| 1. |
- Chen, Ruilin, et al.
(författare)
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Experimental demonstration of real-time optical DFT-S DMT signal transmission for a blue-LED-based UWOC system using spatial diversity reception
- 2023
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Ingår i: Applied Optics. - : Optica Publishing Group. - 1559-128X .- 2155-3165. ; 62:3, s. 541-551
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Tidskriftsartikel (refereegranskat)abstract
- Underwater wireless optical communication (UWOC) has broad prospects in underwater real-time applications. We design and experimentally demonstrate a real-time discrete Fourier transform spread discrete multi-tone (DFT-S DMT) signal transmission based on a field programmable gate array for a blue-LED-based UWOC system with a data rate of up to 30 Mbps over a 15-m underwater channel. The architecture and usage of an on-chip resource as well as power consumption are analyzed and discussed. To reduce the impacts of multipath fading and received intensity fluctuation, spatial diversity reception is also introduced. Furthermore, the receiver sensitivity at a speci-fied bit error rate (BER) threshold and the quality of the images are evaluated using three types of Reed-Solomon (RS) codes. At the BER threshold of 10-4, over 2.8-dB receiver sensitivity improvement is obtained by the DFT-S DMT scheme with the RS (64, 56) code as compared to the uncoded one at the data rate of 30 Mbps. The perform-ance of BER, color difference, and structural similarity in the image transmission of DFT-S DMT is superior to that of the conventional hard clipping quadrature amplitude modulation DMT in a high-data-rate region because of the low peak-to-average-power ratio and ability to mitigate high-frequency fading in a band-limited UWOC system. With schemes of the RS code, DFT-S, and diversity reception, error-free transmission of images is achieved over a 15-m water channel. The proposed UWOC system has the advantages of low power consumption and porta-bility, which foresees a bright future in underwater applications over short to moderate distances.
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| 2. |
- Chesmore, Grace E., et al.
(författare)
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Simons Observatory : characterizing the Large Aperture Telescope Receiver with radio holography
- 2022
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 61:34, s. 10309-10319
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Tidskriftsartikel (refereegranskat)abstract
- We present near-field radio holography measurements of the Simons Observatory Large Aperture Telescope Receiver optics. These measurements demonstrate that radio holography of complex millimeter-wave optical systems comprising cryogenic lenses, filters, and feed horns can provide detailed characterization of wave propagation before deployment. We used the measured amplitude and phase, at 4 K, of the receiver near-field beam pattern to predict two key performance parameters: 1) the amount of scattered light that will spill past the telescope to 300 K and 2) the beam pattern expected from the receiver when fielded on the telescope. These cryogenic measurements informed the removal of a filter, which led to improved optical efficiency and reduced sidelobes at the exit of the receiver. Holography measurements of this system suggest that the spilled power past the telescope mirrors will be less than 1%, and the main beam with its near sidelobes are consistent with the nominal telescope design. This is the first time such parameters have been confirmed in the lab prior to deployment of a new receiver. This approach is broadly applicable to millimeter and submillimeter instruments.
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| 3. |
- Chesmore, Grace E., et al.
(författare)
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Simons Observatory HoloSim-ML : machine learning applied to the efficient analysis of radio holography measurements of complex optical systems
- 2021
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 60:29, s. 9029-9035
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Tidskriftsartikel (refereegranskat)abstract
- Near-field radio holography is a common method for measuring and aligning mirror surfaces for millimeter and sub-millimeter telescopes. In instruments with more than a single mirror, degeneracies arise in the holography measurement, requiring multiple measurements and new fitting methods. We present HoloSim-ML, a Python code for beam simulation and analysis of radio holography data from complex optical systems. This code uses machine learning to efficiently determine the position of hundreds of mirror adjusters on multiple mirrors with few micrometer accuracy. We apply this approach to the example of the Simons Observatory 6 m telescope.
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| 4. |
- Chorey, Devashish, et al.
(författare)
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Simultaneous imaging of CH*, C*2, and temperature in flames using a DSLR camera and structured illumination
- 2023
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 62:14, s. 3737-3746
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Tidskriftsartikel (refereegranskat)abstract
- Measurement of chemical species and temperature mapping in flames is essential to understanding the combustion process. Multiple cameras are conventionally employed for measurement in such scenarios making the experi-mental setup not only cost-intensive but also challenging. To circumvent this, structured illumination (SI)-based methods are reported for multispecies chemiluminescence (CL) imaging using a single camera. In this paper, we demonstrate four-channel SI-based imaging for simultaneous snapshot CH* and C*2 CL imaging and two-color pyrometry for temperature profiles in a butane diffusion flame. We demonstrate our approach using individual species and multiple species imaging. Taking the advantage of the axisymmetric nature of the flame, the Abel trans-form is performed on the line-of-sight averaged images to obtain deconvoluted images. The deconvoluted maps of temperature are compared with the temperature data obtained by using a physical thermocouple probe. (c) 2023 Optica Publishing Group
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| 5. |
- Dahlberg, Tobias, et al.
(författare)
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Optical design for laser tweezers Raman spectroscopy setups for increased sensitivity and flexible spatial detection
- 2021
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 60:16, s. 4519-4523
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a method to double the collection efficiency in Laser Tweezers Raman Spectroscopy (LTRS) by collecting both the forward and back-scattered light in a single-shot multitrack measurement. Our method can collect signals at different sample volumes, granting both the pinpoint spatial selectivity of confocal Raman and the bulk sensitivity of non-confocal Raman simultaneously. Further, we display that our approach allows for reduced detector integration time and laser power. To show this, we measure the Raman spectra of both polystyrene beads and bacterial spores. For spores, we can trap them at 2.5 mW laser power and acquire a high signal-to-noise ratio Power spectrum of the CaDPA peaks using an integration time of 2 x 30 seconds. Thus, our method will enable the monitoring of biological samples sensitive to high intensities for longer times. Additionally, we demonstrate that by a simple modification, we can add polarization sensitivity and retrieve extra biochemical information.
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| 6. |
- Dembele, Vamara, et al.
(författare)
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Correlation properties of a spatially quasi-incoherent imaging interferometer
- 2022
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Ingår i: Applied Optics. - : Optical Society of America. - 1559-128X .- 2155-3165. ; 61:19, s. 5806-5812
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Tidskriftsartikel (refereegranskat)abstract
- The depth-gating capacity of a spatially quasi-incoherent imaging interferometer is investigated in relation to the 3D correlation properties of diffraction field laser speckles. The system exploits a phase-stepped imaging Michelson-type interferometer in which spatially quasi-incoherent illumination is generated by passing an unexpanded laser beam through a rotating diffuser. Numerical simulations and optical experiments both verify that the depth-gating capacity of the imaging interferometer scales as ?/2NA2?λ/2NAp2, where ?λ is the wavelength of the laser and NA?NAp is the numerical aperture of the illumination. For a set depth gate of 150 µm, the depth-gating capacity of the interferometer is demonstrated by scanning a standard USAF target through the measurement volume. The results obtained show that an imaging tool of this kind is expected to provide useful capabilities for imaging through disturbing media and where a single wavelength is required.
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| 7. |
- Fei, Chao, et al.
(författare)
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Underwater wireless optical communication utilizing low-complexity sparse pruned-term-based nonlinear decision-feedback equalization
- 2022
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Ingår i: Applied Optics. - : Optica Publishing Group. - 1559-128X .- 2155-3165. ; 61:22, s. 6534-6543
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Tidskriftsartikel (refereegranskat)abstract
- The nonlinearity of the light-emitting diode (LED) in underwater wireless optical communication (UWOC) systems is considered the one major limiting factor that degrades the system's performance. Volterra series-based nonlinear equalization is widely employed to mitigate such nonlinearity in communication systems. However, the conventional Volterra series-based model is of high complexity, especially for the nonlinearity of higher-order terms or longer memory lengths. In this paper, by pruning away some negligible beating terms and adaptively picking out some of the dominant terms while discarding the trivial ones, we propose and experimentally demonstrate a sparse pruned-term-based nonlinear decision-feedback equalization (SPT-NDFE) scheme for the LED-based UWOC system with an inappreciable performance degradation as compared to systems without the pruning strategy. Meanwhile, by replacing the self/cross beating terms with the terms formed by the absolute operation of a sum of two input samples instead of the product operation terms, a sparse pruned-term-based absolute operation nonlinear decision-feedback equalization (SPT-ANDFE) scheme is also introduced to further reduce complexity. The experimental results show that the SPT-NDFE scheme exhibits comparable performance as compared to the conventional NDFE (nonlinear decision-feedback equalization) scheme with lower complexity (the nonlinear coefficients are reduced by 63.63% as compared to the conventional NDFE scheme). While the SPT-ANDFE scheme yields suboptimal performance with further reduced complexity at the expense of a slight performance degradation, the robustness of the proposed schemes in different turbidity waters is experimentally verified. The proposed channel equalization schemes with low complexity and high performance are promising for power/energy-sensitive UWOC systems.
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| 8. |
- Feng, Xingxing, et al.
(författare)
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Human recognition with the optoelectronic reservoir-computing-based micro-Doppler radar signal processing
- 2022
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Ingår i: Applied Optics. - : Optica Publishing Group (formerly OSA). - 1559-128X .- 2155-3165. ; 61:19, s. 5782-5789
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Tidskriftsartikel (refereegranskat)abstract
- Current perception and monitoring systems, such as human recognition, are affected by several environmental factors, such as limited light intensity, weather changes, occlusion of targets, and public privacy. Human recognition using radar signals is a promising direction to overcome these defects; however, the low signal-to-noise ratio of radar signals still makes this task challenging. Therefore, it is necessary to use suitable tools that can efficiently deal with radar signals to identify targets. Reservoir computing (RC) is an efficient machine learning scheme that is easy to train and demonstrates excellent performance in processing complex time-series signals. The RC hardware implementation structure based on nonlinear nodes and delay feedback loops endows it with the potential for real-time fast signal processing. In this paper, we numerically study the performance of the optoelectronic RC composed of optical and electrical components in the task of human recognition with noisy micro-Doppler radar signals. A single-loop optoelectronic RC is employed to verify the application of RC in this field, and a parallel dual-loop optoelectronic RC scheme with a dual-polarization Mach–Zehnder modulator (DPol-MZM) is also used for performance comparison. The result is verified to be comparable with other machine learning tools, which demonstrates the ability of the optoelectronic RC in capturing gait information and dealing with noisy radar signals; it also indicates that optoelectronic RC is a powerful tool in the field of human target recognition based on micro-Doppler radar signals.
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| 9. |
- Gallardo, Patricio A., et al.
(författare)
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Freeform three-mirror anastigmatic large-aperture telescope and receiver optics for CMB-S4
- 2024
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 63:2, s. 310-321
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Tidskriftsartikel (refereegranskat)abstract
- CMB-S4, the next-generation ground-based cosmic microwave background (CMB) observatory, will provide detailed maps of the CMB at millimeter wavelengths to dramatically advance our understanding of the origin and evolution of the universe. CMB-S4 will deploy large- and small-aperture telescopes with hundreds of thousands of detectors to observe the CMB at arcminute and degree resolutions at millimeter wavelengths. Inflationary science benefits from a deep delensing survey at arcminute resolutions capable of observing a large field of view at millimeter wavelengths. This kind of survey acts as a complement to a degree angular resolution survey. The delensing survey requires a nearly uniform distribution of cameras per frequency band across the focal plane. We present a large-throughput (9.4° field of view), large-aperture (5-m diameter) freeform three-mirror anastigmatic telescope and an array of 85 cameras for CMB observations at arcminute resolutions, which meets the needs of the delensing survey of CMB-S4. A detailed prescription of this three-mirror telescope and cameras is provided, with a series of numerical calculations that indicates expected optical performance and mechanical tolerance.
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| 10. |
- Gudmundsson, Jon E.
(författare)
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Geometrical and physical optics analysis for mm-wavelength refractor telescopes designed to map the cosmic microwave background
- 2020
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Ingår i: Applied Optics. - 1559-128X .- 2155-3165. ; 59:11, s. 3324-3339
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Tidskriftsartikel (refereegranskat)abstract
- We present a compact two-lens high-density polyethylene (HDPE) f/1.6 refractor design that is capable of supporting a 28-deg diffraction-limited field of view at 1-mm wavelengths and contrast it to a similar two-lens refractor using silicon lenses. We compare the optical properties of these two systems as predicted by both geometrical and physical optics. The presented analysis suggests that by relaxing telecentricity requirements, a plastic two-lens refractor system can be made to have a surprisingly large field of view. Furthermore, this HDPE system is found to perform comparably to a similar silicon system across a wide field of view and wavelengths up to 1 mm. We show that for both telescope designs, cold stop spillover changes significantly across the field of view in a way that is somewhat inconsistent with Gaussian beam formalism and simple f-number scaling. We present results that highlight beam ellipticity dependence on both pixel location and pixel aperture size-an effect that is challenging to reproduce in standard geometrical optics. We show that a silicon refractor design suffers from larger cross-polarization compared to the HDPE design. Our results address the limitations of relying solely on geometrical optics to assess relative performance of two optical systems. We discuss implications for future refractor designs.
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