Agile Beam Steering Research Articles

High-Data-Rate and Wide-Steering-Range Optical Wireless Communication via Nonuniform-Space Optical Phased Array

The silicon photonic optical phased array (OPA) featured by high integration and agile beam steering exhibits greatly potential application in optical wireless communication (OWC). In this paper, we demonstrate high-data-rate and long-range OWC using an integrated Silicon-Silicon Nitride OPA chip with 12 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> large aperture. The OPA chip constituted by 128 waveguide grating antennas at nonuniform spacing is employed for wide-steering and small-divergence solid beam steering. In the experiment, we demonstrated 100° wide range communications in horizontal direction via antenna phase tuning. To our best knowledge, 100° is the widest cover range in the reported OPA-based OWC systems. Moreover, the OPA chip is also utilized to achieve up to 32 Gb/s low BER transmission of non-return-to-zero (NRZ) signal over 54 m free space distance. In addition, we also successfully demonstrated more than 50 Gb/s PAM4 signal transmission by measuring clear eye diagrams at the horizontal direction of 0° and 50° over 10 m. Thanks to agile beam steering of the OPA, switching time among arbitrary positions in multi-targets communication can be less than 27 μs. By virtue of tiny beam divergence 0.021° × 0.029° emitted from the OPA, data transmission switching between two targets spaced at 3.5 cm over 20 m can be achieved accurately. The experimental measurement shows the sidelobe crosstalk from the adjacent target channel is less than -25.2 dB. Our demonstrations validate the feasible implementation of the silicon-based OPA in the high-data-rate and wide-steering-range OWC system.

Polarization Agile Beam Steering by Subarray Antenna Module Design to Compensate Wide-Angle Polarization Discrepancy of User Equipment Antenna Radiations at mmW Frequencies

An antenna-in-module (AiM) architecture at millimeter-wave frequencies for a base transceiver system (BTS) is developed for electromagnetic (EM) radiation with an agile polarization tunable capability. This may reduce the polarization mismatch to a user equipment (UE) antenna, where the mismatch becomes severe in wide-angle scans. The AiM first implements a dual-polarization feature on its antenna elements and then integrates active radio frequency (RF) phase shifters and power amplifiers/attenuators to provide dynamically adjustable weightings. Considering the received fields of a UE antenna, the weightings of the AiM antennas are appropriately tuned to obtain the maximum signal strength from the UE antenna. In this article, the theoretical concept and the antenna architecture are presented. Full-wave simulations using HFSS and the measurement results of the AiM prototype are presented to validate its feasibility.

Urban Outdoor Measurement Study of Phased Antenna Array Impact on Millimeter-Wave Link Opportunities and Beam Misalignment

Exploiting multi-antenna technologies for robust beamsteering to overcome the effects of blockage and beam misalignment is the key to providing seamless multi-Gbps connectivity in millimeter-wave (mm-wave) networks. In this paper, we present the first large-scale outdoor mm-wave measurement study using a phased antenna array in a typical European town. We systematically collect fine-grained 3D angle-of-arrival (AoA) and angle-of-departure (AoD) data, totaling over 50,000 received signal strength measurements. We study the impact of phased antenna arrays in terms of number of link opportunities, achievable data rate and robustness under small-scale mobility, and compare this against reference horn antenna measurements. Our results show a limited number of 2–4 distinct spatial link opportunities per receiver location, indicating that the mm-wave multipath richness in a European town is surprisingly similar to that of dense urban metropolises. The results for the phased antenna array reveal that significant losses in estimated data rate occur for beam misalignments in the order of the half-power beamwidth, with significant and irregular variations for larger misalignments. By contrast, the loss for horn antennas is monotonically increasing with the misalignment. Our results strongly suggest that the effect of non-ideal phased antenna arrays must be explicitly considered in the design of agile beamsteering algorithms.

An Optical Phased Array for LIDAR

We have previously demonstrated the development of an Optical Phased Array (OPA) micromechanical system (MEMS) used for beam steering, which shows great advantages over previous mechanisms such as opto-mechanical, acousto-optical (AO) or electro-optical (EO). We aim to integrate the OPA MEMS system into the application of automobile navigation, which is currently primarily dominated by opto-mechanical scanning based systems. Opto-mechanical scanning devices are usually bulky and relatively slow, while competing technologies (AO, EO) utilize devices that while small in size, cannot provide the steering speeds and versatility necessary for many applications. In drawing from phased array concepts that revolutionized RADAR technology by providing a compact, agile alternative to mechanically steered technology, the OPA based LIDAR program seeks to integrate thousands of closely packed optical emitting facets, precise relative electronic phase control of these facets, and all within a very small form factor. Comparing with other competing LIDAR system, the OPA based LIDAR system will have multiple degrees of freedom for phase control which enables not only agile beam steering but also beam forming and multiple beam generation, greatly expanding the diversity of applications.

Stochastic scanning method to shorten acquisition time using liquid crystal optical phased array

Agile beam steering has been previously reported to be one of the unique properties of a liquid crystal optical phased array. We propose a stochastic scanning method using the property of agile beam steering to shorten acquisition time in building a free-space laser communication link. As a specific example, Gaussian stochastic scan enables higher acquisition probability and shorter acquisition time. In addition, there are two factors to influence the results: standard deviation of stochastic scanning angle and the width of the laser beam. Theoretical analysis is presented that the stochastic scanning method is a unique method to speed up the acquisition process in free-space laser communication.

Two-Dimensional Rotorcraft Downwash Flow Field Measurements by Lidar-Based Wind Scanners with Agile Beam Steering

Abstract A major risk to helicopters is the unexpected encounter of degraded visual environments in close-to-ground operations, where a loss of visibility often is caused by clouds of dust (brownout) or snow (whiteout) stirred up by intense downwash. The understanding of the phenomenon is limited, and there is a need for instruments that can measure flow fields on scales larger than a few meters with good resolution. This paper reports on the use of synchronized continuous-wave Doppler lidars for rotorcraft downwash flow field studies. Built from a modified ZephIR wind lidar and a double-prism arrangement for agile beam steering, a wind scanner—WindScanner—has been developed at the Department of Wind Energy at the Technical University of Denmark (DTU) Risø campus. The WindScanner measures the line-of-sight component of the airflow remotely and by rapid steering, the line-of-sight direction and the focus position; all points in space within a cone with a full opening angle of 120° can be reached from about 8 m out to some hundred meters depending on the range resolution required. The first two-dimensional mean wind fields measured in a horizontal plane and in a vertical plane below a hovering search and rescue helicopter are presented. Since the line-of-sight directions of the two synchronized WindScanners were scanned within the plane of interest, the influence of the wind component perpendicular to the plane was avoided. The results also demonstrate the possibilities within less demanding flows encountered within complex terrain and wind-energy-related research for which the WindScanner technology primarily has been developed.

Programmable agile beam steering based on a liquid crystal prism

To meet the application need for agile precision beam steering, a novel liquid crystal prism device with a simple structure, convenient control, low cost and applicable performance is presented, and analysed theoretically and experimentally. The relationships between the optical path and the thickness of the liquid crystal cell under different voltages are investigated quantitatively by using a theoretical model. Analysis results show that the optical path profile of the liquid crystal prism has a quasi-linear slope and the standard deviation of the linear slope is less than 16 nm. The slope ratio can be changed by a voltage, which achieves the programmable beam steering and control. Practical liquid crystal prism devices are fabricated. Their deflection angles and wavefront profiles with different voltages are experimentally tested. The results are in good agreement with the simulated results. The results imply that the agile beam steering in a scope of 100 μrad with a micro-rad resolution is substantiated in the device. The two-dimensional beam steering is also achieved by cascading two liquid crystal prism devices.

Energy-efficient optical acquisition schemes in wireless sensor networks

Energy-efficiency is an essential feature of wireless sensor networks (WSNs) where the longevity of autonomous sensor nodes is limited by their battery life and/or energy-harvesting capability. Base-station-initiated optical wireless communication with nodes equipped with a passive optical transmitter in the form of a corner cube retroreflector (CCR) provides sensor acquisition with no energy expenditure on the part of the sensor node itself and is therefore an attractive option for WSN. However, the return signal from an illuminated sensor node is a stochastic variable dependant on fabrication parameters, ambient conditions and receiver noise so that the sensor acquisition process is inherently error-prone. In this paper we propose an energy-aware, base station-initiated interrogation scheme based on exponentially increasing beam scan areas, that takes into consideration the error-prone trait of CCR-outfitted sensor nodes. We analyse the scheme performance subject to different values of signal variance and various cost functions. We extend the analysis to address the circumstance of a spatially-limited sensor-failure event, such as may be caused by deliberate tampering or by environmental factors. We show that agile beam-steering on the basis of accrued knowledge of contaminated sensor distributions promotes energy-conserving acquisition. The validity of a Poisson spatial distribution model for the sensor dispersion is discussed and the impact of this initial assumption on acquisition error is demonstrated.

Effect of the sampling rate of the tracking system on free-space laser communications

Lasers play an ever-increasing role in aerospace communication systems by providing the most logical connectivity channels. They drive the advancements in modern optoelectronics; however, successful implementation of this technology hinges on having an equally advanced beam-steering system for tracking the communication counterpart in the presence of complex maneuvers and the resident vibration of the airframe. The work presented in this paper concentrates on the development of agile acousto-optic beam-steering systems for laser communication terminals, which use constant-gain controllers augmented with an adaptive Kalman filter. Experimental results are presented to demonstrate communication performance as a function of the sampling rate in the tracking loop.

Advances in Scanning Reflectarray Antennas Based on Ferroelectric Thin-Film Phase Shifters for Deep-Space Communications

Though there are a few examples of scanning phased array antennas that have flown successfully in space, the quest for ldquolow costrdquo high-efficiency large-aperture microwave phased arrays continues. Fixed and mobile applications that may be part of a heterogeneous exploration communication architecture will benefit from the agile (rapid) beam steering and graceful degradation afforded by phased array antennas. The reflectarray promises greater efficiency and economy compared to directly radiating varieties. Implementing a practical scanning version has proven elusive. The ferroelectric reflectarray, under development and described herein, involves phase shifters based on coupled microstrip patterned on films that were laser ablated onto substrates. These devices outperform their semiconductor counterparts from X- through and K-band frequencies. There are special issues associated with the implementation of a scanning reflectarray antenna, especially one realized with thin-film ferroelectric phase shifters. This paper will discuss these issues, which include relevance of phase shifter loss; modulo 2 effects and phase shifter transient effects on bit error rate; scattering from the ground plane; presentation of a novel hybrid ferroelectric-semiconductor phase shifter; and the effect of mild radiation exposure on phase shifter performance.

Superprism effect based on phase velocities.

The superprism effect has been studied in the past by use of the anomalous group velocities of optical waves in photonic crystals. We suggest the possibility of realizing agile beam steering based on purely phase-velocity effects. We present designs of photonic crystal prisms that might make experimental observation of this effect possible.

Experimental demonstration of an optical phased array antenna for laser space communications

The feasibility of an optical phased array antenna applicable for spaceborne laser communications was experimentally demonstrated. Heterodyne optical phase-locked loops provide for a defined phase relationship between the collimated output beams of three single-mode fibers. In the far field the beams interfere with a measured efficiency of 99%. The main lobe of the interference pattern can be moved by phase shifting the subaperture output beams. The setup permitted agile beam steering within an angular range of 1 mr and a response time of 0.7 ms. We propose an operational optical phased array antenna fed by seven lasers, featuring high transmit power and redundance.