Showing papers on "Chirp published in 2017"

High-Order Synchrosqueezing Transform for Multicomponent Signals Analysis—With an Application to Gravitational-Wave Signal

Abstract: This paper puts forward a generalization of the short-time Fourier-based synchrosqueezing transform using a new local estimate of instantaneous frequency. Such a technique enables not only to achieve a highly concentrated time-frequency representation for a wide variety of amplitude- and frequency-modulated multicomponent signals but also to reconstruct their modes with a high accuracy. Numerical investigation on synthetic and gravitational-wave signals shows the efficiency of this new approach.

Nonlinear Chirp Mode Decomposition: A Variational Method

Abstract: Variational mode decomposition (VMD), a recently introduced method for adaptive data analysis, has aroused much attention in various fields. However, the VMD is formulated based on the assumption of narrow-band property of the signal model. To analyze wide-band nonlinear chirp signals (NCSs), we present an alternative method called variational nonlinear chirp mode decomposition (VNCMD). The VNCMD is developed from the fact that a wideband NCS can be transformed to a narrow-band signal by using demodulation techniques. Our decomposition problem is, thus, formulated as an optimal demodulation problem, which is efficiently solved by the alternating direction method of multipliers. Our method can be viewed as a time–frequency filter bank, which concurrently extracts all the signal modes. Some simulated and real data examples are provided showing the effectiveness of the VNCMD in analyzing NCSs containing close or even crossed modes.

Separation of Overlapped Non-Stationary Signals by Ridge Path Regrouping and Intrinsic Chirp Component Decomposition

Abstract: In some applications, it is necessary to analyze multi-component non-stationary signals whose components severely overlap in the time-frequency (T-F) domain. Separating those signal components is desired but very challenging for existing methods. To address this issue, we propose a novel non-parametric algorithm called ridge path regrouping (RPRG) to extract the instantaneous frequencies (IFs) of the overlapped components from a T-F representation (TFR). The RPRG first detects the ridges of a multi-component signal from a TFR and then extracts the desired IFs by regrouping the ridge curves according to their variation rates at the intersections. After the IFs are obtained, component separation is achieved by using the intrinsic chirp component decomposition (ICCD) method. Different from traditional T-F filter-based methods, the ICCD can accurately reconstruct overlapped components by using a joint-estimation scheme. Finally, applications of separating some simulated and experimental micro-Doppler signals are presented to show the effectiveness of the method.

Stable multi-GeV electron accelerator driven by waveform-controlled PW laser pulses

Abstract: The achievable energy and the stability of accelerated electron beams have been the most critical issues in laser wakefield acceleration. As laser propagation, plasma wave formation and electron acceleration are highly nonlinear processes, the laser wakefield acceleration (LWFA) is extremely sensitive to initial experimental conditions. We propose a simple and elegant waveform control method for the LWFA process to enhance the performance of a laser electron accelerator by applying a fully optical and programmable technique to control the chirp of PW laser pulses. We found sensitive dependence of energy and stability of electron beams on the spectral phase of laser pulses and obtained stable 2-GeV electron beams from a 1-cm gas cell of helium. The waveform control technique for LWFA would prompt practical applications of centimeter-scale GeV-electron accelerators to a compact radiation sources in the x-ray and γ-ray regions.

Controlling the velocity of ultrashort light pulses in vacuum through spatio-temporal couplings

Abstract: Due to their broad spectral width, ultrashort lasers provide new possibilities to shape light beams and control their properties, in particular through the use of spatio-temporal couplings. In this context, we present a theoretical investigation of the linear propagation of ultrashort laser beams that combine temporal chirp and a standard aberration known as longitudinal chromatism. When such beams are focused in a vacuum, or in a linear medium, the interplay of these two effects can be exploited to set the velocity of the resulting intensity peak to arbitrary values within the Rayleigh length, i.e. precisely where laser pulses are generally used. Such beams could find groundbreaking applications in the control of laser-matter interactions, in particular for laser-driven particle acceleration.

Generation of narrowband, high-intensity, carrier-envelope phase-stable pulses tunable between 4 and 18 THz.

Abstract: We report on the generation of high-energy (1.9 μJ) far-infrared pulses tunable between 4 and 18 THz frequency. Emphasis is placed on tunability and on minimizing the bandwidth of these pulses to less than 1 THz, as achieved by difference-frequency mixing of two linearly chirped near-infrared pulses in the organic nonlinear crystal DSTMS. As the two near-infrared pulses are derived from amplification of the same white light continuum, their carrier envelope phase fluctuations are mutually correlated, and hence the difference-frequency THz field exhibits absolute phase stability. This source opens up new possibilities for the control of condensed matter and chemical systems by selective excitation of low-energy modes in a frequency range that has, to date, been difficult to access.

Optimised Signal Processing for Nonlinear Ultrasonic Nondestructive testing of Complex Materials and Biological Tissues

Abstract: In this thesis the possibility of nonlinear ultrasonic NDT is investigated for complex materials and biological tissues. The delayed TR-NEWS signal processing methodis developed, which is based on the TR-NEWS method. TR-NEWS is a method well-suited for materials with complex structure: it allows spatio-temporal focusing of a long ultrasonic chirp signal to the region near the receiving transducer, forming an impulse pulse. The received signal power and SNR are increased as a result.Delayed TR-NEWS allows the use of this focused wave pulse as a new basis for either the signal optimisation or, alternatively, for the detection of nonlinearity by the breakdown of linear superposition. This method is used in physical experiments and simulations. The physical experiments are made on an undamaged CFRP block and a porcine skin sample. The skin is tested in a synchronised acoustomechanical setup specially designed in the course of this thesis. In 1D pseudospectral simulations for CFRP, it is determined that while classical nonlinearity cannot probably be detected in ultrasonic NDT, it could be possible to detect nonclassical nonlinear effects such as those from cracks and microdamage.Physical experiments and 2D FEM simulations of linear, undamaged CFRP are compared for studying the delayed TR-NEWS method, its applicability in optimising the focused wave, and also for creating an interaction of waves at the focusing region with a linear superposition prediction. This suggests the possibility of detecting nonlinearities by comparing the actual signal from interaction to the linear prediction.Finally, more 2D simulations are conducted for CFRP with a single contact gap nonlinearity near the focusing region. The nonlinearity is measured by PI and delayed TR-NEWS. It is determined that delayed TR-NEWS is able to detect the defect at least as well as the PI method. It is ascertained that the PM hysteresis model could describe the nonclassical nonlinearity of damaged materials and biological tissues. Asynchronised acoustomechanical test setup is created to test such multiscale nonlinearity. The simultaneous mechanical load test and ultrasonic delayed TR-NEWS test can be used to measure the mechanical properties of skin

Approaching the diffraction-limited, bandwidth-limited Petawatt

Abstract: J-KAREN-P is a high-power laser facility aiming at the highest beam quality and irradiance for performing state-of-the art experiments at the frontier of modern science. Here we approached the physical limits of the beam quality: diffraction limit of the focal spot and bandwidth limit of the pulse shape, removing the chromatic aberration, angular chirp, wavefront and spectral phase distortions. We performed accurate measurements of the spot and peak fluence after an f/1.3 off-axis parabolic mirror under the full amplification at the power of 0.3 PW attenuated with ten high-quality wedges, resulting in the irradiance of ~1022 W/cm2 and the Strehl ratio of ~0.5.

Chirp Rate and Instantaneous Frequency Estimation: Application to Recursive Vertical Synchrosqueezing

Abstract: This letter introduces new chirp rate and instantaneous frequency estimators designed for frequency-modulated signals. These estimators are first investigated from a deterministic point of view, then compared together in terms of statistical efficiency. They are also used to design new recursive versions of the vertically synchrosqueezed short-time Fourier transform, using a previously published method (D. Fourer, F. Auger, and P. Flandrin, “Recursive versions of the Levenberg-Marquardt reassigned spectrogram and of the synchrosqueezed STFT,” in Proc. IEEE Int. Conf. Acoust., Speech Signal Process. , Mar. 2016, pp. 4880–4884). This study paves the way to the real-time computation of a time-frequency representation, which is both invertible and sharply localized in frequency.

Highly Accurate Time-of-Flight Measurement Technique Based on Phase-Correlation for Ultrasonic Ranging

Abstract: Ultrasonic-based distance measurements using time-of-flight (TOF) is a fundamental technique for different applications across a wide variety of fields. In general, cross correlation between a transmitted and received signal is considered to be the optimal TOF estimation technique, which produces a peak at the time delay between them. Cross correlation provides a superior performance in conjunction with a linear chirp. However, as its accuracy depends on the width of the peak, which is inversely proportional to the signal’s bandwidth, it can only be said to be highly accurate if the reflected signal at the receiver is separated in time by more than the width of the correlation peak; otherwise, errors are introduced into the system. To improve its accuracy, the bandwidth of the transmitted signal must be increased, which increases the system cost. In this paper, to solve this problem, a $\text {threshold-based}\,\,\text {phase-correlation}$ technique is proposed, which is able to provide a much narrower peak than cross correlation without increasing the signal’s physical bandwidth. To evaluate the proposed method, in a controlled environment, two experiments were performed under low and high multipath conditions. For an operational range of 600 mm (indoor), the root-mean-square errors were [0.10, 0.56] mm and [0.19, 1.19] mm for low and high multipath environments, respectively, which indicate that the proposed technique is precise enough to support high accuracy applications.

55 GHz Bandwidth Distributed Reflector Laser

Abstract: We have demonstrated a 1300-nm short-cavity distributed reflector (DR) laser having 55 GHz bandwidth (BW), and successful 112-Gb/s transmission using four-level pulse-amplitude-modulation (PAM-4), without any pre-equalization for the transmitter. Two effects were realized in the design and operation of the DR laser: photon–photon ( P–P ) resonance and detuned-loading. The P–P resonance effect was realized between the DFB and distributed Bragg reflector (DBR) modes that coexisted in the cavity of the DR laser. The detuned-loading effect was used to effectively enhance the differential gain through the dynamic change in the mirror reflectivity that occurs on the flank of the DBR mirror due to the frequency chirp under modulation. Despite a limited RC cutoff frequency of 22 GHz, a wide modulation BW of 55 GHz was achieved. It is shown that the RC limitation was counteracted by the combined effects of the detuned-loading, which reduces the damping of relaxation oscillations, and an in-cavity FM–AM conversion effect that created a high-pass filter effect in the modulation response. This will be discussed by way of simulations and experimentally observed eye diagrams for 10 Gb/s NRZ and 28 Gbd PAM-4. The short-cavity DR laser achieved 112-Gb/s PAM-4 transmission over links having a range of dispersions from –28 to +7 ps/nm without precompensation on the transmitter.

Controlling the velocity of ultrashort light pulses in vacuum through spatio-temporal couplings

Abstract: Because of their broad spectral width, ultrashort lasers provide unique possibilities to shape light beams and control their properties, in particular through the use of spatio-temporal couplings. In this context, we present a theoretical investigation of the linear propagation of ultrashort laser beams that combine temporal chirp and a standard aberration known as longitudinal chromatism. When such beams are focused in a vacuum, or in a linear medium, the interplay of these two effects can be exploited to set the velocity of the resulting intensity peak to arbitrary values within the Rayleigh length, i.e., precisely where laser pulses are generally used. Such beams could find groundbreaking applications in the control of laser–matter interactions, in particular for laser-driven particle acceleration.

Effect of matter structure on the gravitational waveform

Abstract: Third-generation ground-based interferometers as well as the planned space-based interferometer LISA are expected to detect a plethora of gravitational wave signals from coalescing binaries at cosmological distance. The emitted gravitational waves propagate in the expanding Universe through the inhomogeneous distribution of matter. Here we show that the acceleration of the Universe and the peculiar acceleration of the binary with respect to the observer distort the gravitational chirp signal from the simplest General Relativity prediction beyond a mere time independent rescaling of the chirp mass, affecting intrinsic parameter estimations for the binaries visible by LISA. We find that the effect due to the peculiar acceleration can be much larger than the one due to the Universe acceleration. Moreover, peculiar accelerations can introduce a bias in the estimation of parameters such as the time of coalescence and the individual masses of the binary. An error in the estimation of the time of coalescence made by LISA will have an impact on the prediction of the time at which the signal will be visible by ground based interferometers, for signals spanning both frequency bands.

Photonic Generation of Dual-Chirp Waveforms With Improved Time-Bandwidth Product

Abstract: We present a photonic method for the generation of dual-chirp signals. In this approach, a single-tone RF signal is first modulated using a modulator in order to generate two optical carriers, which are further modulated by a linearly chirped signal by another modulator. Square-law detection in a photodiode then generates a dual-chirp signal whose center frequency and time-bandwidth product (TBWP) are fourfold increased. The dual-chirping and the improved TBWP can improve the range resolution of the radar system and help avoid the range measurement error caused by the range-Doppler coupling effect. The generation of bandwidth-quadrupled S-band dual-chirp waveforms is demonstrated experimentally. The processing of the dual-chirp signal is also discussed, in order to show its advantages over single-chirp signals. We believe that the proposed approach is a potential solution for the generation of dual-chirp signals with high center frequency and large bandwidth in modern radar systems.

Chirped Bragg Gratings in PMMA Step-Index Polymer Optical Fiber

Abstract: In this letter, we report for the first time, a chirped fiber Bragg grating photo-inscribed in undoped PMMA polymer optical fibre (POF). The chirped polymer optical fiber Bragg gratings (CPOFBGs) were inscribed using an UV KrF excimer laser operating at 248 nm and a 25-mm long chirped phase mask customized for 1550-nm grating inscription. The used laser pulsing frequency was 1 Hz with an energy of 5 mJ per exposure and only few shots for each grating inscription were employed. The reflection amplitude spectrum evolution of a CPOFBG is investigated as a function of the applied strain, temperature, and pressure. These results can potentiate further developments in different sensing fields, such as liquid level monitoring, splits, and transverse cracks in structural health monitoring by local pressure analysis or even biomedical field. Furthermore, CPOFBGs could present some critical advantages preferably replacing their silica counterparts as well as the uniform polymer FBGs.

Chirped-Pulse Phase-Sensitive Reflectometer Assisted by First-Order Raman Amplification

Abstract: The use of linearly chirped probe pulses in phase-sensitive optical time-domain reflectometry (ΦOTDR) technology has been recently demonstrated to allow for high-resolution, quantitative, and dynamic temperature or strain variation measurements in a simple and very robust manner This new sensing technology, known as chirped-pulse ΦOTDR, had a maximum reported sensing range of 11 km In this paper, a 75-km sensing range with 10-m spatial resolution is demonstrated by using bidirectional first-order Raman amplification The system is capable of performing truly linear, single-shot measurements of strain perturbations with an update rate of 1-kHz and 1-nϵ resolution The time-domain trace of the sensor exhibits a signal-to-noise ratio (SNR) in the worst point of >3 dB, allowing to monitor vibrations up to 500 Hz with remarkable accuracy To demonstrate the capabilities of the proposed system, we apply 20 dB (with only 300-ms analysis window and no postprocessing) and no evidence of nonlinearity in the acoustic response The optical nonlinear effects that the probe pulse could suffer along the sensing fiber are thoroughly studied, paying special attention to potential distortions of the pulse shape, particularly in its instantaneous frequency profile Our analysis reveals that, for proper values of peak power, the pulse does not suffer any major

Chirp Spread Spectrum Toward the Nyquist Signaling Rate—Orthogonality Condition and Applications

Abstract: With the proliferation of Internet-of-Things (IoT), the chirp spread spectrum (CSS) technique is re-emerging for communications. Although CSS can offer high processing gain, its poor spectral efficiency and the lack of orthogonality among different chirps tend to limit its potential. In this paper, we derive the condition to orthogonally multiplex an arbitrary number of linear chirps. For the first time in the literature, we show that the maximum modulation rate of the linear continuous-time chirps satisfying the orthogonality condition can approach the Nyquist signaling rate, the same as single-carrier waveforms with Nyquist signaling or orthogonal frequency-division multiplexing signals. The performance of the proposed orthogonal CSS is analyzed in comparison to the emerging LoRa systems for IoT applications with power constraint, and its capability for high-speed communications is also demonstrated in the sense of Nyquist signaling.

Simultaneous Real-Time Ranging and Velocimetry via a Dual-Sideband Chirped Lidar

Abstract: A dual-sideband (DSB) chirped lidar for simultaneous real-time ranging and velocimetry is proposed and demonstrated, in which a Mach–Zehnder modulator (MZM) is applied to generate the required optical DSB frequency-modulated continuous-wave (FMCW) signal. The inherent opposite frequency chirp and contrary wavelength offset to the optical carrier of the two generated sidebands make it possible to measure the distance and velocity by frequency mixing without complex post digital signal processing, meanwhile, make the measurement of velocity immune to the nonlinearity of the FMCW optical signals. An experiment is carried out, in which an 8–18 GHz saw-tooth FMCW signal is used to drive an MZM, generating a wideband optical DSB FMCW signal. The distance and the velocity are simultaneously derived from the real-time frequency spectra. Accurate velocimetry with a nonlinear FMCW signal is also investigated.

Analytical solutions to the finite-pulse Bloch model for multidimensional coherent spectroscopy

Abstract: We present perturbative analytical solutions to the optical Bloch equations at third order, with finite duration Gaussian pulse envelopes. We find that a given double-sided Feynman diagram in this approximation can be conveniently described in the frequency domain as a product of the expression in the impulsive limit and a finite-pulse factor. Finite-pulse effects are Feynman-diagram-dependent, however, and include nontrivial phase corrections that can occur even in the case of transform-limited pulses. The results constitute a practical framework for modeling phenomena in multidimensional coherent spectroscopy that cannot easily be captured in the impulsive limit, including the roles of bandwidth, resonance, and pulse chirp.

GMTI and Parameter Estimation via Time-Doppler Chirp-Varying Approach for Single-Channel Airborne SAR System

Abstract: Conventionally, a single-channel synthetic aperture radar (SC-SAR) system can hardly detect weak moving targets simply. In this paper, a time-Doppler chirp-varying (TDCV) filter is proposed for ground moving target indication and parameter estimation with the airborne SC-SAR system. The proposed method is easy to implement and mainly includes three steps. First, a traditional 2-D frequency range-Doppler algorithm is used to generate an original image. Second, the second-order range cell migration (RCM) phase term is partly compensated in the range frequency and azimuth time domain, and the rest of second-order RCM phase term is compensated in 2-D frequency domain. The whole processing, which is referred to as the TDCV approach, is employed to acquire a new TDCV image. Third, compared the original image with the new image, the clutter scatterers are nearly motionless while the moving targets are translated along the range direction due to their nonzero radial velocities. After the cancellation between two normalized images, the clutter background would be significantly suppressed since the two images generated by the same data. As a result, the moving targets can be indicated and the range difference of the moving target between two images can be exploited to estimate their radial velocities. The results obtained by applying the proposed method into a set of real SAR data are consistent with the analysis presented in this paper.

Target Detection in Analog Terrestrial TV-Based Passive Radar Sensor: Joint Delay-Doppler Estimation

Abstract: Due to 64- $\mu \text{s}$ line fly-back time of the analog television (ATV) signal producing a range ambiguity at ranges corresponding to the multiples of 19.2 km, it seems that we cannot determine the targets’ ranges in ATV-based passive bistatic radars (PBRs). Based on this standpoint, all discovered works on a target-detection problem in an ATV-based PBR have focused on the Doppler information in echoes of the television video carrier signal not range information. To cope with the severe range ambiguity of the ATV signal and make it possible to jointly estimate targets’ delays and Doppler shifts, we propose a new detector performing target detection in a layered manner. In each layer, one target is detected. Detection in each layer is done using a generalized likelihood ratio detector. Interference due to the detected target in the first layer is estimated and subtracted from the received signal. From the first layer’s interference canceled signal, another target (if exist) is detected in the second layer. The interference due to the second layer’s detected target is estimated and subtracted. These detection and interference cancellation steps are carried out in each layer, until all the targets are detected. The proposed detector is also implemented based on the chirp z-transform to efficiently obtain targets’ Doppler shifts over a limited range of Doppler frequencies. To obtain an effective cancellation of the strong interfering targets as well as off-grid targets, a robust version of resulting algorithm is also presented. Extensive simulation results are provided to demonstrate the high performance of the resulting target-detection algorithms.

A 260-mW Ku-Band FMCW Transceiver for Synthetic Aperture Radar Sensor With 1.48-GHz Bandwidth in 65-nm CMOS Technology

Abstract: Monolithic integration of synthetic aperture radar (SAR) transceiver with small size, lightweight, and low power consumption is suitable for uploading to a compact unmanned aerial vehicle (UAV) for SAR imaging This paper presents a monolithic frequency-modulated continuous-wave (FMCW) SAR transceiver that works at Ku-band and centers at 15 GHz Techniques to address the special requirements of UAV SAR are proposed A digital-tunable mixed-signal-mode FMCW chirp synthesizer is designed to be power efficient, to provide a tunable chirp rate, and to enable digital minimization of the root-mean-square (RMS) frequency errors A saturated driver-amplifier-power-amplifier chain and an input-load peak-staggering low-noise amplifier are implemented to nullify the ripple effects so that the degradations of imaging performances can be prevented Moreover, a 12th order active-RC bandpass filter is used to suppress the intermediate frequency interferences of both ground reflections and antenna leakage A binary-weighted programmable gain amplifier and a successive approximation analog-to-digital converter are also integrated into the chip Fabricated using a 65-nm complementary metal-oxide-semiconductor technology, the prototype demonstrates 148-GHz chirp bandwidth and <186-kHz rms frequency errors in a programmable modulation period from 118 to 10 ms The transmitter and receiver RF front end attains 11- and 051-dB ripples, respectively The function of the FMCW SAR transceiver is validated through the delay line and near-field ranging tests The SAR imaging experiment with a distance of around 110 m is successfully carried out using the chip prototype and a range migration algorithm At 12-V supply, the transceiver chip consumes 2594 mW

Optical filter requirements in an EML-based single-sideband PAM4 intensity-modulation and direct-detection transmission system.

Abstract: The feasibility of a single sideband (SSB) PAM4 intensity-modulation and direct-detection (IM/DD) transmission based on a CMOS ADC and DAC is experimentally demonstrated in this work. To cost effectively build a >50 Gb/s system as well as to extend the transmission distance, a low cost EML and a passive optical filter are utilized to generate the SSB signal. However, the EML-induced chirp and dispersion-induced power fading limit the requirements of the SSB filter. To separate the effect of signal-signal beating interference, filters with different roll-off factors are employed to demonstrate the performance tolerance at different transmission distance. Moreover, a high resolution spectrum analysis is proposed to depict the system limitation. Experimental results show that a minimum roll-off factor of 7 dB/10GHz is required to achieve a 51.84Gb/s 40-km transmission with only linear feed-forward equalization.

Nonlinear Pulse Compression to Sub-40 fs at $4.5~\mu$ J Pulse Energy by Multi-Pass-Cell Spectral Broadening

Abstract: We report on the pulse compression of an 18.5 MHz repetition rate pulse train from 230 fs to sub-40 fs by nonlinear spectral broadening in a multi-pass cell and subsequent chirp removal. The compressed pulse energy is $4.5~\mu \text{J}$ , which corresponds to 84 W of average power, with a compression efficiency of 88%. This recently introduced compression scheme is suitable for a large pulse energy range and for high average power. In this paper, we show that it can achieve three times shorter pulses than previously demonstrated.