Research

 

Here are some of the exciting research projects in the group.

Active research projects

Volumetric Additive Manufacturing

The new field of Volumetric Additive Manufacturing (VAM) optically prints 3D structures into a sealed, fixed volume of liquid photosensitive resin via tomographically computed projections. Since resin need not move during printing, writing into very high viscosity or even solid materials becomes possible, enabling final print material properties previously unattainable in additive manufacturing. Prints typically take tens of seconds to a few minutes - about 100x faster than stereolithography - with resoluti...

Holographic Photopolymers

Diffusive photopolymers were first developed by Bruce Booth at Dupont for holography. We use a two-polymer approach introduced by Lisa Dhar and colleagues at Lucent. These materials contain two monomers, in which the first monomer is thermally or optically gelled, providing a physical scaffold to support encapsulated elements or photo-patterned index structures. Linear (one photon) absorption of incident light polymerizes the second monomer, locally depleting it in the exposed region. This causes diffusiona...

STED-Inspired Super Resolution Lithography

 The integrated circuits in your computer or car require manufacturing processes capable of patterning billions of nanometer-scale features every second with near perfect accuracy.  Moore's Law, the 50-year trend of continually smaller structures resulting in continually more powerful electronics, is possibly nearing its end.  The challenge faced by the semiconductor industry is that current photolithography tools are constrained to transfer patterns with feature sizes larger than the "diffraction limit" wh...

Stem-cell Laden Implants for Cartilage Defect Repair

Three dimensional printing of polymers can be done through a moving orifice (e.g. fused deposition) or by photopolymerizing a liquid (e.g. stereolithography).  In 2013, we developed a new form of stereolithographic printer using an image projector, a PDMS coated window and a moving platform, as shown below.  This system can print significantly faster than the traditional scanning laser and recoating blade.  We exploit this speed to print at very small (~micron) scale and very soft (KPa to MPa) polymers that...

OECT Device Physics

Organic electrochemical transistors (OECTs) are thin-film transistors with an organic semiconductor channel between source and drain electrodes. OECTs are structured much like organic field-effect transistors (OFETs) with the distinction that OECTs have an electrolyte layer between the channel and the gate electrode instead of a standard dielectric.  We develop and validate models that provide quantitative explanations for previously unexplained characteristics. Ultimately, these models inform the design of...

Gradient Index Lenses

Holographic photopolymers were developed, as the name implies, for holography.  However, they can be programmed with a variety of gradient index (GRIN) structures including diffractive and refractive lenses.  The polymers self develop in respnse to light, enabling complex 3D GRIN structure not possible with traditional processes that rely on diffusion.  We have created a number of specialized exposure systems operating from the micron to the 10 mm scale to implenent unusual optical functions, correct for ab...

Completed research projects

Quantitative 3D phase metrology

Holographic photopolymers allow us to record complex 3D refractive index structures with scale down to ~100 nm in volumes as large as cubic cm.  Modelling and device optimizatoin requires us to precisely and accurately measure these 3D index structures which is generally not possible with off-the-shelf instrumentation.  We have thus developed a number of different custom microscopic and tomographic measurement systems specifically for quantifying properties at the micron scale within much larger 3D volumes....

3D Optical Waveguides

Holographic photopolymers can be cast onto and around other optical elements, then patterned with a 3D routed waveguide to form hybrid integrated photonics.  While multi-photon initiation can be used to improve localization of the written feature, we have explored single-photon initiation due to its greater control at lower laser power and higher write speed.  For example, a milliwatt laser focus translated through the  3D volume of a holographic photopolymer writes an optical waveguide with a cross section...

Holographic Optical Data Storage

A major driver for the development of holographic photopolymers was the concept of optically storing data in a 3D volume.  The traditional approach to this problem was to spatially modulate a laser beam with an image of ~one million bits, record a hologram of this image, then use Bragg selectivity to record subsequent images at the same location to achive storage densities as high as several Tbit/square inch. Starting while at a Silicon Valley startup, Siros Technologies, we explored an alternative approach...