Although traditional spectroscopic techniques offer broadband, high-resolution capability, they typically require cumbersome dispersive optics with moving parts to achieve the necessary resolving power and sensitivity. However, dispersive optics based spectrometers are bulky, expensive, and fragile. As such, the traditional techniques are not suitable for air or space vehicle applications due to the strict size and weight requirements of these platforms. Especially, spectrophotometry at shortwave infrared (SWIR) wavelengths of light is of particular interest to geologists and environmental scientists who have shown it to be a useful tool for predicting soil texture distribution, detecting mineral deposits, quantifying clay mineral content, and differentiating between native and invasive plant species. To that end, we report a miniaturized SWIR spectrometer that is based on a quantum dot absorptive filter array. First, a library of quantum dots with absorption features spanning across the SWIR are synthesized and each batch is dispersed in a polymer matrix. The polymer prevents quantum dots from aggregating in high loading and these composites are deposited onto a lithographically patterned microwell to form a tightly spaced filter array. The filter array is calibrated to generate the “training data” and this calibration file is used to reconstruct a spectrum of interest. This SWIR spectrometer has significant advantages over conventional spectrometers, such as small form-factor for portability, robustness due to the absence of expensive and fragile dispersive optics, and quick acquisition due to the multiplexed filter array from which any arbitrary spectrum can be detected without scanning and be deconvoluted using a sophisticated algorithm.

Quantum dot absorptive filter array based shortwave infrared miniaturized spectrometer

254th National Meeting (2017)

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