Browsing by Author "Flynn, Christopher"

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    Advancement of fiber image guide based snapshot imaging spectrometer technology for bioimaging and environmental applications
    (2023-08-08) Flynn, Christopher; Tomasz Tkaczyk, Tomasz
    Hyperspectral imaging spectrometers provide detailed and continuous spectral data in addition to spatial information found in commercial RGB or monochromatic cameras. The addition of spectral information can provide valuable insight in many fields such as but not limited to biomedical imaging, smart farming, environmental monitoring, and remote sensing. Key to monitoring dynamic events is fast, snapshot acquisition of the hyperspectral datacube and then quick turnaround of raw data into decipherable hyperspectral images and spectra. Previous implementations of fiber based imaging spectrometers were focused on breadboard proof of concept designs and were not optimized for field imaging. This thesis details the development of two generations of imaging spectrometers for remote sensing of crop health and the advancement of fiber image guide based snapshot imaging spectrometer technology including fiber bundle fabrication, system level integration and ruggedization, and in-the-field application based data collection. Examples of remote sensing data for smart farming with spectral data informing plant stress from abiotic stressors such as water stress and soil minerology are presented. Design and implementation of components and housing will enable the snapshot imaging spectrometers to image dynamic targets in a variety of environments, including from an aerial platform. To enable miniaturization and high level integration, optical fiber fabrication using 2-photon 3D printing is presented. 2-photon fabrication of fiber bundles was pursued via investigation of individual fibers and fiber components such as fiber couplers, then small arrays in air, and then scale up and the addition of cladding.
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    Fabrication of waveguide directional couplers using 2-photon lithography
    (Optica Publishing Group, 2023) Flynn, Christopher; Cao, Haimu; Applegate, Brian E.; Tkaczyk, Tomasz S.; Bioengineering; Electrical and Computer Engineering
    Advances in 2-photon lithography have enabled in-lab production of sub-micron resolution and millimeter scale 3D optical components. The potential complex geometries are well suited to rapid prototyping and production of waveguide structures, interconnects, and waveguide directional couplers, furthering future development and miniaturization of waveguide-based imaging technologies. System alignment is inherent to the 2-photon process, obviating the need for manual assembly and allowing precise micron scale waveguide geometries not possible in traditional fused fiber coupler fabrication. Here we present the use of 2-photon lithography for direct printing of multi-mode waveguide couplers with air cladding and single mode waveguide couplers with uncured liquid photoresin cladding. Experimental results show reproducible coupling which can be modified by selected design parameters.
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    Radiometric and design model for the tunable light-guide image processing snapshot spectrometer (TuLIPSS)
    (Optical Society of America, 2021) Zheng, Desheng; Flynn, Christopher; Stoian, Razvan I.; Lu, Jiawei; Cao, Haimu; Alexander, David; Tkaczyk, Tomasz S.; Bioengineering; Electrical and Computer Engineering; Physics and Astronomy
    The tunable light-guide image processing snapshot spectrometer (TuLIPSS) is a novel remote sensing instrument that can capture a spectral image cube in a single snapshot. The optical modelling application for the absolute signal intensity on a single pixel of the sensor in TuLIPSS has been developed through a numerical simulation of the integral performance of each optical element in the The tunable light-guide image processing snapshot spectrometer (TuLIPSS) is a novel remote sensing instrument that can capture a spectral image cube in a single snapshot. The optical modelling application for the absolute signal intensity on a single pixel of the sensor in TuLIPSS has been developed through a numerical simulation of the integral performance of each optical element in the TuLIPSS system. The absolute spectral intensity of TuLIPSS can be determined either from the absolute irradiance of the observed surface or from the tabulated spectral reflectance of various land covers and by the application of a global irradiance approach. The model is validated through direct comparison of the simulated results with observations. Based on tabulated spectral reflectance, the deviation between the simulated results and the measured observations is less than 5% of the spectral light flux across most of the detection bandwidth for a Lambertian-like surface such as concrete. Additionally, the deviation between the simulated results and the measured observations using global irradiance information is less than 10% of the spectral light flux across most of the detection bandwidth for all surfaces tested. This optical modelling application of TuLIPSS can be used to assist the optimal design of the instrument and explore potential applications. The influence of the optical components on the light throughput is discussed with the optimal design being a compromise among the light throughput, spectral resolution, and cube size required by the specific application under consideration. The TuLIPSS modelling predicts that, for the current optimal low-cost configuration, the signal to noise ratio can exceed 10 at 10 ms exposure time, even for land covers with weak reflectance such as asphalt and water. Overall, this paper describes the process by which the optimal design is achieved for particular applications and directly connects the parameters of the optical components to the TuLIPSS performance.
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    Ruggedized, field-ready snapshot light-guide-based imaging spectrometer for environmental and remote sensing applications
    (Optica Publishing Group, 2022) Flynn, Christopher; Stoian, Razvan I.; Weers, Brock D.; Mullet, John E.; Thomasson, J. Alex; Thomasson, J. Alex; Alexander, David; Tkaczyk, Tomasz S.; Tkaczyk, Tomasz S.; Bioengineering
    A field-ready, fiber-based high spatial sampling snapshot imaging spectrometer was developed for applications such as environmental monitoring and smart farming. The system achieves video rate frame transfer and exposure times down to a few hundred microseconds in typical daylight conditions with ∼63,000 spatial points and 32 spectral channels across the 470nm to 700nm wavelength range. We designed portable, ruggedized opto-mechanics to allow for imaging from an airborne platform. To ensure successful data collection prior to flight, imaging speed and signal-to-noise ratio was characterized for imaging a variety of land covers from the air. The system was validated by performing a series of observations including: Liriope Muscari plants under a range of water-stress conditions in a controlled laboratory experiment and field observations of sorghum plants in a variety of soil conditions. Finally, we collected data from a series of engineering flights and present reassembled images and spectral sampling of rural and urban landscapes
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    Visible and short-wave infrared fiber-based snapshot imaging spectrometer with a custom high-throughput relay system
    (Optica Publishing Group, 2023) Lu, Jiawei; Zheng, Desheng; Stoian, Razvan-Ionut; Flynn, Christopher; Alexander, David; Tkaczyk, Tomasz S.; Bioengineering; Electrical and Computer Engineering; Physics and Astronomy
    This paper presents the design and fabrication of a fiber-based snapshot imaging spectrometer working in both visible (490 nm-732 nm) and short-wave infrared (1090 nm - 1310 nm) ranges. To maximize the light collection efficiency, a custom relay system with 0.25 NA and 20 mm field of view (FOV) was designed and integrated. The bench setup showed that the custom relay system could fully resolve 10 µm fiber cores over the entire FOV among visible and short-wave infrared ranges. The numerical aperture (NA) match provided a 2.07X fold throughout improvement in the visible range and about 10X fold in the SWIR range compared to the previous generations, enabling imaging with a fast frame rate and under low illumination conditions. The presented imaging spectrometer generated spectral datacubes with 35000 spatial samplings and 23 spectral channels. Spectral urban imaging results obtained by the spectrometer in both visible and SWIR ranges are presented. Finally, we collected spectral images of apple bruising to show potential applications in the food quality industry.