Delay Dispersion Research Articles

Active Tunable Pulse Shaping Using MoS2‐Assisted All‐Dielectric Metasurface

While optical pulse shapers have important applications in classical and quantum communication regimes and laser resonant cavities, engineering of group delay dispersion (GDD) remains one of their greatest challenges. Herein, by taking advantage of the electrically tunable optical properties of 2D material and the low‐loss nature of dielectric material. This paper demonstrates how an active tunable all‐dielectric metasurface assisted by 2D material can be leveraged to shape the temporal profile of a pulse. The proposed metasurface consists of an array of nanobars covered by a 2D sheet and positioned on a distributed Bragg reflector (DBR) as a perfect mirror to design a phase‐only modulator. Upon introducing in‐plane asymmetries, the quasi‐bound state in the continuum (QBIC) resonance emerges under normal incidence, which subsequently leads to achieving both significant GDD and the two regimes of pulse stretching and compressing via boosting the effect of the permittivity variation of molybdenum disulfide (MoS2). The monolayer MoS2 proves to be an excellent substitute for other tunable materials with inherent dissipative loss in the visible frequency range. Following such an active tunable geometrically fixed configuration, various pulse‐shaping operations are achieved, including compression (peak intensity up to 350%), expansion (peak intensity from 60%), splitting, and higher‐order distortion.

3D nanopolymerization and damage threshold dependence on laser wavelength and pulse duration.

The dependence of the polymerization and optical damage thresholds in multi-photon polymerization (MPP) lithography was studied using a broadly-tunable laser system with group delay dispersion (GDD) control. The order of non-linearity and the light-matter interaction mechanisms were investigated using the resolution bridges method for non-photosensitized SZ2080TM and photosensitized SZ2080TM + IRG369 prepolymers. Energy deposition, voxel dimension growth, and the size of the dynamic fabrication window (DFW) were measured in the 700-1300nm wavelength range at three different pulse durations measured at the sample - 100, 200 and 300fs. Polymerization was observed at all wavelengths and pulse durations without significant differences in the achieved minimal spatial dimension ( nm). This was achieved despite the broad range of excitation wavelengths used which spanned two- and three-photon absorption bands, and the differences in the absorption spectra of the prepolymers. The lateral and longitudinal voxel growth dynamics revealed an abrupt change in the power dependence of polymerization and a significant variation of the DFW - from 1 at 1250nm to 29 at 700nm. This result can be interpreted as a consequence of a change in the instantaneous refractive index and a lowering of the polymerization but not the damage threshold. The optimization of energy delivery to the material by a wavelength-tunable laser source with pulse duration control was experimentally validated. These findings are uncovering the complexity of polymerization mechanisms and are useful in further development of MPP technology.

Reaching the Frequency Resolution Limit in a Single-Shot Spectrum of an Ultra-Short Signal Pulse Using an Analog Optical Auto-Correlation Technique

This work demonstrated a high-resolution spectrum obtained from a single ultra-short high-frequency signal pulse using a new analog optical auto-correlation method that revolutionizes the signal detection and measurement technique. It provides unprecedented capability to reach the fundamental limit in Physics. This technique allows us to increase the observation/measurement time by converting a Radio Frequency (RF) signal in the optical domain and keeping the “live-signal” in a fiber-optic-recirculation-loop circuit over an extended time that could be a million times longer than the pulse width. The dispersion delay of the two RF modulation sidebands is used to perform an analog time correlation. It effectively stretches time by million times. As a result, it provides a frequency-space “snapshot” of ultra-short events without the need for a high-speed analog-to-digital converter (ADC). A single 30 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ns</i> -short two-tone pulse separated by 25 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MHz</i> was resolved in a 50 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GHz</i> wideband real-time frequency spectrum. This technique allowed us to push the physical limit in the spectral resolution of an ultra-short signal and enable a new technology to manipulate, process, and analyze ultra-short electromagnetic signals and transient events. It also provokes a fundamental question: Is the uncertainty principle limiting the frequency determination for a wave in a continuum state?

Decay rate of the solutions to the Bresse-Cattaneo system with distributed delay

&lt;abstract&gt;&lt;p&gt;This study examines the pace at which solutions to a Bresse system in combination with the Cattaneo law of heat conduction and the dispersed delay term degradation. We establish our major finding utilizing the energy approach in the Fourier space.&lt;/p&gt;&lt;/abstract&gt;

Bargaining in small dynamic markets

This paper studies trade in endogenously evolving markets exhibiting few traders at any given point in time. Traders arrive in the market and bargain until they complete a trade. We find that, unlike large markets, small markets feature trade delay and price dispersion, even when sellers and buyers are homogeneous and matching frictions are small. We characterize transaction prices as a function of the endogenous evolution of the market composition and economic conditions, providing several novel comparative statics results. Our analysis highlights the need to incorporate sub-market structures into the theoretical study of job, real estate, and rental markets, where trade opportunities are typically constrained by both the geographical location and individual characteristics of each trader.

The maturation of exploratory behavior in adolescent Mus spicilegus on two photoperiods.

Dispersal from the natal site or familial group is a core milestone of adolescent development in many species. A wild species of mouse, Mus spicilegus, presents an exciting model in which to study adolescent development and dispersal because it shows different life history trajectory depending on season of birth. M. spicilegus born in spring and summer on long days (LD) disperse in the first 3 months of life, while M. spicilegus born on shorter autumnal days (SD) delay dispersal through the wintertime. We were interested in using these mice in a laboratory context to compare age-matched mice with differential motivation to disperse. To first test if we could find a proxy for dispersal related behavior in the laboratory environment, we measured open field and novel object investigation across development in M. spicilegus raised on a LD 12 h:12 h light:dark cycle. We found that between the first and second month of life, distance traveled and time in center of the open field increased significantly with age in M. spicilegus. Robust novel object investigation was observed in all age groups and decreased between the 2nd and 3rd month of life in LD males. Compared to male C57BL/6 mice, male M. spicilegus traveled significantly longer distances in the open field but spent less time in the center of the field. However, when a novel object was placed in the center of the open field, Male M. spicilegus, were significantly more willing to contact and mount it. To test if autumnal photoperiod affects exploratory behavior in M. spicilegus in a laboratory environment, we reared a cohort of M. spicilegus on a SD 10 h:14 h photoperiod and tested their exploratory behavior at P60-70. At this timepoint, we found SD rearing had no effect on open field metrics, but led to reduced novel object investigation. We also observed that in P60-70 males, SD reared M. spicilegus weighed less than LD reared M. spicilegus. These observations establish that SD photoperiod can delay weight gain and blunt some, but not all forms of exploratory behavior in adolescent M. spicilegus.

Supermode Characteristics of Nested Multiple Hollow-Core Anti-Resonant Fibers

Mode-division multiplexing (MDM) can achieve ultra-high data capacity in optical fiber communication. Several impressive works on multicore fiber (MCF), multi-mode fiber, and few-mode multicore fiber have made significant achievements in MDM. However, none of the previous works can simultaneously maintain the transmission loss, chromatic dispersion (CD), and differential group delay (DGD) at a relatively low level. A nested multiple hollow-core anti-resonant fiber (NMH-ARF) has significant potential for applications in MDM. This study proposes a novel NMH-ARF with its structural design based on the traditional single-core nested anti-resonant fiber. We increased the number of nodes between capillaries. By changing the position of the nested tubes, several interconnected areas form when a single core is separated. We investigated the mode-coupling theory and transmission characteristics of this fiber. This fiber structure showed a low sensitivity to bending and achieved a super-low DGD and a super-low confinement loss (CL) at a wavelength of 1.55 µm while keeping CD relatively low.

Signal recovery in optical wireless communication using photonic convolutional processor.

Deep neural networks (DNNs) have been applied to recover signals in optical communication systems and have shown competence of mitigating linear and nonlinear distortions. However, as the data throughput increases, the heavy computational cost of DNNs impedes them from rapid and power-efficient processing. In this paper, we propose an optical communication signal recovery technology based on a photonic convolutional processor, which is realized by dispersion delay unit and wavelength division multiplexing. Based on the photonic convolutional processor, we implement an optoelectronic convolutional neural network (OECNN) for signal post-equalization and experimentally demonstrate on 16QAM and 32QAM of an optical wireless communication system. With system parameters optimization, we verify that the OECNN can achieve accurate signal recovery where the bit error ratio (BER) is below the 7% forward error correction threshold of 3.8×10-3 at 2Gbps. With adding the OECNN-based nonlinear compensation, compared with only linear compensation, we improve the quality (Q) factor by 3.35 dB at 16QAM and 3.30 dB at 32QAM, which is comparable to that of an electronic neural network. This work proves that the photonic implementation of DNN is promising to provide a fast and power-efficient solution for optical communication signal processing.

Second and third-order dispersion compensating mirror pairs for the spectral range from 1.2-3.2µm.

We demonstrate the design, production, characterization and application of two dispersive complementary mirror pairs compensating second- and third-order dispersion, respectively. Both mirror pairs operate in the spectral range from 1.2-3.2µm. This is an unprecedented bandwidth of over 1.4 octaves which can drive further improvements in Cr:ZnS, Cr:ZnSe and other laser systems with a central wavelength around 2µm. The first pair provides a constant group delay dispersion of -100fs2, while the second one enables the compensation of the third-order dispersion that is introduced by a TiO2 crystal.

A Framework for Predicting Airfare Prices Using Machine Learning

Many academics have concentrated on applying machine learning to retrieve information from databases to enable researchers to perform better. A difficult issue in prediction models is the selection of practical strategies that yield satisfactory forecast accuracy. Traditional software testing techniques have been extended to testing machine learning systems; however, they are insufficient for the latter because of the diversity of problems that machine learning systems create. Hence, the proposed methodologies were used to predict flight prices. A variety of artificial intelligence algorithms are used to attain the required, such as Bayesian modeling techniques such as Stochastic Gradient Descent (SGD), Adaptive boosting (ADA), Decision Trees (DT), K-nearest neighbor (KNN), and Logistic Regression (LR), have been used to identify the parameters that allow for effective price estimation. These approaches were tested on a data set of an extensive Indian airline network. When it came to estimating flight prices, the results demonstrate that the Decision tree method is the best conceivable Algorithm for predicting the price of a flight in our particular situation with 89% accuracy. The SGD method had the lowest accuracy, which was 38 %, while the accuracies of the KNN, NB, ADA, and LR algorithms were 69 %, 45 %, and 43 %, respectively. This study's presented methodologies will allow airline firms to predict flight prices more accurately, enhance air travel, and eliminate delay dispersion. Index Terms— Machine learning, Prediction model, Airline price prediction, Software testing,

Robust unbalanced Gires-Tournois mirror for group delay dispersion measurement evaluation by white light interferometer

A robust unbalanced Gires-Tournois interferometer (GTI) mirror for evaluating group delay dispersion (GDD) measurement by scanning white light interferometer is presented, and a novel processing algorithm based on scanning white light interferometer (WLI) is proposed to extract group delay and group delay dispersion characteristics with improved accuracy and low level of noise. The GDD measurement evaluation method is based on error analysis of manufacturing errors and spectral measurement. Spectral measurement is carried out to determine the resonance wavelength of GTI mirror. The sample was prepared by ion beam sputtering deposition. The relative errors of refractive index and layer thickness for the sample are estimated through reverse engineering based on multi-angle transmittance measurements. A novel processing algorithm the extrema searching method (ESM) is proposed that search the positions of multi-order extrema from reconstructed interferogram intensity to exact the GDD characteristics of the sample. GDD measurements performed by WLI with different processing methods are added to comparison including windowed Fourier transform, wavelet transform and time-domain scanning method. The results show that our method is reliable and effective for GDD measurement with a good accuracy and low level of noise.

Compact optical grating compressor.

A novel design of a grating-based optical pulse compressor is proposed. The proposed compressor provides a large group delay dispersion while keeping the compressor linear size small. The design of the proposed compressor is based on a traditional Treacy compressor with a straightforward modification of inserting two lenses between the compressor's gratings. This simple alternation aims to substantially increase group delay dispersion of the compressor or alternatively to decrease the compressor size while maintaining its group delay dispersion. A theoretical description of the enhanced compressor has been developed in the paraxial approximation. A detailed numerical model has been built to calculate the compressor parameters more accurately. These theoretical studies have revealed that the enhanced optical compressor provides a significant increase in the group delay dispersion compared to a standard Treacy compressor.

The effects of plasma on the magnification and time delay of strongly lensed fast radio bursts

ABSTRACT The number of identified fast radio bursts (FRBs) will continue to increase rapidly with current and planned future facilities. Strongly lensed FRBs are also expected to be found, which can provide precise time delays and thus have rich applications in cosmology and fundamental physics. However, the radio signal of lensed FRBs will be deflected by the plasma in lens galaxies in addition to the deflection by gravity. Such deflections by both gravity and plasma will cause frequency-dependent time delays, which are different from the dispersion delay and the geometric delay caused by gravitational lensing. Depending on the lensing and plasma models, the frequency–time-delay relationship of the lensed images can show distinguishing behaviours either between the multiple images or from the dispersion relation. Such phenomena cannot be neglected in future studies, especially at low radio frequencies, as plasma exists in lens galaxies in general. More importantly, such information provides not only a potential way to search for lensed FRBs but also constraints on the mass and plasma distributions in lens galaxies. In particular, plasma may make the missing central images observable at low radio frequencies.

Dispersion-division multiple access: A temporal holography-based method

Multiple access methods are the backbone of today’s most communication systems. Increasing the efficiency of these schemes is a challenging engineering task. This paper introduces dispersion-division multiple access, a novel multiple-access technique that can improve the efficiency of multiple-access communication systems. When two (or more) pulses experience different Group Delay Dispersion (GDD) values on a propagation medium, they can be synchronized to overlap in time for combining the phase and amplitude of those pulses. This paper suggests the recoverability of these pulses while being mixed in the transmitter by propagating the combined pulse in a negative Group Velocity Dispersion (GVD)medium with GDD values corresponding to the minus of the corresponding GDD values in the input. This method shares similarities with coherent holography, with the only difference being that in spatial coherent holography, the combined wave-fronts are recorded in a plate, encoding the phase information of a three-dimensional object into intensity. However, the proposed method does not record the combined pulse and immediately sends it through the channel. In addition to the excellent simplicity provided by this method, the performed simulations also validate its notable performance in increasing the number of channels under low Bit Error Rates (BER).

Complementary dispersive mirror pair produced in one coating run based on desired non-uniformity.

We report a novel one-coating-run method for producing an octave-spanning complementary dispersive mirror (DM) pair. The anti-phase group delay dispersion (GDD) oscillations are realized by two mirrors of the DM pair due to the certain thickness difference. Both mirrors are deposited within a single coating run enabled by the non-uniformity of the ion beam sputtering coating plant, which is obtained by tuning the distance between the source target and coating substrates. Since the DM pair is produced in a single deposition run, the GDD performance is more robust against deposition errors than that of the conventional complementary DM pair, in which two separated coating runs are necessary. Moreover, the new DM pair is compatible for both laser polarizations under the same angle of incidence, which could effectively reduce the difficulties of alignment for their implementation in laser systems than the double angle DM pair. The new DM pair is successfully applied to compress pulses from a Ti: Sapphire laser system down to 4.26 fs in pulse duration.

Study of the effect of higher-order dispersions on photoionisation induced by ultrafast laser pulses applying a classical theoretical method

We investigated the effect of higher order dispersion on ultrafast photoionisation with Classical Trajectory Monte Carlo (CTMC) method for hydrogen and krypton atoms. In our calculations we used linearly polarised ultrashort 7 fs laser pulses, 6.5 times 10^{14} mathrm {W/cm^{2}} intensity, and a central wavelength of 800 nm. Our results show that electrons with the highest kinetic energies are obtained with transform limited (TL) pulses. The shaping of the pulses with negative second- third- or fourth- order dispersion results in higher ionisation yield and electron energies compared to pulses shaped with positive dispersion values. We have also investigated how the Carrier Envelope Phase (CEP) dependence of the ionisation is infuenced by dispersion. We calculated the left-right asymmetry as a function of energy and CEP for sodium atoms employing pulses of 4.5 fs, 800 nm central wavelength, and 4 times 10^{12}mathrm {W/cm^{2}} intensity. We found that the left-right asymmetry is more pronounced for pulses shaped with positive Group Delay Dispersion (GDD). It was also found that shaping a pulse with increasing amounts of GDD in absolute value blurs the CEP dependence, which is attributed to the increasing number of optical cycles.

FBG Sensor with enhanced resolution based on temporal spectroscopy and nonlinear effect

A unique technique to achieve high resolution interrogation of Fiber Bragg Grating(FBG) sensor based on dispersive time delay and Four wave mixing(FWM) effect is proposed. The wavelength shift induced by small strain or temperature on uniform FBG significantly enhances the time shift of the pulse reflected from linearly chirped fiber Bragg grating(LCFBG) by utilizing two stage FWM process in combination with wavelength–to-time mapping effect of LCFBG. The proposed scheme presents high robustness to power fluctuations in the system. A high strain sensitivity of 6.59 ps/με and temperature sensitivity of 72.5 ps/oC with corresponding strain and temperature resolution of 0.15 με and 0.01oC respectively is attained using the proposed scheme. The significance of the proposed scheme lies in enhancement of the time shift of the pulse without the usage of high dispersive device and simultaneous realization of temperature compensation and high strain sensitivity.

Real-time adaptive ultrashort pulse compressor for dynamic group delay dispersion compensation.

The optical dispersion effect in ultrafast pulse laser systems broadens the laser pulse duration and reduces the theoretical peak power. The present study proposes an adaptive ultrashort pulse compressor for compensating the optical dispersion using a direct optical-dispersion estimation by spectrogram (DOES) method. The DOES has fast and accurate computation time which is suitable for real time controller design. In the proposed approach, the group delay dispersion (GDD) and its polarity are estimated directly from the delay marginal of the trace obtained from a single-shot frequency-resolved optical gating (FROG). The estimated GDD is then processed by a closed-loop controller, which generates a command signal to drive a linear deformable mirror as required to achieve the desired laser pulse compression. The dispersion analysis, control computation, and deformable mirror control processes are implemented on a single field programmable gate array (FPGA). It is shown that the DOES dispersion computation process requires just 0.5 ms to complete. Moreover, the proposed pulse compressor compensates for both static dispersion and dynamic dispersion within five time steps when closed-loop controller is performed at a frequency of 100 Hz. The experimental results show that the proposed pulse compressor yields an effective fluorescence intensity improvement in a multiphoton excited fluorescence microscope (MPEFM).

Cascaded Dispersive Delay Structure Based on Periodic Glide Symmetric Microstrip Stubs

A novel cascaded dispersive delay structure based on a periodic glide symmetric stub-loaded microstrip transmission line is presented. Two group delay peaks are superposed to realize a group delay response that illustrates linear characteristics versus frequency. Two examples with slopes 0.83 and 2 ns/GHz, respectively, are proposed. Verified by experiments, the simulated and measured group delays show a well agreement.

Inhibition of the Translation Initiation Factor eIF4A Enhances Tumor Cell Radiosensitivity.

A fundamental component of cellular radioresponse is the translational control of gene expression. Because a critical regulator of translational control is the eukaryotic translation initiation factor 4F (eIF4F) cap binding complex, we investigated whether eIF4A, the RNA helicase component of eIF4F, can serve as a target for radiosensitization. Knockdown of eIF4A using siRNA reduced translational efficiency, as determined from polysome profiles, and enhanced tumor cell radiosensitivity as determined by clonogenic survival. The increased radiosensitivity was accompanied by a delayed dispersion of radiation-induced γH2AX foci, suggestive of an inhibition of DNA double-strand break repair. Studies were then extended to (-)-SDS-1-021, a pharmacologic inhibitor of eIF4A. Treatment of cells with the rocaglate (-)-SDS-1-021 resulted in a decrease in translational efficiency as well as protein synthesis. (-)-SDS-1-021 treatment also enhanced the radiosensitivity of tumor cell lines. This (-)-SDS-1-021-induced radiosensitization was accompanied by a delay in radiation-induced γH2AX foci dispersal, consistent with a causative role for the inhibition of double-strand break repair. In contrast, although (-)-SDS-1-021 inhibited translation and protein synthesis in a normal fibroblast cell line, it had no effect on radiosensitivity of normal cells. Subcutaneous xenografts were then used to evaluate the in vivo response to (-)-SDS-1-021 and radiation. Treatment of mice bearing subcutaneous xenografts with (-)-SDS-1-021 decreased tumor translational efficiency as determined by polysome profiles. Although (-)-SDS-1-021 treatment alone had no effect on tumor growth, it significantly enhanced the radiation-induced growth delay. These results suggest that eIF4A is a tumor-selective target for radiosensitization.