I am a Ph.D. candidate in Applied Physics at the Capasso Group in Harvard University, studying structured light, inverse design, and new sensing paradigms in the domains of flat optics (e.g., metasurfaces and metalenses) and nanophotonics. My undergraduate Physics degree is from the California Institute of Technology, with research mentorship from Prof. Sandra Troian and a senior thesis in interfacial fluid dynamics and microfabrication. I am grateful to be supported by the Agency for Science, Technology and Research (A*STAR) in Singapore, having received the National Science Scholarship for both B.S. and Ph.D. studies.
In short, my research centres around the arbitrary structuring (in terms of intensity, phase, polarization, for instance) of light and the dark. I employ scalable material platforms, differentiable design, and compact form factors, for applications in Augmented/Virtual Reality (AR/VR), non-invasive medical diagnostics, and remote sensing.
Structured light: Generation and Detection
Beyond the visible intensity variations of light that we can directly see and perceive, light encodes fine details about the world around us in other invisible dimensions, such as its phase and polarization. I study how information can be encoded, manipulated, and retrieved in electromagnetic radiation. One highly promising platform to this end is metasurfaces, which comprise tiny precisely-engineed nanostructures on a surface. Such nanostructures endow the surface with properties that cannot be attained in the bulk material. I have used such metasurfaces to engineer light containing exotic optical singularities, which may have applications in super-resolution microscopy and precision metrology. For more information, see the Harvard press release here.
Above: Scanning Electron Microscope (SEM) images of titanium dioxide nanopillars (left) and nanofins (right) in a metasurface. See the paper here.
Above: Various perspectives on an engineered optical singularity that has a heart-shaped cross-section. Middle: Intensity plot (log-scaled). Right: Phase plot. See the paper here.
Nanofabriation techniques sculpt the world at scales that are much smaller than the human hair or even the wavelength of visible light. These techniques rearrange matter at the smallest regimes to solve problems at and beyond the human scale. Semiconductor foundries routinely push the limits of the impossible - precisely stacking structures just a few dozen atoms across to produce the billions of electronic gates in modern chips. Such advanced nanofabrication techniques can also be used to produce multifunctional optical devices like metalenses. I have engineered ultra-deep holes in silicon membranes just 5 microns thick (20 times thinner than a human hair) so that the membrane behaves as a high quality lens for infrared light. These through-silicon-vias (TSVs) are much smaller (~200 nm) and have a much higher aspect ratio (~30:1) than those found in the semiconductor industry. Such "holey" metalenses may find application in ultralightweight sensors and rollable optics. For more information, see the Harvard press release here.
Above: Various perspectives on a metalens comprising ultra-deep through-holes in a 5-micron thick silicon membrane. Top: SEM images of both sides of the perforated membrane. Bottom right: Focused ion beam (FIB) cross-section showing the deep holes passing through the membrane. See the paper here.
Manipulating the nanoworld requires special eyes to perceive these tiny features. At this scale, we "see" by bouncing electrons off nanostructures. While some nanostructures can be directly visualized in this manner, ultra-high resolution images at the atomic scale require careful preparation using special tools and very large electron microscopes (sometimes filling a large room). I frequently use a device known as the Focused Ion Beam (FIB), which mills samples at the nanoscale using energetic beams of heavy ions, obliterating most materials in its path. The milled samples are then suitable for analysis in massive Scanning Transmission Electron Microscopes (STEM). STEMs are the ultimate eyes for the nano-world as they are able to identify even individual atoms in a material!
Above: A tiny lamella (thin flake) being attached to a Transmission Electron Microscope (TEM) grid in a Focused Ion Beam (FIB) machine. At this point, the lamella is only 1 micron thick; after further thinning and processing, it will be only a few tens of nanometers thick. Source: taken by self in Harvard's Center for Nanoscale Systems.
Above: Darkfield Scanning Transmission Electron Microscope (STEM) image of individual silicon atoms in the (110) plane. Each dumbbell-like blob is actually two individual silicon atoms! The image was captured using a 200 keV JEOL ARM-200F STEM. Source: taken by self in Harvard's Center for Nanoscale Systems.