Optical Beamforming Research Articles

Optical Beamformer Based on Diffraction Order Multiplexing (DOM) of an Arrayed Waveguide Grating

A simplified beamforming architecture using a wavelength-selective optical true time delay (OTTD) module is proposed for phased array antenna (PAA) systems. Based on diffraction order multiplexing of an arrayed waveguide grating (AWG), the beamformer can realize multiple simultaneous time delays with only one OTTD module. We design, fabricate, and characterize a compact integrated optical beamformer using this structure for an eight-element X -band PAA system. The time delays generated by the fabricated beamformer are measured to be in the range from 0 to 278 ps in 5.7 ps increments of eight diffraction orders. The measured overall variation in the insertion loss of this device is less than 1.85 dB from 1527 to 1607 nm. The experimental results demonstrate that the proposed architecture can offer many advantages, such as multibeam capability, low insertion loss, a small footprint, and high resolution.

Next Generation Fiber-Wireless Fronthaul for 5G mmWave Networks

mmWave radio, although instrumental for achieving the required 5G capacity KPIs, necessitates the need for a very large number of access points, which places an immense strain on the current network infrastructure. In this article, we try to identify the major challenges that inhibit the design of the Next Generation Fronthaul Interface in two upcoming distinctively highly dense environments: in Urban 5G deployments in metropolitan areas, and in ultra-dense Hotspot scenarios. Second, we propose a novel centralized and converged analog Fiber-Wireless Fronthaul architecture, specifically designed to facilitate mmWave access in the above scenarios. The proposed architecture leverages optical transceivers, optical add/drop multiplexers and optical beamforming integrated photonics towards a Digital Signal Processing analog fronthaul. The functional administration of the fronthaul infrastructure is achieved by means of a packetized Medium Transparent Dynamic Bandwidth Allocation protocol. Preliminary results show that the protocol can facilitate Gb/s-enabled data transport while abiding to the 5G low-latency KPIs in various network traffic conditions.

Optical Beamforming Network for Multi-Beam Operation With Continuous Angle Selection

We propose an optical beamforming network (OBFN) for multi-beam operation and continuous selection of the beam angles. The OBFN is based on the use of wavelength-division multiplexing elements for the generation and manipulation of the signals that correspond to different beams and different antenna elements (AEs), and on the use of optical delay lines for the introduction of tunable time delays to these signals. We analyze the operating principle of the proposed OBFN in the downlink and uplink directions of a wireless system, and we experimentally demonstrate its proof of concept in the downlink direction up to the photodetection stage, using a $2\times 4$ setup based on commercial components. The implemented OBFN has the potential to support the steering of two beams and the excitation of four AEs. Using microwave signals with 15-GHz carrier frequency, high-order modulation formats, and symbol rates up to 1 Gbaud, we modulate two optical carriers and investigate the performance of the OBFN in four experimental cases, employing different combinations of signals, steering angles, and antenna excitation schemes. Through the analysis of the expected radiation pattern and off-line measurements of the BER of the decoded signals at the intended steering angles, we validate the feasibility of the proposed OBFN. The vision for actual implementations of the proposed OBFN would be enabled by means of photonic integration techniques.

基于反谐振波导微环的光控波束延时网络设计

基于反谐振波导微环的光控波束延时网络设计

Performance analysis and comparison of optical signal processing beamforming networks: a survey

Forthcoming wireless systems are developed to support greater data rate and extra coverage area. This can be achieved with the help of multiple input multiple output and smart antenna techniques. One of the major rapidly emerging areas of communication is the smart antenna system which aids in attaining better coverage by increasing the signal strength only in the chosen direction. With effective optical beamforming techniques, the smart antenna systems demonstrate to be more competent in terms of excellence of signals in wireless communication. In this paper, a succinct outline of the smart antenna, an analysis and the comparison of different architectures of optical signal processing beamforming network (OSPBFN) is presented. The performance of OSPBFN is analyzed and the comparison is done for different architectures with the antenna radiation parameters. This paper can enhance the understanding of the ongoing research work in the area of OSPBFN.

Automatic Monitor-Based Tuning of an RF Silicon Photonic 1X4 Asymmetric Binary Tree True-Time-Delay Beamforming Network

Photonic beamforming networks are promising candidates to achieve power-efficient transmission in future cellular communication systems. However, sensitivity to process and temperature variations necessitates an automatic calibration solution to enable robust operation. This paper demonstrates fully automatic monitor-based tuning of an integrated optical ring resonator-based 1X4 asymmetric binary tree optical beamforming network (OBFN). The proposed monitor-based tuning algorithm compensates fabrication variations and thermal crosstalk by controlling micro-heaters individually using information from electrical monitors. This algorithm is demonstrated on an OBFN that operates at 30 GHz with 2 GHz bandwidth and is fabricated in a standard silicon photonics foundry process. Successful calibration of the OBFN from a severely degraded initial response to the well-defined group delay responses required for a targeted radiating angle over 60 $^{\circ }$ (−30 $^{\circ }$ to 30 $^{\circ }$ ) in a linear beamforming antenna array is achieved. This fully automatic tuning approach opens the possibility of employing silicon OBFNs in real wideband mm-wave wireless communication systems.

Millimeter wave beamforming receivers using a Si-based OBFN for 5G wireless communication systems

Abstract Since next-generation (5G) wireless communication systems require high-speed processing of large amounts of data and wider bandwidth, the millimeter wave (mmWave) band becomes increasingly important and transmission technologies require a large number of antennas. Therefore, it is necessary to study technologies that can implement a very small antenna considering the characteristics of the mmWave band. In this study, we propose a high-performance miniature analog beamformer implementation technique that can operate in the mmWave band. The proposed method uses silicon (Si) photonics technology, which not only can process large amounts of data at the speed of light, but is also compatible with CMOS processes and can be miniaturized due to high refractive index. The SiN-based optical beamforming network (OBFN) chip used in satellite communications has been redesigned into a Si-based OBFN. In particular, we propose four types of Mach–Zehnder modulator (MZM) structures, including the design used in the existing satellite communication OBFN system. The feasibility and performance were tested with commercial optical simulation software to carry out virtual prototyping and create foundry-ready designs. Simulation results confirm that the proposed schemes are efficient at implementing miniature array antennas in the mmWave band and are suitable for high-performance ultra-small analog beamformers and massive multiple-input multiple-output (MIMO) implementations for 5G wireless communication systems.

Building 5G Millimeter-Wave Wireless Infrastructure: Wide-Scan Focal-Plane Arrays With Broadband Optical Beamforming

A wide-scan and broadband focal-plane array (FPA) concept is introduced in this article, which provides high antenna gain and effective isotropic radiated power (EIRP) with electronic beamsteering within a relatively large field of view (FoV), up to +/-20°. The antenna uses a bifocal double-reflector concept that optimizes the illumination of the focal-plane region. In this way, we have reduced the required size of the feed array and have maximized the number of simultaneously active array elements. By using a photonics beamformer, a broadband system for the 20-40-GHz band can be created with a fiber-based interface to a central processing unit. This hybrid antenna system is a very interesting concept for future 5G and beyond [5G millimeter-wave (mm-wave) base stations, two-way satellite communication systems, and point-to-point wireless backhaul systems]. A silicon BiCMOS low-noise amplifier (LNA) and a photonic integrated circuit (PIC) for the optical beamformer have been developed and integrated into the overall system. A system-level demonstrator was developed and experimentally validated in receive mode. Our concept provides an antenna gain of more than 40 dBi over an FoV of +/-15° at 28.5 GHz.

Deep Learning for Tuning Optical Beamforming Networks

In communication between planes and satellites, Optical Beamforming Networks (OBFNs), which rely on many small and flat Phased Array Antennas (PAAs), need to be tuned in order to receive signals from specific angles. In this paper, we develop a deep neural network representation of tuning OBFNs. The problem of tuning an OBFN is in many aspects similar to training a deep neural network. We present a way to exploit the special structure of OBFNs into deep neural network and an algorithm for tuning OBFNs based on feedback that can be easily measured in real system. Training data, which consists of full signals, can be measured, and therefore is used in this paper. For pilot signals, the desired signal is known explicitly. Given the configuration of OBFNs and all nominal parameters required, it was verified in simulation that the deep neural network can be used to tune large scale OBFNs for any desired delays.

Ultra-Low-Loss Silicon Nitride Optical Beamforming Network for Wideband Wireless Applications

Three optical ring resonator (ORR)-based integrated ultra-low-loss silicon nitride $\text{1}\times \text{4}$ optical beamforming networks (OBFNs) for millimeter-wave (mmW) beamsteering are reported. The group delay ripple of multi-ORR delay line was theoretically optimized and quantitatively studied by applying a genetic algorithm. The optimized 3-ORR delay true time delay (TTD) responses were experimentally achieved with $\text{208.7}\,\text{ps}$ and $\text{172.4}\,\text{ps}$ of delay tuning range for bandwidth of $\text{6.3}\,\text{GHz}$ and $\text{8.7}\,\text{GHz}$ , corresponding to a phase shift of $\text{17.1}\pi$ and $\text{14.1}\pi$ for $\text{41}\,\text{GHz}$ mmW signal. The TTD performance of the 3-ORR delay line was also verified by controlling the delay of $\text{3}\,\text{Gbps}$ data stream. A $\text{22}^{\circ }$ beamsteering angle equivalent OBFN delay distribution was achieved for $\text{41}\,\text{GHz}$ half-wavelength dipole antenna array. Both the theoretical analysis and experiments exhibit that the topology with one ring shared could balance the system complexity and TTD bandwidth well. Using heterodyne up-conversion technology and a single delay path, $\text{41}\,\text{GHz}$ mmW signal with $\text{3}\,\text{Gbps}$ OOK NRZ data modulation was generated and delayed.

Scalable and reconfigurable true time delay line based on an ultra-low-loss silica waveguide.

A scalable and reconfigurable on-chip optical true time delay line consisting of Mach-Zehnder interferometer (MZI) switches and delay waveguides is proposed and demonstrated with the ultra-low-loss silica waveguide platform. The MZI switches provide the reconfiguration of the light traveling paths and hence different delays. Our proposed structure can be easily scaled to an M bit delay line with a slight increase in dimensions. The footprint of our fabricated 1bit delay line is 33 mm×13 mm (length×width) and can provide a delay of 6.0ps with an insertion loss of 1.2dB at the operating wavelength of 1550nm, while the footprint of the 4bit delay line is 43 mm×14 mm and can provide a discrete delay tuning from 6.0 to 90.2ps with a delay deviation lower than 0.2ps and a tuning response time of 0.84ms. The insertion losses are lower than ∼2.34 dB, and the extinction ratios are greater than 20.42dB. The average switching power is ∼132.6 mW. Our proposed optical true time delay lines could find applications for optical beamforming in phased array antennas.

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Low-Loss Si3N4 TriPleX Optical Waveguides: Technology and Applications Overview

An overview of the most recent developments and improvements to the low-loss TriPleX Si3N4 waveguide technology is presented in this paper. The TriPleX platform provides a suite of waveguide geometries (box, double stripe, symmetric single stripe, and asymmetric double stripe) that can be combined to design complex functional circuits, but more important are manufactured in a single monolithic process flow to create a compact photonic integrated circuit. All functionalities of the integrated circuit are constructed using standard basic building blocks, namely straight and bent waveguides, splitters/combiners and couplers, spot size converters, and phase tuning elements. The basic functionalities that have been realized are: ring resonators and Mach–Zehnder interferometer filters, tunable delay elements, and waveguide switches. Combination of these basic functionalities evolves into more complex functions such as higher order filters, beamforming networks, and fully programmable architectures. Introduction of the active InP chip platform in a combination with the TriPleX will introduce light generation, modulation, and detection to the low-loss platform. This hybrid integration strategy enables fabrication of tunable lasers, fully integrated filters, and optical beamforming networks.

Optical wireless communication using positive real-valued orthogonal frequency-division multiplexing and optical beamforming

The relatively unsatisfactory performance of optical wireless communication (OWC) with respect to WiFi and millimeter-wave communications has formed a key issue preventing its commercialization. We experimentally demonstrate an OWC technology using a combination of positive real-valued orthogonal frequency-division multiplexing (OFDM) and optical beamforming (OB). Due to the intensity-modulation and direct-detection aspects of OWC systems, a positive real-valued OFDM signal can be suitably utilized to maximize the OWC data rate. Further, the OB technique, which can focus laser light on a desired target, can be utilized to increase the OWC data rate and transmission distance. Our experimental results show that the received optical signal power and electrical signal increase by up to 42 and 25 dB, respectively. Further, the data rate increases by a factor of 200 with OB over the conventional approach.

Visible light communication using TDMA optical beamforming

Optical beamforming is a technique to focus light-emitting diode (LED) light on a desired target and has been used to improve the performance of visible light communications (VLC). In this article, we propose and demonstrate a VLC technology based on time-division multiple access (TDMA) optical beamforming to accommodate multiple target devices. It focuses LED light on each different target device in each different time slot. Our results show that the proposed technique can accommodate multiple target devices and also gives the benefit of optical beamforming (5~10 dB gain) to each target device. Our results also show that the transmission distance increases from 110 to 200 cm with the TDMA optical beamforming.

Smart Optical Shape Sensor Using Electronically Controlled Lens and Laser Line Illumination Scanning

Proposed is a smart single viewing axis optical laser line illumination-based 3-D shape sensor that uses an electronically controlled variable focus lens (ECVFL) for 3-D optical beamforming. Specifically, the novel sensor design deploys laser line illumination scanning and camera-based spatial image processing of the target illuminated laser line spot that leads to a faster 3-D shape reconstruction versus the previously demonstrated point scanned ECVFL-based 3-D shape sensor. The proposed sensor is experimentally demonstrated using a liquid ECVFL and transverse direction motion mechanics to successfully 3-D map 40-mm depth steep surface profile objects with a mean measurement error of <5%. The line illumination sensor demonstrates a 53 times shorter 3-D mapping time per scanned point when compared with the point-scan-based sensor. The proposed 3-D shape sensor is suitable for scenarios where high transverse resolution inspections is required of objects having holes, crevices, or other complex external structures.

Performance evaluation of optical beamforming-based wideband antenna array (Invited Paper)

A wideband-generalized pattern multiplication approach to evaluate the performance of an optical beamforming-based wideband antenna array is proposed and experimentally demonstrated, which enables the far-field measurement of a large wideband array with a small anechoic chamber. Because the optimum reception of a wideband microwave signal is highly related to the time-domain distortions of the beamforming system, a correlation-receiver-based radiation pattern is applied to take the fidelity of the wideband signals into account. A four-element optical beamforming system is built to verify the feasibility of the proposed method. The results achieved by the proposed method agree well with the conventional direct measurements.

Control Strategy of True Time Delay Lines

ABSTRACTThis article presents the control of adjustable true time delays applied to an optical beamforming system. First is introduced the response of ring resonators of two and four ports and the cascade and lattice structures. The coupling factor and the phase modulation are employed as the control parameters for the adjustable group delay. The strategy of control is proposed and applied to a cascade of five ring resonators for producing wideband true time delays in the picosecond–nanosecond range with 2-GHz bandwidth and extremely low ripple. Ripples lower than 0.1% were obtained for the adjusted group delays. The proposed strategy can be simply extended if more resonators are added to increase the bandwidth of the system.

Dispersion-engineered multicore fibers for distributed radiofrequency signal processing.

We report a trench-assisted heterogeneous multicore fiber optimized in terms of higher-order dispersion and crosstalk for radiofrequency true time delay operation. The analysis of the influence of the core refractive index profile on the dispersion slope and effective index reveals a tradeoff between the behavior of the crosstalk against fiber curvatures and the linearity of the propagation group delay. We investigate the optimization of the multicore fiber in the framework of this tradeoff and present a design that features a group delay relative error below 5% for an optical wavelength range up to 100 nm and a crosstalk level below -80 dB for bending radii larger than 103 mm. The performance of the true time delay line is validated in the context of microwave signal filtering and optical beamforming for phased array antennas. This work opens the way towards the development of compact fiber-integrated solutions that enable the implementation of a variety of distributed signal processing functionalities that will be key in future fiber-wireless communications networks and systems.

Frequency tracking optical beamforming system using uncooled Fabry‐Perot lasers

ABSTRACTWe present a novel optical beamforming network that is able to use an uncooled Fabry‐Perot (FP) laser as the optical source. This is achieved by tracking the frequency and power drift of an FP laser and compensating these changes with programmable amplitude and phase in a liquid crystal‐on‐silicon Fourier domain optical processor. The system realizes six microwave phase shifters that operate simultaneously over 12–39.5 GHz with amplitude and phase response variation of 6.1 dB and 14.8°, respectively, under the conditions of changing laser current. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2537–2540, 2016