The monitoring of Earth’s atmosphere requires routine measurements of many gasses and aerosols. The most common technique to perform this task is hyperspectral imaging (HSI). However, with the push to integrate HSI sensing capabilities on small platforms, e.g. cubesats and UAVs, the development of smaller, cheaper, higher performing, and low power HSI systems is necessary. Current HSI systems are composed of a large and complex assortment of lenses, filters and cameras that are large, heavy, expensive, and intolerant to physical shocks—all things that make them challenging for use in space-based sensing and imaging applications. The metamaterial filter described in this work eliminates the need for many of the previously necessary optics because it can spectrally filter light independent of the lights angle of incidence—this allows for a focused beam of light to be filtered by the metamaterial. This is in distinct contrast to grating-based HSI systems where the spectrometer requires collimated light. Additionally, the metamaterial filter is designed to filter light only at the desired spectral bands; this is a great benefit for small-platform systems because of the substantially reduced data rate and required computational resources.
An angle-insensitive metamaterial spectral filter (MS) that demonstrates great potential as a spectral disperser within hyperspectral imaging (HSI) was simulated and analyzed. The innovation of the MS is its operation on the principle of coupled resonances, whereby coupling the classical narrowband Fabry-Perot (FP) resonance and a broadband cavity mode (CM) resonance can tune its dispersive spectral behavior. This results in the MS transmitting a narrow passband within a broad stopband for a focused light cone. Compared to conventional methods, this novel approach has the potential to reduce the size, weight, and power (SWaP) of a HSI system. Currently, hyperspectral sensors require bulky dispersion controlling optics to collimate the incoming beam due to physical limitations set forth by the disperser. Because the disperser is usually a transmission/reflection grating, the angle of the incident beam significantly impacts whether the correct wavelength is incident on the sensor. At even a slightly off-normal (AoI), the beam could either miss the sensor entirely, or create cross talk between adjacent pixels. This fundamental limitation produces difficulties in managing obliquely incident light, hence the need for collimation. To get around this, the AoI insensitive metamaterial will be used in the place of the disperser and collimated optics to properly deliver obliquely incident light to the detector. When applied correctly, the MS can be used within a remote sensing detector to provide high performance spectroscopy that is similar to larger heritage sensors.
The health of Earth’s atmosphere and its ecosystems are of vital importance to humanity. To assess the current state of the atmosphere and its rate of degradation, the monitoring of atmospheric gasses and particulates is necessary. The development of next-generation Low size, weight, and power (SWaP) sensors and instruments which are required for this task is a high priority for NASA’s Earth Science Technology Office (ESTO). The primary tool to monitor atmospheric gasses is hyperspectral imaging (HSI). Current HSI systems are composed of a large and complex assortment of lenses, filters and cameras that are large, heavy, expensive, and intolerant to physical shocks—all things that make them challenging for use in space-based sensing and imaging applications. As an alternative, a Low SWaP sensor is made possible by integrating a compact HSI sensor onto a CubeSat or SmallSat platform, which is much cheaper to deploy vs. a conventional satellite. To facilitate this, metamaterials are employed at the detector level to reduce the optical components required for HSI, while still providing comparable performance. The metamaterial studied here replaces a conventional grating disperser in a HSI system, by being compatible with a focused beam (fast optics) while spectrally filtering a particular spectral channel.
We have developed a low SWaP-C enabling Metamaterial Spectrometer (MMS) device for hyperspectral imaging in the MWIR. Our chip-based MMS device couples a Distributed Bragg Stack filter with a sub-wavelength dielectric resonator metasurface. The former gives the device a narrow passband, while the latter can be pixelated into an arbitrary number of parallel spectral channels, each with an independently engineerable center wavelength and bandwidth to create a hyperspectral or multispectral filter. The all-dielectric structure provides low optical loss vs. metallic plasmonic resonators. The metasurface resonators are engineered to accept light across a wide angle-of-incidence cone while being integrated directly into existing focal plane array (FPA) detectors. A wide acceptance cone of light eliminates the need for collimating optics, thereby reducing the SWaP requirements of the MMS relative to competing technologies. The MMS can be fabricated on a wafer scale using standard nanofabrication techniques, which are cost-effective for highvolume manufacturing. Although our initial prototype has been implemented in the MWIR, the generalized MMS structure can be implemented in other infrared spectral ranges by via appropriate choices of materials and rescaling of dimensions. Potential commercial applications of the hyperspectral MMS include environmental monitoring, medical diagnostics, antiterrorism, forensics, and food safety.
In this project we develop a handheld, portable, highly selective and sensitive chem/biosensor that has potential applications in both airborne and water-based environmental sensing. The device relies on a plasmonic chip of subwavelength-scale periodic gold rods engineered to resonate in the near infrared. The chip is functionalized with a novel class of proteins that exhibit large conformational changes upon binding to a specific target analyte. The subsequent change in local refractive index near the surface of the gold is one to two orders of magnitude greater than current conventional methods, which produces a readily measurable 5 to 10 percent difference in light transmission. This allows us to forgo traditional, bulky tabletop setups in favor of a compact form factor. Using commercially available optics to construct a transmission-based optical train, measured changes in bulk refractive index are presented here. While synthesis of binding protein efforts are focused on heme as analyte for proof of concept validation, the functionalized protein can be engineered to pair with a wide variety of analytes with minimal alterations to the plasmonic chip or device design. Such flexibility allows for this device to potentially meet the needs of first responders and health care professionals in a multitude of scenarios.
We present research results centered on development of a highly sensitive handheld chem/biosensor device using a novel class of engineered proteins, designed to undergo extreme conformational changes upon binding their target, which in turn cause extreme changes in refractive index in the protein layer. These proteins are attached to a detector chip with a structured metasurface, to translate the refractive index change into an enhanced shift in surface plasmon resonances (SPR), thereby improving the sensitivity of the overall detector relatively to current commercially available SPR systems. Theoretical calculations have demonstrated the potential of the conformational changes in the engineered proteins to provide the desired change in refractive index. A plasmonic chip with a simple grating metasurface structure was designed to maximize the SPR shift. A prototype chip and a prototype for the overall device housing were fabricated with the inclusion of all other required (commercially available) optical components. The proposed device holds considerable promise as a low-cost, highly sensitive, field-deployable detection system for chemical and biological toxins.
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