible with silicon photonic circuits. Our group is investigating two approaches, one that utilizes the intrinsic third-order nonlinear optical response of silicon to enable microcavity-enhanced spontaneous down conversion generation of entangled photon pairs, and another, that involves the hybrid integration of 5 nm diameter semiconductor nanocrystals (e.g. PbSe quantum dots) in microcavities integrated in full photonic circuits, the latter done in collaboration with the group of Frank van Veggel at the University of Victoria.
For more, check out: Single Photon Sources
Quantum Emitter Interactions with Metal Nanoparticles
Light-matter interaction strength can also be enhanced in the vicinity of individual metal nanoparticles (dimensions on the order of tens of nanometres). In collaboration with Stephen Hughes' group at Queen's university, we have investigated the nonlinear interaction of quantum emitters site-selectively located at specific locations in the vicinity of Au nanoparticles, and we are collaborating with Dan Bizzotto's group in order to experimentally realize such metal nanorod-quantum emitter hybrid particles.
For more, check out: Nanoparticles