Recovery Of Waveforms Research Articles

Spectral recovery of broadband waveforms via cross-phase modulation based tunable Talbot amplifier

Physical processes in the Fourier domain play a crucial role in various applications such as spectroscopy, quantum technology, ranging, radio-astronomy, and telecommunications. However, the presence of stochastic noise poses a significant challenge in the detection of broadband spectral waveforms, especially those with limited power. In this study, we propose and experimentally demonstrate a cross-phase modulation (XPM) based spectral Talbot amplifier to recover the broadband spectral waveforms in high fidelity. Through the combination of spectral phase filtering and XPM nonlinear effect in an all-fiber configuration, we demonstrate spectral purification of THz-bandwidth spectral waveforms submerged in strong noise. The proposed spectral Talbot amplifier provides tunable amplification factors from 3 to 10, achieved by flexible control on the temporal waveform of the pump and the net dispersion. We demonstrate up to 10-dB remarkable improvement on optical signal-to-noise ratio (OSNR) while preserving the spectral envelope. Furthermore, our system allows frequency-selective reconstruction of noisy input spectra, introducing a new level of flexibility for spectral recovery and information extraction. We also evaluate numerically the impact of pump intensity deviation on the reconstructed spectral waveforms. Our all-optical approach presents a powerful means for effective recovery of broadband spectral waveforms, enabling information extraction from a noise-buried background.

An Ultra-Fast Temporal Talbot Array Illuminator

We propose an all-optical temporal Talbot array illuminator (T-TAI) enabling denoising passive amplification of broadband ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 10 GHz- bandwidth) optical signals. The key element is an ultra-fast temporal phase grating based on cross-phase modulation. Whereas previous implementations of the T-TAI suffer from the bandwidth limitations inherent to electro-optic systems, the all-optical nature of the proposed approach allows to simultaneously realize high amplification factors and sampling rates, which in turn allows for the efficient processing of broadband signals. In our experiments, we demonstrate a (signal bandwidth) × (amplification factor) product exceeding 370 GHz, more than an order of magnitude improvement as compared with previous electro-optic implementations. We show the prospects of the proposed approach through the recovery of noisy high-speed optical waveforms, namely a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\sim$</tex-math></inline-formula> 10 Gbps data signal buried in a much stronger noise background. Additionally, we experimentally demonstrate that the T-TAI samples preserve the full complex information (amplitude and phase) of the incoming signal. The proposed approach should prove useful in multiple fields requiring the detection of weak and noisy broadband signals as well as for other related applications, such as photonics-assisted analog-to-digital conversion.

Recovery of Love wave overtone waveforms and dispersion curves from single-station seismograms using time-warping

SUMMARY Time-warping is a signal processing technique that, when applied to an isolated measurement of a transient signal that propagates in a waveguide, allows contributions to that signal from individual mode numbers to be isolated and extracted. Dispersion curves for individual mode numbers can, in turn, be recovered. Isolation of contributions associated with individual mode numbers is possible because after time-warping—a special environmentally dependent non-uniform sampling—is applied, the signal energy corresponding to each mode number is isolated in the frequency spectrum of the time-warped signal. Here we derive the time-warping transform for teleseismic Love waves, assuming the Earth structure is approximately known, and we illustrate the utility of time-warping using both synthetic and measured seismograms.

Home Use of a Percutaneous Wireless Intracortical Brain-Computer Interface by Individuals With Tetraplegia.

Objective.Individuals with neurological disease or injury such as amyotrophic lateral sclerosis, spinal cord injury or stroke may become tetraplegic, unable to speak or even locked-in. For people with these conditions, current assistive technologies are often ineffective. Brain-computer interfaces are being developed to enhance independence and restore communication in the absence of physical movement. Over the past decade, individuals with tetraplegia have achieved rapid on-screen typing and point-and-click control of tablet apps using intracortical brain-computer interfaces (iBCIs) that decode intended arm and hand movements from neural signals recorded by implanted microelectrode arrays. However, cables used to convey neural signals from the brain tether participants to amplifiers and decoding computers and require expert oversight, severely limiting when and where iBCIs could be available for use. Here, we demonstrate the first human use of a wireless broadband iBCI.Methods.Based on a prototype system previously used in pre-clinical research, we replaced the external cables of a 192-electrode iBCI with wireless transmitters and achieved high-resolution recording and decoding of broadband field potentials and spiking activity from people with paralysis. Two participants in an ongoing pilot clinical trial completed on-screen item selection tasks to assess iBCI-enabled cursor control.Results:Communication bitrates were equivalent between cabled and wireless configurations. Participants also used the wireless iBCI to control a standard commercial tablet computer to browse the web and use several mobile applications. Within-day comparison of cabled and wireless interfaces evaluated bit error rate, packet loss, and the recovery of spike rates and spike waveforms from the recorded neural signals. In a representative use case, the wireless system recorded intracortical signals from two arrays in one participant continuously through a 24-hour period at home.Significance.Wireless multi-electrode recording of broadband neural signals over extended periods introduces a valuable tool for human neuroscience research and is an important step toward practical deployment of iBCI technology for independent use by individuals with paralysis. On-demand access to high-performance iBCI technology in the home promises to enhance independence and restore communication and mobility for individuals with severe motor impairment.

Full recovery of ultrafast waveforms lost under noise

The ability to detect ultrafast waveforms arising from randomly occurring events is essential to such diverse fields as bioimaging, spectroscopy, radio-astronomy, sensing and telecommunications. However, noise remains a significant challenge to recover the information carried by such waveforms, which are often too weak for detection. The key issue is that most of the undesired noise is contained within the broad frequency band of the ultrafast waveform, such that it cannot be alleviated through conventional methods. In spite of intensive research efforts, no technique can retrieve the complete description of a noise-dominated ultrafast waveform of unknown parameters. Here, we propose a signal denoising concept involving passive enhancement of the coherent content of the signal frequency spectrum, which enables the full recovery of arbitrary ultrafast waveforms buried under noise, in a real-time and single-shot fashion. We experimentally demonstrate the retrieval of picosecond-resolution waveforms that are over an order of magnitude weaker than the in-band noise. By granting access to previously undetectable information, this concept shows promise for advancing various fields dealing with weak or noise-dominated broadband waveforms.

Recovery of pure wavelength modulation second harmonic signal waveforms in distributed feedback diode laser-based photoacoustic spectroscopy

Application of second harmonic signal waveforms in distributed feedback diode laser (DFB DL)-based wavelength modulation (WM) spectroscopy is limited by the waveform distortions arising from modulation characteristics of DFB DL. The principle and implementation of a technique for the recovery of pure-WM second harmonic signal waveforms are proposed and particular attention is devoted to the problem in DFB DL-based photoacoustic spectroscopy (PAS). The disturbance factors responsible for the distorted second harmonic signal are analyzed, and their characteristics are utilized to eliminate the distortion. A simple and practical prototype for water vapor detection is assembled to demonstrate and validate this technique. The waveform of the recovered second harmonic signal in WM-PAS using the technique matches that of a calculated pure-WM second harmonic signal using a Fourier decomposition of the Lorentzian profile well with a high regression coefficient, R2=0.9948. This offers the advantage of simplifying the spectral analysis, which, otherwise, would require a numerous calculation if the distortions were considered.

Signal Processing Techniques of Dispersive Waves for Recovery of Input Waveforms

Signal Processing Techniques of Dispersive Waves for Recovery of Input Waveforms

Abnormal loading of the major joints in knee osteoarthritis and the response to knee replacement

Knee osteoarthritis is common and patients frequently complain that they are ‘overloading’ the joints of the opposite leg when they walk. However, it is unknown whether moments or co-contractions are abnormal in the unaffected joints of patients with single joint knee osteoarthritis, or how they change following treatment of the affected knee. Twenty patients with single joint medial compartment knee osteoarthritis were compared to 20 asymptomatic control subjects. Gait analysis was performed for normal level gait and surface EMG recordings of the medial and lateral quadriceps and hamstrings were used to investigate co-contraction. Patients were followed up 12 months post-operatively and the analysis was repeated. Results are presented for the first 14 patients who have attended follow-up. Pre-operatively, adduction moment impulses were elevated at both knees and the contra-lateral hip compared to controls. Co-contraction of hamstrings and quadriceps was elevated bilaterally. Post-operatively, moment waveforms returned to near-normal levels at the affected knee and co-contraction fell in the majority of patients. However, abnormalities persisted in the contra-lateral limb with partial or no recovery of both moment waveforms and co-contraction in the majority. Patients with knee osteoarthritis do experience abnormal loads of their major weight bearing joints bilaterally, and abnormalities persist despite treatment of the affected limb. Further treatment may be required if we are to protect the other major joints following joint arthroplasty.

The use of QSD (q-sequence deconvolution) to recover superposed, transient evoked-responses

Objective: We describe q-sequence deconvolution (QSD), a new data acquisition/analysis method for evoked-responses that solves the problem of waveform distortion at high stimulus repetition-rates, due to response overlap. QSD can increase the sensitivity of clinically useful evoked-responses because it is well known that high stimulus repetition-rates are better for detecting pathophysiology. Methods: QSD is applicable to a variety of experimental conditions. Because some QSD-parameters must be chosen by the experimenter, the underlying principles and assumptions of the method are described in detail. The theoretical and mathematical bases of the QSD method are also described, including some equivalent computational formulations. Results: QSD was applied to recordings of the human auditory brainstem response (ABR) at stimulus repetition-rates that overlapped the responses. The transient ABR was recovered at all rates tested (highest 160/s), and showed systematic changes with stimulus repetition-rate within a single subject. Conclusions: QSD offers a new method of recovering brain evoked-response activity having a duration longer than the time between stimuli. Significance: The use of this new technique for analysis of evoked responses will permit examination of brain activation patterns across a broad range of stimulus repetition-rates, some never before studied. Such studies will improve the sensitivity of evoked-responses for the detection of brain pathophysiology. New measures of brain activity may be discovered using QSD. The method also permits the recovery of the transient brain waveforms that overlap to form ‘ steady-state’ waveforms. An additional benefit of the QSD method is that repetition-rate can be isolated as a variable, independent of other stimulus characteristics, even if the response is a nonlinear function of rate.

Effect of spectral notches on robust waveform recovery methods for machinery diagnostics

Recovery of pulselike waveforms from vibration response measurements is often a goal in reciprocating machinery diagnostics. One such method, which makes use of inverse filtering, uses cepstral windowing in an attempt to make the procedure ‘‘robust.’’ It has been observed that, under certain conditions, the timing of the (cepstrally windowed) waveforms recovered from several consecutive machine cycles may occur at one of two distinct values. This behavior stems from a zero lying close to the unit circle in the response spectrum. Small changes in the measured response will cause such a zero to fluctuate between minimum and nonminimum phase conditions, resulting in corresponding phase differences of 2π between cycles. Subsequent cepstral windowing (smoothing) of the phase curves tends to ‘‘smear’’ this difference out over a broader frequency range, causing the recovered waveforms to be grouped into two distinctly different times, depending on whether π was added or subtracted at the frequency of the zero. The timing differences between these two groups is a function of the frequency of the zero, the characteristics of the transfer function, and the cepstral window width. Waveform recovery procedures that try to take this behavior into account have been investigated, and will be discussed. [Work supported by Robert Bosch GmbH.]

Improvement of Fetal Umbilical and Aortic Doppler Waveforms with Persistent Placental Disease

Doppler acquired velocity waveforms of fetal and maternal vessels have been analyzed as both a predictor and an index of fetal health. Increases in downstream impedance reflected by a decrease in placental tertiary villi arterioles or an obliterative angiopathy of the placenta are thought to be responsible for the increased impedance and hence the abnormal waveforms identified. We present a case of improvement of abnormal fetal velocity waveforms (including reversed diastolic flow in the fetal abdominal aorta). Despite improvement of umbilical and aortic waveforms there was evidence of placental disease with a decrease in the number of placental tertiary villi arterioles. The recovery of fetal waveforms was associated with maternal bed rest and oxygen therapy.

Separation of overlapping waveforms having known temporal distributions

A simple Fourier technique is described that allows isolation of component waveforms from recordings of time-shifted, overlapping, linear sums of these components. This procedure can be applied if certain assumptions are satisfied, namely, the times of occurrences of the underlying component waveforms are known, the component waveforms are time-invariant, and there are at least as many different recordings as there are underlying component waveforms. The method is a type of adaptive inverse filtering, and can be generalized to allow recovery of waveforms that have been distorted by many time-invariant linear processes in addition to time delays. An application of the technique to human scalp-recorded event-related potentials (ERPs) is discussed which allows resolution of overlapping stimulus-locked and response-locked waveform complexes. Some possible effects of violating the assumptions of the procedure are explored for this example. The method should prove of value when it is impossible to record the underlying component waveforms in isolation, and the waveshapes, rather than their times of occurrence, are important experimental dependent variables.

Signal averager interface between a Biomation 6500 transient recorder and an LSI-11 microcomputer

This paper describes the design and implementation of a versatile and compact signal averager interface between a Biomation 6500 transient recorder and an LSI-11 microcomputer. The design allows for fast signal averaging in excess of 1 kHz and is also easily software configurable and controllable. This permits the rapid recovery of high-speed waveforms at a minimum sampling time of 2 ns (500 MHz sampling rate). The interface has been incorporated into an LSI-11 system using the RT-11 V3B operating system and found to perform very satisfactorily.

Recovery of undersampled periodic waveforms

A periodic waveform, with known period, sampled every T seconds, can be recovered by plotting each sample in the appropriate place in a composite period, even when T is greater than the period of the waveform. When the period is unknown, a multiplicity of trial periods are used and the most satisfactory reconstruction is chosen. This paper discusses an organized technique for making such trials. An example is given in which the technique has been used to reconstruct a sampled waveform of infrared radiance of the earth as seen from the LES-9 satellite.