Showing papers on "Chirp published in 2019"

Ultrafast optical pulse shaping using dielectric metasurfaces

Abstract: Advances in ultrafast lasers, chirped pulse amplifiers, and frequency comb technology require fundamentally new pulse-modulation strategies capable of supporting unprecedentedly large bandwidth and high peak power while maintaining high spectral resolution. We demonstrate how dielectric metasurfaces can be leveraged to shape the temporal profile of a near-infrared femtosecond pulse. Finely tailored pulse-shaping operations, including splitting, compression, chirping, and higher-order distortion, are achieved using a Fourier-transform setup embedding metasurfaces able to manipulate, simultaneously and independently, the amplitude and phase of the constituent frequency components of the pulse. Exploiting metasurfaces to manipulate the temporal characteristics of light expands their impact and opens new vistas in the field of ultrafast science and technology.

Theory of Frequency-Modulated Combs in Lasers with Spatial Hole Burning, Dispersion, and Kerr Nonlinearity.

Abstract: Frequency-modulated (FM) frequency combs constitute an exciting alternative to generate equidistant spectra. The full set of Maxwell-Bloch equations is reduced to a single master equation for lasers with fast gain dynamics to provide insight into the governing mechanisms behind phase locking. It reveals that the recently observed linear frequency chirp is caused by the combined effects of spatial hole burning, group velocity dispersion, and Kerr nonlinearity due to asymmetric gain. The comparison to observations in various semiconductor lasers suggests that the linear chirp is general to self-starting FM combs.

Massively parallel coherent laser ranging using soliton microcombs

Abstract: Coherent ranging, also known as frequency-modulated continuous-wave (FMCW) laser based ranging (LIDAR) is currently developed for long range 3D distance and velocimetry in autonomous driving. Its principle is based on mapping distance to frequency, and to simultaneously measure the Doppler shift of reflected light using frequency chirped signals, similar to Sonar or Radar. Yet, despite these advantages, coherent ranging exhibits lower acquisition speed and requires precisely chirped and highly-coherent laser sources, hindering their widespread use and impeding Parallelization, compared to modern time-of-flight (TOF) ranging that use arrays of individual lasers. Here we demonstrate a novel massively parallel coherent LIDAR scheme using a photonic chip-based microcomb. By fast chirping the pump laser in the soliton existence range of a microcomb with amplitudes up to several GHz and sweep rate up to 10 MHz, the soliton pulse stream acquires a rapid change in the underlying carrier waveform, while retaining its pulse-to-pulse repetition rate. As a result, the chirp from a single narrow-linewidth pump laser is simultaneously transferred to all spectral comb teeth of the soliton at once, and allows for true parallelism in FMCW LIDAR. We demonstrate this approach by generating 30 distinct channels, demonstrating both parallel distance and velocity measurements at an equivalent rate of 3 Mpixel/s, with potential to improve sampling rates beyond 150 Mpixel/s and increase the image refresh rate of FMCW LIDAR up to two orders of magnitude without deterioration of eye safety. The present approach, when combined with photonic phase arrays based on nanophotonic gratings, provides a technological basis for compact, massively parallel and ultra-high frame rate coherent LIDAR systems.

Spectral phase control of interfering chirped pulses for high-energy narrowband terahertz generation.

Abstract: Highly-efficient optical generation of narrowband terahertz radiation enables unexplored technologies and sciences from compact electron acceleration to charge manipulation in solids. State-of-the-art conversion efficiencies are currently achieved using difference-frequency generation driven by temporal beating of chirped pulses but remain, however, far lower than desired or predicted. Here we show that high-order spectral phase fundamentally limits the efficiency of narrowband difference-frequency generation using chirped-pulse beating and resolve this limitation by introducing a novel technique based on tuning the relative spectral phase of the pulses. For optical terahertz generation, we demonstrate a 13-fold enhancement in conversion efficiency for 1%-bandwidth, 0.361 THz pulses, yielding a record energy of 0.6 mJ and exceeding previous optically-generated energies by over an order of magnitude. Our results prove the feasibility of millijoule-scale applications like terahertz-based electron accelerators and light sources and solve the long-standing problem of temporal irregularities in the pulse trains generated by interfering chirped pulses. Optical generation of terahertz radiation is needed for many applications, but gaining high efficiency is still a challenge. The authors report a method to overcome dispersion effects in interfering chirp pulses used for THz pulse production by tuning their relative spectral phase, enabling 0.6 mJ of THz energy output.

Interleaved Chirp Spreading LoRa-Based Modulation

Abstract: LoRa has established itself as one of the leading technologies within evolving low power wide area networks. In the patented LoRa modulation, a linearly increasing basis chirp signal spans the LoRa bandwidth. Cyclic shifts of this basis chirp signal create a multidimensional space for the orthogonal signaling of nonbinary LoRa symbols. The number of bits per LoRa symbol as well as the symbol rate depend on an applied spreading factor (SF) that could vary between 7 and 12. In this paper, interleaved chirp spreading LoRa (ICS-LoRa) is proposed as a physical layer-inspired approach to enhance data rates of the capacity-limited LoRa networks. In ICS-LoRa, interleaved versions of the nominal LoRa chirp signals constitute a new multidimensional space with the purpose of adding one extra bit within each transmitted ICS-LoRa symbol. The proposed interleaving pattern of ICS-LoRa maintains the same communication robustness of nominal LoRa. The ICS interleaving pattern is also designed to simplify implementation where both ICS-LoRa modulation and demodulation can share the same ICS-interleaver block. An accurate approximation for BER performance of the proposed ICS-LoRa is derived in order to evaluate the underlying reception sensitivities. It is shown that the 14% capacity gain of ICS-LoRa with an SF of 7 is associated with a sensitivity loss at the scale of only 0.8 dB. On the other hand, ICS-LoRa achieves more than 8% in capacity gain with virtually no impact on sensitivity performance when using an SF of 12 that governs the maximum coverage range.

Photonics-based radar with balanced I/Q de-chirping for interference-suppressed high-resolution detection and imaging

Abstract: Photonics-based radar with a photonic de-chirp receiver has the advantages of broadband operation and real-time signal processing, but it suffers from interference from image frequencies and other undesired frequency-mixing components, due to single-channel real-valued photonic frequency mixing. In this paper, we propose a photonics-based radar with a photonic frequency-doubling transmitter and a balanced in-phase and quadrature (I/Q) de-chirp receiver. This radar transmits broadband linearly frequency-modulated signals generated by photonic frequency doubling and performs I/Q de-chirping of the radar echoes based on a balanced photonic I/Q frequency mixer, which is realized by applying a 90° optical hybrid followed by balanced photodetectors. The proposed radar has a high range resolution because of the large operation bandwidth and achieves interference-free detection by suppressing the image frequencies and other undesired frequency-mixing components. In the experiment, a photonics-based K-band radar with a bandwidth of 8 GHz is demonstrated. The balanced I/Q de-chirping receiver achieves an image-rejection ratio of over 30 dB and successfully eliminates the interference due to the baseband envelope and the frequency mixing between radar echoes of different targets. In addition, the desired de-chirped signal power is also enhanced with balanced detection. Based on the established photonics-based radar, inverse synthetic aperture radar imaging is also implemented, through which the advantages of the proposed radar are verified.

A High-Resolution 220-GHz Ultra-Wideband Fully Integrated ISAR Imaging System

Abstract: In this paper, an ultra-wideband fully integrated imaging radar at sub-terahertz (sub-THz) frequencies is presented, which demonstrates a fine lateral resolution without using any focal lens/mirror. We have achieved a lateral resolution of 2 mm for an object at 23-cm distance as well as a range resolution of 2.7 mm. To achieve the decent range resolution, in a frequency modulation continuous wave radar configuration, a state-of-the-art chirp bandwidth (BW) of 62.4 GHz at a center frequency of 221.1 GHz is generated and efficiently radiated. We have presented a design technique for the optimal design of the passive embedding around the core transistor to maximize the tuning BW of the voltage controlled oscillator. At the receiver side, to maximize the intermediate frequency level, a subharmonic mixer is utilized, which is designed for the lowest conversion loss. Finally, to obtain the fine lateral resolution, we have implemented near-field beamforming algorithm based on the inverse synthetic aperture radar (ISAR) systems. The synthesized beamwidth is less than 0.5°; hence, high-resolution images are reconstructed. The system is fabricated in a 55-nm BiCMOS process. To the best of our knowledge, this is the first imaging radar at THz/sub-THz frequencies, which utilizes ISAR to achieve a high lateral resolution while the radar system is fully integrated.

Stepped-Frequency Continuous-Wave Radar With Self-Injection-Locking Technology for Monitoring Multiple Human Vital Signs

Abstract: This article proposes a single-conversion stepped-frequency continuous-wave (SCSFCW) radar that combines a stepped-frequency continuous-wave (SFCW) radar and a self-injection-locked (SIL) radar to benefit from the range resolution and the Doppler sensitivity of the two radars. An 8.5–9.5-GHz prototype SCSFCW radar system that comprises a subharmonic up/down converter with a 3–3.5-GHz stepped chirp local-oscillator (LO) signal and a 2.5-GHz SIL IF signal was developed to monitor the vital signs, i.e., respiration rate (RR) and heart rate (HR), of multiple humans. The coherence and range of the developed system were significantly enhanced by using a low pulse repetition frequency (PRF). In the experiment, the minimum distinguishable radial spacing between the vibrating frequencies of the metal plates that are not azimuthally overlapped with one another corresponds to a theoretical range resolution of 15 cm. However, owing to scattering by the human body, the minimum radial spacing for distinguishing between the vital signs of the individuals is three times than that for distinguishing between the metal plates in a similar experimental setup. Accordingly, the monitoring of up to three human vital signs using the developed system was demonstrated with a range-vital-Doppler map.

Abruptly autofocused and rotated circular chirp Pearcey Gaussian vortex beams.

Abstract: In this Letter, we introduce a new class of abruptly autofocued and rotated circular chirp Pearcey Gaussian vortex beams (AARCCPGVBs) which tend to abruptly autofocused circular chirp Pearcey vortex beams or chirp Gaussian vortex beams by adjusting the spatial distribution factors. Different from other rotated beams [Opt. Lett.31, 694 (2006) OPLEDP0146-959210.1364/OL.31.000694 and Opt. Lett.31, 2199 (2006)OPLEDP0146-959210.1364/OL.31.002199], the AARCCPGVBs are autofocused abruptly, maintain a low rotating speed before the focal point, and rotate abruptly and quickly in the focal point. Further, the position of the focal point in the propagating direction can also be controlled by adjusting the chirp factor.

Velocity Synchronous Linear Chirplet Transform

Abstract: Linear transform has been widely used in time–frequency analysis of rotational machine vibration. However, the linear transform and its variants in current forms cannot be used to reliably analyze rotational machinery vibration signals under nonstationary conditions because of their smear effect and limited time variability in time–frequency resolution. As such, this paper proposes a new time–frequency method, named velocity synchronous linear chirplet transform (VSLCT). The proposed VSLCT is an extended version of the current linear transform. It can effectively alleviate the smear effect and can dynamically provide desirable time–frequency resolution in response to condition variations. The smearing problem is resolved by using linear chirplet bases with frequencies synchronous with shaft rotational velocity, and the time–frequency resolution is made responsive to signal condition changes using time-varying window lengths. To successfully implement the VSLCT, a kurtosis-guided approach is proposed to dynamically determine the two time-varying parameters, i.e., window length and normalized angle. Therefore, the VSLCT does not require the user to provide such parameters and hence avoids the subjectivity and bias of human judgment that is often time-consuming and knowledge-demanding. This method can also analyze normal monocomponent frequency-modulated signal.

9.4 A 145GHz FMCW-Radar Transceiver in 28nm CMOS

Abstract: Indoor radar applications detecting people, vital signs and minute gestures require a high range resolution. This paper presents a 145GHz FMCW radar transceiver with on-chip antennas in 28nm bulk CMOS. An RF bandwidth of 13GHz yields an 11mm range resolution, and the high RF carrier permits greater velocity and MIMO-angular resolution. An external chirp signal at 16.1GHz is upconverted to 145GHz via a cascade of two frequency triplers in the RX and TX. For MIMO operation, a central chirp signal from a sub-sampling PLL integrated in 28nm CMOS [1] is distributed to multiple TRX chips on a PCB, eliminating mm-wave signal routing. The radar operates over a 0.15-to-10m range using fast sawtooth chirps of 5-to-$50 \mu \mathrm {s}$ duration. The beat frequency at IF fits between 400kHz and 15MHz. The on-chip TX leakage produces a strong beat near DC, suppressed via active highpass filtering. However, group delays of the PA and LNA can shift the beat into the RX passband. This is overcome by delaying the 16.1GHz RX chirp on chip. The chip dissipates 500mW in continuous mode, with the option of a low-power, duty-cycled FM transmission mode (for close ranges) enabled via fast powering built into the transceiver.

Table-top high-energy 7 μm OPCPA and 260 mJ Ho:YLF pump laser.

Abstract: We present a state-of-the-art compact high-energy mid-infrared (mid-IR) laser system for TW-level eight-cycle pulses at 7 μm. This system consists of an Er:Tm:Ho:fiber MOPA which serves as the seeder for a ZGP-based optical parametric chirped pulse amplification (OPCPA) chain, in addition to a Ho:YLF amplifier which is Tm:fiber pumped. Featuring all-optical synchronization, the system delivers 260 mJ pump energy at 2052 nm and 16 ps duration at 100 Hz with a stability of 0.8% rms over 20 min. We show that chirp inversion in the OPCPA chain leads to excellent energy extraction and aids in compression of the 7 μm pulses to eight optical cycles (188 fs) in bulk BaF2 with 93.5% efficiency. Using 21.7 mJ of the available pump energy, we generate 0.75 mJ energy pulses at 7 μm due to increased efficiency with a chirp inversion scheme. The pulse quality of the system’s output is shown by generating high harmonics in ZnSe which span up to harmonic order 13 with excellent contrast. The combination of the passive carrier-envelope phase stable mid-IR seed pulses and the high-energy 2052 nm picosecond pulses makes this compact system a key enabling tool for the next generation of studies on extreme photonics, strong field physics, and table-top coherent X-ray science.

Dual-chirp Fourier domain mode-locked optoelectronic oscillator

Abstract: Optoelectronic oscillators (OEOs) have been widely investigated to generate ultra-pure single-frequency microwave signals. Here, we propose and experimentally demonstrate a dual-chirp Fourier domain mode-locked (FDML) OEO to generate dual-chip microwave waveforms. In the proposed FDML OEO, a frequency-scanning dual-passband microwave photonics filter based on phase-modulation-to-intensity-modulation conversion using an optical notch filter and two laser diodes is incorporated into the OEO cavity. Fourier domain mode-locking operation is achieved by synchronizing the scanning period of the filter to the cavity round-trip time. Tunable dual-chirp microwave waveforms with a large time-bandwidth product are generated directly from the FDML OEO cavity in the experiment, which can be used in modern radar systems to improve its range-Doppler resolution.

Octave-spanning single-cycle middle-infrared generation through optical parametric amplification in LiGaS2.

Abstract: We report the generation of extremely broadband and inherently phase-locked mid-infrared pulses covering the 5 to 11 µm region. The concept is based on two stages of optical parametric amplification starting from a 270-fs Yb:KGW laser source. A continuum seeded, second harmonic pumped pre-amplifier in β-BaB2O4 (BBO) produces tailored broadband near-infrared pulses that are subsequently mixed with the fundamental pump pulses in LiGaS2 (LGS) for mid-infrared generation and amplification. The pulse bandwidth and chirp is managed entirely by selected optical filters and bulk material. We find an overall quantum efficiency of 1% and a mid-infrared spectrum smoothly covering 5-11 µm with a pulse energy of 220 nJ at 50 kHz repetition rate. Electro-optic sampling with 12-fs long white-light pulses directly from self-compression in a YAG crystal reveals near-single-cycle mid-infrared pulses (32 fs) with passively stable carrier-envelope phase. Such pulses will be ideal for producing attosecond electron pulses or for advancing molecular fingerprint spectroscopy.

TOA Estimation of Chirp Signal in Dense Multipath Environment for Low-Cost Acoustic Ranging

Abstract: In this paper, a novel time of arrival (TOA) estimation method is proposed based on an iterative cleaning process to extract the first path signal. The purpose is to address the challenge in dense multipath indoor environments that the power of the first path component is normally smaller than other multipath components, where the traditional match filtering (MF)-based TOA estimator causes huge errors. Along with parameter estimation, the proposed process is trying to detect and extract the first path component by eliminating the strongest multipath component using a band-elimination filter in fractional Fourier domain at each iterative procedure. To further improve the stability, a slack threshold and a strict threshold are introduced. Six simple and easily calculated termination criteria are proposed to monitor the iterative process. When the iterative “cleaning” process is done, the outputs include the enhanced first path component and its estimated parameters. Based on these outputs, an optimal reference signal for the MF estimator can be constructed, and a more accurate TOA estimation can be conveniently obtained. The results from numerical simulations and experimental investigations verified that, for acoustic chirp signal TOA estimation, the accuracy of the proposed method is superior to those obtained by the conventional MF estimators.

Joint Time–Frequency Scattering

Abstract: In time series classification and regression, signals are typically mapped into some intermediate representation used for constructing models. Since the underlying task is often insensitive to time shifts, these representations are required to be time-shift invariant. We introduce the joint time–frequency scattering transform, a time-shift invariant representation that characterizes the multiscale energy distribution of a signal in time and frequency. It is computed through wavelet convolutions and modulus non-linearities and may, therefore, be implemented as a deep convolutional neural network whose filters are not learned but calculated from wavelets. We consider the progression from mel-spectrograms to time scattering and joint time–frequency scattering transforms, illustrating the relationship between increased discriminability and refinements of convolutional network architectures. The suitability of the joint time–frequency scattering transform for time-shift invariant characterization of time series is demonstrated through applications to chirp signals and audio synthesis experiments. The proposed transform also obtains state-of-the-art results on several audio classification tasks, outperforming time scattering transforms and achieving accuracies comparable to those of fully learned networks.

Lamb Wave Mode Decomposition Based on Cross-Wigner-Ville Distribution and Its Application to Anomaly Imaging for Structural Health Monitoring

Abstract: Lamb waves are characterized by their multimodal and dispersive propagation, which often complicates analysis. This paper presents a method for separation of the mode components and reflected components in sensor signals in an active structural health monitoring (SHM) system. The system is trained using linear chirp signals but works for arbitrary excitation signals. The training process employs the cross-Wigner-Ville distribution (xWVD) of the excitation signal and the sensor signal to separate the temporally overlapped modes in the time-frequency domain. The mode decomposition method uses a ridge extraction algorithm to separate each signal component in the time-frequency distribution. Once the individual modes are separated in the time-frequency domain, they are reconstructed in the time domain using the inverse xWVD operation. The propagation impulse response associated with each component can be directly estimated for chirp inputs. The estimated propagation impulse response can be used to separate the modes resulting from arbitrary excitation signals as long as their frequency components fall in the range of the chirp signal. The usefulness of the mode decomposition algorithm is demonstrated on a new health monitoring system for composite structures. This system performs anomaly imaging using the first arriving mode extracted from sensor array signals acquired from the structure. The anomaly maps are computed using a sparse tomographic reconstruction algorithm. The reconstructed map can locate anomalies on the structure and estimate their boundaries. Comparisons with methods that do not employ mode decomposition and/or sparse reconstruction techniques indicate a substantially better performance for the method of this paper.

High-performance optical chirp chain BOTDA by using a pattern recognition algorithm and the differential pulse-width pair technique

Abstract: Optical chirp chain Brillouin optical time-domain analysis (OCC-BOTDA) has the capabilities of fast measurement, high Brillouin threshold, and freedom from the nonlocal effect; at the same time, however, it also has problems introduced by transient stimulated Brillouin scattering. The influence of the transient interaction is reflected as the broadened asymmetric Brillouin spectrum, the ghost peak, and the frequency shift of the main peak. This introduces difficulty in computing the fiber Brillouin frequency shift with good measurement accuracy. Besides, the OCC modulation causes additional noise due to the uneven amplitude response for different frequency components. In this work, we propose a high-performance OCC-BOTDA using the principal component analysis (PCA) based pattern recognition algorithm and differential pulse-width pair (DPP) technique. After building the Brillouin spectrum database (i.e., all patterns), the fiber intrinsic Brillouin frequency shift can be recognized by the PCA algorithm from a nonstandard Brillouin spectrum profile, resulting in good measurement accuracy. Meanwhile, the DPP technique, subtracting between two Brillouin signals generated by two wide-width pump pulses, is utilized to reduce the OCC modulation noise and avoid the pulse self-phase modulation effect in long-range BOTDA sensing. In the experiment, a temperature measurement with 1.3 MHz measurement precision, 4 m spatial resolution, and 5 s measurement time is achieved over a 100 km single-mode fiber.

Direct digital predistortion technique for the compensation of laser chirp and fiber dispersion in long haul radio over fiber links

Abstract: Analog Radio-over-Fiber (A-RoF) communication technology constitutes a promising technique for next generation radio access networks thanks to its relatively low bandwidth requirements. Within this context, an efficient predistortion technique is proposed, which can be applied to reduce the impairments of A-RoF systems due to the combined effects of frequency chirp of the laser source and chromatic dispersion of the optical channel. The radio frequency signal is firstly put in digital form through an analog to digital converter, then the predistortion operation is realized, and finally the resulting signal is put again into analog form. A comprehensive analysis on the theoretical basis of the proposed approach is presented, together with the approximations introduced, which makes it practically realizable. The improvements on the quality of the received signal due to the proposed solution are illustrated with reference to scenarios of applicative interest. The performance of proposed technique is evaluated in terms of adjacent channel leakage ratio and error vector magnitude when long term evolution signal is applied at the input.

Effects of the modulated vortex and second-order chirp on the propagation dynamics of ring Pearcey Gaussian beams.

Abstract: The evolution of the chirped ring Pearcey Gaussian vortex (CRPGV) beams in free space is numerically investigated. The optical bottle beam and two-consecutive optical bottle beam can be directly generated from a ring Pearcey Gaussian beam with central vortices and the second-order chirp in free space. In particular, the focusing intensity will decrease when the vortices’ locations are far away from the center of the beam or the topological charges are smaller. Our results show that the beam shapes, the normalized focusing intensity, and the focal length of the CRPGV beams can be controlled by choosing different beam parameters.

Coulomb interactions in high-coherence femtosecond electron pulses from tip emitters

Abstract: Tip-based photoemission electron sources offer unique properties for ultrafast imaging, diffraction, and spectroscopy experiments with highly coherent few-electron pulses. Extending this approach to increased bunch-charges requires a comprehensive experimental study on Coulomb interactions in nanoscale electron pulses and their impact on beam quality. For a laser-driven Schottky field emitter, we assess the transverse and longitudinal electron pulse properties in an ultrafast transmission electron microscope at a high photoemission current density. A quantitative characterization of electron beam emittance, pulse duration, spectral bandwidth, and chirp is performed. Due to the cathode geometry, Coulomb interactions in the pulse predominantly occur in the direct vicinity to the tip apex, resulting in a well-defined pulse chirp and limited emittance growth. Strategies for optimizing electron source parameters are identified, enabling advanced ultrafast transmission electron microscopy approaches, such as phase-resolved imaging and holography.

The Performance of Chirp Signal Used in LEO Satellite Internet of Things

Abstract: The technology of chirp spread spectrum (CSS) has been around for decades, widely used in the fields of radar and sonar. In recent years, CSS has been used in the IEEE 802.15.4a and Long Range (LoRa) Internet of Things (IoT), called LoRa modulation. On the other hand, CSS has never been used in low-Earth-orbit (LEO) satellite communication systems for low-data-rate transmission. CSS applied in LoRa as a kind of successful commercial IoT technology will promote research on its application in satellite communication for IoT. Recently, new types of chirp signals with the same chirp rate have become available to realize multiple accesses. This letter examines those types of chirp signal and the revised SCS called Asymmetry Chirp Signal (ACS) is proposed for better performance in LEO satellite IoT.

Mitigating Range Ambiguities With Advanced Nonlinear Frequency Modulation Waveform

Abstract: Range ambiguity suppression is a technical challenge for current synthetic aperture radar systems. A potential solution is to orthogonally modulate the transmitting pulses; however, these orthogonal waveforms (e.g., up-down chirp waveforms) actually cannot reduce the cross correlation energy (CCE). Nonlinear frequency modulation (NLFM) waveform can change the time–frequency relationship to adjust the energy distribution within the bandwidth to reduce the CCE. In this letter, a novel orthogonal NLFM waveform optimization framework is proposed. Through this framework, advanced NLFM waveforms with low sidelobe and CCE are constructed. Furthermore, point and distributed scene simulation results are presented to verify the practicability of the proposed waveforms. In addition, the system scheme, waveform design, and range ambiguity suppression performance are detailed.

Super chirped rogue waves in optical fibers

Abstract: The super rogue wave dynamics in optical fibers are investigated within the framework of a generalized nonlinear Schrodinger equation containing group-velocity dispersion, Kerr and quintic nonlinearity, and self-steepening effect. In terms of the explicit rogue wave solutions up to the third order, we show that, for a rogue wave solution of order n, it can be shaped up as a single super rogue wave state with its peak amplitude 2n+1 times the background level, which results from the superposition of n(n+1)/2 Peregrine solitons. Particularly, we demonstrate that these super rogue waves involve a frequency chirp that is also localized in both time and space. The robustness of the super chirped rogue waves against white-noise perturbations as well as the possibility of generating them in a turbulent field is numerically confirmed, which anticipates their accessibility to experimental observation.

A Scalable 79-GHz Radar Platform Based on Single-Channel Transceivers

Abstract: This paper presents a scalable E-band radar platform based on single-channel fully integrated transceivers (TRX) manufactured using 130-nm silicon–germanium (SiGe) BiCMOS technology. The TRX is suitable for flexible radar systems exploiting massive multiple-input-multiple-output (MIMO) techniques for multidimensional sensing. A fully integrated fractional-N phase-locked loop (PLL) comprising a 39.5-GHz voltage-controlled oscillator is used to generate wideband frequency-modulated continuous-wave (FMCW) chirp for E-band radar front ends. The TRX is equipped with a vector modulator (VM) for high-speed carrier modulation and beam-forming techniques. A single TRX achieves 19.2-dBm maximum output power and 27.5-dB total conversion gain with input-referred 1-dB compression point of −10 dBm. It consumes 220 mA from 3.3-V supply and occupies $3.96~\mathrm {mm^{2}}$ silicon area. A two-channel radar platform based on full-custom TRXs and PLL was fabricated to demonstrate high-precision and high-resolution FMCW sensing. The radar enables up to 10-GHz frequency ramp generation in 74–84-GHz range, which results in 1.5-cm spatial resolution. Due to high output power, thus high signal-to-noise ratio (SNR), a ranging precision of 7.5 $\mu \text{m}$ for a target at 2 m was achieved. The proposed architecture supports scalable multichannel applications for automotive FMCW using a single local oscillator (LO).