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Nanomagnetism and Thermal Control
Published papers (partial list)
- Steven A. Miller, Yoshitomo Okawachi, Sven Ramelow, Kevin Luke, Avik Dutt, Alessandro Farsi, Alexander L. Gaeta, and Michal Lipson, Tunable frequency combs based on dual microring resonators, , 07 Aug. 2015.
- Christopher T. Phare, Yoon-Ho Daniel Lee, Jaime Cardenas, Michal Lipson, Graphene electro-optic modulator with 30 GHz bandwidth, Nature Photonics, 13 July 2015.
- Brian Stern, Xiaoliang Zhu, Christine P. Chen, Lawrence D. Tzuang, Jaime Cardenas, Keren Bergman, and Michal Lipson, On-chip mode-division multiplexing switch, Optica, Vol. 2, No. 6, 29 May 2015.
The theory of Transformation Optics reveals that the geometry of space and its constitutive media have the same effect on electromagnetic waves. This unexpected result allows the implementation of virtual geometries through specially designed, inhomogeneous dielectrics, allowing the design of many innovative and unconventional photonic devices, such as invisibility cloaks, lenses with sub-diffraction limited resolution.
Using Transformation Optics we were one of the first groups to experimentally demonstrate invisibility cloaking in the optical domain. We were able to transform the distorted reflection from a deformed mirror into the reflection that would have bounced from a perfectly flat one by tailoring how light travels in the region immediately in front of the deformed mirror.
Another application of Transformation Optics is to create devices with a very wide range of operation wavelengths. Leveraging on this characteristic, we've designed a light concentrator with a wavelength-independent focusing spot, aimed at solar energy harvesting.
Our group has also demonstrated that Transformation Optics can be successfully integrated with conventional silicon photonics to improve existing devices. Using a Luneburg lens, we were able to increase the alignment robustness of inverse nanotapers, commonly used to couple light into and out of silicon waveguides, and a key element in the future mass production and packaging of silicon photonic chips.
Some of our work is aimed controlling heat transfer at the nanoscale using near-field thermal radiation. When objects that support an infrared surface polariton resonance (e.g., doped silicon, silicon dioxide, silicon carbide) are brought to submicron distances, they can exchange heat through coupling of their surface wave. This heat conduction channel presents unique features compared to conventional heat transfer. For example, even though the heat transfer still occurs through thermal radiation, it can overcome the black-body radiation limit by several orders of magnitude (see Fig. 1 left). Furthermore, this heat transfer channel field is concentrated on a very narrow frequency range (see Fig. 1 right), as opposed to usual heat transfer channels (i.e., physical contact with broadband phonon distribution). These unique features are expected to yield exciting new applications, such as efficient contact-free cooling or heating of nanostructures, or new types of devices for thermal control such as thermal rectifiers and thermal transistors.
Fig. 1: (Left) Simulation of radiative heat transfer in the near-field, overcoming the far-field black-body radiation limit by several orders of magnitude. (Right) Spectral distribution of heat transfer in the near-field between two SiO2 plates, showing quasi-monochromatic behavior, as opposed to conventional heat transfer.
We demonstrated near-field radiative cooling of thermally isolated nanostructures, without any physical contact, by several degrees through an oxidized probe that acts as a heat sink (Fig. 2). This method could, in principle, efficiently cool down localized hotspots by tens of degrees at submicrometer gaps, or be used for moving micro and nano structures (MEMS and NEMS) that cannot be touched.
Fig. 2: Top-view SEM image of a probe that can cool a suspended SiO2 membrane without contact between the two.
We also demonstrated near-field heat transfer between two integrated nanobeams that are displaced relative to each other with an integrated MEMS actuator. This work demonstrates that near-field heat transfer can be the dominant heat conduction channel between nanostructures, even when these are integrated on a same substrate. We expect this platform to be a key enabler for the development of thermal control devices based on near-field heat transfer, such as thermal rectifiers and thermal transistors.