Abstract
Spectral sensing is increasingly used in applications ranging from industrial process monitoring to agriculture. Sensing is usually performed by measuring reflected or transmitted light with a spectrometer and processing the resulting spectra. However, realizing compact and mass-manufacturable spectrometers is a major challenge, particularly in the infrared spectral region where chemical information is most prominent. Here we propose a different approach to spectral sensing which dramatically simplifies the requirements on the hardware and allows the monolithic integration of the sensors. We use an array of resonant-cavity-enhanced photodetectors, each featuring a distinct spectral response in the 850-1700 nm wavelength range. We show that prediction models can be built directly using the responses of the photodetectors, despite the presence of multiple broad peaks, releasing the need for spectral reconstruction. The large etendue and responsivity allow us to demonstrate the application of an integrated near-infrared spectral sensor in relevant problems, namely milk and plastic sensing. Our results open the way to spectral sensors with minimal size, cost and complexity for industrial and consumer applications.
Highlights
1, Francesco Pagliano[1], Spectral sensing is increasingly used in applications ranging from industrial process monitoring to agriculture
Optical spectroscopy has been used for decades for quantifying the chemical composition of objects with dimensions ranging from a few nanometers to millions of kilometers
The need for in-situ and on-the-field sensing has been driving the quest for spectral sensors with reduced footprint, increased portability and lower cost, suitable for consumer applications and embedding into smartphones[1–4], and several portable spectroscopy products have reached the market
Summary
1, Francesco Pagliano[1], Spectral sensing is increasingly used in applications ranging from industrial process monitoring to agriculture. We report a NIR spectral sensor, which is suitable for diffuse transmittance/reflectance measurements, is fully integrated, and has no moving parts It is based on a small array of detectors with distinct spectral responses. Our approach is motivated by the observation that the intermediate step of spectral reconstruction is not needed—the signals from the detectors can be directly used to train a model for the sensing problem at hand, in the same way as the signals from cone cells are used to train human perceptive abilities. This observation greatly simplifies the requirements on the hardware, leading to a simple and compact sensor design
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