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Research

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Novel Photonic Materials and Fabrication

Shaping novel nanophotonic materials

Silicon Photonics

Enabling the next generation of computing systems

Nanomagnetism and Thermal Control
Nano-Electromagnetism

Manipulating waves at the nanoscale

Sensing and Optofluidics

Sensing and manipulating biological analytes

Optomechanics

Controlling the interaction between phonons and photons

Nonlinear Optics

Generating extreme nonlinearities in nanophotonic structures

Nanomagnetism and Thermal Control

Published papers (partial list)

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.

The refractive index map of the cloaking medium (left) which implements the virtual space required for the invisibility effect is implemented in a silicon platform via effective medium theory, where the distribution density of sub-wavelength silicon posts controls the local effective index of the medium (right).

The light concentrator, also fabricated using sub-wavelength silicon structures (top left), is designed to guide light to a focusing spot independent of its wavelength (bottom left), as the experimental results collected via Near-field Scanning Optical Microscopy demonstrate (right).

The Luneburg lens is designed to improve the robustness of fiber-to-waveguide couplers by collecting light from the optical fiber and delivering it to the silicon nanotaper with very low sensitivity to the misalignment between the two (left). The 3-d lens is fabricated in silicon in the same platform as the waveguides (top right) with a height profile patterned via Focused Ion Beam (bottom right).

Heat Transfer

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.

Nanomag Fig 1 

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.  

Nanomag Fig2

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.  

Nanomag Fig3

Fig 3.: SEM images of the suspended nanobeam system used to measure near-field heat transfer on an integrated substrate.

Recent News

Prof. Lipson ranked among top 1% of researchers for most cited papers in physics

Prof. Lipson ranked among top 1% of researchers for most cited papers in physics by Thomas Reuters.