Clayton R. Otey

Near-Field Radiative Cooling of Nanostructures

We measure near-field radiative cooling of a thermally isolated nanostructure up to a few degrees and show that in principle this process can efficiently cool down localized hotspots by tens of degrees at submicrometer gaps. This process of cooling is achieved without any physical contact, in contrast to heat transfer through conduction, thus enabling novel cooling capabilities. We show that the measured trend of radiative cooling agrees well theoretical predictions and is limited mainly by the geometry of the probe used here as well as the minimum separation that could be achieved in our setup. These results also pave the way for realizing other new effects based on resonant heat transfer, like thermal rectification and negative thermal conductance.

Numerically exact calculation of electromagnetic heat transfer between a dielectric sphere and plate

Near-field electromagnetic heat transfer holds great potential for the advancement of nanotechnology. Whereas far-field electromagnetic heat transfer is constrained by Plancks blackbody limit, the increased density of states in the near-field enhances heat transfer rates by orders of magnitude relative to the conventional limit. Such enhancement opens new possibilities in numerous applications, including thermal-photo-voltaics, nano-patterning, and imaging. The advancement in this area, however, has been hampered by the lack of rigorous theoretical treatment, especially for geometries that are of direct experimental relevance. Here we introduce an efficient computational strategy, and present the first rigorous calculation of electromagnetic heat transfer in a sphere-plate geometry, the only geometry where transfer rate beyond blackbody limit has been quantitatively probed at room temperature. Our approach results in a definitive picture unifying various approximations previously used to treat this problem, and provides new physical insights for designing experiments aiming to explore enhanced thermal transfer.

Negative differential thermal conductance through vacuum

We propose a scheme for achieving negative differential thermal conductance in near-field electromagnetic thermal transfer. As an example, we show that the scheme can be implemented with two slabs of silicon carbide brought in close proximity to each other. We also describe how a bistable thermal switch can be constructed in this manner.

Temporal coupled mode theory for thermal emission from a single thermal emitter supporting either a single mode or an orthogonal set of modes

We propose a temporal coupled mode theory for thermal emission from a single emitter supporting either a single mode or an orthogonal set of modes. This temporal coupled mode theory provides analytic insights into the general behaviors of resonant thermal emitters. We validate the coupled mode theory formalism by a direct numerical simulation of the emission properties of single emitters.

Completely Capturing Light Pulses in a Few Dynamically Tuned Microcavities

We describe a dynamically tuned system capable of capturing light pulses incident from a waveguide in a pair of microcavities. We use coupled mode theory to design a method for determining how to tune the microcavity resonant frequencies. The results show that pulses can be captured almost completely, with arbitrarily small reflected power. We optimize the pulse capture bandwidth by varying the cavity coupling constants and show that the maximum bandwidth is comparable to the resonant-frequency tuning range. Our system may be implemented using refractive-index tuning in a 2-D silicon photonic crystal slab. Current technology would allow for capture of pulses with widths as low as ~100 ps, with a holding time limited only by cavity loss rates.

Capturing light pulses into a pair of coupled photonic crystal cavities

We describe finite-difference time-domain simulations of a two-dimensional photonic crystal implementation of a two-resonator system capable of capturing light pulses from a waveguide. As much as 99.61% of incident pulse energy is captured in simulations. The release of near-perfect Gaussian pulses is also demonstrated.

Slow and Stopped Light in Coupled Resonator Systems

In the first part of this chapter, a theoretical overview is presented on the different approaches to the use of dynamic tuning for coherent optical pulse stopping and storage in coupled resonator systems, which are amenable to fabrication in on-chip devices such as photonic crystals. The use of such dynamic tuning overcomes the delay-bandwidth constraint of slow-light structures. The second part of this chapter presents a discussion on recent experimental work that has demonstrated the possibility of such dynamic tuning in on-chip systems.

Ultrahigh contrast and large-bandwidth thermal rectification in near-field electromagnetic thermal transfer between nanoparticles

We exploit the unique properties of electromagnetic waves in nanophotonic structures to enhance the capabilities for active control of electromagnetic thermal transfer at nanoscale. We show that the near-field thermal transfer between two nanospheres can exhibit thermal rectification effect with very high contrast, and with large operating bandwidth. In this system, the scale invariance properties of the resonance modes result in a large difference in the coupling constants between relevant modes in the forward and reverse scenarios. Such a difference in coupling constants provides a new mechanism for thermal rectification.

Nanophotonics for energy applications: Thermal rectification and solar cell light trapping

The use of nanophotonic structures creates novel opportunities for energy transfer. We present a design of photon-based thermal rectifier that enables near uni-directional photon heat flow. We also show that nanophotonic structures can achieve light trapping efficiency beyond the conventional Yablonovitch limit.

Dynamics of optical modes in modulated photonic structures

The introduction of dynamics in nanophotonic structures creates new opportunities for controlling light. Here we show that one can use just two dynamically tuned cavities to capture a light pulse. We also introduce the use of dynamic modulation to create complete optical isolation.