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Efficient Spectroscopy of Exoplanets at Small Angular Separations with Vortex Fiber Nulling
摘要： Instrumentation designed to characterize potentially habitable planets may combine adaptive optics and high-resolution spectroscopy techniques to achieve the highest possible sensitivity to spectral signs of life. Detecting the weak signal from a planet containing biomarkers will require exquisite control of the optical wavefront to maximize the planet signal and significantly reduce unwanted starlight. We present an optical technique, known as vortex fiber nulling (VFN), that allows polychromatic light from faint planets at extremely small separations from their host stars (～λ/D) to be efficiently routed to a diffraction-limited spectrograph via a single-mode optical fiber, while light from the star is prevented from entering the spectrograph. VFN takes advantage of the spatial selectivity of a single-mode fiber to isolate the light from close-in companions in a small field of view around the star. We provide theoretical performance predictions of a conceptual design and show that VFN may be utilized to characterize planets detected by radial velocity (RV) instruments in the infrared without knowledge of the azimuthal orientation of their orbits. Using a spectral template-matching technique, we calculate an integration time of ～400, ～100, and ～30 hr for Ross 128 b with Keck, the Thirty Meter Telescope, and the Large Ultraviolet/Optical/Infrared Surveyor, respectively.
关键词： techniques: spectroscopic,instrumentation: adaptive optics,instrumentation: high angular resolution
更新于2025-09-10 09:29:36
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Mitigating Chromatic Dispersion with Hybrid Optical Metasurfaces
摘要： Metasurfaces control various properties of light via scattering across a large number of subwavelength-spaced nanostructures. Although metasurfaces appear to be ideal photonic platforms for realizing and designing miniaturized devices, their chromatic aberrations have hindered the large-scale deployment of this technology in numerous applications. Wavelength-dependent diffraction and resonant scattering effects usually limit their working operation wavelengths. In refractive optics, chromatic dispersion is a significant problem and is generally treated by cascading multiple lenses into achromatic doublets, triplets, and so on. Recently, broadband achromatic metalenses in the visible have been proposed to circumvent chromatic aberration but their throughput efficiency is still limited. Here, the dispersion of refractive components is corrected by leveraging the inherent dispersion of metasurfaces. Hybrid refractive-metasurface devices, with nondispersive refraction in the visible, are experimentally demonstrated. The dispersion of this hybrid component, characterized by using a Fourier plane imaging microscopy setup, is essentially achromatic over about 150 nm in the visible. Broadband focusing with composite plano-convex metasurface lenses is also proposed. These devices could find applications in numerous consumer optics, augmented reality components, and all applications including imaging for which monochromatic performance is not sufficient.
关键词： metasurfaces,nanophotonics,hybrid optics,dispersion
更新于2025-09-10 09:29:36
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High sensitivity strain sensor based on twin hollow microspheres
摘要： A sensor based on 2 hollow core microspheres is proposed. Each microsphere was produced separately through fusion splicing and then joined. The resultant structure is a Fabry-Perot interferometer with multiple interferences that can be approximated to a 4-wave interferometer. Strain characterization was attained for a maximum of 1350 με, achieving a linear response with a sensitivity of 3.39 (cid:1) 0.04 PM/με. The fabrication technique, fast and with no chemical hazards, as opposed to other fabrication techniques, makes the proposed sensor a compelling solution for strain measurements in hash environments.
关键词： strain measurement,fiber optics sensors,Fabry-Perot
更新于2025-09-10 09:29:36
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[IEEE 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Espoo, Finland (2018.8.27-2018.9.1)] 2018 12th International Congress on Artificial Materials for Novel Wave Phenomena (Metamaterials) - Real Sources in Complex Spaces
摘要： We utilize complex transformation optics (CTO) to mimic complex source point (CSP) fields. It is shown that the CSP fields can be exactly reproduced via planar metamaterial slabs associated with the proper complex coordinate transformations. CTO extends the real-valued coordinate transformations to complex-valued coordinate transformations. Of conventional TO, one can also control the amplitude of the fields in addition to their phase paths. In the present paper, we demonstrate that CSP fields can be produced through appropriate material tensors prescribed by the corresponding complex coordinate transformations.
关键词： Complex transformation optics,complex source point,metamaterials,Gaussian beams
更新于2025-09-10 09:29:36
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Fiber-optic UTC(k) timescale distribution with automated link delay cancelation
摘要： In this paper we describe the idea and practical realization of an automated calibrator of fiber-optic UTC(k) distribution system, along with a high-resolution shifter of 1 PPS signal, which allows to cancel to the propagation delay and thus to produce the 1 PPS at the remote system output with practically zeroed offset. The solution was experimentally verified with ten different optical paths, up to 300 km long. The rms offset of the output timescale in our experiments was 7.1 ps, and maximum absolute value did not exceed 15 ps.
关键词： fiber optics,Delay cancelation,time and frequency transfer,UTC
更新于2025-09-10 09:29:36
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Repeatability of Cone Spacing Measures in Eyes With Inherited Retinal Degenerations
摘要： PURPOSE. To determine short-term variability of adaptive optics scanning laser ophthalmoscopy (AOSLO)–derived cone spacing measures in eyes with inherited retinal degenerations (IRD) and in normal eyes. METHODS. Twenty IRD patients and 10 visually normal subjects underwent AOSLO imaging at two visits separated by no more than 1 month (NCT00254605). Cone spacing was measured in multiple macular regions in each image by three independent graders. Variability of cone spacing measures between visits, between graders, and between eyes was determined and correlated with standard clinical measures. RESULTS. Cone spacing was measured in 2905 regions. Interobserver agreement was high both in normal eyes and eyes with IRD (mean intraclass correlation coef?cient [ICC] ? 0.838 for normal and 0.892 for eyes with IRD). Cone spacing measures were closely correlated between visits (ICC > 0.869 for both study groups). Mean relative intervisit spacing difference (absolute difference in measures divided by the mean at each region) was 4.0% for normal eyes and 4.9% for eyes with IRD. Cone spacing measures from fellow eyes of the same subject showed strong agreement for all subjects (ICC > 0.85 for both study groups). CONCLUSIONS. Adaptive optics scanning laser ophthalmoscopy–derived macular cone spacing measures were correlated between observers, visits, and fellow eyes of the same subject in normal eyes and in eyes with IRD. This information may help establish the role of cone spacing measures derived from images of the cone mosaic obtained with AOSLO as a sensitive biomarker for longitudinal tracking of photoreceptor loss during disease progression and in response to treatment. (ClinicalTrials.gov number, NCT00254605.)
关键词： retinal,adaptive optics,photoreceptor,imaging,retinitis pigmentosa,retinal degeneration
更新于2025-09-10 09:29:36
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Retinal Vascular Branching in Healthy and Diabetic Subjects
摘要： PURPOSE. To measure the effect of nonproliferative diabetic retinopathy (NPDR) on retinal branching. To compare vascular branching in healthy and diabetic subjects with established biophysical models. METHODS. Vascular bifurcations in arteries and veins were imaged in 17 NPDR and 26 healthy subjects with the Indiana adaptive optics scanning laser ophthalmoscope (AOSLO). Vessel measurements were grouped according to parent vessel diameters into large ((cid:2)50 ~ <100 lm) and small ((cid:2)20 ~ <50 lm) sizes. Vessel diameters and bifurcation angles were measured manually. Vascular diameters were compared with predictions of Murray’s law using curve ?tting. For analysis of bifurcation angles, two models from Zamir were compared: one based on the power required for blood pumping, the other based on drag force between blood and vascular wall. RESULTS. For normal larger vessels, the exponent relating the parent and daughter branching diameters was signi?cantly less than the value of 3 predicted by Murray’s law (arteries: 2.59; veins: 1.95). In NPDR, the best-?t exponent was close to 3 for arteries but close to 2 in healthy subjects in veins, (arteries: 3.09; veins: 2.16). For both small arteries and veins, diabetics’ exponent differed from healthy subjects (P < 0.01). Bifurcation angles in the healthy subjects (788 6 with a standard error (SE) of 0.98) were not much different than in NPDR (798 6 SE 1.38). The model based on minimizing pumping power predicted the measurements better than the one minimizing the vascular drag and lumen surface area. CONCLUSIONS. The relation between parent and daughter branch diameters changes in diabetes, but the branching angles do not.
关键词： adaptive optics scanning laser ophthalmoscopy,diabetic retinopathy,vascular branching,Murray’s law
更新于2025-09-10 09:29:36
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Improvement of the third order nonlinear optical properties of nematic liquid crystal under the influence of different compositional percentage of doped SWCNT and the external electric field
摘要： In this research, the nematic liquid crystal (NLC) was doped with varying concentration (0-1 % wt.) of single walled carbon nanotubes (SWCNTs) at room temperature to study the nonlinear optical (NLO) properties of E5CN7@CNT cell.The third order NLO properties such as the nonlinear susceptibility, the nonlinear refraction (NLR) and the nonlinear absorption (NLA) were determined by using Z-scan techniques. The nonlinear studies have been done using a continuous wave (CW) He: Ne laser at 632.8 nm.Doping SWCNTs to eutectic uniaxial NLC (E5CN7) enhanced the third order nonlinear susceptibility, ??(3) and consequently the nonlinearity properties of composite systems improved.It is found that at lower concentration of CNTs (c< 0.75 % wt.), the third order nonlinear susceptibility are increased, but for concentration 0. 5<c<1 % wt., the third order nonlinear susceptibility are decreased. The negative sign of the observed NLR index, indicates that the E5CN7@CNT exhibits self-defocusing type optical nonlinearity. The two photon absorption (TPA) behavior, corresponding to negative sign NLA of samples. The reorientation of samples molecules amplifies upon the application of electric field, then nonlinearity increases.
关键词： Composite materials,Nematic liquid crystal,Carbon nanotubes,Third order nonlinear susceptibility,Nonlinear optics,Electric field,Z-scan method
更新于2025-09-10 09:29:36
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Signal Processing for Fiber Optic Systems
摘要： This paper reviews the digital signal processing (DSP) methods used in coherent fiber optic communication systems. With the advances in high speed DSP, linear impairments such as chromatic dispersion (CD) and polarization mode dispersion (PMD) can be compensated for using fixed/adaptive equalizers. It is also possible to compensate for the interplay between dispersion and nonlinearity by digital back propagation (DBP), in which the virtual fibers whose signs of dispersion, loss and nonlinear coefficients are opposite of those of the transmission fiber, are realized in the digital domain by numerically solving the nonlinear Schr?dinger equation (NLSE). DSP equalization enhances the transmission performance and error-free reach of coherent fiber optic systems significantly.
关键词： Chromatic dispersion,nonlinear fiber optics,digital signal processing,fiber optic communications,perturbation techniques,polarization mode dispersion,digital back propagation,coherent communications
更新于2025-09-10 09:29:36
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[IEEE 2018 15th European Radar Conference (EuRAD) - Madrid, Spain (2018.9.26-2018.9.28)] 2018 15th European Radar Conference (EuRAD) - Simulation of Near Field RCS to Reproduce Measurement Condition
摘要： Different approaches are presented to simulate the near field Radar Cross Section (RCS) of a perfectly conducting electrically large object. This type of environment is usually found in measurements at large anechoic chambers where the far field condition cannot be achieved, making it impossible to approximate the incident field by a planewave. Each approach will be implemented with Physical Optics (PO) for extremely large targets and an accelerated version of the Method of Moments for moderately large objects. The fast MoM method are either the Multilevel Adaptive Cross Approximation (MLACA) for an iterative solution or the Multiscale Compressed Block Decomposition (MSCBD) for a direct solution. This development and the performed simulations have been done with CAPITOLE-RCS commercial software developed by NEXIO.
关键词： physical optics,method of moments,radar cross-sections,inverse synthetic aperture radar,Numerical simulation,anechoic chambers
更新于2025-09-10 09:29:36