Boston Chapter of the IEEE Photonics Society

Abstract:  Compact and smart optical sensors have had a major impact on people's lives over the last decade.  Although the spatial information provided by optical imaging systems is readily deployed, there is an untapped potential in the spectroscopic domain. By transforming molecular information into wavelength-domain data, optical spectroscopy techniques have become some of the most popular scientific tools for examining the composition and nature of materials and chemicals. However, spectroscopic techniques are not widely found outside the laboratory setting because (a) miniaturized, high-throughput, and low-cost systems are not available and (b) because of the reliance on domain-specific expertise for interpreting complex spectral signals.  In this talk, we aim to address some of these challenges by combining modern computation with physical domain knowledge. In particular, we focus on two aspects where computational techniques either enable new instruments with a compact form factor or improve our ability to perform analyte detection and quantification in complex environments.

Computational spectrometers, either fiber/waveguide or free space-based, have emerged as interesting candidates for modern spectroscopy applications. As opposed to conventional grating-based spectrometers, these computational spectrometers do not require explicit orthogonal imaging in the far-field for wavelength distinction, but rather employ a non-orthogonal wavelength dispersion mechanism with subsequent calibration and reconstruction processes. Here, we discuss a class of such devices that rely on sampling the Talbot pattern that are intended to bring high-resolution, spectroscopic analysis capabilities to the form-factor of a watch.  In the second part, we develop an analyte quantification algorithm for Raman spectroscopy based on spectral shaping modeling. It uses a hierarchical Bayesian inference model with a minimum training sample size requirement.  Together, this body of work hopes to make spectroscopic tools widely available for applications ranging from security to healthcare.

Biography:  Rajeev J. Ram has worked in the areas of physical optics and electronics for much of his career. In the early 1990’s, he developed the III-V wafer bonding technology that led to record brightness light emitting devices at Hewlett-Packard Laboratory (Lumileds) in Palo Alto. While at HP Labs, he worked on the first commercial deployment of vertical cavity surface emitting lasers.  He developed semiconductor lasers without population inversion, semiconductor lasers that employ condensation of massive particles (polariton lasers), and threshold-less lasers. Since 1997, Ram has been on the Electrical Engineering and Computer Science faculty at the Massachusetts Institute of Technology (MIT) and a member of the Research Laboratory of Electronics and the Microsystems Technology Laboratory. He has served on the Defense Sciences Research Council advising DARPA on new areas for investment and served as a Program Director at the newly founded Advanced Research Project Agency-Energy. His group at MIT has developed energy-efficient photonics for microprocessor systems, microfluidic systems for the control of cellular metabolism, and record-efficiency light sources.  He co-founded AyarLabs which provides optical I/O for integrated electronics and Pharyx which develops microbioreactors for automated cell culture.  He is a MacVicar Faculty Fellow, a Bose Research Fellow at MIT, and a Fellow of the Optical Society of America and IEEE Fellow.

Location:  MIT Lincoln Laboratory Forbes Road