Rectangular Aperture Research Articles

A Full-Aperture Image Synthesis Method for the Rotating Rectangular Aperture System Using Fourier Spectrum Restoration

The novel rotating rectangular aperture (RRA) system provides a good solution for space-based, large-aperture, high-resolution imaging tasks. Its imaging quality depends largely on the image synthesis algorithm, and the mainstream multi-frame deblurring approach is sophisticated and time-consuming. In this paper, we propose a novel full-aperture image synthesis algorithm for the RRA system, based on Fourier spectrum restoration. First, a numerical simulation model is established to analyze the RRA system’s characteristics and obtain the point spread functions (PSFs) rapidly. Then, each image is used iteratively to calculate the increment size and update the final restored Fourier spectrum. Both the simulation’s results and the practical experiment’s results show that our algorithm performs well in terms of objective evaluation and time consumption.

Computational vector fiducial for deflectometry system alignment.

One of deflectometry's cardinal strengths is its ability to measure highly dynamically sloped optics without needing physical null references. Accurate surface measurements using deflectometry, however, require precise calibration processes. In this Letter, we introduce an alignment technique using a computational fiducial to align a deflectometry system without additional hardware equipment (i.e., algorithmic innovation). Using the ray tracing program, we build relationships between the plane of the screen and detector and algorithmically generate a fiducial pattern for the deflectometry configuration. Since the fiducial pattern is based on ideal system geometry, misalignment of the unit under test with its target position causes a discrepancy between the actual image on the camera detector and the ideal fiducial image. We leverage G and C vector polynomials to quantify misalignment and estimate the alignment status through a reverse optimization method. Simulation and experimental results demonstrate that the proposed algorithm can align the 195mm×80mm of a rectangular aperture freeform optic within 10 µm of peak-to-valley accuracy. The computational fiducial-based alignment algorithm is simple to apply and can be an essential procedure for conventional methods of deflectometry system alignment.

Comparison of numerical integration methods for calculating diffraction of a plane electromagnetic wave by a rectangular aperture

We discuss features of the calculation of a Fraunhofer integral by traditional quadrature numerical integration methods and a special collocation Levin method when calculating the diffraction of a plane electromagnetic wave by a rectangular aperture. For the quadrature numerical integration methods, a criterion for the assessment of the integration step is derived depending on the screen size and required calculation accuracy. Advantages of the use of the special collocation Levin method in comparison with the traditional quadrature numerical integration methods are shown.

Measuring the topological charge and ellipticity of elliptic vortex

The intensities and phase profiles of the elliptic optics vortex beam both are determined by the topological charge (TC) and ellipticity. This paper presents an efficient and simple method for measuring the TC and ellipticity of elliptic vortex. By observing the diffraction patterns, the TC modulus and ellipticity can be probed with the suitable rectangular aperture, and the TC sign can be detected with the suitable right triangular aperture. The scheme works well even for high-order elliptic vortex with topological charge value as high as ± 18, and ellipticity range from 0.5 to 2 at least. Obviously, the measurement of TC and ellipticity have important research value for promoting the application of elliptical vortex.

X-band TE101 rectangular aperture cavity for in vivo EPR tooth dosimetry after radiation emergency

The TE101 mode rectangle EPR cavity was newly developed to achieve X-band in vivo EPR tooth dosimetry for the rescue of nuclear emergency. An aperture for sample detection was opened on the cavity's surface. Its characteristics were evaluated by measuring DPPH and intact human incisor samples. Remarkable radiation induced signal from EPR spectrum of 1Gy–8Gy irradiated teeth was observed. In vivo measurements of rat was performed to verify its application for in vivo tooth dosimetry.

Driving methods for liquid crystal lens with rectangular aperture and four voltages

The driving methods for a liquid crystal lens with a rectangular aperture and four applied voltages are discussed. The properties of the liquid crystal lens can be controlled by amplitudes, phases, and frequencies of the voltages. Three driving methods, including the amplitude method, phase method, and constant voltage method, are used to tune the focal length. The advantage of these methods is that the effective voltage in the aperture center can be controlled to be greater than the liquid crystal threshold voltage without applying a bias voltage. It is found that the constant voltage method to tune the lens by the phases and the amplitudes of the four voltages in sync keeping a constant voltage in the aperture center leads to lower optical aberrations and shorter response time.

High-Order Bandpass Polarization Rotator Based on Aperture-Coupled Patch Resonators

In this letter, a low-profile 90° polarization rotator with a fourth-order bandpass filtering response is proposed by using aperture-coupled patch resonators elements. The presented polarization rotator is constituted on a five-layer structure consists of two orthogonal rectangular apertures etched on two different layers, and are sandwiched between two single-mode square patch resonators and a dual-mode corner-truncated square patch resonator. Moreover, the property of 90° polarization rotation is obtained by properly exciting two orthogonal modes within the corner-truncated square patch resonator and the polarization selective characteristic of two orthogonal rectangular apertures. The proposed polarization rotator is designed and analyzed with the direct coupling matrix method. To validate the design concept, a design example is fabricated and measured. Measured results well reveal that our proposed structure has its attractive advantages of ultrathin profile, high-order filtering response, high polarization purity, and stable performance under oblique incidence.

Topological antennas: Aperture radiators, leaky-wave surfaces, and orbital angular momentum beam generation

The emerging field of topological photonics has extended our capability to control and manipulate electromagnetic waves. Thus far, however, research has focused on realizing defect-immune waveguides for on-chip communication. Making similar advancement for antennas, which are an integral component and crucial to the performance of wireless devices, could lead to a parallel impact on wireless communication. In particular, the requirement for impedance matching that is fundamental to current antenna technology constitutes a major limitation to transmitting and receiving free-space signals in terms of bandwidth and power efficiency. Here, we show how reciprocal photonic topological insulator (PTI) metasurfaces can be designed to enable a unique radiation mechanism needless of impedance matching. This relies on the fact that counter-propagating spin states are decoupled from each other; hence, this self-matching characteristic spans the entire bandwidth of the PTI’s bandgap. Specifically, we present two strategies for out-coupling spin-polarized edge modes: (1) in the form of an end-fire antenna at the abrupt termination of the PTI with free space and (2) in the form of a leaky-wave antenna by engineering the dispersion of the edge mode to lie above the light line. In the first approach, we compare our results to conventional rectangular waveguide apertures and planar Vivaldi antennas, which either have a large profile or flared ends to obtain gradual impedance matching. In the second approach, we demonstrate how our structure can emit orbital angular momentum (OAM) beams with various orbital charge numbers by simply varying the length of the PTI interface when made into a circular loop. The reduced device area and complexity due to removing the need for any matching network and the ability to easily multiplex OAMs of any charge, in addition to the wideband and high efficiency performance, make the proposed topological antennas highly attractive for many applications.

Moiré microstructure generated binary amplitude gratings for suppression of high diffraction orders

We propose 2D gratings with 2D sinusoidal-like transmittance for spectral analysis in a wide wavelength range. Our design deploys the concept of the multiplicative superimposition of two mutually inclined or orthogonally crossed 1D binary amplitude gratings with appropriately selected opening numbers. In result the trapezoidal transmittance function without the 3rd and even harmonics is obtained in two perpendicular directions corresponding to the so-called subtractive and additive moiré patterns. The distance between main diffraction orders, i.e., -1, 0 and +1 in both directions is easily controlled by adjusting the angle between component grating lines. The moiré microstructure acting as 2D diffraction grating comprises 4 sided parallelogram holes up to the angle of 90 degrees for which they become rectangles. Diffraction efficiencies and free-standing parameters of our grating and the solutions reported in the literature, i.e., the inclined rectangular aperture grating (IRAG) and the grating with hexagonal holes are calculated and compared. Additionally, the methods of design for the literature reported gratings which start from square or rectangular shape apertures are introduced for the sake of comprehensive treatment of gratings with suppressed high diffraction orders. Design considerations are corroborated by the moiré Fourier spectra numerical simulations, their visualizations and experimental works.

Fraunhofer diffraction simulation of a vortex beam through any apertures

A general Matlab program is designed to simulate the Fraunhofer diffraction patterns of a vortex beam through any apertures, which are usually used to compare with the experimental results in detecting the topological charge of a vortex beam. Two significant matrices are suggested in the above program: one related to the aperture, the other concerned with the field of vortex beam. Using the fast Fourier transform function provided within the Matlab software itself to process the dot product of the above two matrices, one obtains the field on the observation screen. The program is applied to a rectangular aperture and an annular triangle aperture. The results agree well with the computational analysis of previous references. This paper is to describe how Matlab can be used to perform complex mathematical calculations without bogging down the student with the details of the numerical methods and it may be particularly useful for both upper-level undergraduates and graduate students who engage in the study of topological charge detection and identification.

Compact Full Ka-Band Waveguide Directional Coupler Based on Rectangular Aperture Array with Stairs.

This article presents a compact 3 dB waveguide directional coupler with full waveguide bandwidth. It consists of a pair of rectangular waveguides with stairs structures in the coupling region. The waveguides are placed parallel to each other along their broad wall, which has a rectangular aperture array. The compact size, broad bandwidth, good in-band coupling flatness, and good return loss are achieved by using the proposed structure. For verification purposes, a prototype of the proposed coupler was designed, manufactured, and measured. The experimental results show that over the full waveguide bandwidth a return loss of input port better than 17.46 dB, coupling strength varying between −2.74 dB and −3.80 dB, power-split unbalance within 0.76 dB, and an isolation better than 20.82 dB were obtained. The length of the coupling region was only 15.82 mm.

Metamaterial inspired dielectric resonator MIMO antenna for isolation enhancement and linear to circular polarization of waves

In this communication, a novel dielectric resonator-based multiple-input-multiple- output antenna with a metasurface module (Meta-MIMO) is investigated and analyzed. Dielectric resonator antenna is excited through a rectangular aperture and creates HEM11δ mode inside the ceramic. The salient features of the proposed configuration are: (a) metasurface module converts the linear polarized waves into circularly polarized waves; (b) suspended metasurface improves the isolation value between the antenna ports. It is verified from the measured results that the proposed antenna operates well over the 3.8–4.2 GHz frequency range. Different diversity parameters are within the desired limit, which confirms it as an efficient MIMO radiator.

Isolating and enhancing single-photon emitters for 1550nm quantum light sources using double nanohole optical tweezers.

Single-photon sources are required for quantum technologies and can be created from individual atoms and atom-like defects. Erbium ions produce single photons at low-loss fiber optic wavelengths, but they have low emission rates, making them challenging to isolate reliably. Here, we tune the size of gold double nanoholes (DNHs) to enhance the emission of single erbium emitters, achieving 50× enhancement over rectangular apertures previously demonstrated. This produces enough enhancement to show emission from single nanocrystals at wavelengths not seen in our previous work, i.e., 400 and 1550nm. We observe discrete levels of emission for nanocrystals with low numbers of emitters and demonstrate isolating single emitters. We describe how the trapping time is proportional to the enhancement factor for a given DNH structure, giving us an independent way to measure the enhancement. This shows a promising path to achieving single emitter sources at 1550nm.

3D-Printed Quasi-Absolute Electromagnetic Encoders for Chipless-RFID and Motion Control Applications

This paper presents electromagnetic encoders useful for chipless-RFID and motion control applications. The encoders consist in a pair of linear chains of rectangular apertures implemented by means of 3D printing. One of these chains is periodic and acts as a clock, whereas the other chain contains an identification (ID) code. With these two aperture chains, the ID code can be synchronously read, so that the relative velocity between the tag and the reader is irrelevant. Additionally, it is shown in the paper that by properly designing the reader, it is possible to determine the motion direction. The sensitive part of the reader is a microstrip line loaded with three complementary split ring resonators (CSRRs) etched in the ground plane and fed by three harmonic signals. By encoder motion, the characteristics of the local medium surrounding the CSRRs are modified, and the harmonic signals are amplitude modulated (AM) at the output port of the line, thereby providing the clock signal (which gives the encoder velocity), the ID code (providing also the quasi-absolute position) and the direction of motion. A fabricated prototype encoder is characterized by reading it with a dedicated reader.

RISE: robust iterative surface extension for sub-nanometer X-ray mirror fabrication.

Precision optics have been widely required in many advanced technological applications. X-ray mirrors, as an example, serve as the key optical components at synchrotron radiation and free electron laser facilities. They are rectangular silicon or glass substrates where a rectangular Clear Aperture (CA) needs to be polished to sub-nanometer Root Mean Squared (RMS) to keep the imaging capability of the incoming X-ray wavefront at the diffraction limit. The convolutional polishing model requires a CA to be extended with extra data, from which the dwell time is calculated via deconvolution. However, since deconvolution is very sensitive to boundary errors and noise, the existing surface extension methods can hardly fulfill the sub-nanometer requirement. On one hand, the figure errors in a CA were improperly modeled during the extension, leading to continuity issues along the boundary. On the other hand, uncorrectable high-frequency errors and noise were also extended. In this study, we propose a novel Robust Iterative Surface Extension (RISE) method that resolves these problems with a data fitting strategy. RISE models the figure errors in a CA with orthogonal polynomials and ensures that only correctable errors are fit and extended. Combined with boundary conditions, an iterative refinement of dwell time is then proposed to compensate the errors brought by the extension and deconvolution, which drastically reduces the estimated figure error residuals in a CA while the increase of total dwell time is negligible. To our best knowledge, RISE is the first data fitting-based surface extension method and is the first to optimize dwell time based on iterative extension. An experimental verification of RISE is given by fabricating two elliptic cylinders (10 mm × 80 mm CAs) starting from a sphere with a radius of curvature around 173 m using ion beam figuring. The figure errors in the two CAs greatly improved from 204.96 nm RMS and 190.28 nm RMS to 0.62 nm RMS and 0.71 nm RMS, respectively, which proves that RISE is an effective method for sub-nanometer level X-ray mirror fabrication.

Rotated rectangular aperture imaging through multi-frame blind deconvolution with Hyper-Laplacian priors.

Rotated rectangular aperture imaging has many advantages in large aperture telephoto systems due to its lower cost and lower complexity. This technology makes it possible to build super large aperture telescopes. In this paper, we combine the ideas of deblurring with rotated rectangular aperture imaging and propose an image synthesis algorithm based on multi-frame deconvolution. In the specific reconstruction process, Hyper-Laplacian priors and sparse priors are used, and an effective solution is developed. The simulation and real shooting experiments show that our algorithm has excellent performance in visual effect and objective evaluation. The synthetic images are significantly sharper than the results of the existing methods.

A Novel Single Layer Wideband Reflectarray Design Using Two Degrees of Freedom Elements

A broadband linearly polarized single-layer reflectarray antenna constructed with element cells of spiral-dipoles is presented in this communication. The proposed method achieves the phase change requirements by continuously adjusting the two degrees of freedom (TDF) elements. Then, a linear and smooth phase response covering 360° is obtained by adjusting the TDF. Furthermore, by introducing four rectangular rings around the spiral-dipoles, a relatively slow phase change slope can be obtained and the maximum differences between the achieved phase acquired by element and ideal phase at 6.5 and 9.5 GHz are 20° and 58°, respectively, enlarging the operating bandwidth. A reflectarray prototype with a rectangular aperture of 300 mm in diameter is designed, fabricated, and experimentally verified. The results include a measured gain of 26.5 dBi at 8 GHz with an aperture efficiency of 55%; the 1 dB gain bandwidth can reach 35%. The proposed structure can be extrapolated to higher frequencies due to its single-layer performance. Its benefits include a reduction in manufacturing costs and the mitigation of alignment errors.

Near-Field Transverse Resolution in Planar Source Reconstructions

This article deals with the classical question of estimating the achievable resolution in terms of the configuration parameters in inverse source problems. In particular, the study focuses on the case of a planar surface magnetic current which is to be reconstructed from near-field observed over a bounded rectangular aperture parallel to the source domain. Resolution formulas are well known for far-field or Fresnel-zone configurations, and also for near-field cases, when data are full-view or a measurement aperture is an unbounded plane. For the case of bounded near-field observations, the resolution estimations mainly rely on some asymptotic arguments in order to mimic far-field reasoning. Here, the plan is to improve these results and to work out a resolution estimation that precisely captures the spatially varying behavior entailed by the near-field and aspect-limited configuration. To this end, the pertinent radiation operator is inverted by an adjoint inversion scheme (a back-propagation-like method) and the corresponding point-spread function is analytically estimated. Numerical examples show that the derived resolution estimation clearly points out the role of the geometrical parameters of the configuration and it is more accurate than other literature results.

Progress on the Upgrade of EDIPO, a 15 T Large Aperture Dipole

The upgraded magnet assembly of the EDIPO test facility aims at generating 15 T at 4.2 K and 85% of short sample limit in a large rectangular aperture and over a uniform field length of 1000 mm. During 2020 the design studies have concentrated on two flared-end block-coil design options with four double-pancake coils, two per pole. The coils are planned to be produced using Nb3Sn Rutherford cable with 44 × 1.1 mm diameter strands, which results in significantly larger dimensions compared to the typical cables used in accelerator magnets. Two sections of dummy superconducting cable have been produced, and dedicated tooling was developed to study the wind-ability of such high aspect ratio cable and provide input to define the geometrical parameters of the coil flared ends. This paper describes two magnet designs proposed for EDIPO focusing on the magnetic and the mechanical design.

Topological Dislocations for Plasmonic Mode Localization in Arrays of Nanoscale Rectangular Au Apertures: Implications for Optical Communications

We study the localization of plasmonic modes on topological dislocations obtained by an abrupt change in the geometry of unit cells in a plasmonic metasurface comprised of a nanoscale array of rect...