Electromagnetic & Photonics

Conventional phase-contrast and differential interference contrast microscopy have long been indispensable in biology for examining unstained specimens. They are, however, inherently qualitative. Quantitative phase imaging (QPI) is a technique capable of providing the accurate cellular data used to develop effective metrics that permit accurate assessment of disease and treatment response. It has been applied to a variety of live cell imaging studies. ECE researchers are investigating QPI systems using novel spectral interferometry techniques.

A recently developed technique, spectral modulation interferometry (SMI), modulates sample information onto a spectrally oscillating carrier via optical interferometry. A single spectrum contains a continuous set of spatial, temporal, or spectroscopic information. SMI offers high-sensitivity, speckle-free phase images and presents a way to accurately quantify the dynamic behaviors of live cells.

ECE researchers are developing flexible, multifunctional, biocompatible fibers for electrical, optical, and chemical communication with neural circuits in the brain. This technology will advance the fundamental understanding of neural circuits related to behavior by manipulating and monitoring single cell or small neuron group activities in the 3-D circuits. It can also lead to new therapeutic strategies for treating neurological disorders, including closed-loop treatment of epileptic seizures and brain tumors. We are developing flexible fibers and fabrics for distributed pressure sensing and interrogation of neural circuits in animal brains. We also have developed the first carbon nanofiber-based electrodes in fibers for miniaturized and biocompatible neural interface.

ECE researchers have been designing, manufacturing, and investigating nano-enabled photonics-electronics devices and systems (NePEDS). We are using this technology to target applications in health assessment, monitoring, and interventions; solar energy harvesting and conversion; and optoelectronics information technology. 

Converting today’s microscopes, whose main goal is to offer visualization, into full quantification tools would allow new applications for scientists and commercial users. But in practice there are many challenges due to the multiple modes a microscope supports, including phase contrast, differential interference contrast, and polarized light. Special hardware is required to convert these modes into a quantitative tool, making integration difficult and expensive. ECE researchers are developing low-cost, highly integrable techniques via spectral interferometry that can be added to commercial microscopes via a compact accessory.

ECE researchers have been developing a sensor system based on a reduced-mode single crystal sapphire optical fiber and serial sapphire fiber Bragg gratings (FBGs). We have demonstrated the use of these FBGs for ultra-high temperature sensing up to 1500° C, built and field-tested a prototype sensor system at the Virginia Tech Power Plant, and demonstrated the operation of acoustic FBGs in a single mode acoustic waveguide. This new technology holds significant promise for distributed sensing of strain, temperature, pressure, and corrosion in the extreme conditions present in nuclear power plants. 

Standard digital holography employs a 2-D sensing array, such as a charge-coupled device (CCD), to capture holographic information. However, these methods are restricted by the finite size of the pixel elements in the 2-D array, leading to problems with image resolution, limited field of view, and remote sensing applications. We have been studying a single-pixel digital holographic technique (called optical scanning holography) in which 3-D (holographic) information is acquired by 2-D active laser scanning. Potential applications of the technique include holographic TV, 3-D coding and decoding, 3-D holographic microscopy and 3-D optical remote sensing. In computer-generated holography, intensive computation often causes bottlenecks, and we are also developing rapid algorithms for 3-D holographic display and holographic cryptography.

ECE researchers recently developed a rigorous wave theory of nanoparticle scattering that has been experimentally applied to nanoparticle sensing. Upon illumination, an individual nanoparticle scatters the incoming light in all directions. This slightly changes the arrival timing of the original light. By measuring this timing change and its spatial pattern, we may determine the size of the nanoparticle and its orientation. These measurements are only possible because of the high sensitivity imaging techniques developed by ECE researchers. Such a quantification tool promises to characterize nanoparticle dynamics in previously impossible ways. For example, it may provide high speed monitoring of nano-assembly processes at single particle level. It may also enable 3-D position and orientation tracking of single nanoparticles for studying intra-cellular processes.

The skies are a crowded place, with new satellites and new signals regularly adding to the noise. Radio astronomy, which detects and analyzes signals from stars and other interstellar bodies, must compete with these signals to bring us clear data. ECE research is improving radio astronomy equipment so it can cut through interference and coexist with traditional radio systems.

Accessing and understanding the human brain is a delicate and difficult task. Researchers in the ECE department have developed tools which use flexible fiberoptic threads to infiltrate the brain—and provide important real-time data without damaging the surrounding tissue. These threads grant access to deeper parts of the brain, providing previously impossible insights.