Optimizing and extending the response of near-infrared spectral sensors
Don van Elst defended his PhD thesis at the Department of Applied Physics and Science 果冻传媒 on February 18.
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Spectrometers rely on light to see inside materials without having to break apart the materials of interest. However, traditional spectrometers are not portable, which makes it difficult to use them outside of laboratory settings. The solution is to miniaturize the technology, but making them smaller can affect device performance. Therefore, to overcome this challenge, PhD researcher Don van Elst looked at spectral sensing chips that can provide the spectral information needed for the characterization of materials without having the complexity of a spectrometer.
Light interacts differently with a material depending on its wavelength, producing unique electromagnetic spectra in reflection or transmission. These spectra have fascinated humanity for centuries and they provide a powerful tool to see inside materials, without having to break them apart.
Due to this non-destructive nature, spectroscopy is used in a wide field of applications ranging from agrifood and soil analysis to pharmaceutics and astronomy.
Key challenge
A couple of decades ago, the only way to get detailed information on a spectrum in a wide range of wavelengths was through the use of large and costly spectrometers.
These still offer the best resolution and wavelength range, but are difficult to take into the field, and the rapid advances in consumer products and industry have accelerated the demand for miniaturized and portable solutions.
One of the key challenges when miniaturizing spectrometers is maintaining their performance while reducing their size. Different approaches have been explored, each with its own set of advantages and limitations. For instance, grating-based devices, MEMS-based devices, and waveguide-based spectrometers all offer compact solutions but come with trade-offs in terms of size, speed and bandwidth.
Wavelength-selective responses
To overcome these challenges, Don van Elst proposed a robust multipixel array with wavelength-selective responses as part of his PhD research. These spectral sensing chips provide the spectral information needed for the characterization of materials without having the complexity of a spectrometer.
Similar to how our eyes have 3 different types of colour cones, which for example allows us to identify how ripe a banana is, these chips have 16 鈥渃ones鈥� with responses in the near-infrared. This allows us to see properties of materials that are not visible to the human eye. In particular, Van Elst developed a cleanroom process based on optical lithography to fabricate these spectral sensors.
Main feature
A main feature of Van Elst鈥檚 approach is the choice of prioritizing high optical throughput over ultrahigh resolution.
Beyond this, to enhance the sensors' functionality even further, Van Elst explored tailoring its response to specific applications. By varying the number of channels and their individual responses, this customization optimized the signal-to-noise ratio and possibly reduced fabrication complexity, making the sensors more cost-effective and efficient, while maintaining high sensing performance.
Additionally, a pilot was performed to extend the sensors' spectral range into the short-wave infrared, widening the view even further and opening up new possibilities for applications.
In summary, Van Elst鈥檚 research outlines advancements in the development of cost-effective integrated spectral sensors, making them more efficient, versatile, and suitable for a wide range of applications.
Title of PhD thesis: . Supervisors: Andrea Fiore and Jaime G贸mez Rivas.