Two-dimensional Beam Steering Research Articles

Design and Measurement of a Two-Dimensional Beam-Steerable Metasurface for Ka-Band Communication Systems

This study introduces a steerable metasurface reflector designed for the Ka-band, enabling one-dimensional and two-dimensional beam steering. The paper elaborates on the design considerations, manufacturing process, and experimental findings. The unit cell design incorporates a Varactor diode as the tuning element, facilitating a dynamic phase range exceeding 300° with minimal metasurface beam steering losses. Notably, the experimental results are in good agreement with the simulation outcomes. The advantages of employing this metasurface reflector include rapid beam steering, cost-effective production implementation, support for both one-dimensional and two-dimensional beam steering, low reflection loss, high-resolution beam steering, and continuous beam steering capabilities.

Cost-effective 3D-printed rotatable reflectors for two-dimensional beam steering

In this paper, we have developed a 2D optical scanning module comprising cascaded 3D-printed one-axis rotating mirrors with large areas (30×30mm2 for the X-direction scan and 60×25mm2 for the Y-direction scan). Each mirror device contains a square or rectangular silicon substrate coated with aluminum, serving as the mirror. A 3D-printed structure, including the mirror frame (with four embedded mini permanent magnets on the backside), torsion springs, and base, is combined with the mirror; two electromagnets are situated under the mirror as the actuation mechanism. We apply DC voltage to the electromagnets to create magnetic force. The electromagnets can interact with the permanent magnets to make the mirror rotate. The X scan of the 2D scanning module can achieve a static optical scan angle of ∼11.8deg at the -X corners, and the corresponding Y-scan angle is ∼4.5deg, both with 12 VDC. Moreover, we have observed a fan-shaped distortion, a phenomenon not thoroughly studied previously for combining two single-axis scan mirrors. Therefore, we also perform a simulation to establish and demonstrate a correlation between the simulation prediction and experimental results. The 2D scanning module can be a low-cost alternative to the expensive conventional galvanometer scanners, and it can be used to upgrade a rangefinder to a simplified LiDAR.

Butler matrix enabled multi-beam optical phased array for two-dimensional beam-steering and ranging

Based on the wavelength transparency of the Butler matrix (BM) beamforming network, we demonstrate a multi-beam optical phased array (MOPA) with an emitting aperture composed of grating couplers at a 1.55 μm pitch for wavelength-assisted two-dimensional beam-steering. The device is capable of simultaneous multi-beam operation in a field of view (FOV) of 60° × 8° in the phased-array scanning axis and the wavelength-tuning scanning axis, respectively. The typical beam divergence is about 4° on both axes. Using multiple linearly chirped lasers, multi-beam frequency-modulated continuous wave (FMCW) ranging is realized with an average ranging error of 4 cm. A C-shaped target is imaged for proof-of-concept 2D scanning and ranging.

Dynamic beam steering for wireless optical power transfer in IoT applications.

The alignment of a receiver with a pencil beam in a wireless optical power transfer (WOPT) system employing a resonance beam charging (RBC) technology limits the establishment of a resonance cavity. Accurate tracking necessitates precise and dependable monitoring, which requires the exact placement of transmitting and receiving devices. Herein, we present a concept of a two-dimensional (2D) beam steering mechanism for RBC-based WOPT systems utilizing dispersed laser beams. The proposed approach allows a significant improvement, including reduction of scanning times and minimization of errors, in relation to conventional pencil-beam-based systems. Experimental results reveal 14% faster acquisition time efficiency, an 18% improvement in pointing accuracy, and a 24% enhancement in tracking accuracy. These results establish the prerequisites for the implementation of dispersed beam steering in the RBC-based WOPT system. This capability empowers the system to charge movable devices and Internet of Things devices consistently in smart factories.

Pattern reconfigurable antenna with two-dimensional beam steering capability using metasurface

A two-dimensional (2-D) beam steering pattern reconfigurable antenna with an active partially reflecting surface (PRS) is presented in this paper. The proposed design incorporates a U-slot patch antenna functioning as a radiator and a superstrate composed of an active PRS layer. The PRS superstrate layer consists of 6 × 6 unit cells, divided into four sections, each comprised of 3 × 3 unit cells. To achieve reconfigurability, each unit cell within the PRS layer is loaded with two PIN diodes. Phase inconsistency can be introduced by changing the states of the PIN diode at different sections, which causes the PRS antenna to change the direction of its main beam. By controlling the operating states of PIN diodes within each unit cell, a total of sixteen radiation patterns can be generated. The proposed antenna supports 2-D beam steering in both the xz- and yz-planes, allowing for a maximum steered angle of ±40°. The performance of the fabricated antenna is experimentally verified at an operating frequency of 3.5 GHz. The proposed antenna is suitable for the 5G NR frequency band n78 and operates within the frequency range of 3.3 to 3.8 GHz.

Hybrid integrated thin-film lithium niobate-silicon nitride electro-optical phased array incorporating silicon nitride grating antenna for two-dimensional beam steering.

This study proposes a solid-state two-dimensional beam-steering device based on an electro-optical phased array (EOPA) in thin-film lithium niobate (TFLN) and silicon nitride (SiN) hybrid platforms, thereby eliminating the requirement for the direct etching of TFLN. Electro-optic (EO) phase modulator array comprises cascaded multimode interference couplers with an SiN strip-loaded TFLN configuration, which is designed and fabricated via i-line photolithography. Each EO modulator element with an interaction region length of 1.56 cm consumed a minimum power of 3.2 pJ/π under a half-wave voltage of 3.64 V and had an estimated modulation speed of 1.2 GHz. Subsequently, an SiN dispersive antenna with a waveguide grating was tethered to the modulator array to form an EOPA, facilitating the out-of-plane radiation of highly defined near-infrared beams. A prepared EOPA utilized EO phase control and wavelength tuning near 1550 nm to achieve a field-of-view of 22° × 5° in the horizontal and vertical directions. The proposed hybrid integrated platform can potentially facilitate low-power and high-speed beam steering.

Modulo-addition operation enables terahertz programmable metasurface for high-resolution two-dimensional beam steering.

Electrically controlled terahertz (THz) beamforming antennas are essential for various applications such as wireless communications, security checks, and radar to improve coverage and information capacity. The emerging programmable metasurface provides a flexible, cost-effective platform for THz beam steering. However, scaling such arrays to achieve high-gain beam steering faces several technical challenges. Here, we propose a pixelated liquid crystal THz metasurface with a crossbar structure, thereby increasing the array scale to more than 3000. The coding pattern on the programmable device is generated by the modulo-addition of the coding sequences on the top and bottom layers. We experimentally demonstrate the programmable liquid crystal metasurface capable of active beam deflection in the upper half-space. This scale-up of programmable devices opens exciting opportunities in pencil beamforming, high-speed information processing, and optical computing.

Two-Dimensional Dynamic Beam Steering by Tamm Plasmon Polariton

The dynamic steering of a beam reflected from a photonic structure supporting Tamm plasmon polariton is demonstrated. The phase and amplitude of the reflected wave are adjusted by modulating the refractive index of a transparent conductive oxide layer by applying a bias voltage. It is shown that the proposed design allows for two-dimensional beam steering by deflecting the light beam along the polar and azimuthal angles.

Reconfigurable Transmitarray Based on Frequency Selective Surface for 2D Wide-Angle Beam Steering

A novel reconfigurable transmitarray (RTA) with two-dimensional (2D) wide beam steering capability is presented herein. Different from the traditional RTA with the discrete phase compensation (one-bit or multi-bits phase shift), a second order parallel bandpass filter model is used to realize the RTA elements with a 180° continuous phase compensation. A sandwich structure composed of the two patches with rectangular slots and the middle ground sheet with the cruciform slot is constructed for the phase shift characteristics of the frequency selective surface (FSS), and two varactor diodes are loaded across the rectangular slots on the two top and bottom patches. The simulated results show that the proposed elements could achieve continuous transmission phase compensation from 0° to 180° with a 3 dB insert loss within the operating band of 11.8–12.6 GHz. The RTA prototype with 16×16 elements and an aperture size of 6λ0×6λ0 at 12.2 GHz is fabricated and measured for experimental verification. The measured results show that its beam scanning range can reach ±50° in both horizontal and vertical planes with a peak gain of 22.76 dBi and a aperture efficiency of 24.65%. Furthermore, the sidelobe levels (SLLs) are lower than −17.8 dB, which is much better than most RTAs. The proposed RTA has potential applications in radar, microwave imaging and wireless communication systems with low-cost fabrication and a stable performance.

Integrated lithium niobate optical phased array for two-dimensional beam steering.

Optical phased arrays (OPAs) with high speed, low power consumption, and low insertion loss are appealing for various applications, including light detection and ranging, free-space communication, image projection, and imaging. These OPAs can be achieved by fully harnessing the advantages of integrated lithium niobate (LN) photonics, which include high electro-optical modulation speed, low driving voltage, and low optical loss. Here we present an integrated LN OPA that operates in the near-infrared regime. Our experimental results demonstrate 24 × 8° two-dimensional beam steering, a far-field beam spot with a full width at half maximum of 2 × 0.6°, and a sidelobe suppression level of 10 dB. Furthermore, the phase modulator of our OPA exhibits a half-wave voltage of 6 V. The low power consumption exhibited by our OPA makes it highly attractive for a wide range of applications. Beyond conventional applications, our OPA's high speed opens up the possibility of novel applications such as high-density point cloud generation and tomographic holography.

Highly Tunable Cascaded Metasurfaces for Continuous Two-Dimensional Beam Steering.

Cascaded metasurfaces can exhibit powerful dynamic light manipulation by mechanically tuning the far-field interactions in the layers. However, in most current designs, the metasurfaces are separated by gaps smaller than a wavelength to form a total phase profile, representing the direct accumulation of the phase profiles of each layer. Such small gap sizes may not only conflict with the far-field conditions but also pose great difficulties for practical implementations. To overcome this limitation, a design paradigm taking advantage of a ray-tracing scheme that allows the cascaded metasurfaces to operate optimally at easily achievable gap sizes is proposed. Enabled by the relative lateral translation of two cascaded metasurfaces, a continuous two-dimensional (2D) beam-steering device for 1064nm light is designed as a proof of concept. Simulation results demonstrate tuning ranges of ±45° for biaxial deflection angles within ±3.5mm biaxial translations, while keeping the divergence of deflected light less than 0.007°. The experimental results agree well with theoretical predictions, and a uniform optical efficiency is observed. The generializeddesign paradigm can pave a way towards myriad tunable cascaded metasurface devices for various applications, including but not limited to light detection and ranging (LiDAR) and free space optical communication.

Machine learning assisted two-dimensional beam-steering for integrated optical phased arrays

Optical phased arrays (OPAs) offer promising beam-steering solutions for ultra-small light detection and ranging applications and free-space optical communication systems. The paper presents a new machine learning assisted two-dimensional beam formation and steering technique, which calibrates phase errors via a convolutional neural network architecture to mitigate phase errors emanating from fabrication imperfections, thermal crosstalk and wavelength tuning effects. The technique is experimentally validated on an eight-channel OPA, and the results demonstrate strong control predictive capabilities with a very low mean squared error of 0.0026 and a high correlation coefficient of 0.97 after training. Reconstructed signals derived from a subset of predicted control inputs yielded a maximum lateral peak intensity deviation of a single pixel resolution (0.15°) from the ground truth, and no observable longitudinal displacement error, for a full-width at half-maximum beam-width of approximately 1.5°.

Fully Integrated Solid-State LiDAR Transmitter on a Multi-Layer Silicon-Nitride-on-Silicon Photonic Platform

We report a LiDAR transmitter incorporating both a hybrid-integrated tunable external cavity laser and a high-resolution 2-D optical phased array beam-steerer. Widely tunable single-mode lasing over a span of approximately 100 nm is achieved with >42 dB side-mode-suppression-ratio, 18 mW output power, and 2.8 kHz linewidth. Two-dimensional beam steering in a field-of-view of 140° × 16° exhibits a beam divergence of 0.051° × 0.016° measured in full width at half maximum. Leveraging the low propagation loss, negligible nonlinear loss, and low thermal sensitivity of silicon nitride, and combining the high mode confinement and efficient thermal tuning of silicon, the device affirms the feasibility of high-power on-chip lasing, power bottleneck elimination, and low on-chip insertion loss. It represents the first demonstration of a fully integrated LiDAR transmitter on the multi-layer silicon-nitride-on-silicon photonic platform, revealing the potential of complementary integration in the effort toward a LiDAR transmitter of sufficient optical power budget.

Two-Dimensional Beam Steering Using a Stacked Modulated Geodesic Luneburg Lens Array Antenna for 5G and Beyond

Antennas for future communication systems are required to be highly directive and steerable to compensate for the high path loss in the millimeter-wave band. In this work, we propose a linear array of modulated geodesic Luneburg lens (the so-called water drop lens) antennas operating at 56–62 GHz. The lens array antenna features 2-D beam scanning with low structural complexity. The lenses are fully metallic and implemented in parallel plate waveguides (PPWs), meaning that they are highly efficient. Each lens is fed with 13 rectangular waveguides surrounded by glide-symmetric holes to suppress leakage. The lenses provide <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{110}^{\circ} $ </tex-math></inline-formula> beam coverage in the H-plane with scan losses below 1 dB. In order to scan in the E-plane, we use a feeding network based on a 1:4 power divider and three phase shifters. In this configuration, the array can scan <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathrm{60}^{\circ} $ </tex-math></inline-formula> in the E-plane, albeit with higher scanning losses than in the H-plane. The lens array is manufactured and a good agreement between simulated and experimental results is obtained.

Inverse design of perimeter-controlled InAs-assisted metasurface for two-dimensional dynamic beam steering.

The current commercially viable light detection and ranging systems demand continuous, full-scene, and dynamic two-dimensional point scanning, while featuring large aperture size to ensure long distance operation. However, the biasing architecture of large-area arrays with numerous individually controlled tunable elements is substantially complicated. Herein, inverse design of a perimeter-controlled active metasurface for two-dimensional dynamic beam steering at mid-infrared regime is theoretically presented. The perimeter-control approach simplifies biasing architecture by allowing column-row addressing of the elements. The metasurface consists of a periodic array of plasmonic patch nanoantennas in a metal-insulator-metal configuration, wherein two active layers of indium arsenide are incorporated into its building block. The metasurface profile facilitates wide phase modulation of on the reflected light at the individual element level through applying independent voltages to its respective columns and rows. The multi-objective genetic algorithm (GA) for optimizing user-defined metrics toward shaping desired far-zone radiation pattern is implemented. It is demonstrated that multi-objective GA yields better results for directivity and spatial resolution of perimeter-controlled metasurface by identifying the design tradeoffs inherent to the system, compared to the single-objective optimizer. A high directivity and continuous beam scanning with full and wide field-of-view along the azimuth and elevation angles are respectively maintained.

Spectrally Scanning LiDAR Based on Wide-Angle Agile Diffractive Beam Steering

Spectral scan, or beam steering by only wavelength tuning enables inertia-less fast-scanning LiDAR, while the field of view is fundamentally limited by the total available wavelength range and the dispersion ability of common gratings. Here, we propose to relieve the restriction by combining a diffraction grating and a low-cost diffractive element, which enables wide-angle two-dimensional beam steering. An FoV far beyond the reach of other spectral scan methods can be achieved. Several diffractive elements samples are fabricated to demonstrate spectrally scanning field of views of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.7^{\circ } \times 10^{\circ }$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$7.7^{\circ } \times 29^{\circ }$ </tex-math></inline-formula> from an 100-nm wavelength tuning range. Also, to show the potential to further extend the spectral scan range, blazed diffractive elements are fabricated with high diffraction efficiency, which corresponds to a spectral scan range up to 40.3°. Based on the structure, a solid-state coherent LiDAR system is built. Three-dimensional imaging with mm-level range resolution is demonstrated.

Beam steering at the nanosecond time scale with an atomically thin reflector

Techniques to mold the flow of light on subwavelength scales enable fundamentally new optical systems and device applications. The realization of programmable, active optical systems with fast, tunable components is among the outstanding challenges in the field. Here, we experimentally demonstrate a few-pixel beam steering device based on electrostatic gate control of excitons in an atomically thin semiconductor with strong light-matter interactions. By combining the high reflectivity of a MoSe2 monolayer with a graphene split-gate geometry, we shape the wavefront phase profile to achieve continuously tunable beam deflection with a range of 10°, two-dimensional beam steering, and switching times down to 1.6 nanoseconds. Our approach opens the door for a new class of atomically thin optical systems, such as rapidly switchable beam arrays and quantum metasurfaces operating at their fundamental thickness limit.

Electronically Steerable Parasitic Patches for Dual-Polarization Reconfigurable Antenna Using Varactors

This paper presents a dual-polarized reconfigurable antenna loading electronically steerable parasitic patches. The proposed dual-polarized antenna is surrounded by four parasitic patches each of which is mounted by two varactor diodes on the ground. By tuning the varactors, continuous two-dimensional beam-steering can be achieved for each of the polarization. A prototype of the proposed antenna is fabricated and measured. Excellent agreement between the simulated and measured results is observed. It is observed that the maximum beam-scanning angles in E-plane and H-plane are greater than ±25∘, which is suitable for 5G base station applications.

A Novel Wideband and High-Efficiency Electronically Scanning Transmitarray Using Transmission Metasurface Polarizer

Inspired by the recent progress of metasurfaces, a novel wideband and high-efficiency electronically reconfigurable transmitarray (TA) is presented that can enable two-dimensional (2-D) beam steering and multiple beam mode switching in a digital manner. The proposed unit cell consists of a reconfigurable anisotropic metallic resonator, which locates between a pair of orthogonally oriented subwavelength metal gratings. One-bit phase quantization is obtained by controlling the ON or OFF state of two positive-intrinsic-negative (p-i-n) diodes integrated on the anisotropic metallic resonator layer. To choke the radio frequency (RF) signal effectively, a bias layer is connected by the metallic via hole to the center of the resonator, where the electric field is minimal. The simulated results show that the proposed unit cell can achieve a low insertion loss of 1 dB from 9.3 to 10.9 GHz for two phase states. Then, the radiation performance of a 10 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times\,\,10$ </tex-math></inline-formula> element array fed by a pyramidal horn antenna is theoretically calculated, simulated, and measured. The measured maximum gain is 19.1 dBi at 10.0 GHz with an aperture efficiency of 25.8% and a 3 dB gain bandwidth of 15.9%. The measured results demonstrate the 2-D beam scanning capability within the 50° range.

Non-Mechanical Beam Steering and Adaptive Beam Control Using Variable Focus Lenses for Free-Space Optical Communications

Free-space optical communications (FSOCs) are gaining popularity as a promising solution to the capacity crunch of aerial and satellite backhaul networks for next-generation mobile communication systems. A major technical challenge associated with such FSOC systems in motion is the pointing, acquisition, and tracking (PAT). To facilitate PAT, it is absolutely necessary to steer the optical beam over a wide angle and also adjust the beam divergence angle adaptively to the link condition and the amount of pointing error. The conventional methods to steer the optical beam and/or to adjust the beam divergence angle rely on mechanical mechanisms. Recently, the optical beam steering technique using variable focus lenses has been proposed and demonstrated. By using an on-axis variable focus lens followed by two decentered variable focus lenses, we can steer the optical beam over a wide range in a non-mechanical fashion. In this paper, we explore the possibility of using variable focus lenses for the realization of beam steering and adaptive beam control for FSOCs. For this purpose, we employ three variable focus lenses, one on-axis lens for adaptive beam divergence control and two decentered lenses for two-dimensional beam steering. We demonstrate the simultaneous beam steering and adaptive beam control capability of this variable focus lens-based system over a 104-m long free-space optical link. We evaluate the maximum beam steering angle and beam quality as we vary the offset distance of decentered variable focus lenses. Also evaluated experimentally is the impact of gravity on the beam quality. Finally, we show that the beam steering and adaptive beam control techniques implemented by variable focus lenses improve the performance of 10-Gb/s FSOC system considerably in the presence of pointing errors.