Browsing by Author "Cao, Haimu"

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    Development of Fiber Arrays for Hyperspectral Imaging Spectroscopy Using 2-Photon Polymerization Technique
    (2023-09-08) Cao, Haimu; Tkaczyk, Tomasz; Veeraraghavan, Ashok
    Fiber-based snapshot imaging spectrometers have emerged as indispensable tools in hyperspectral imaging, finding widespread applications in diverse fields such as biomedical imaging, remote sensing, and astronomy. These spectrometers possess the unique ability to capture intricate spectral information from a scene, making them valuable assets in scientific research and industrial applications. However, their development and fabrication have traditionally been intricate, time-consuming, and costly endeavors, often involving manual assembly of commercial components, leading to large output areas in excess of 20 mm in diameter that only immense optics can accommodate. To address these limitations and push the boundaries of imaging spectrometer technology, this thesis aims to find a new approach that can simplify the fabrication process while further miniaturizing the fiber array. Therefore, I propose a design strategy and proof-of-concept snapshot imaging spectrometer using an array of optical fibers fabricated through the cutting-edge technique of Two-Photon Polymerization (2PP). Leveraging the capabilities of the Nanoscribe GmbH Quantum X system, which enables the precise 3D printing of optical quality structures with submicron resolution and exceptional smoothness (less than 5 nm roughness), this work aims to showcases the development of small core fibers and integrated arrays while demonstrating the functionality of the new snapshot imaging spectrometer. The prototype system features a 3D-printed fiber array with dimensions of 40x80, offering a pitch of 6 microns at the input and 80 microns at the output, with each core having a diameter of 5 µm. Incorporated into a prism-based imaging spectrometer, this fiber array facilitates the realization of 48 spectral channels, ranging from 465 nm to 700 nm, showcasing its ability for multi-spectral imaging. To validate the performance of the system, preliminary imaging results were obtained using a USAF target and a color printed letter C, alongside spectral comparisons to a commercial spectrometer. The obtained results unequivocally demonstrate the functionality and immense potential of the 3D-printed fiber-based snapshot imaging spectrometer. Further characterization tests, such as crosstalk and throughput, will be done in the future. We envision this imaging spectrometer to become a platform technology and encompass applications spanning from biomedical imaging, through environmental imaging and remote sensing, etc.
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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.