Beam Steering Elements Research Articles

Design and development of a low-cost hyperspectral imaging setup via a machine-learningbased approach

This article presents a potential solution for developing a low-cost hyperspectral imaging (HSI) setup by preserving pertinent information acquired from a conventional hyperspectral imaging setup. Conventional hyperspectral images (HSI) of three different types of leaves, gongura (Hibiscus sabdariffa), amaranthus (Amaranthus viridis), and banana (Musa acuminata) were acquired with 204 wavelengths/bands. The spectra are processed using linear discriminant analysis (LDA) to find a set of signature wavelengths for leaf classification. Afterwards, 20 visible range wavelengths (440 to 700 nm) were found to be incorporated into a low-cost setup involving a monochromator, beam steering elements, and a smartphone camera with associated machine learning (ML) classifiers. For building the datasets, we extracted 90 spectra from the images captured using the conventional HSI setup under the full spectra range (397 nm to 1003 nm). Similarly, 90 spectra were extracted from the images captured from the low-cost setup under the 20 signature wavelengths. For further experimentation, we split the datasets into Dataset-A, containing 70% of the total spectra, and the remaining 30% in Dataset-B for HSI as well as low-cost setup. Dataset- B was reserved to evaluate the robustness of the classifiers on an unseen dataset. LDA surpasses the other classifiers in leaves classification for HSI as well as low-cost setup. For the HSI setup, LDA achieved a 100% average score for performance matrices (classification accuracy, precision, Recall, and F1-score) on dataset A as well as on dataset B. Moreover, for the low-cost setup, LDA achieved 98.33% ± 4.99% classification accuracy, 98.89% ± 3.33% precision, 98.33% ± 4.99% recall, and 98.22% ± 5.33% F1-score on dataset A. Additionally, LDA achieved 96.29% classification accuracy, 96.67% precision, 96.29% recall, and 96.28% F1-score for dataset B. The promising results indicated that the low-cost set-up closely emulates the HSI system’s performance in terms of performance metrics, delivering a low-cost HSI system for various applications in the future.

Non-Mechanical Multiplexed Beam-Steering Elements Based on Double-Sided Liquid Crystal Metasurfaces

We propose, optimize, fabricate and test beam-steering elements based on double-sided liquid-crystal (LC) metasurfaces allowing for diffractive and spectral multiplexing, and thus covering three different beam deflection directions each. While straightforward parallel design requires one diffractive beam-steering element per a direction determined by Bragg’s law, double-sided LC-metasurfaces are remarkably flexible and allow optimization for three operation modes at different applied voltages: zero-voltage mode with dominant +1 order red light and +2 order blue light diffraction; intermediate mode at 1.4–1.6 V voltage with dominant +1 order blue light diffraction; and transparent mode at 5 V voltage. We comprehensively study three such elements with 6, 8 and 10 micrometer periods and verify their capability of deflecting blue and red light beams with 40–70% efficiencies in nine target directions with 10 ms characteristic switching times.

Achromatic doublet electrowetting prism array for beam steering device in foveated display.

A foveated display is a technology that can solve the problem of insufficient angular resolution (relative to the human eye) for near-eye display. In a high-resolution foveated display, a beam steering element is required to track the human gaze. An electrowetting prism array is a transmissive non-mechanical beam steering device, that allows a light and compact optical system to be configured and a large aperture possible. However, the view is obstructed by the sidewall of the prism array. When the size of the cell prism is 7mm, the prism array has an 87% fill-factor. To push the fill-factor to 100%, the cell prisms were magnified using a lens array. Image processing was performed such that the image produced by the lens array was identical to the original. Beam steering by refraction is accompanied by chromatic dispersion, which causes chromatic aberration, making colors appear blurry. The refractive index condition to reduce chromatic dispersion was obtained using the doublet structure of the electrowetting prism. The chromatic dispersion was reduced by 70% on average.

Swept Source Lidar: simultaneous FMCW ranging and nonmechanical beam steering with a wideband swept source.

Light detection and ranging (lidar) has long been used in various applications. Solid-state beam steering mechanisms are needed for robust lidar systems. Here we propose and demonstrate a lidar scheme called "Swept Source Lidar" that allows us to perform frequency-modulated continuous-wave (FMCW) ranging and nonmechanical beam steering simultaneously. Wavelength dispersive elements provide angular beam steering, while a laser frequency is continuously swept by a wideband swept source over its whole tuning bandwidth. Employing a tunable vertical-cavity surface-emitting laser and a 1-axis mechanical beam scanner, three-dimensional point cloud data has been obtained. Swept Source Lidar systems can be flexibly combined with various beam steering elements to realize full solid-state FMCW lidar systems.

Precise and robust optical beam steering for space optical instrumentation

We present a novel optical beam steering technique for fiber to free-space to fiber-coupling schemes on optical breadboards, which is based on a glass plate and a pair of glass wedges. Our approach permits much finer adjustments of the beam direction and position when compared to conventional beam steering techniques that use adjusting elements of the same mechanical precision. This results in a much increased precision, accuracy, and stability. Furthermore, the presence of a beam steering element in proximity to the fiber coupler allows a great simplification of the design of this element which is typically considered as the most complex and sensitive element on an optical fiber breadboard. Overall, a beam steering precision of better than $$5\,\upmu $$rad and $$5\,\upmu $$m is demonstrated, resulting in a resolution in coupling efficiency of 0.1%. Likewise, we demonstrate a fiber-to-fiber-coupling efficiency of more than 89.8%, with a stability of 0.2% in a stable temperature environment and 2% fluctuations over a temperature range from 10 to 40 °C over a measurement time of 14 h. Finally, we observe no non-reversible change in the coupling efficiency after performing a series of tests over large temperature variations ($$\varDelta T > 30$$ K). This technique can find direct application in proposed missions for quantum experiments in space (Bongs et al. in STE-QUEST space–time explorer and quantum equivalence principle space test, Technical report STE-QUEST, European Space Agency, 2013; Kaltenbaek et al. in EPJ Quantum Technol 3(1):5, 2016; Carraz et al. in Microgravity Sci Technol 26:139, 2014), e.g., in space-based quantum sensing, where precisely controlled laser light is used to cool and manipulate atoms, or in inter-satellite quantum key distribution.

Elements of a dielectric laser accelerator

We experimentally demonstrate several physical concepts necessary for the future development of dielectric laser accelerators—photonic elements that utilize the inelastic interaction between electrons and the optical near fields of laser-illuminated periodic nanostructures. To build a fully photonic accelerator, concatenation of elements, large energy gains, and beam steering elements are required. Staged acceleration is shown using two spatio-temporally separated interaction regions. Further, a chirped silicon grating is used to overcome the velocity dephasing of subrelativistic electrons with respect to its optical near fields, and last, a parabolic grating geometry serves for focusing of the electron beam.

Terahertz epsilon-near-zero cut-through metal-slit array antenna

Metamaterials can give rise to unprecedented refractive indices and drive the rapid development of metadevices with on-demand electromagnetic properties. Recent advances in terahertz science demand high-performance optical elements beyond conventional designs of naturally occurring materials in the terahertz wave band. However, how an epsilon-near-zero (ENZ) structure can exploit terahertz metadevices is still not fully demonstrated based on a physical analysis. Here, inspired by the ENZ concept, we demonstrate a design guideline of a terahertz ENZ cut-through metal-slit array antenna. Measurements by a terahertz imager visualize the beam profile of a terahertz wave, and the measured permittivity of 0.26 agrees well with that of 0.27 obtained by simulation and theory. The terahertz ENZ antenna provides a wide range of potential applications such as high-directivity antennas, beam dividers, beam-steering elements, phase-control devices, and novel filters.

Two-dimensional beam steering using a thermo-optic silicon photonic optical phased array

Many components for free-space optical (FSO) communication systems have shrunken in size over the last decade. However, the steering systems have remained large and power hungry. Nonmechanical beam steering offers a path to reducing the size of these systems. Optical phased arrays can allow integrated beam steering elements. One of the most important aspects of an optical phased array technology is its scalability to a large number of elements. Silicon photonics can potentially offer this scalability using CMOS foundry techniques. A phased array that can steer in two dimensions using the thermo-optic effect is demonstrated. No wavelength tuning of the input laser is needed and the design allows a simple control system with only two inputs. A benchtop FSO link with the phased array in both transmit and receive mode is demonstrated.

Varactor diode integrated dipole‐EBG base‐station antenna: Enhancing tilted radiation pattern

ABSTRACTThe new dipole‐electromagnetic bandgap subarray antenna with an improved steerable beam is designed for base‐station antennas. The proposed antenna consists of four dipole array antenna mounted on the tunable mushroom structure to steer element pattern. Whereas past array antenna utilizes fixed element pattern, beam steering element pattern is used to track the maximum of the array pattern to improve the scan loss of the array pattern. A dipole antenna on 4 × 4 mushroom structure is designed as a compact single element capable of steerable radiation within 0°–27°. The consistent gain around 11.5–12.1 dB is achieved at 3.3 GHz within 0°–27° with the tilted element pattern whereas the gain reduces to 9.4–10.2 dB with fixed element pattern. The antenna radiation pattern is simulated and measured varying capacitances. The measured bandwidth of the antenna covers 3.2–3.55 GHz, which is partial WIMAX band. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:1794–1799, 2015

Transmission phase control by stacked metal-dielectric hole array with two-dimensional geometric design

Transmission phase control is experimentally demonstrated using stacked metal-dielectric hole arrays with a two-dimensional geometric design. The transmission phase varies drastically with small frequency shifts due to structural resonances. Laterally propagating surface plasmon polaritons excited by the periodic hole array roughly determine the resonance frequency, whereas localized resonances in each hole determine the dispersion. The transmission phase at various frequencies is directly evaluated using interferometric microscopy, and the formation of an inclined wavefront is demonstrated using a beam steering element in which the hole shapes gradually change in-plane from square to circular.

Sensing change

The first femtosecond laser-fabricated refractive index sensor without material removal that compensates for changes in temperature has been demonstrated by researchers at the Memorial University of Newfoundland in Canada. Dr Ping Lu and Professor Qiying Chen devised a fibre Mach-Zehnder interferometer structure with a femtosecond laser irradiated spot and a taper as the two beam-steering elements of the interferometer. This device, which is compact, simple to use, easy to fabricate and low in cost, could be employed for refractive index sensing in a wide range of practical applications.

Broadband gradient index microwave quasi-optical elements based on non-resonant metamaterials

Utilizing non-resonant metamaterial elements, we demonstrate that complex gradient index optics can be constructed exhibiting low material losses and large frequency bandwidth. Although the range of structures is limited to those having only electric response, with an electric permittivity always equal to or greater than unity, there are still numerous metamaterial design possibilities enabled by leveraging the non-resonant elements. For example, a gradient, impedance matching layer can be added that drastically reduces the return loss of the optical elements due to reflection. In microwave experiments, we demonstrate the broadband design concepts with a gradient index lens and a beam-steering element, both of which are confirmed to operate over the entire X-band (roughly 8-12 GHz) frequency spectrum.

Design and simulation of planar electro-optic switches in ferroelectrics

Conceptual design and numerical simulation of two polarization dependent planar optical switches based on the electro-optic effect in ferroelectrics operating at 1.55 μm wavelength are presented. The first design is a 3×3 optical switch based entirely on electro-optic beam steering (prism) elements and ion-exchanged lenses for collimation. The second design is a 1×N optical switch based on a combination of electro-optic beam steering and electro-optic focusing (lens) elements. The scalability of this device has been improved by compensating the in-plane divergence of the laser. Analytical expressions for the dependence of scalability are presented.

Non-display applications and the next generation of liquid crystal over silicon technology

The next generation of applications for liquid crystal (LC) over silicon technology will be non-display oriented systems such as adaptive optical interconnects, optical switches and optical image processors. These new non-display applications have a different set of material parameters, which means that existing display-based materials are not entirely optimal. This is particularly the case when the application is driven by phase modulation at high frame rates (more than 1 kHz). An example of such a non-display application is in adaptive optical interconnects. Optical data transmission between printed circuit boards is becoming more and more important as the data rate in electronic systems increases into the gigahertz region. One way of avoiding the data bottlenecks in board to board interconnects is to use optical links to transmit the data. Recent research into free-space optical links has shown that a high level of manufacturing tolerance must be used to maintain the link. However, one way of avoiding these limitations is to use a reconfigurable LC phase hologram as a beam-steering element to compensate for movement between the boards and maintain the optical data path.

Phase modulation with the next generation of liquid crystal over silicon technology

Liquid crystal materials are fast becoming the de facto standard in modern commercial display technology and large amounts of research and development have gone into optimising the materials used in these many types of display. One of the most exciting technologies based on liquid crystal materials is the combination of their optical modulation characteristics with the power and compactness of a silicon VLSI backplane. The next generation of applications for liquid crystal over silicon technology are already starting to emerge in laboratories, however there are severe limitations as the liquid crystal materials have all been optimised for amplitude or intensity modulation when in fact the ability to modulate the phase of the light is more desirable. One example of such an application is adaptive optical interconnects. Data transmission within and between printed circuit boards is becoming more and more important as the data rates in electronic systems increase into the GHz region. One way of avoiding potential data bottlenecks in board to board interconnects is to use optical links to transmit the data. Recent research into free-space optical links has shown that a high level of manufacturing tolerance must be used to maintain the link, however, this can be avoided by incorporating a liquid crystal phase hologram as a beam steering element to compensate for movement between the boards and maintain the optical data path.

Adaptive Optical Interconnect Using an FLC SLM

Optical interconnects between boards are becoming more and more important as the data rate in electronic systems increases into the GHz regions. One way of avoiding data bottlenecks in board to board interconnects is to use optical links to transmit the data. Such systems must be made from either guided wave technologies such as optical fibres or by using free-space propagation. Recent research into free-space optical links has shown that a high level of manufacturing tolerance and vibrational control must be used to maintain the link. One possible approach to avoiding these constraints is to use a reconfigurable liquid crystal phase hologram as a beam steering element to compensate for movement in the boards and maintain the optical data path.

Circularly-Polarized Phase Shifter for Use in Phased Array Antennas

An X-band, circularly-polarized, nonreciprocal, ferrite phase shifter has been developed whose size and electrical performance are favorably suited for use in transmission or reflection-type phased arrays requiring element center-to-center spacings of about 0.5 /spl lambda/. The phase shifter has the same configuration as a Faraday rotator with a ferrite rod located at the center of a circular waveguide with an axially applied field. If a circularly polarized wave is passed through this geometry, a nonreciprocal phase-current characteristic is obtained. The array antenna is configured so that no phase-control field reversals are needed between transmit and receive modes of RADAR operation. The radiating element has been designed as an integral part of the beam steering element using waveguide array simulator techniques, this paper will discuss various design problems and performance of the beam steering element. A 1300-element phased array was constructed and tested. Its performance, as it relates to the phase-setting accuracy of 1300 phase-shifter constituents, is stated briefly.