Optical Phased Array Antenna Research Articles

Broadband Beam-Scanning Phased Array Based on Microwave Photonics

A one-dimensional active broadband phased array based on microwave photonics that works in the Ku band is proposed to achieve a large instantaneous bandwidth. The phased array uses a feeding network based on microwave photonics to provide the true time delay and a wide operating bandwidth. The array is mainly composed of a broadband horn antenna, an RF transmitting/receiving module, an optical network module, and a temperature control module. The form of a horn was selected for the antenna unit, and it was fed through a waveguide to obtain a wide operating bandwidth. An optical fiber delay line that could realize the true time delay at different frequencies was adopted for the time-delay module of the optical network. To obtain a large time delay and small quantization error, a hybrid time-delay diagram utilizing electrical and optical time delays was used in the design. In addition, a temperature control module was added to the antenna system to enhance the stability of the photonic time-delay module. For verification, a prototype of the presented antenna system was designed, fabricated, and measured. The experimental results showed that the optical phased array antenna was able to scan ±20° from 12 GHz to 17 GHz, and the beam pointing did not appear to be offset over the wide operating bandwidth.

Design of high-efficiency and large-field silicon-based transceiver integrated optical phased array

With the rapid development of photonic integrated circuits, optical phased array (OPA) technology has attracted much attention in recent years because it can turn quickly without mechanical structure, and has been widely studied in the fields of light detection and ranging (LiDAR). However, the two-dimensional optical phased array antenna is still limited by the antenna spacing, and it is difficult to expand the scanning range. We propose a two-dimensional silicon-based optical phased array (OPA) transceiver with high efficiency and a large field of view. The structure adjusts the phase of the two dimensions of the antenna through the external waveguide phase shifter of the antenna array and further scans the two dimensions of the far field. We take an 8 × 8 array as an example, reasonably design the array structure, and optimize the performance of some functional devices. Finally, the scanning range of 14.9°×11.2° can be achieved. At the same time, we can realize the free switching of the OPA receiving and transmitting functions through an optical switch.

Underwater Wireless Laser-Based Communications Using Optical Phased Array Antennas

Underwater Wireless Laser-Based Communications Using Optical Phased Array Antennas

Si Photonics FMCW LiDAR Chip with Solid-State Beam Steering by Interleaved Coaxial Optical Phased Array.

LiDAR has attracted increasing attention because of its strong anti-interference ability and high resolution. Traditional LiDAR systems rely on discrete components and face the challenges of high cost, large volume, and complex construction. Photonic integration technology can solve these problems and achieve high integration, compact dimension, and low-cost on-chip LiDAR solutions. A solid-state frequency-modulated continuous-wave LiDAR based on a silicon photonic chip is proposed and demonstrated. Two sets of optical phased array antennas are integrated on an optical chip to form a transmitter-receiver interleaved coaxial all-solid-state coherent optical system which provides high power efficiency, in principle, compared with a coaxial optical system using a 2 × 2 beam splitter. The solid-state scanning on the chip is realized by optical phased array without a mechanical structure. A 32-channel transmitter-receiver interleaved coaxial all-solid-state FMCW LiDAR chip design is demonstrated. The measured beam width is 0.4° × 0.8°, and the grating lobe suppression ratio is 6 dB. Preliminary FMCW ranging of multiple targets scanned by OPA was performed. The photonic integrated chip is fabricated on a CMOS-compatible silicon photonics platform, providing a steady path to the commercialization of low-cost on-chip solid-state FMCW LiDAR.

Archimedean spiral waveguide as efficient all-optical phase modulator for space laser beam pointing

Silicon nanophotonics is contributing to the development of devices with small dimensions and low energy consumption. In optical systems for space applications, whether in large or small satellites, such as CubeSat, the demand for photonic devices has been a necessity, mainly in the communication subsystem, due to limitations in the conventional optical beam pointing subsystems. Silicon nanophotonics can be a solution in this case as it allows for the construction of an optical beam pointing system without moving parts, such as optical phased array antennas, in which the component responsible for the pointing functionality is the optical phase modulator. With this objective, we propose an efficient non-resonant all-optical modulator based on an Archimedean spiral waveguide topology by means of the indirect thermo-optical effect. Computational results are presented and discussed.

Optimization of the silicon-based aperiodic optical phased array antenna.

Beam engineering is one of the most important functionalities in light detection and ranging (LiDAR). In this work, a silicon optical phased array (OPA) is employed to control the beam profile. Machine-learning-based genetic algorithm optimization is utilized to suppress the sidelobes of the far field pattern assuming the random distribution of aperiodic arrays. The optimized mainlobe position versus wavelength relationship in two-dimensional aperiodic arrays is distinctly different from prior works. Analysis was performed to show the effect of fabrication error of arrays on the side mode suppression ratio. Our study provides an effective pathway to optimize the random distributed OPAs within a controllable time frame among the vast number of parameters.

Comparison between optimal configuration algorithms of fiber phased array

Optical fiber phased array can be used in high-power laser beam combination, lidar and other areas. The configuration of the optical fiber array is different from the microwave phased array, which has periodic problems that affect the energy intensity distribution of the main lobe. Starting from the physical model, in this paper we establish a theoretical model of optical phased array antenna array based on a set of concentric circular ring lattices, and propose a theory of the rapid synthesis of randomly configured interference field strengths through using analytical continuation method and Fourier transform method. The problem of sampling bandwidth and sampling number that should be paid attention to in the numerical simulation of discrete sampling are discussed, and the problem of quickly realizing the numerical simulation of multi-beam interference field is solved. Genetic algorithm and particle swarm algorithm for optimizing the configuration of optical phased array antennas are investigated with different populations. The convergence speeds and optimization efficiencies of the two algorithms are compared and analyzed. It is demonstrated that the peak side-lobe ratio PSR can be achieved to be better than 0.270 by the genetic algorithm optimized configuration array under the real fabricate parameter. The proposed method is expected to be used in the actual optical phased array antenna configuration to guide the optimal design of the antenna with low side lobes, and the proposed model is also expected to provide a certain reference value for the study of optimizing the non-differentiable objective function.

Integrated Optical True Time Delay Network Based on Grating-Assisted Contradirectional Couplers for Phased Array Antennas

Phased array antennas (PAAs) play a key role in many fields such as radar systems and wireless communication systems. Since PAAs based on optical methods outperform the electronic counterparts in beam directivity and instantaneous bandwidth, optical PAAs have aroused wide research interests. Here, we report and experimentally demonstrate an integrated 4-channel optical true time delay network for PAAs. The true time delay unit is based on a grating-assisted contradirectional coupler, assisted by index chirp engineering and asymmetric apodization. A linear group delay with both positive and negative dispersion coefficients can be obtained. For the 4-channel time delay network, the measured dispersion coefficient of each channel is 10.35, 4.00, −4.32 and −14.38 ps/nm with 7 nm available bandwidth, respectively. The calculated beam scanning angle can range from 36.4 degree to −33.9 degree for the beam steering. This time delay network can be extended to large scale with more delay units and cascaded structures, thus wider scanning range and better beam directivity can be achieved.

Design and Simulation of Thermo-Optic Phase Shifters With Low Thermal Crosstalk for Dense Photonic Integration

We investigate and demonstrate the thermal crosstalk problem in integrated photonic circuits with metal and silicon doped heaters. Further, we illustrate that due to the localized heating effect, integrated doped heaters are out-performed in terms of thermal crosstalk as compared to integrated metal heaters. To mitigate thermal crosstalk and enhance phase tuning efficiency further, a CMOS compatible air-filled trench region is realized between the doped heater and the adjacent element. The performances of three fundamental building blocks of integrated photonic circuits, namely, a PN phase shifter, an optical attenuator, and a ring resonator, are tested by full-wave thermal, charge, and optical simulations. Additionally, the impact of thermal crosstalk on the performance of integrated PN phase shifters and optical attenuators is examined thoroughly. The proposed low crosstalk thermal phase shifters might be very beneficial for densely routed complex integrated photonic circuits like photonic transceivers for data centers, optical phased array antennas, and photonic reservoirs.

Beam Steering with a Nonlinear Optical Phased Array Antenna.

Transition metal dichalcogenides (TMDCs) exhibit high second harmonic (SH) generation in the visible due to their noncentrosymmetric crystal structure in odd-layered form and direct bandgap transition when thinned down to a monolayer. In order to emit the SH radiation into a desired direction, one requires a means to control the phase of the in-plane nonlinear polarization. Here, we couple the SH response of a monolayer MoS2 to an optical phased array antenna and demonstrate controllable steering of the nonlinear emission. By exploiting the intrinsic SH generation by the phased array antenna we achieve uniform emission efficiency into a broad angular range. Our work has relevance for novel optoelectronic applications, such as programmable optical interconnects and on-chip LIDAR.

Side-lobe level reduction in bio-inspired optical phased-array antennas.

Phased arrays are expected to play a critical role in visible and infrared wireless systems. Their improved performance compared to single element antennas finds uses in communications, imaging, and sensing. However, fabrication of photonic antennas and their feeding network require long element separation, leading to the appearance of secondary radiation lobes and, consequently, crosstalk and interference. In this work, we experimentally show that by arranging the elements according to the Fermat's spiral, the side lobe level (SLL) can be reduced. This reduction is proved in a CMOS-compatible 8-element array, revealing a SLL decrement of 0.9 dB. Arrays with larger numbers of elements and inter-element spacing are demonstrated through an spatial light modulator (SLM) and an SLL drop of 6.9 dB is measured for a 64-element array. The reduced SLL, consequently, makes the proposed approach a promising candidate for applications in which antenna gain, power loss, or information security are key requirements.

Dynamically controlled plasmonic nano-antenna phased array utilizing vanadium dioxide [Invited

We propose and analyze theoretically an approach for realizing a tunable optical phased-array antenna utilizing the properties of VO2 for electronic beam steering applications in the near-IR spectral range. The device is based on a 1D array of slot nano-antennas engraved in a thin Au film grown over VO2 layer. The tuning is obtained by inducing a temperature gradient over the device, which changes the refractive index of the VO2, and hence modifies the phase response of the elements comprising the array, by producing a thermal gradient within the underlying PCM layer. Using a 10-element array, we show that an incident beam can be steered up to ±22° with respect to the normal, by applying a gradient of less than 10°C.

Programmable RF photonic phase shifters based on FD-OP for optically controlled beamforming

Programmable RF photonic phase shifter that can achieve a full 360° phase shift with little RF signal amplitude variation and low phase noise (PN) is presented. It is based on a two-dimensional (2D) Fourier-domain optical processor (FD-OP) which comprises an array liquid crystal on silicon (LCoS) pixels to control the amplitude and phase of the spectral components by programming. It can realize multiple photonic RF phase shifters simultaneously applied in optical controlled phased array antennas. Experimental results show the RF phase shifter can achieve a continuous 0–360° phase shift with low amplitude variation of <2.5dB and a phase deviation of <2° at 15GHz.

Beam-Scanning Planar Lens Based on Metal–Dielectric–Metal Waveguide Arrays

Under specific illumination conditions, periodic arrays of metal–dielectric–metal (MDM) waveguides act as uniform optical phased-array antenna where the phase of the radiating optical wave can be controlled by modifying the refractive index distribution of the dielectric material. Based on this property, we propose a planar gradient index MDM-based lens which can transform spherical waves of the transverse-magnetic surface plasmon polariton waves to plane waves with specific beam deflections by adjusting the refractive index configurations. Using numerical simulations based on two-dimensional finite-difference time-domain method, it is confirmed that beam focusing and splitting with multiple dflection angles can also be achieved.

Beam steering for wireless optical links based on an optical phased array in silicon

The ability to steer optical beams, crucial to the operation of high-speed optical wireless links may be achieved using optical phased array antennas which have significant potential in this application. The beam formed by the phased array antennas is steered by tuning the relative phase difference between the adjacent antenna elements which may be achieved nonmechanically. In this paper, the characteristics and behaviour of two dimensional optical phased arrays with a structure composed of 2 × 2, 4 × 4, and 16 × 16 antenna elements in beam steering are verified. The wavelength beam steering of −0.16°/nm is measured along the θ direction with a required steering range (between main lobes) of 1.97° within a −3 dB envelop of 5° extent in the θ direction and 7° extent in the Φ direction. To achieve two-dimensional beam steering, thermo-optic beam steering can be used in Φ direction. It is found that the thermo-optic phase tuning departs the expected quadratic dependence and is well characterised by a quartic dependence upon heater current or voltage.

Wideband plasmonic beam steering in metal gratings

We demonstrate controllable light deflection in thick metal gratings with periodic subwavelength slits filled with an active material. Under specific illumination conditions, the grating becomes nearly transparent and acts as a uniform optical phased-array antenna where the phase of the radiating elements is controlled by modifying the index of refraction of the material that fills each slit. The beam-steering operational regime occurs in a wide wavelength band, and it is relatively insensitive to the input angle.

Performance evaluation of a liquid-crystal-on-silicon spatial light modulator

2-D optical phased array antennas formed by a liquid crystal on silicon (LCOS) spatial light modulator are described for free-space laser communication and high-resolution wavefront control. The device consists of an 2-D array of 1024×768 phase modulator elements, each with controlled voltage, and can induce a phase shift from 0 to 2 for wavelengths up to the near IR. When the device is used as a wavefront corrector, 18.7 waves peak-valley (at 632.8 nm) of aberration in the optical system is corrected to a residual of 1/9 wave peak-valley, or 1/30 wave rms. The Strehl ratio improved from 0.006 to 0.83 after correction. An additional linear phase ramp was added to the correction phase ramp to simultaneously correct and steer the laser beam. Continuous steering over ±4 mrad in the X-Y plane with a steering accuracy higher than 10 µrad has been obtained. The 1-D beam-steering efficiency is 80% at the maximum steering angle of 4 mrad. These results suggest that an LCOS device can be used to achieve very high-resolution wavefront control at very high efficiency.

Communication performance analysis of microsatellites using an optical phased array antenna

The clustering of satellites in cooperative fly formation con- stellations produces a lightweight, low cost, highly reliable and supra- performance space system. One way to communicate between the sat- ellites is by a laser beam with a narrow divergence angle. To maintain line of sight between the transmitter and the receiver during the commu- nication time, a steering device has to be incorporated into the commu- nication system. We adopt a 2-D optical phased array (OPA) antenna. An OPA antenna is an attractive option for a steering device as it is light- weight, compact, and provides agile and inertia-free 2-D beam steering. We integrate two fields of study—OPA and laser communication theory—to attain a new perspective on communication system design. We theoretically analyze and model a laser intersatellite link using a 2-D OPA antenna and illustrate the model by a numerical simulation. The microsatellite antenna gain distribution statistics are derived from the OPA theory using the Monte Carlo method. We apply the results to evaluate system performance, particularly the effect of OPA phase er- rors. © 2003 Society of Photo-Optical Instrumentation Engineers.

InP-based PIC for an optical phased-array antenna at 1.06 μm

We have demonstrated the feasibility of a photonic integrated circuit (PIC) for phase control at a wavelength of 1.06 /spl mu/m in an optical phased array telescope antenna system.

Three-element fiber-type optical phased array antenna with high-speed two-dimensional optical beam steering

A fiber-type optical phased array antenna is proposed as a new configuration of phased array antennas operating in the optical frequency domain. The proposed antenna consists of fibers that connect an optical beamforming network consisting of integrated optical waveguides to an array antenna consisting of microlenses as the element antenna. High-speed two-dimensional optical beam steering can be achieved by reducing the relative phase fluctuation between element antennas and the generation of the grating lobe. In an experiment on the three-element fiber-type optical phased array antenna, three 1 × 2 variable power dividers and four variable phase shifters are integrated on a LiNbO3 substrate as the optical beamforming network, and graded-index-fiber (GIF) lenses are used as the antenna elements. These components are connected through polarization-maintaining fibers (PMF). The 3-dB bandwidth of the integrated variable phase shifter is from dc to 924 MHz, and the optical beam steering range of the three-element array is 0.2°; they are arranged in a triangle. The parameters of the GIF lens are optimized and it is estimated that at the maximum gain coefficient a grating lobe level of –14.5 dB and a gain coefficient of 0.815 can be obtained. © 1999 Scripta Technica, Electron Comm Jpn Pt 1, 82(8): 42–51, 1999