True Time Delay Device Research Articles

Slow Light Mode at the Degenerate Band Edge for True Time Delay Applications

Tuneable true time delay device is designed at the degenerate band edge (DBE) by using two coupled periodic silicon ridge waveguides. The holes of the two ridge waveguides are well-tuned to let four modes couple and degenerate at the bandgap providing a slow light mode (the DBE mode). Transfer matrix method is utilized to trace and verify the slow light mode in the device. A 25-unit cell device ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~ \boldsymbol {\mu m}$ </tex-math></inline-formula> length device) is constructed to realize the slow mode at the DBE with 70% transmission and 42.5 ps signal delay over 130 GHz dispersion free bandwidth. Liquid crystal cladding layer is incorporated to provide continuous control of the slow mode velocity around the DBE resonance for UWB antenna array beamforming applications.

Photonic Beamforming for 5G and Beyond: A Review of True Time Delay Devices Enabling Ultra-Wideband Beamforming for mmWave Communications

The next generations of wireless communications are promising high capacity, low latency, and high throughput, enabled by millimeter wave spectrum. Beamforming and beam steering are key requirements for millimeter wave systems due to the fundamental limitations of such high frequencies. Traditional phased array antennas are narrow band and conventional beamforming techniques are too bulky, energy hungry, and expensive to integrate into consumer electronics. Therefore, new approaches of beamforming and beamsteering are required for 5G and beyond due to shortcomings of existing technologies. Here we present a comprehensive review of the photonic true time delay units for application in beamforming of next generations of wireless communications. The prospects and progress of several photonic techniques are discussed here along with their challenges. The fundamental focus of this endeavor will be on the on-chip Silicon-on-Insulator based approaches which enable utilizing conventional CMOS fabrication process for integration with other optical components for compact photonic integrated circuit.

MmW Rotman Lens-Based Sensing: An Investigation Study.

A Rotman lens is a wideband true-time delay device. Due to its simplistic structure with wave/signal routing capabilities, it has been widely utilized as a beamforming device in numerous communication systems. Since the basic Rotman lens design incorporates multiple input, output, and dummy ports, in this study, and for the first time, we utilized a Rotman lens as a sensor. The main idea was to gather abundant information from available Rotman lens ports to obtain better sensing performance. The realized lens is optimized to work in the millimeter wave (mmW) band from 27 to 29 GHz with a focus on a central frequency of 28 GHz. The design has a footprint of 140 × 103 × 0.8 mm3. The polarity correlator was used to characterize the material under investigation.

THzPrism: Frequency-Based Beam Spreading for Terahertz Communication Systems

With large available bandwidths, Terahertz (THz) band communication has been envisioned as a key technique to satisfy the increasing demand for ultra-high-speed wireless communications. To overcome severe path loss of THz signals, large antenna array based beamforming, i.e., directional communication, is required for THz communications. Beamforming increases distance coverage, but it significantly reduces angular coverage, which severely limits the efficiency and flexibility of THz systems. In this letter, a novel phased array architecture called THzPrism is designed to conduct beamforming for THz systems. The key idea of THzPrism is to insert several true time delay devices in a phased array so as to achieve frequency-based beam spreading. As a result, THzPrism can significantly enlarge angular coverage while maintaining the distance coverage for THz systems. Both theoretical analysis and numerical results are conducted to validate the effectiveness of THzPrism.

Low-Loss Continuously Tunable Optical True Time Delay Based on Si3N4 Ring Resonators

We design, fabricate, and characterize ultra-low loss continuously tunable optical true time delay devices based on Si3N4 ring resonators in a side-coupled integrated spaced sequence of resonators (SCISSOR) structure. A large tunable delay range up to 3.4 ns is demonstrated using the Balanced SCISSOR delay tuning scheme, for a record loss of only 0.89 dB/ns of delay. By optimizing the coupler design a device delay bandwidth of over 10 GHz is achieved with over 0.5 ns maximum time delay. This ultra-low loss delay line can enable distortion free operation for RF signals used in RF beamforming and other applications. Additionally, this device has the potential to be integrated with active photonic components to be part of a fully integrated photonic integrated circuit in an electronically scanned phased array system; utilizing a silicon photonics platform including heterogeneous integration.

A Review on the Development of Rotman Lens Antenna

Rotman lenses are the beguiling devices used by the beamforming networks (BFNs). These lenses are generally used in the radar surveillance systems to see targets in multiple directions due to its multibeam capability without physically moving the antenna system. Now a days these lenses are being integrated into many radars and electronic warfare systems around the world. The antenna should be capable of producing multiple beams which can be steered without changing the orientation of the antenna. Microwave lenses are the one who support low-phase error, wideband, and wide-angle scanning. They are the true time delay (TTD) devices producing frequency independent beam steering. The emerging printed lenses in recent years have facilitated the advancement of designing high performance but low-profile, light-weight, and small-size and networks (BFNs). This paper will review and analyze various design concepts used over the years to improve the scanning capability of the lens developed by various researchers.

Hardware Demonstration of Extremely Compact Optical True Time Delay Device for Wideband Electronically Steered Antennas

An optical true time delay device is demonstrated that is capable of supporting 112 antennas with 81 different delays (>; 6 bits) in a volume 16 × 5 × 4 including the box with electronics. It uses a free-space design based on the White cell, and alignment is made simple, fast, and robust by the use of slow-tool diamond turning of many optics on a single substrate. Pointing accuracy of the 12 objective mirrors is better than 10 μrad, and surface roughness is ≈ 45 nm RMS. Delays vary from 0 to 25 ns in 312.5 ps increments. Short delays are implemented using delay rods of high refractive index, and long delays using folded mirror trains. Total insertion loss from fiber to detector was 7.82 dB for the no-delay path, and 10.22 dB for the longest lens train. A three-state tip-style MEMS micromirror array is used to select among the delays, with tilt angles ±1.4° plus flat, and switching time <; 100 μs for the entire array. An InP wideband optical combiner photodetector array converts the optical signal to RF with 20 GHz bandwidth. The unit survived temperature cycling 0 to 50 C and random vibration on three axes (9.84 g RMS) with no degradation of signal.

True Time Delay Photonic Circuit Based on Perfluorpolymer Waveguides

A high-performance 4-bit optical true time delay device is realized on a perfluoropolymer integrated optic platform. The integrated waveguide circuit is based on athermal arrayed wavegide grating with monolithically integrated delay lines in a wavelength-selective recirculating loop configuration. The device provides precise delay length control (i.e., 1 m) over 16 channels with 40-ps incremental time delays. The device offers athermal operation over the 0°C-50°C range with a maximum insertion loss of 6.8 dB and a polarization shift of 0.4 nm. This compact device (20 × 32 × 3 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) promises applications in code-division multiple access and phased arrayed antenna systems, where the large channel counts with high resolution delay length controls and small footprints are required.

Improved Dielectric Properties of Low-Temperature-Sintered (Ba,Sr)TiO3-Based Ceramics by Ge Substitution

Multilayer microwave dielectric materials with low sintering temperature are required for microwave phase shifters, filters, and true-time delay devices. We investigated the sintering and dielectric properties of (Ba0.6Sr0.4)(Ti1-xGex)O3 (BSTG; 0.05≤x≤0.3) ceramics. As the Ge concentration was increased, the lattice constant of BSTG ceramics decreased, and Ba2Ge2TiO8, which is the liquid phase at low temperature, was formed. Ba2Ge2TiO8 liquid phase may increase the sintering density. The effect of Ge substitution is the decrease in the sintering temperature from over 1400 to 1150 °C in BST system ferroelectric ceramics. With increasing Ge concentration, the dielectric constant decreased from 2190 to 530, and the dielectric loss decreased up to 0.001 (at 1 MHz) with sintering at 1150 °C for 2 h. When Ge was substituted at 0.05 and 0.1 mol of Ti in the BST at 1150 °C, the dielectric constant, dielectric loss, tunability, Curie temperature, and figure of merit were 2184 and 1529, 0.002 and 0.001, 27 and 23%, -11 and -18 °C, and 135 and 230, respectively. These compositions show microwave dielectric properties comparable to those of (Ba0.5Sr0.5)TiO3 ferroelectrics, which are the important materials for tunable devices such as varactors, phase shifters, and frequency agile filters.

UWB time‐domain antennas beam scanning

AbstractUltra‐wideband (UWB) antenna is indispensable in impulse radar that transmits and receives short electromagnetic pulse signals and preserves the waveform well. Phased array antenna systems cannot meet the demand of the system. Optical true‐time delay techniques open the possibility of ultra‐wide bandwidth antenna systems, while at the same time meeting the stringent weight and size requirements. Continuously tunable true‐time delay techniques can provide continuous beam scanning. With advanced optoelectronic technique, fast wavelength tuning speed is possible. To detect and track moving‐target [Bi and Ren, Prog Electomagn Res 87 (2008), 15–41)], UWB time‐domain antenna array beam scanning is studied in this article. First, the theory of time‐domain antenna array scanning is analyzed, some useful conclusions are achieved. Then, an experiment system of UWB time‐domain antenna array scanning is built, which includes an antenna array, fiber‐optic true‐time delay device, and other equipments. Finally, the theoretical and experimental results combined to are made to validate the theory of UWB time‐domain antenna array beam scanning. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1110–1112, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25102

Real-time all-optical performance monitoring using optical bit-shape correlation

A new optical performance monitoring technique of an optical link in real time is experimentally demonstrated. Rather than comparing bit streams or analyzing eye diagrams, we use a novel optical correlator to compare the shapes of the individual received bits to a standard. The all-optical correlator outputs a pulse whose strength directly measures the degradation of the bit during transmission. Results are produced within three bit periods in real time instead of requiring statistical analysis of long data streams. The correlator is based on a simplified White cell-based true-time delay device.

Reconfigurable Delay Time Polymer Planar Lightwave Circuit for an X-band Phased-Array Antenna Demonstration

A 4-bit polymer optoelectronic true-time delay (TTD) device is demonstrated. The planar lightwave circuit (PLC) is composed of monolithically integrated low-loss passive polymer waveguide delay lines and five cascaded 2 times 2 polymer thermooptic switches. Waveguide junction offsets and air trenches simultaneously reduce the bending loss and device area. Simulations are used to optimize the trench and offset structures for fabrication. The 16 time delays generated by the device are measured to be in the range from 0 to 177 ps in 11.8-ps increments. The packaged PLC has an insertion loss of up to 14.9 dB, and the delay switching speed is 2 ms. An eight-element X-band phased-array antenna system is constructed to demonstrate the beam-steering capabilities of the 4-bit-delay devices. The TTD devices are shown to steer the far-field radiation pattern between 0deg and -14.5deg

Phase error corrected 4-bit true time delay module using a cascaded 2 × 2 polymer waveguide switch array

A fully integrated 4-bit true time delay device using polymer optical switches and waveguide delay lines is demonstrated. The fabricated device, which contains five 2x2 thermo-optic switches, has a maximum power consumption of 143 mW and a switching time less than 3 ms. The rf phase error, which is affected by the optical switch cross talk, is also theoretically analyzed and proved to be negligible by experimental results.

Active integrated photonic true time delay device

A photonic true time delay cell with two waveguide couplers and five semiconductor optical amplifiers is demonstrated. The five semiconductor optical amplifiers provide gain in the 1550-nm region and port selection to determine the time delay. With the amplifiers off the signal are blocked with extinction ratios of more than 10 dB. In the experiments reported here, the delay of 20 ns was provided by an optical fiber. Because of the potential for nanosecond switching times, the device has application in very agile phased array antenna applications, in optical switching and routing, and in optical filtering.

Demonstration of a linear optical true-time delay device by use of a microelectromechanical mirror array.

We present the design and proof-of-concept demonstration of an optical device capable of producing true-time delay(s) (TTD)(s) for phased array antennas. This TTD device uses a free-space approach consisting of a single microelectromechanical systems (MEMS) mirror array in a multiple reflection spherical mirror configuration based on the White cell. Divergence is avoided by periodic refocusing by the mirrors. By using the MEMS mirror to switch between paths of different lengths, time delays are generated. Six different delays in 1-ns increments were demonstrated by using the Texas Instruments Digital Micromirror Device as the switching element. Losses of 1.6 to 5.2 dB per bounce and crosstalk of -27 dB were also measured, both resulting primarily from diffraction from holes in each pixel and the inter-pixel gaps of the MEMS.

Polynomial-based optical true-time delay devices with microelectromechanical mirror arrays.

We previously reported optical true-time delay devices, based on the White cell, to support phased-array radars. In particular, we demonstrated a quadratic device, in which the number of delays obtainable was proportional to the square of the number of times the light beam bounced in the cell. Here we consider the possibilities when a microelectromechanical (MEM) tip/tilt mirror array with multiple stable states is used. We present and compare designs for quadratic, quartic, and octic cells using MEM mirror arrays with two, three, and five micro-mirror tilt angles. An octic cell with a three-state MEM can produce 6,339 different delays in just 17 bounces.

Wavelength-selective true time delay for optical control of phased-array antenna

Performance of an optically controlled phased-array antenna system employing novel single-chip optical wavelength selective true time-delay devices is reported. High-resolution time-delays are demonstrated using integrated delay lines. Extension to two-dimensional (2-D) antenna arrays with independent control of azimuth and elevation by using mid-stage optical wavelength conversion is proposed and demonstrated. An optical true-time-delay steered two-element X-band antenna was assembled to verify the wide instantaneous bandwidth operation.

Tunability in Ba1–xSrxTiO3-based Ferroelectrics

ABSTRACTFerroelectrics are presently of interest for phase shifters, filters, and true time delay devices. Voltage tunable paraelectrics have the potential to lower device cost and reduce power consumption compared with presently available devices. In order to improve device performance to acceptable levels, materials must have high tunability, low dielectric constant, low loss tangent, and low leakage current. Using existing predictive techniques, compositions of Ba0.6Sr0.4TiO3-based ferroelectrics with charge-compensated substitutions for Ti4+ were synthesized. Results of capacitance measurements are used to obtain dielectric constant and tunability in the paraelectric (T &gt; TC) regime. The relevance to device requirements is discussed. Results for substituted samples are compared to those for (unsubstituted) Ba0.6Sr0.4TiO3. Discussion of the impact of the results on predictive techniques for tunability is addressed.

Chirped-pulse programming of optical coherent transient true-time delays

Programming an optical coherent transient true-time delay device with two frequency-chirped pulses provides a novel means of performing broadband (> >GHz) true-time delay with a wide dynamic range of delays with fine temporal resolution. We have demonstrated true-time delays exceeding 2micros with sub-100-ps resolution. Chirped-pulse programming has the advantages over the previously proposed brief pulse programming [Opt. Lett. 21 1102 (1996)] of reduced instantaneous power requirements and the ability to control the true-time delay by frequency shifting the programming pulses.

Optically produced true-time delays for phased antenna arrays

A device is described for generating true-time delays optically for microwave signals used in beam steering and beam shaping in phased-array antennas. The device can be adapted to provide delays from picoseconds to nanoseconds. A single, compact unit should provide parallel delays for more than 64 independent antenna elements with a greater than 6-bit resolution. The time delays are produced by multiple reflections in a mirror configuration with continuous refocusing. A single spatial light modulator selects independent optical path lengths for each of the parallel antenna elements. Amplitude control for beam shaping can be integrated into the device. The unit can be made rugged for harsh environments by use of solid-block construction. The operation of the true-time delay device is described, along with the overall system configuration. Preliminary experimental data are given.