Showing papers in "Applied Optics in 2018"

Terahertz detection of alcohol using a photonic crystal fiber sensor.

Abstract: Ethanol is widely used in chemical industrial processes as well as in the food and beverage industry. Therefore, methods of detecting alcohol must be accurate, precise, and reliable. In this content, a novel Zeonex-based photonic crystal fiber (PCF) has been modeled and analyzed for ethanol detection in terahertz frequency range. A finite-element-method-based simulation of the PCF sensor shows a high relative sensitivity of 68.87% with negligible confinement loss of 7.79×10−12 cm−1 at 1 THz frequency and x-polarization mode. Moreover, the core power fraction, birefringence, effective material loss, dispersion, and numerical aperture are also determined in the terahertz frequency range. Owing to the simple fiber structure, existing fabrication methods are feasible. With the outstanding waveguiding properties, the proposed sensor can potentially be used in ethanol detection, as well as polarization-preserving applications of terahertz waves.

Deep-learning-generated holography

Abstract: We present a method for computer-generated holography based on deep learning. The inverse process of light propagation is regressed with a number of computationally generated speckle data sets. This method enables noniterative calculation of computer-generated holograms (CGHs). The proposed method was experimentally verified with a phase-only CGH.

Nanoscale, tunable, and highly sensitive biosensor utilizing hyperbolic metamaterials in the near-infrared range.

Abstract: A plethora of research in recent years has been reported on biosensing in the surface plasmon resonant systems. However, very little research has reported a tunable and highly sensitive biosensor in a nanoscale platform. In this regard, we propose a nanoscale hyperbolic metamaterial (HMM)-based prism coupled waveguide sensor (PCWS) in the near-infrared range. The HMM layer makes up one of the constituents of the PCWS—comprised of a periodically arranged assembly of silver nanostrips. The structure is numerically simulated by the finite difference time domain method. It is demonstrated that the sensitivity of the reflected light can be tuned through the refractive index (RI) of the solution. Moreover, the effects of alteration of constituents of PCWS on the sensitivity have been analyzed. Results show that the sensitivity of PCWS can be harnessed by altering the thickness, slant angle of HMM layer, volume fraction (f) of metal in the HMM layer, and the incidence angle of light. For this purpose, the structure is numerically simulated by the finite difference time domain method. In the optimum design of the proposed sensor, the maximum value of sensitivity is achieved as high as S=3450 nm/refractive index unit with θ=10° and ϕ=10° and a metamaterial thickness of 250 nm. Moreover, the structure has a nanoscale footprint of 600 nm×400 nm×200 nm.

Multilayer graphene-based metasurfaces: robust design method for extremely broadband, wide-angle, and polarization-insensitive terahertz absorbers.

Abstract: In this study, by using an equivalent circuit method, a polarization-insensitive terahertz (THz) absorber based on multilayer graphene-based metasurfaces (MGBMs) is systematically designed, providing an extremely broad absorption bandwidth (BW). The proposed absorber is a compact, three-layer structure, comprising square-, cross-, and circular-shaped graphene metasurfaces embedded between three separator dielectrics. The equivalent-conductivity method serves as a parameter retrieval technique to characterize the graphene metasurfaces as the components of the proposed circuit model. Good agreement is observed between the full-wave simulations and the equivalent-circuit predictions. The optimum MGBM absorber exhibits >90% absorbance in an extremely broad frequency band of 0.55–3.12 THz (BW=140%). The results indicate a significant BW enhancement compared with both the previous metal- and graphene-based THz absorbers, highlighting the capability of the designed MGBM absorber. To clarify the physical mechanism of absorption, the surface current and the electric-field distributions, as well as the power loss density of each graphene metasurface, are monitored and discussed. The MGBM functionality is evaluated under a wide range of incident wave angles to prove that the proposed absorber is omnidirectional and polarization-insensitive. These superior performances guarantee the applicability of the MGBM structure as an ultra-broadband absorber for various THz applications.

D-shaped photonic crystal fiber plasmonic refractive index sensor based on gold grating

Abstract: In this work, we proposed a high-resolution D-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) sensor based on gold grating. Gold grating is introduced to modulate the resonance wavelength and enhance the refractive index (RI) sensitivity. Structure parameters of PCF and gold grating are analyzed by the finite element method for optimizing the SPR sensor. The simulation results indicate that air hole pitch, air hole diameter, and gold thickness and grating constant have little influence on the sensitivity of the refractive index, which reduces the requirement of precise processing. For improving the resolution of RI sensing, a two-feature (2F) interrogation method, which combines wavelength interrogation and amplitude interrogation, is used. The maximum theoretical resolution of the SPR sensor reaches to 5.98×10-6 RIU in the range of 1.36-1.38, and the wavelength sensitivity reaches to 3340 nm/RIU. The proposed SPR sensor shows potential applications for developing a high-sensitivity, real-time, and fast-response SPR-RI sensor.

Proposal for realizing an all-optical half adder based on photonic crystals.

Abstract: In this paper, we aim to propose an optical structure for realizing half-adder operation without using the nonlinear Kerr effect. Constructive and destructive interference of optical beams is the main working mechanism of the proposed structure. The phase difference required for the destructive interface will be created by choosing different lengths for the input waveguides of the XOR gate. For the proposed structure, the on-off contrast ratios for SUM and CARRY are 9.77 dB and 6.98 dB, respectively. Also, the delay time and footprint of the proposed structure are about 4 ps and 1056 μm2, respectively.

Optimized digital speckle patterns for digital image correlation by consideration of both accuracy and efficiency.

Abstract: The technique of digital image correlation (DIC), which has been widely used for noncontact deformation measurements in both the scientific and engineering fields, is greatly affected by the quality of speckle patterns in terms of its performance. This study was concerned with the optimization of the digital speckle pattern (DSP) for DIC in consideration of both the accuracy and efficiency. The root-mean-square error of the inverse compositional Gauss-Newton algorithm and the average number of iterations were used as quality metrics. Moreover, the influence of subset sizes and the noise level of images, which are the basic parameters in the quality assessment formulations, were also considered. The simulated binary speckle patterns were first compared with the Gaussian speckle patterns and captured DSPs. Both the single-radius and multi-radius DSPs were optimized. Experimental tests and analyses were conducted to obtain the optimized and recommended DSP. The vector diagram of the optimized speckle pattern was also uploaded as reference.

Dual-band tunable perfect metamaterial absorber based on graphene

Abstract: In this paper, a dual-band perfect metamaterial absorber based on graphene is proposed in the terahertz region. The metamaterial absorber consists of two sizes of graphene disks and a gold film separated by a dielectric spacer in a unit cell. The numerical results demonstrate that the dual-band perfect absorption can be achieved by the superposition of the specific absorption peaks induced by different disks. The resonance frequency can be tuned via controlling the graphene conductivity and the sizes of the disks. The metamaterial absorber can achieve selectively frequency tunability and it can tune each resonance independently. And the dual-band absorption will not be changed when the small disks move along the diagonal within the range of our research. In addition, owing to the symmetry of the structure, the absorber is insensitive to polarization and can keep a high absorptivity with a wide angle. The flexible and simple design makes it possible for our proposed single-layer graphene absorber to be applied in many metamaterial fields, such as sensing, detecting, and cloaking objects.

Efficient illumination angle self-calibration in Fourier ptychography.

Abstract: Fourier ptychography captures intensity images with varying source patterns (illumination angles) in order to computationally reconstruct large space-bandwidth-product images. Accurate knowledge of the illumination angles is necessary for good image quality; hence, calibration methods are crucial, despite often being impractical or slow. Here, we propose a fast, robust, and accurate self-calibration algorithm that uses only experimentally collected data and general knowledge of the illumination setup. First, our algorithm makes a fast direct estimate of the brightfield illumination angles based on image processing. Then, a more computationally intensive spectral correlation method is used inside the iterative solver to further refine the angle estimates of both brightfield and darkfield images. We demonstrate our method for correcting large and small misalignment artifacts in 2D and 3D Fourier ptychography with different source types: an LED array, a galvo-steered laser, and a high-NA quasi-dome LED illuminator.

On the use of deep neural networks in optical communications

Abstract: Information transfer rates in optical communications may be dramatically increased by making use of spatially non-Gaussian states of light. Here, we demonstrate the ability of deep neural networks to classify numerically generated, noisy Laguerre-Gauss modes of up to 100 quanta of orbital angular momentum with near-unity fidelity. The scheme relies only on the intensity profile of the detected modes, allowing for considerable simplification of current measurement schemes required to sort the states containing increasing degrees of orbital angular momentum. We also present results that show the strength of deep neural networks in the classification of experimental superpositions of Laguerre-Gauss modes when the networks are trained solely using simulated images. It is anticipated that these results will allow for an enhancement of current optical communications technologies.

Ultrahigh sensitivity refractive index sensor of a D-shaped PCF based on surface plasmon resonance.

Abstract: We propose a D-shaped photonic crystal fiber (PCF) refractive index sensor with ultrahigh sensitivity and a wide detection range. The gold layer is deposited on the polished surface, avoiding filling or coating inside the air holes of the PCF. The influences of the gold layer thickness and the diameter of the larger air holes are investigated. The sensing characteristics of the proposed sensor are analyzed by the finite element method. The maximum sensitivity can reach 31,000 nm/RIU, and the refractive index detection range is from 1.32 to 1.40. Our proposed PCF has excellent sensing characteristics and is competitive in sensing devices.

Graphene-based metasurface for a tunable broadband terahertz cross-polarization converter over a wide angle of incidence.

Abstract: In this paper, using a graphene-based metasurface, we demonstrate a unique design to develop a highly efficient, broadband, mid-infrared cross-polarization converter. The proposed graphene-based metasurface structure comprises periodical ϕ-shaped graphene on the top surface of a noble-metal-backed dielectric silicon dioxide (SiO2). The reported structure converts the incident linearly polarized wave into cross-polarized components with a peak polarization conversion ratio of more than 0.9 over a large band. Furthermore, the metasurface structure exhibits the full width at half-maximum bandwidth of 41.98% with respect to its center frequency of 5.98 THz. The physical insights behind electromagnetic polarization conversion are supported by field distributions and retrieved electromagnetic parameters. The structure works as a broadband cross-polarization converter up to 40° incident angle for both TE and TM polarizations. In addition, the structure is found to be as thin as ∼λ/6 with respect to lowermost frequency of the polarization conversion. The period of the unit cell is ∼λ/24 to support the fact that the structure can be treated as a metasurface.

Design of a plasmonic sensor based on a square array of nanorods and two slot cavities with a high figure of merit for glucose concentration monitoring.

Abstract: In this paper, a plasmonic nanosensor, by using a nanorod array in a square resonator coupled with two slot cavities, with properties for the detection of glucose concentration in water, is proposed and analyzed. We investigated the sensing feature by changing the concentration of the glucose from 0 to 60%. Obtained results show that, by placing different water samples in a square resonator and two cavities, resonance wavelengths can be changed. These resonances demonstrate different dependence on the glucose concentration of water samples. Further, varying the physical parameters of the configuration can also change the resonance wavelength and can be simply tuned. These features recommend flexibility to propose the structure. Simulation results show that the values of sensitivity and figure of merit can be obtained as 892 nm/RIU and 3.5×106 RIU−1, respectively, which can help researchers to discover applications in the plasmonic sensor domain.

Fiber-coupled vapor cell for a portable Rydberg atom-based radio frequency electric field sensor.

Abstract: We demonstrate a movable, Rydberg atom-based radio frequency (RF) electric (E) field probe. The technique is based on electromagnetically induced transparency and Autler–Townes splitting. Two fibers attached to a 10 mm cubic Cs133 vapor cell are used to couple counter-propagating probe and control lasers through the cell. This all-dielectric fiber-coupled sensor can be moved from the optics table to locations more suitable for RF (gigahertz to sub-terahertz) E-field measurements and calibrations.

Zeonex-based asymmetrical terahertz photonic crystal fiber for multichannel communication and polarization maintaining applications.

Abstract: We report on the design, in-depth analysis, and characterization of a novel elliptical array shaped core rectangular shaped cladded photonic crystal fiber (PCF) for multichannel communication and polarization maintaining applications of terahertz waves. The asymmetrical structure of air holes in both core and cladding results in increased birefringence, while a compact geometry and different cladding air hole size makes the dispersion characteristic flat. The modal characteristics of the PCF are calculated using a finite element method. The simulated results show a near-zero dispersion flattened property of ±0.02 ps/THz/cm, high birefringence of 0.063, low effective material loss of 0.06 cm−1, and negligible confinement loss of 5.45×10−13 cm−1 in the terahertz frequency range. Additionally, the core power fraction, effective area, physical attributes, and potential fabrication possibilities of the fiber are discussed.

Polymer-optical-fiber-based sensor system for simultaneous measurement of angle and temperature.

Abstract: This paper presents a polymer-optical-fiber (POF)-based sensor system for simultaneous measurement of angle and temperature. The main contribution is obtaining a sensor with higher temperature sensitivity and lower hysteresis on the angle measurements. The annealing was made on the fibers under the conditions of low relative humidity and under water, and a third set of samples without any heat treatment was applied for comparison with the annealed ones. Results of temperature and angle characterization show that the fibers annealed under water presented higher temperature sensitivity and lower errors when compared with the fibers annealed with low humidity or the fibers without annealing. Furthermore, the fibers annealed under water also presented lower hysteresis on the angle characterization. For these reasons, such fibers were employed for the temperature and angle measurements, which results in a sensor system capable of simultaneously measuring the angle and temperature with root-mean-squared error of 0.82°C for temperature and 2.20° for angle, which is further reduced to 1.20° after the application of a dynamic compensation technique for POF curvature sensors.

High-sensitivity birefringent and single-layer coating photonic crystal fiber biosensor based on surface plasmon resonance.

Abstract: A birefringent single-layer coating photonic crystal fiber biosensor based on surface plasmon resonance is proposed to realize high sensitivity, which is easy to implement, in that only gold is deposited externally. The birefringent nature of the structure provides the sensor with high sensitivity. The results show that the biosensor can obtain the wavelength sensitivity of 15180 nm/refractive index unit (RIU) and high linearity with the analyte RI range of 1.40–1.43, corresponding to the resolution of 5.6818×10−6 RIU. Owing to the high sensitivity and simple structure, the proposed sensor can find important applications in biochemical and biological analyte detection.

Design of a large aperture tunable refractive Fresnel liquid crystal lens.

Abstract: A large aperture tunable lens based on liquid crystals, which is considered for near-to-eye applications, is designed, built, and characterized. Large liquid crystal lenses with high quality are limited by very slow switching speeds due to the large optical path difference (OPD) required. To reduce the switching time of the lens, the thickness is controlled through the application of several phase resets, similar to the design of a Fresnel lens. A main point of the paper is the design of the Fresnel structure to have a minimal effect on the image quality. Our modeling and experimental results demonstrate that minimal image degradation due to the phase resets is observable when the segment spacing is chosen by taking into account human eye resolution. Such lenses have applications related to presbyopia and, in virtual reality systems, to solve the well-known issue of accommodation–convergence mismatch.

Single-image-based nonuniformity correction of uncooled long-wave infrared detectors: a deep-learning approach.

Abstract: Fixed-pattern noise (FPN), which is caused by the nonuniform opto-electronic responses of microbolometer focal-plane-array (FPA) optoelectronics, imposes a challenging problem in infrared imaging systems. In this paper, we successfully demonstrate that a better single-image-based non-uniformity correction (NUC) operator can be directly learned from a large number of simulated training images instead of being handcrafted as before. Our proposed training scheme, which is based on convolutional neural networks (CNNs) and a column FPN simulation module, gives rise to a powerful technique to reconstruct the noise-free infrared image from its corresponding noisy observation. Specifically, a comprehensive column FPN model is utilized to depict the nonlinear characteristics of column amplifiers in the readout circuit of FPA. A large number of high-fidelity training images are simulated based on this model and the end-to-end residual deep network is capable of learning the intrinsic difference between undesirable FPN and original image details. Therefore, column FPN can be accurately estimated and further subtracted from the raw infrared images to obtain NUC results. Comparative results with state-of-the-art single-image-based NUC methods, using real-captured noisy infrared images, demonstrate that our proposed deep-learning-based approach delivers better performances of FPN removal, detail preservation, and artifact suppression.

3D-printed polymer antiresonant waveguides for short-reach terahertz applications

Abstract: In this work, we present a 3D-printed waveguide that provides effective electromagnetic guidance in the THz regime. The waveguide is printed using low-cost polycarbonate and a conventional fused deposition modeling printer. Light guidance in the hollow core is achieved through antiresonance, and it improves the energy effectively transported to the receiver compared to free space propagation. Our demonstration adds to the field of 3D-printed terahertz components, providing a low-cost way of guiding terahertz radiation.

Ultra-fast all-optical decoder based on nonlinear photonic crystal ring resonators

Abstract: In this paper, a 2-to-4 all-optical decoder based on photonic crystal ring resonators is introduced. The photonic crystal structure has a 2D square chalcogenide rod lattice whose maximum response time is 2 ps. Three ring resonators including nonlinear rods with 9×10-17 m2/W for a Kerr coefficient carry out a switching operation at 1550 nm wavelength. The switching speed of the device is 500 GHz, which is more than that in previously presented works. Also, the small size of the structure is sufficient for optical integrated circuits.

Polymer-coated FBG sensor for simultaneous temperature and strain monitoring in composite materials under cryogenic conditions.

Abstract: A polymer-coated fiber Bragg grating (PCFBG) is examined for real-time temperature and strain monitoring in composite materials at cryogenic temperatures. The proposed sensor enables the simultaneous measurement of temperature and strain at extremely low temperatures by tracking the changes in the reflected center wavelengths from a pair of PCFBGs embedded in a composite material. The cryogenic temperature sensing was realized by introducing polymer coatings onto bare FBGs, which resulted in high temperature sensitivity under cryogenic conditions. A comparison of wavelength responses of the Bragg grating with and without a polymer coating toward temperatures ranging from 25°C to −180°C was performed. The polymer-coated FBG exhibited a sensitivity of 48 pm/°C, which is 10 times greater than that of the bare FBGs. In addition, the encapsulation of the FBG in a capillary tube made it possible to evaluate the strain accumulated within the composite during operation under cryogenic conditions.

Acousto-optic tunable filter spectrometers in space missions [Invited].

Abstract: Spectrometers employing acousto-optic tunable filters (AOTFs) rapidly gain popularity in space, and in particular on interplanetary missions. They allow for reducing volume, mass, and complexity of the instrumentation. To date, space operations of 11 AOTF spectrometers are reported in the literature. They were used for analyzing ocean color, greenhouse gases, atmospheres of Mars and Venus, and for lunar mineralogy. More instruments for the Moon, Mars, and asteroid mineralogy are in flight, awaiting launch, or in the state of advanced development. The AOTFs are used in point (pencil-beam) spectrometers for selecting echelle diffraction orders, or in hyper-spectral imagers and microscopes. We review the AOTF-employing devices flown in space or ready to set off. The paper considers basic principles of the AOTF and science applications of the AOTF spectrometers, and describes developed instruments in some detail. We also address some advanced developments for future missions and plans. In addition, we discuss lessons learned during instrument design, build, calibration, and exploitation, and advantages and limitations in implementing the AOTF-based systems in space instrumentation.

Simultaneous polarimeter retrievals of microphysical aerosol and ocean color parameters from the "MAPP" algorithm with comparison to high-spectral-resolution lidar aerosol and ocean products.

Abstract: We present an optimal-estimation-based retrieval framework, the microphysical aerosol properties from polarimetry (MAPP) algorithm, designed for simultaneous retrieval of aerosol microphysical properties and ocean color bio-optical parameters using multi-angular total and polarized radiances. Polarimetric measurements from the airborne NASA Research Scanning Polarimeter (RSP) were inverted by MAPP to produce atmosphere and ocean products. The RSP MAPP results are compared with co-incident lidar measurements made by the NASA High-Spectral-Resolution Lidar HSRL-1 and HSRL-2 instruments. Comparisons are made of the aerosol optical depth (AOD) at 355 and 532 nm, lidar column-averaged measurements of the aerosol lidar ratio and Angstrom exponent, and lidar ocean measurements of the particulate hemispherical backscatter coefficient and the diffuse attenuation coefficient. The measurements were collected during the 2012 Two-Column Aerosol Project (TCAP) campaign and the 2014 Ship-Aircraft Bio-Optical Research (SABOR) campaign. For the SABOR campaign, 73% RSP MAPP retrievals fall within ±0.04 AOD at 532 nm as measured by HSRL-1, with an R value of 0.933 and root-mean-square deviation of 0.0372. For the TCAP campaign, 53% of RSP MAPP retrievals are within 0.04 AOD as measured by HSRL-2, with an R value of 0.927 and root-mean-square deviation of 0.0673. Comparisons with HSRL-2 AOD at 355 nm during TCAP result in an R value of 0.959 and a root-mean-square deviation of 0.0694. The RSP retrievals using the MAPP optimal estimation framework represent a key milestone on the path to a combined lidar+polarimeter retrieval using both HSRL and RSP measurements.

Large depth of focus dynamic micro integral imaging for optical see-through augmented reality display using a focus-tunable lens.

Abstract: We have developed a three-dimensional (3D) dynamic integral-imaging (InIm)-system-based optical see-through augmented reality display with enhanced depth range of a 3D augmented image A focus-tunable lens is adopted in the 3D display unit to relay the elemental images with various positions to the micro lens array Based on resolution priority integral imaging, multiple lenslet image planes are generated to enhance the depth range of the 3D image The depth range is further increased by utilizing both the real and virtual 3D imaging fields The 3D reconstructed image and the real-world scene are overlaid using an optical see-through display for augmented reality The proposed system can significantly enhance the depth range of a 3D reconstructed image with high image quality in the micro InIm unit This approach provides enhanced functionality for augmented information and adjusts the vergence-accommodation conflict of a traditional augmented reality display

Lensless light-field imaging with Fresnel zone aperture: quasi-coherent coding

Abstract: We propose a new type of lensless camera enabling light-field imaging for focusing after image capture and show its feasibilities with some prototyping. The camera basically consists only of an image sensor and Fresnel zone aperture (FZA). Point sources making up the subjects to be captured cast overlapping shadows of the FZA on the sensor, which result in overlapping straight moire fringes due to multiplication of another virtual FZA in the computer. The fringes generate a captured image by two-dimensional fast Fourier transform. Refocusing is possible by adjusting the size of the virtual FZA. We found this imaging principle is quite analogous to a coherent hologram. Not only the functions of still cameras but also of video cameras are confirmed experimentally by using the prototyped cameras.

High-power visibly emitting Pr3+:YLF laser end pumped by single-emitter or fiber-coupled GaN blue laser diodes

Abstract: We demonstrate the high-power continuous-wave operation of a Pr3+:YLF laser end pumped by blue laser diodes. As the pump source, we used four 5 W single-emitter blue laser diodes and a >20 W fiber-coupled module. In single-emitter-diode pumping, we obtained pump-limited output powers of 6.7 and 3.7 W at 640 and 607 nm, respectively. We successfully suppressed thermal aberration and obtained an output power of 3.4 W at a slope efficiency of 25% at 640 nm with good beam quality in the fiber-coupled module pumping.

Holographic waveguide heads-up display for longitudinal image magnification and pupil expansion.

Abstract: The field of view of traditional heads-up display systems is limited by the size of the projection optics. Our research is focused on overcoming this limitation by coupling image-bearing light into a waveguide using holographic elements, propagating the light through that waveguide, and extracting the light several times with additional holographic optical elements. With this configuration, we demonstrated both longitudinal magnification and pupil expansion of the heads-up display. We created a ray-trace model of the optical system to optimize the component parameters and implemented the solution in a prototype that demonstrates the merit of our approach. Longitudinal magnification is achieved by encoding optical power into the hologram injecting the light into the waveguide, while pupil expansion is obtained by expanding the size of the hologram extracting the light from the waveguide element. To ensure uniform intensity of the image, the diffraction efficiency of the extracting hologram is modulated according to the position. Our design has a 12°×8° field of view at a viewing distance of 10 in. (250 mm), with infinite longitudinal magnification and a 1.7× lateral pupil expansion.

Adaptive beam control techniques for airborne free-space optical communication systems

Abstract: In this paper, we study two adaptive beam control techniques, where the beam divergence angle is adjusted at the transmitter to (i) maximize link availability or (ii) minimize transmitter power while maintaining target link availability. For this purpose, we provide closed-form expressions about the link availability and optimum beam divergence angle under the effect of generalized two-dimensional Gaussian distribution of the alignment error between the transmitter and receiver. These simple and closed-form expressions reduce the computational complexity for performance optimization. Thus, they can be used to (i) reduce the power consumption required for adaptive beam control and (ii) facilitate the fast operation of the control techniques. The results show that the adaptive beam control techniques can improve system performance under various scenarios.

Phaseless computational ghost imaging at microwave frequencies using a dynamic metasurface aperture.

Abstract: We demonstrate a dynamic metasurface aperture as a unique tool for computational ghost imaging at microwave frequencies. The aperture consists of a microstrip waveguide loaded with an array of metamaterial elements, each of which couples energy from the waveguide mode to the radiation field. With a tuning mechanism introduced into each independently addressable metamaterial element, the aperture can produce diverse radiation patterns that vary as a function of tuning state. Here, we show that fields from such an aperture approximately obey speckle statistics in the radiative near field. Inspired by the analogy with optical correlation imaging, we use the dynamic aperture as a means of illuminating a scene with structured microwave radiation, receiving the backscattered intensity with a simple waveguide probe. By correlating the magnitude of the received signal with the structured intensity patterns, we demonstrate high-fidelity, phaseless imaging of sparse targets. The dynamic metasurface aperture as a novel ghost imaging structure can find application in security screening, through-wall imaging, as well as biomedical diagnostics.