Image Spectrometer Captures and Calibrates Record Amounts of Data Rapidly

Researchers at Rice University have developed a compact, fiber-based image spectrometer for remote sensing. Called the Tunable Light-Guide Image Processing Snapshot Spectrometer (TuLIPSS), the device combines high spatial resolution with large amounts of spectral information and can deliver data to a detector instantly. At only 600 × 150 × 150 mm, it is almost small enough for use aboard unmanned aerial vehicles. According to the researchers, it could be made even smaller.

Bundles of optic fibers in Rice University’s TuLIPSS spectrometer deliver spatial and spectral data to a detector in an instant. The data can then be processed for quick environmental or biological analysis. Courtesy of the Modern Optical Instrumentation and Bio-Imaging Laboratory.

TuLIPSS captures hyperspectral data in a data cube without requiring any scanning, in contrast to systems that scan a scene line-by-line and reassemble the scene later. The lens in TuLIPSS focuses light onto a bundle of optical fibers. These fibers collect more than 30,000 spatial samples and 61 spectral channels in the 450- to 750-nm range, which are split by prisms into their component bands and passed on to a detector. The detector then feeds these data points to software that recombines them into the desired images or spectra.

Professor Tomasz Tkaczyk and researcher Ye Wang led the development of a portable spectrometer able to capture far more data much quicker than other fiber-based systems. The TuLIPSS camera will be useful for quick analysis of environmental and biological data. Courtesy of Jeff Fitlow.

The fiber array is tightly packed at the input and rearranged into individually addressable rows at the output. “To increase the spatial sampling for our new fiber bundle design, we placed the fibers into multiple rows with gaps between each row,” said professor Tomasz Tkaczyk, who led the research. “An added benefit of this design is that the size of the gaps can be changed to tune the balance between spatial and spectral sampling to meet specific application requirements.”

Commercially available small-diameter fibers suitable for imaging spectroscopy are typically 125 to 250 μm in diameter, which can drive up the size of the fiber bundle. To keep the device compact, the researchers used a commercially available multicore fiber ribbon in which each fiber has a 10-μm core. They also optimized the fibers’ numerical apertures to increase light-gathering ability.

The researchers also developed a rapid method for collecting spectra from the more than 30,000 fibers. Their method takes less than five minutes to calibrate all the spatial samplings of the system and requires acquisition of only a few images. “Our new rapid calibration method for imaging spectrometers with high spatial sampling could also be extended to calibrate fiber bundles and other imaging devices,” Tkaczyk said.

The researchers tested the spectrometer by using it to image urban traffic to show its spectral imaging capability and potential for use in remote sensing applications. Courtesy of the Modern Optical Instrumentation and Bio-Imaging Laboratory/Tomasz S. Tkaczyk, Rice University.

The researchers demonstrated the new spectrometer by using it to image distant scenes and vegetation on the Rice University campus. They showed that their instrument could provide about an order of magnitude more information than has been reported for other fiber-based systems.

“These tests demonstrated the system’s spectral imaging capability and showed its significant promise for use in environmental and remote sensing applications,” Tkaczyk said. The researchers are now working on further improvements to the device. They want to make the fiber bundle even more compact by using custom fiber ribbons and are also examining ways to increase the system’s light throughput.

“Compact imaging spectrometers such as the one we developed can be used on unmanned aerial vehicles to help increase crop production or inform response after a disaster based on detected pollution,” Tkaczyk said. In the biomedical field, the system could increase the efficiency of diagnostic tests or help scientists better understand biological processes.

The research was published in Optics Express, a publication of OSA, The Optical Society (https://doi.org/10.1364/OE.27.015701).

Continuously captured images of moving traffic in the Houston neighborhood around Rice University show how the TuLIPSS spectrometer filters motion blur in dynamic situations. The full-color video is a composite of the filtered spectral data captured by the device. The portable spectrometer has shown that it is able to capture more data more quickly than other fiber-based systems. Courtesy of the Modern Optical Instrumentation and Bio-Imaging Laboratory.