Delay Dispersion Research Articles

Identification and validation of ventricular rhythmic risk subgroups in hypertrophic cardiomyopathy by clustering analysis including left ventricular strain analysis

Abstract Background The excess mortality in hypertrophic cardiomyopathy (HCM) patients is mainly attributed to the occurrence of ventricular arrhythmia (VA).The prediction of VA remains challenging and could be improved. Purpose The study aimed to characterize the VA risk profile in HCM patients through clustering analysis combining conventional parameters with information derived from left ventricular longitudinal strain analysis (LV-LS). Methods 434 HCM patients (65% men, mean age 56 years) were retrospectively included from two referral centers and followed longitudinally (mean duration 6 years). The validation cohort included 177 HCM patients from an other tertiary French center. Mechanical and temporal parameters were automatically extracted from the LV-LS segmental curves of each patient in addition to conventional clinical and imaging data. A total of 287 features were analyzed using a clustering approach (k-means). The first endpoint for VA included suspected SCD, aborted cardiac arrest, appropriate ICD therapy (AIT), sustained ventricular tachycardia (SVT) and non-sustained ventricular tachycardia (NSVT) during follow-up. Results From the derivation cohort, 4 clusters were identified with a higher rhythmic risk for clusters 1 and 4 (VA rates of 26%(28/108), 13%(13/97), 12%(14/120), and 31%(34/109) for cluster 1,2,3 and 4 respectively) (Figure 1). These 4 clusters differed mainly by the LV mechanics. Patients from cluster 4 had a severe and homogeneous decrease of myocardial deformation (global longitudinal strain (GLS) -11%, normal value ≥ -20%) associated with LV and left atrium (LA) remodeling (left atrial volume index (LAVI) 46.6 vs. 41.5 ml/m², p=0.04 and LVEF 59.7 vs. 66.3%, p < 0.001) and impaired exercise capacity (% predicted peak work 58.6 vs. 69.5%; p= 0.025). Patients from cluster 1 showed a marked deformation delay and temporal dispersion on the segmental analysis associated with a moderate decrease of the GLS (-15.3%; p <0.0001 for GLS comparison between clusters). Patients from clusters 2 and 3 had a small GLS decrease (GLS -17.2 and -16.3%, respectively) with a less severe phenotype for cluster 2 and older patients for cluster 3 (mean age 62.1 vs. 54.1 years; p < 0.0001). The clustering analysis in the validation population resulted in the creation of 4 clusters overlapping the derivation cohort with similar characteristics (Figure 2). Clusters 1’ and 4’ had a higher incidence of ventricular arrhythmia with a VA rate of 22%(5/23), 18%(16/88), 0%(0/17), and 20%(10/49) for clusters 1’,2’,3’ and 4’ respectively. Conclusion Machine-learning-based cluster analysis processing LV-LS parameters in HCM patients identified 4 clusters with specific LV-strain patterns and different rhythmic risk levels. In the future, the automatic extraction and analysis of LV strain parameters could help to improve the risk stratification for SCD in HCM patients.Clustering analysisExternal validation

Efficient multi-objective design method for optical coatings

The modern design of high-performance optical coatings demands a comprehensive consideration of multiple properties. We propose an efficient multi-objective optimization method utilizing an adaptive weighted sum method, exploring the lexicographic optimization and geometry-based adaptive weights determination method. Broadband negative dispersive mirrors have been designed that demonstrates notable improvements in performances of spectrum, group delay dispersion and electric field distribution. In addition, we employ Deep-learning method to enhance the optimization. The mapping between different design parameters and results has been learned, which helps the optimization to directly approach the optimal design. It extends the novel method to diverse designs utilizing the similar kinds of merit functions and subsequently accelerates the design by 120 times.

Minimal wave speed for a two-group epidemic model with nonlocal dispersal and spatial-temporal delay

In this paper, a two-group SIR reaction-diffusion epidemic model with nonlocal dispersal and spatial-temporal delay based on within-group and inter-group transmission mechanisms is investigated. The basic reproduction number R0 is calculated using the method of next-generation matrix. The critical wave speed cm* is determined by analyzing the distribution of roots of the characteristic equation. When R0>1 and wave speed c⩾cm*, the existence of traveling waves connecting disease-free and endemic steady states is obtained by constructing sub- and super-solutions and a Lyapunov functional, and applying Schauder’s fixed-point theorem and a limit argument. When R0>1 and 0<c<cm*, the nonexistence of traveling waves connecting disease-free and endemic steady states is proven by contradiction and two-sided Laplace transform. This indicates that the critical wave speed cm* is exactly the minimum wave speed. Numerical simulations are carried out to illustrate theoretical results. The dependence of the minimal speed cm* on time delay, diffusion rates and contact rates is discussed, showing that the longer the latent period and the lower the diffusion rates of infected individuals and the inter-group transmission rates between groups, the slower the spread of disease.

All-solid-state continuous-wave mode-locked Er:Lu2O3 laser at 3 µm

In this paper, we demonstrated stable continuous-wave passively mode-locked operation of an Er:Lu2O3 laser at 3 µm, utilizing a semiconductor saturable absorber mirror (SESAM). By operating the laser in a dry nitrogen environment and utilizing a thermoelectric cooler (TEC) temperature control device to mitigate the thermal effects of Er:Lu2O3 and enhance laser stability, we further compensated for group delay dispersion within the laser cavity through chirped mirrors, an shortest pulse duration of 12.0 ps at a average output power of 150 mW was achieved, which occurred at a center wavelength of 2844 nm, and a pulse repetition rate of 83.5 MHz. Additionally, we achieved a maximum continuous-wave mode-locked output power of 213 mW at an absorbed pump power of 8.3 W, equivalent to a pulse energy of 1.3 nJ. The RF spectrum analysis of the pulse train indicated a high SNR of nearly 70 dB, signifying excellent stability. To the best of our knowledge, This is the first report on the realization of an ultrashort pulse width mode-locked Er:Lu2O3 laser in the mid-infrared band.

Acousto-optic femtosecond laser beam shaping for bottle-beam generation

Abstract This study explores the properties of a laser beam shaping system comprising an acousto-optic dispersive delay line (AODDL) and an acousto-optic tunable filter (AOTF) for ultrashort laser pulse shaping. The system demonstrates the AODDL’s ability to generate signals with arbitrarily positioned transmission windows and investigates the impact of spectral width on field distributions. The AOTF’s frequency scanning and simultaneous control of two and three spectral components are presented. The experimental setup utilizes femtosecond laser radiation, and the results highlight the system’s versatility for programmable spectral and spatial filtering, offering potential applications in advanced optical manipulation.

Generation and evolution dynamics of gain-guided dissipative solitons in a Tm-doped fiber laser

The generation of dissipative solitons from a mode-locked fiber laser can enhance emission energy, while the insertion of a bandwidth filter exposes the system to complexity. This study presents the first generation and evolution dynamics of gain-guided dissipative solitons (GGDSs) in Tm-doped fiber lasers exploiting the finite gain bandwidth. The results highlight the intricate interplay of finite gain bandwidth with dispersion and nonlinearity in governing the dynamics of GGDSs. An increase in pump power significantly broadens the emission spectrum, which in turn introduces the finite gain bandwidth to the generation of GGDSs. Consequently, linear chirp accumulates, promoting high-energy ultrashort pulse generation after external compression. However, an increase in round-trip group delay dispersion leads to a narrower spectral bandwidth, which can weaken the influence of the finite gain bandwidth, resulting in decreased soliton energy and broader pulse duration. The investigation of GGDS evolution dynamics within the cavity also provides us with a deeper insight into the characteristics of GGDS. Overall, this research offers important guidance for designing high-performance Tm-doped fiber lasers with simple structures that fully exploit the finite gain bandwidth.

Generation of high-energy self-mode-locked pulses in a Tm-doped fiber laser

The incorporation of a material-based or artificial saturable absorber into a fiber laser cavity imposes a limitation on energy enhancement owing to its low damage threshold and high environmental sensitivity. To address this issue, one promising alternative approach is the utilization of the self-mode-locking technique. Here, we present a robust self-mode-locked Tm-doped fiber laser with high pulse energy emission. A simple and compact fiber laser structure is realized by utilizing a section of a Tm-doped fiber, serving both as a gain medium and a saturable absorber. Thus, the operational stability is enhanced, especially under high-energy conditions. Furthermore, the realization of high-energy pulses is accomplished through the integration of dispersion management technique. Experimental results reveal that the maximum single-pulse energy increases from 34.8 pJ to 120.2 nJ as the round-trip group delay dispersion decreases from −0.43 to −12.40 ps2. The proposed self-mode-locked Tm-doped fiber laser under high-energy operation exhibits remarkable performance. Our results provide a simple approach to obtaining a mid-infrared laser source with high pulse energy and hold significant potential for advancing high-energy laser systems.

Multiple-reflections single-shot dispersion scan for fast ultrashort-pulse measurements

A single-shot non-interferometric ultrashort-pulse measurement method based on the dispersion scan (d-scan) technique with a substantially extended time span for the pulses to be measured is presented. While single-shot d-scan is typically used for rather short femtosecond pulses, the presented multiple-reflections d-scan (MR d-scan) technique allows measurement of both short and long femtosecond pulses. Single-shot d-scan is currently limited to pulses with a maximum duration of 60 fs using a chromatic dispersion, i.e., a group delay dispersion (GDD) of 4400 fs2 at 840 nm provided by customized random nonlinear crystals. MR d-scan achieves a GDD of 31100 fs2 at 820 nm in this work, but can generally achieve an increase in GDD of up to two orders of magnitude. MR d-scan works with commonly available output couplers, does not rely on a homogeneous, precisely imaged beam profile and has an in-line configuration. As an example, long femtosecond double pulses are measured and reconstructed.

Scalable photonic reservoir computing based on pulse propagation in parallel passive dispersive links

We propose and demonstrate a scalable photonic reservoir computing system based on pulse propagation in parallel passive dispersive links. The approach features a simple structure and is composed of passive components, such as dispersive elements and ring resonators. The system utilizes a pulsed laser and employs a multi-channel architecture with dispersive elements for pulse broadening and ring resonators for delay stacking. It is verified for its capability to handle both digital tasks (2-bit Boolean logic operations, header recognition) and analog tasks (Mackey-Glass time-series prediction, Lorenz 63 time-series prediction). A major advantage of the approach lies in its scalability. It has been confirmed that more complex tasks can be processed by using a system with more channels, along with dispersive elements and ring resonators with larger dispersion amounts and delays, respectively.

Dynamic control of cascaded four-wave mixing via re-configurable dispersion.

We integrate a spatial light modulator-based dispersion controller into a cascaded four-wave mixing (CFWM) system. By tuning the group delay dispersion (GDD) and fourth-order dispersion (FOD) terms, we control the CFWM phase matching and demonstrate an output bandwidth tuning of over 3.3×. At the maximum bandwidth, our system covers the telecommunications S-, C-, and L-bands (1466-1641 nm) with an average output power of 300 mW, which is contained in 52 individual lines spaced 374 GHz apart. This method represents a reconfigurable alternative to photonic crystal fibers for dispersion engineering and allows for the use of step-index fiber and customizable power spectral density (PSD) profiles.

Dispersion mismatch correction for evident chromatic anomaly in low coherence interferometry.

The applications of ultrafast optics to biomedical microscopy have expanded rapidly in recent years, including interferometric techniques like optical coherence tomography and microscopy (OCT/OCM). The advances of ultra-high resolution OCT and the inclusion of OCT/OCM in multimodal systems combined with multiphoton microscopy have marked a transition from using pseudo-continuous broadband sources, such as superluminescent diodes, to ultrafast supercontinuum optical sources. We report anomalies in the dispersion profiles of low-coherence ultrafast pulses through long and non-identical arms of a Michelson interferometer that are well beyond group delay or third-order dispersions. This chromatic anomaly worsens the observed axial resolution and causes fringe artifacts in the reconstructed tomograms in OCT/OCM using traditional algorithms. We present DISpersion COmpensation Techniques for Evident Chromatic Anomalies (DISCOTECA) as a universal solution to address the problem of chromatic dispersion mismatch in interferometry, especially with ultrafast sources. First, we demonstrate the origin of these artifacts through the self-phase modulation of ultrafast pulses due to focusing elements in the beam path. Next, we present three solution paradigms for DISCOTECA: optical, optoelectronic, and computational, along with quantitative comparisons to traditional methods to highlight the improvements to the dynamic range and axial profile. We explain the piecewise reconstruction of the phase mismatch between the arms of the spectral-domain interferometer using a modified short-term Fourier transform algorithm inspired by spectroscopic OCT. Finally, we present a decision-making guide for evaluating the utility of DISCOTECA in interferometry and for the artifact-free reconstruction of OCT images using an ultrafast supercontinuum source for biomedical applications.

Frequency- and polarization-dependent lensing of gravitational waves in strong gravitational fields

The propagation of gravitational waves can be described in terms of null geodesics by using the geometrical optics approximation. However, at large but finite frequencies the propagation is affected by the spin-orbit coupling corrections to geometrical optics, known as the gravitational spin Hall effect. Consequently, gravitational waves follow slightly different frequency- and polarization-dependent trajectories, leading to dispersive and birefringent phenomena. We study the potential for detecting the gravitational spin Hall effect in hierarchical triple black hole systems, consisting of an emitting binary orbiting a more massive body acting as a gravitational lens. We calculate the difference in time of arrival with respect to the geodesic propagation and find that it follows a simple power-law dependence on frequency with a fixed exponent. We calculate the gravitational spin Hall-corrected waveform and its mismatch with respect to the original waveform. The waveform carries a measurable imprint of the strong gravitational field if the source, lens, and observer are sufficiently aligned, or for generic observers if the source is close enough to the lens. We present constraints on dispersive time delays from GWTC-3, translated from limits on Lorentz invariance violation. Finally, we address the sensitivity of current and future ground detectors to dispersive lensing. Our results demonstrate that the gravitational spin Hall effect can be detected, providing a novel probe of general relativity and the environments of compact binary systems. Published by the American Physical Society 2024

Negative group delay SSPP mode based on coupled periodic cells

To realize negative group delay (NGD) of spoof surface plasmon polaritons (SSPPs), two coupling strips are introduced within the U-shaped cell for SSPP waveguide. Furthermore, two such cells are coupled to form a double-structured NGD unit. At lower frequencies, the constructed unit can implement both TE and TM modes with the NGD feature, and the maximum NGD values of – 0.42 ns for TE mode is achieved at 1.83 GHz. Since the TM mode is alongside the stopband, a wide NGD band of 2.01–3.25 GHz is yielded, with a small NGD value. However, as this unit is applied to SSPP waveguides to compensate for positive delays, the measured NGD maximum is 2.81 ns at 1.93 GHz and 9.65 ns at 2.42 GHz, due to the influence of waveguide structure on the NGD unit. The proposed unit structure exhibits promising applications in delay equalization and dispersion compensation for microwave system.

Accurate optical dispersion identification for linear deformable mirror with spatial-spectral interferometry

In ultrashort laser pulse systems, optical dispersion can cause severe distortion of the spectral phase and thus significantly affect the pulse shape. To address this problem, this study places a linear deformable mirror (LDM) at the Fourier plane of a blazed grating for dispersion control, and reconstructs the spectral phase modulated by the LDM using single-shot spatial-spectral interferometry. An iterative algorithm and closed-loop optimization process are used to drive the LDM to generate orthogonal modes of Legendre polynomials with a signal-to-background ratio (SBR) of more than 10 dB. The identified LDM modes are then used as the basis for spectral phase modulation. It is shown that the group delay dispersion (GDD), third order dispersion (TOD), fourth order dispersion (FOD), and fifth order dispersion (5OD) can be accurately obtained by the linear combination of identified Legendre modes. In addition, the maximum phase error between the generated and target dispersions is less than 0.15 rad, while the error between the pulse widths produced by the generated dispersion and the target dispersion, respectively, is less than 3.5 %. Overall, the results confirm that the linear superposition of the generated Legendre modes enables the accurate dispersion modulation of ultrashort laser pulses.

Compact compressor based on unparallel gratings

The pulse compressor is one of the essential components in a high-power laser system, which is often bulky. Here, we propose a compact compressor based on a Treacy compressor with two unparallel gratings and a mirror. Two gratings provide a negative group delay dispersion, and the mirror has two functions. One is to make the beam enter the compressor twice, and the other is to make the optical path between the grating pair folded to reduce the volume of the compressor. The relation between the group delay dispersion and the incident angle in three-dimensional space is derived. The results show that a small spatial incident angle can produce a large negative dispersion when the perpendicular distance between the gratings is the same. The parameter limits of the designed structure are also discussed, and the volume of compact compressor under the simulated parameters is two-thirds of the conventional compressor when the constraints are satisfied. This work is applicable to the optimal design of grating-based compressors with different parameters.

A novel collocation method with a coronavirus optimization algorithm for the optimal control of COVID-19: A case study of Wuhan, China

In this study, we develop a numerical optimization approach to address the challenge of optimal control in the spread of COVID-19. We evaluate the impact of various control strategies aimed at reducing the number of exposed and infectious individuals. Our novel approach employs Legendre wavelets, their derivative operational matrix, and a collocation method to transform the COVID-19 transmission optimal control model into a nonlinear programming (NLP) problem. To solve this problem, we employ a coronavirus optimization algorithm (COVIDOA) to determine the optimal control, state variables, and objective value. We investigate three control plans for this highly contagious disease, focusing on individual protection, rapid detection and treatment, detection with delay in treatment, and environmental viral dispersion as time-based control functions. These strategies are applied within an SEIR-type control model specific to COVID-19 in China, designed to mitigate disease spread. Lastly, we analyze the effects of various parameters within the COVID-19 spread model. Our numerical results highlight the significant impact of strategies that minimize the number of exposed and infectious individuals, particularly those related to rapid detection, detection delay, and environmental viral dispersion, in controlling and preventing the transmission of the COVID-19 virus.

Risk profiles for ventricular arrhythmias in hypertrophic cardiomyopathy through clustering analysis including left ventricular strain.

AimsThe prediction of ventricular arrhythmia (VA) in hypertrophic cardiomyopathy (HCM) remains challenging. We sought to characterize the VA risk profile in HCM patients through clustering analysis combining clinical and conventional imaging parameters with information derived from left ventricular longitudinal strain analysis (LV-LS). MethodsA total of 434 HCM patients (65% men, mean age 56 years) were included from two referral centers and followed longitudinally (mean duration 6 years). Mechanical and temporal parameters were automatically extracted from the LV-LS segmental curves of each patient in addition to conventional clinical and imaging data. A total of 287 features were analyzed using a clustering approach (k-means). The principal endpoint was VA. Results4 clusters were identified with a higher rhythmic risk for clusters 1 and 4 (VA rates of 26%(28/108), 13%(13/97), 12%(14/120), and 31%(34/109) for cluster 1,2,3 and 4 respectively). These 4 clusters differed mainly by LV-mechanics with a severe and homogeneous decrease of myocardial deformation for cluster 4, a small decrease for clusters 2 and 3 and a marked deformation delay and temporal dispersion for cluster 1 associated with a moderate decrease of the GLS (p < 0.0001 for GLS comparison between clusters). Patients from cluster 4 had the most severe phenotype (mean LV mass index 123 vs. 112 g/m2; p = 0.0003) with LV and left atrium (LA) remodeling (LA-volume index (LAVI) 46.6 vs. 41.5 ml/m2, p = 0.04 and LVEF 59.7 vs. 66.3%, p < 0.001) and impaired exercise capacity (% predicted peak VO2 58.6 vs. 69.5%; p = 0.025). ConclusionProcessing LV-LS parameters in HCM patients 4 clusters with specific LV-strain patterns and different rhythmic risk levels are identified. Automatic extraction and analysis of LV strain parameters improves the risk stratification for VA in HCM patients.

Measurement of third order coherence by in situ autocorrelation for determining three-photon cross-sections.

We show theoretically that the third order coherence at zero delay can be obtained by measuring the second and third order autocorrelation traces of a pulsed laser. Our theory enables the measurement of a fluorophore's three-photon cross-section without prior knowledge of the temporal profile of the excitation pulse by using the same fluorescent medium for both the measurement of the third order coherence at zero delay as well as the cross-section. Such an in situ measurement needs no assumptions about the pulse shape nor group delay dispersion of the optical system. To verify the theory experimentally, we measure the three-photon action cross-section of Alexa Fluor 350 and show that the measured value of the three-photon cross-section remains approximately constant despite varied amounts of chirp on the excitation pulses.

Six-orders-of-magnitude-spanning dispersion measurement via Kalman filtering-aided white-light interferometry.

Dispersion plays a great role in ultrafast laser oscillators, ultrashort pulse amplifiers, and many other nonlinear optical dynamics. Therefore, dispersion measurement is crucial for device characterization, system design and nonlinear dynamics investigation therein. In this work, we demonstrate a versatile approach, i.e., Kalman filtering-aided white-light interferometry, for group delay dispersion (GDD) characterization. Extended Kalman filter is adopted to track the cosine-like interferogram, and to eliminate the unintended bias and the envelope, providing a nearly ideal phase retrieval and GDD estimation. The measurement range could span from tens of fs2 to tens of ps2, with an uncertainty of about 0.1%, enabling precise GDD measurement for diverse optical components, ranging from a millimeter-thick glass slide to highly dispersive chirped fiber Bragg gratings. Benefited by the simplicity, convenient setup, and easy operation as well as relatively low cost, this approach would help photonic device characterization, dispersion management and nonlinear dynamics investigation in the laboratory and work plant.

Optical Solitons with Differential Group Delay and Inter-Modal Dispersion Singlet

This paper introduces a state of the art investigation into the interaction between soliton propagation and differential group delay, offering a fresh perspective often neglected in previous studies. Motivated by the imperative to comprehend soliton behavior within inter-modal dispersion environments, it presents three innovative methodologies aimed at uncovering novel optical soliton solutions. Through the utilization of cutting-edge algorithms, these approaches unveil the emergence of solitons in hitherto unexplored contexts. The research makes significant strides through extensive numerical simulations, which not only validate theoretical conjectures but also offer practical insights. Furthermore, it delineates crucial parameter limitations essential for the existence of solitons, thus furnishing valuable guidance for future research endeavors and practical applications.