@article{altaqui_schrickx_gyurek_sen_escuti_brendan t. o'connor_kudenov_2022, title={Cephalopod-inspired snapshot multispectral sensor based on geometric phase lens and stacked organic photodetectors}, volume={61}, ISSN={["1560-2303"]}, DOI={10.1117/1.OE.61.7.077104}, abstractNote={Abstract. Multispectral imaging (MSI) is a valuable sensing modality for applications that require detecting a scene’s chemical characteristics. Existing MSI techniques utilize a filter wheel or color filter arrays, which are subject to reduced temporal or spatial resolution. In this work, we present a cephalopod-inspired multispectral organic sensor (CiMOS) based on geometric phase lenses (GPLs) and organic photovoltaics (OPVs) to enable aberration-based color sensing. We mimic the approach by which animals with single-type photoreceptors perceive colors via chromatic aberration. The intrinsic chromatic aberration of GPLs allows for multispectral sensing by stacking precisely patterned OPVs within specific spectrally dependent focal lengths. We provide simulations and a proof of concept of the CiMOS and highlight its advantages, including its simple design and snapshot multi-color detection using only a single axial position. Experimental results demonstrate the sensor’s ability to detect four colors with full width at half maximum spectral resolution as low as 35 nm.}, number={7}, journal={OPTICAL ENGINEERING}, author={Altaqui, Ali and Schrickx, Harry and Gyurek, Sydney and Sen, Pratik and Escuti, Michael and Brendan T. O'Connor and Kudenov, Michael}, year={2022}, month={Jul} }
 @article{kudenov_altaqui_williams_2022, title={Practical spectral photography II: snapshot spectral imaging using linear retarders and microgrid polarization cameras}, volume={30}, ISSN={["1094-4087"]}, DOI={10.1364/OE.453538}, abstractNote={Despite recent advances, customized multispectral cameras can be challenging or costly to deploy in some use cases. Complexities span electronic synchronization, multi-camera calibration, parallax and spatial co-registration, and data acquisition from multiple cameras, all of which can hamper their ease of use. This paper discusses a generalized procedure for multispectral sensing using a pixelated polarization camera and anisotropic polymer film retarders to create multivariate optical filters. We then describe the calibration procedure, which leverages neural networks to convert measured data into calibrated spectra (intensity versus wavelength). Experimental results are presented for a multivariate and channeled optical filter. Finally, imaging results taken using a red, green, and blue microgrid polarization camera and the channeled optical filter are presented. Imaging experiments indicated that the calculated spectra’s root mean square error is highest in the region where the camera’s red, green, and blue filter responses overlap. The average error of the spectral reflectance, measured of our spectralon tiles, was 6.5% for wavelengths spanning 425-675 nm. This technique demonstrates that 12 spectral channels can be obtained with a relatively simple and robust optical setup, and at minimal cost beyond the purchase of the camera.}, number={8}, journal={OPTICS EXPRESS}, author={Kudenov, Michael W. and Altaqui, Ali and Williams, Cranos}, year={2022}, month={Apr}, pages={12337–12352} }
 @article{altaqui_schrickx_sen_li_rech_lee_balar_you_kim_escuti_et al._2021, title={Bio-inspired spectropolarimetric sensor based on tandem organic photodetectors and multi-twist liquid crystals}, volume={29}, ISSN={["1094-4087"]}, url={https://doi.org/10.1364/OE.431858}, DOI={10.1364/OE.431858}, abstractNote={Simultaneous spectral and polarimetric imaging enables versatile detection and multimodal characterization of targets of interest. Current architectures incorporate a 2×2 pixel arrangement to acquire the full linear polarimetric information causing spatial sampling artifacts. Additionally, they suffer from limited spectral selectivity and high color crosstalk. Here, we demonstrate a bio-inspired spectral and polarization sensor structure based on integrating semitransparent polarization-sensitive organic photovoltaics (P-OPVs) and liquid crystal polymer (LCP) retarders in a tandem configuration. Color tuning is realized by leveraging the dynamic chromatic retardation control of LCP films, while polarization sensitivity is realized by exploiting the flexible anisotropic properties of P-OPVs. The structure is marked by its ultra-thin design and its ability to detect spectral and polarimetric contents along the same optical axis, thereby overcoming the inherent limitations associated with conventional division-of-focal plane sensors.}, number={26}, journal={OPTICS EXPRESS}, publisher={The Optical Society}, author={Altaqui, Ali and Schrickx, Harry and Sen, Pratik and Li, Lingshan and Rech, Jeromy and Lee, Jin-Woo and Balar, Nrup and You, Wei and Kim, Bumjoon J. and Escuti, Michael and et al.}, year={2021}, month={Dec}, pages={43953–43969} }
 @article{kudenov_scarboro_altaqui_boyette_yencho_williams_2021, title={Internal defect scanning of sweetpotatoes using interactance spectroscopy}, volume={16}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0246872}, abstractNote={While standard visible-light imaging offers a fast and inexpensive means of quality analysis of horticultural products, it is generally limited to measuring superficial (surface) defects. Using light at longer (near-infrared) or shorter (X-ray) wavelengths enables the detection of superficial tissue bruising and density defects, respectively; however, it does not enable the optical absorption and scattering properties of sub-dermal tissue to be quantified. This paper applies visible and near-infrared interactance spectroscopy to detect internal necrosis in sweetpotatoes and develops a Zemax scattering simulation that models the measured optical signatures for both healthy and necrotic tissue. This study demonstrates that interactance spectroscopy can detect the unique near-infrared optical signatures of necrotic tissues in sweetpotatoes down to a depth of approximately 5±0.5 mm. We anticipate that light scattering measurement methods will represent a significant improvement over the current destructive analysis methods used to assay for internal defects in sweetpotatoes.}, number={2}, journal={PLOS ONE}, author={Kudenov, Michael W. and Scarboro, Clifton G. and Altaqui, Ali and Boyette, Mike and Yencho, G. Craig and Williams, Cranos M.}, year={2021}, month={Feb} }
 @article{altaqui_sen_schrickx_rech_lee_escuti_you_kim_kolbas_brendan t. o'connor_et al._2021, title={Mantis shrimp-inspired organic photodetector for simultaneous hyperspectral and polarimetric imaging}, volume={7}, ISSN={["2375-2548"]}, url={https://doi.org/10.1126/sciadv.abe3196}, DOI={10.1126/sciadv.abe3196}, abstractNote={Semitransparent polarization-sensitive organic detectors reveal unprecedented degrees of freedom for multidimensional imaging.}, number={10}, journal={SCIENCE ADVANCES}, publisher={American Association for the Advancement of Science (AAAS)}, author={Altaqui, Ali and Sen, Pratik and Schrickx, Harry and Rech, Jeromy and Lee, Jin-Woo and Escuti, Michael and You, Wei and Kim, Bumjoon J. and Kolbas, Robert and Brendan T. O'Connor and et al.}, year={2021}, month={Mar} }
 @article{altaqui_kolbas_escuti_brendan t. o'connor_kudenov_2021, title={Organic-based photodetectors for multiband spectral imaging}, volume={60}, ISSN={["2155-3165"]}, DOI={10.1364/AO.417069}, abstractNote={Using organic photodetectors for multispectral sensing is attractive due to their unique capabilities to tune spectral response, transmittance, and polarization sensitivity. Existing methods lack tandem multicolor detection and exhibit high spectral cross talk. We exploit the polarization sensitivity of organic photodetectors, together with birefringent optical filters to design single-pixel multispectral detectors that achieve high spectral selectivity and good radiometric performance. Two different architectures are explored and optimized, including the Solc-based and multitwist-retarder-based organic photodetectors. Although the former demonstrated a higher spectral resolution, the latter enables a more compact sensor as well as greater flexibility in device fabrication.}, number={8}, journal={APPLIED OPTICS}, author={Altaqui, Ali and Kolbas, Robert M. and Escuti, Michael J. and Brendan T. O'Connor and Kudenov, Michael W.}, year={2021}, month={Mar}, pages={2314–2323} }
 @article{kudenov_altaqui_williams_2021, title={Snapshot spectral imaging using Solc-based multivariate optical filters and pixelated polarization cameras}, volume={11833}, ISSN={["1996-756X"]}, DOI={10.1117/12.2596580}, abstractNote={Despite recent advances, customized multispectral cameras can be challenging or costly to deploy in some use cases. Complexities span electronic synchronization, multi-camera calibration, parallax and spatial coregistration, and data acquisition from multiple cameras, all of which can hamper their ease of use. This paper discusses a generalized procedure for multispectral sensing using a pixelated polarization camera and Solc stages to create multivariate optical filters. We then describe some preliminary experimental results of a fabricated filtered camera system. Finally, classification of the imagery is achieved using either shallow or deep neural networks. We also discuss the potential of using a color red, green, and blue microgrid polarization camera to detect upwards of 12 spectral channels using readily available standard off-the-shelf components.}, journal={POLARIZATION SCIENCE AND REMOTE SENSING X}, author={Kudenov, Michael W. and Altaqui, Ali and Williams, Cranos}, year={2021} }
 @article{schrickx_sen_booth_altaqui_burleson_rech_lee_biliroglu_gundogdu_kim_et al._2021, title={Ultra-High Alignment of Polymer Semiconductor Blends Enabling Photodetectors with Exceptional Polarization Sensitivity}, volume={10}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.202105820}, abstractNote={AbstractPhotodetectors that can sense not only light intensity but also light's polarization state add valuable information that is beneficial in a wide array of applications. Polymer semiconductors are an attractive material system to achieve intrinsic polarization sensitivity due to their anisotropic optoelectronic properties. In this report, the thermomechanical properties of the polymer semiconductors PBnDT‐FTAZ and P(NDI2OD‐T2) are leveraged to realize bulk heterojunction (BHJ) films with record in‐plane alignment. Two polymer blends with distinct weight average molar masses (Mw) are considered and either a strain‐ or rub‐alignment process is applied to align the polymer blend films. Optimized processing yields films with dichroic ratios (DR) of over 11 for the high Mw system and nearly 17 for the low Mw system. Incorporating the aligned films into photodetectors results in a polarized photocurrent ratio of 15.25 with corresponding anisotropy ratio of 0.88 at a wavelength of 530 nm, representing the highest reported photocurrent ratio for photodiodes that can operate in a self‐powered regime. The demonstrated performance showcases the ability of polymer semiconductors to achieve BHJ films with exceptional in‐plane polymer alignment, enabling high performance polarization sensitive photodetectors for incorporation into novel device architectures.}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Schrickx, Harry M. and Sen, Pratik and Booth, Ronald E. and Altaqui, Ali and Burleson, Jacob and Rech, Jeromy J. and Lee, Jin-Woo and Biliroglu, Melike and Gundogdu, Kenan and Kim, Bumjoon J. and et al.}, year={2021}, month={Oct} }
 @article{altaqui_kudenov_2019, title={Phase-shifting interferometry in fiber-based channeled spectropolarimeter}, volume={11132}, ISSN={["1996-756X"]}, DOI={10.1117/12.2529975}, abstractNote={Channeled spectropolarimetry measures the spectral dependence of the polarization states of light. This technique is marked by its snapshot feature, in that the complete polarization states can be determined simultaneously from a single intensity spectrum. However, without athermalization, it suffers from high sensitivity to temperature, which in turn, degrades the polarimetric reconstruction accuracy. In this paper, we present a calibration technique for a fiber-based channeled spectropolarimetry that leverages phase-shifting interferometry to accurately demodulate the retarders' phase, thereby improving the accuracy of the acquired Stokes parameters. Additionally, it enables robust spectropolarimetric performance that is insensitive to environmental perturbations. Experimental results demonstrate that calibrations using phase-shifting interferometry improve the Stokes reconstruction results by approximately a factor of 3 when compared to the reference beam calibration method.}, journal={POLARIZATION SCIENCE AND REMOTE SENSING IX}, author={Altaqui, Ali and Kudenov, M. W.}, year={2019} }
 @article{altaqui_kudenov_2019, title={Phase-shiftinginterferometry-based Fourier transform channeled spectropolarimeter}, volume={58}, ISSN={["2155-3165"]}, DOI={10.1364/AO.58.001830}, abstractNote={Channeled spectropolarimetry is a snapshot technique for measuring the spectral dependence of the state of polarization of light. However, it suffers from two major limitations, namely, its high sensitivity to environmental perturbations and its susceptibility to channel crosstalk. These limitations reduce the polarimetric reconstruction accuracy of the spectropolarimeter. A new calibration technique for channeled spectropolarimetry is presented that utilizes the concept of phase-shifting interferometry to accurately acquire and demodulate the retardation phase factors, thereby improving the accuracy of the Stokes data reconstruction as well as enabling more robust performance. The new technique also enables the acquisition of high-resolution intensity spectrum by adopting a dual-scan measurement technique for reducing crosstalk. Experimental results show that calibrations using phase-shifting interferometry yield higher data reconstruction accuracy as compared to the self-calibration technique.}, number={7}, journal={APPLIED OPTICS}, author={Altaqui, Ali and Kudenov, M. W.}, year={2019}, month={Mar}, pages={1830–1840} }
 @article{altaqui_kudenov_2019, title={Thermal stabilization of a fiber-based channeled spectropolarimetry}, volume={58}, ISSN={["1560-2303"]}, DOI={10.1117/1.OE.58.12.124102}, abstractNote={Abstract. Channeled spectropolarimetry (CSP) is a spectral modulation technique that furnishes snapshot polarimetric measurements. Among the different spectropolarimetric methods, fiber-based techniques are fundamental requirements in specific biomedical procedures, such as endoscopy. However, the optical fiber exhibits high sensitivity to temperature changes, which subsequently incurs errors in the polarimetric reconstructions. We present a calibration technique for fiber-based CSP that leverages phase-shifting interferometry (PSI) to acquire and demodulate the fiber’s retardation phase accurately. This technique provides high robustness against temperature variations and improved polarimetric reconstruction performance. Experimental results demonstrated that the PSI calibrations offer higher stability and accuracy, at different optical fiber temperatures, as compared to reference-beam calibrations.}, number={12}, journal={OPTICAL ENGINEERING}, author={Altaqui, Ali and Kudenov, Michael W.}, year={2019}, month={Dec} }