Negative Dispersion Research Articles

Broadband mid-infrared metalens with polarization-controlled at-will chromatic dispersion.

Mid-infrared metalenses are promising for potential applications in a range of fields, including molecular detection, imaging, and optical sensing. To fulfil the different requirements of these diverse application scenarios, engineering of the ability to control the chromatic dispersion of these lenses at will is vitally important. Herein, we demonstrate broadband mid-infrared metalenses with polarization-controlled at-will chromatic dispersion capability based on all-silicon metasurfaces. Both polarization-insensitive and polarization-sensitive mid-infrared metalenses with at-will chromatic dispersion capabilities are demonstrated numerically for operation at wavelengths ranging from 3.75 μm to 4.75 μm. The average focusing efficiency of all these metalenses exceeds 40% in the wavelength range of interest, and the highest focusing efficiency ranges up to 67%. The mid-infrared metalenses with at-will chromatic dispersion proposed here may be beneficial for mid-infrared sensing, communications, and imaging applications in the future.

Studying the Operation of an All-PM Yb-Doped Fiber Laser Oscillator at Negative and Positive Net Cavity Dispersion

Chirped fiber Bragg gratings in Yb-doped fiber lasers allow tuning the net cavity dispersion, thus enabling access to pulse dynamics beyond the typical all-normal-dispersion dissipative soliton regime. This Letter demonstrates an ultrafast dispersion-managed all-polarization-maintaining fiber oscillator mode-locked with a nonlinear optical loop mirror. Using a chirped fiber Bragg grating inside the oscillator, it can work at net cavity dispersion in the range from -0.098 ps$^2$ up to +0.067 ps$^2$ and above at the wavelength of 1 $\mathrm{\mu}$m. Depending on the configuration, the system can deliver stable pulses with energies up to 2.3 nJ and pulse durations as short as 98 fs.

Inferring SARS-CoV-2 RNA shedding into wastewater relative to the time of infection.

Since the start of the coronavirus disease-2019 (COVID-19) pandemic, there has been interest in using wastewater monitoring as an approach for disease surveillance. A significant uncertainty that would improve the interpretation of wastewater monitoring data is the intensity and timing with which individuals shed RNA from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) into wastewater. By combining wastewater and case surveillance data sets from a university campus during a period of heightened surveillance, we inferred that individual shedding of RNA into wastewater peaks on average 6 days (50% uncertainty interval (UI): 6-7; 95% UI: 4-8) following infection, and that wastewater measurements are highly overdispersed [negative binomial dispersion parameter, k = 0.39 (95% credible interval: 0.32-0.48)]. This limits the utility of wastewater surveillance as a leading indicator of secular trends in SARS-CoV-2 transmission during an epidemic, and implies that it could be most useful as an early warning of rising transmission in areas where transmission is low or clinical testing is delayed or of limited capacity.

Stability and non-linear dynamic analysis of Kerr optical frequencycombs in dual-coupled microcavities with high-order dispersion

We investigate the stability and nonlinear dynamics of the Kerr optical frequency comb inside a dual coupled microcavity with high-order dispersion effect based on the theoretical model of coupled nonlinear Schrödinger equation. The effects of different high-order dispersion parameters on the evolution and spectral characteristics of the optical field in the cavity are also explored. Theoretical results indicate that the addition of the third-order dispersion enlarges the stability domain of the parametric space and transforms the periodically varying soliton breathers and chaos into stable bright soliton. In order to obtain an accurate Kerr optical frequency comb spectral envelope, higher-order dispersion should be considered. Moreover, high-order dispersion terms have a significant effect on the spectral characteristics of the optical frequency comb, such as the spectral envelope frequency shift and the dispersive wave spectral position. Specifically, the third-order dispersion and positive fourth-order dispersion can broaden the spectrum and enhance the dispersive waves; while the negative fourth-order dispersion can suppress the dispersive wave generation and obtain a symmetric soliton frequency comb; the fifth-order dispersion can regulate the drift direction and speed of the optical solitons. The theoretical results are of great value for dispersion regulation and design and also for stability studies in double-coupled microcavity experiments.

Herriott multi-pass block material stretcher and grism compressor in chirped-pulse amplification

We report a femtosecond chirped-pulse amplification (CPA) system based on block material stretcher and grism compression. An optical material block is employed in Herriott multi-reflection configuration as a pulse stretcher, and a transmission grating is combined with dispersion prism to form grism as a compressor which can provide the negative second and third-order dispersion. By optimizing the prism vertex angle and grating line density, the grism can completely compensate for the third-order material dispersion. We obtain shorter compressed pulses. In the experiment, the stretched pulses are amplified by regenerative amplifier, which amplifies the 800 nm seed pulse to 2.30 W under the 11.4 W, 527 nm, 1 kHz pumping conditions, and the spectral width of the amplified pulse is 26.7 nm. The amplified pulses are compressed to 39.6 fs, which is close to the Fourier transform limit of 35.2 fs. The design of the system simplifies the structure of the conventional chirped pulse amplification system, reduces the space size of the optical path, and improves the operational stability of the laser system. With the block material stretcher and grism compressor, the whole CPA laser system is very compact and can be used as a reliable light source for subsequent amplification as well as ultrafast phenomenon studies.

Fully negative near-zero ultra-flat dispersion photonic crystal fibers in E+S+C+L band

We demonstrate a modified hexagonal three-layer air-hole photonic crystal fiber (PCF) which presents a good ability of dispersion management. The proposed PCF not only achieved an ultra-flattened all-negative dispersion characteristics of 0.15085 ps/(km·nm) fluctuation within the wavelength range of E+S+C+L wavelength band but also has been able to obtain other interesting features such as low confinement loss. Furthermore, the quadrilateral and octagonal structures are investigated to compare the superiority of different structures and analyze why we chose the hexagonal one.

Temporal-filtering dissipative soliton in an optical parametric oscillator

Abstract Dissipative solitons have been realized in mode-locked fiber lasers in the theoretical framework of the Ginzburg–Landau equation and have significantly improved the pulse energy and peak power levels of such lasers. It is interesting to explore whether dissipative solitons exist in optical parametric oscillators in the framework of three-wave coupling equations in order to substantially increase the performance of optical parametric oscillators. Here, we demonstrate a temporal-filtering dissipative soliton in a synchronously pumped optical parametric oscillator. The temporal-gain filtering of the pump pulse combined with strong cascading nonlinearity and dispersion in the optical parametric oscillator enables the generation of a broad spectrum with a nearly linear chirp; consequently, a significantly compressed pulse and high peak power can be realized after dechirping outside the cavity. Furthermore, we realized, for the first time, dissipative solitons in an optical system with a negative nonlinear phase shift and anomalous dispersion, extending the parameter region of dissipative solitons. The findings may open a new research block for dissipative solitons and provide new opportunities for mid-infrared ultrafast science.

Engineering the chemical structure of H-shaped reactive molecules for negative dispersion of retardation

Dependence of retardation dispersion on the chemical structure of H-shaped reactive molecules.

Broad-spectrum noise-like pulse and Q-switched noise-like pulse in a Tm-doped fiber laser

We experimentally and numerically study the broad-spectrum noise-like pulse (NLP) in a Tm-doped fiber laser (TDFL). The 3-dB spectral width of the NLP is 126 nm, which is, to the best of our knowledge, the broadest spectrum that has been directly obtained from negative dispersion TDFLs. The NLP can transform into another dynamic pulse operation, a Q-switched noise-like pulse (QSNLP). Since the QSNLP showed a noise-like structure within a Q-switched envelope, compared to conventional Q-switched mode-locked pulse, it is break-free during amplification. It offers excellent potential for obtaining high-energy pulses. The numerical studies demonstrate the existence of the NLPs and the rationality of the existence of QSNLP based on the experiment condition. Our work also enriches the operation of bunching structure pulses in fiber lasers.

The multi-dimensionality of competitive balance: evidence from European football

PurposeThe purpose of this paper is to address the problem of designing league regulatory mechanisms given the multi-dimensionality of competitive balance and the proliferation of empirical measures.Design/methodology/approachA three-stage approach is adopted. Firstly, a taxonomy of empirical measures of competitive balance is proposed, identifying two fundamental dimensions – win dispersion and performance persistence. Secondly, a simple two-team model of league competitive balance is used to explore the dispersion–persistence relationship. Third, correlation and regression analysis of seven empirical measures of competitive balance for the 18 best-attended top-tier domestic football leagues in Europe over the 10 seasons, 2008–2017, are used to (1) validate the proposed categorisation of empirical measures into two dimensions; and (2) investigate the nature of the dispersion–persistence relationship across leagues.FindingsThe simple model of league competitive balance implies a strong positive dispersion–persistence relationship when persistence effects increase for big-market teams relative to those for the small-market teams. However, the empirical evidence indicates that while leagues such as the Spanish La Liga exhibit a strong positive dispersion–persistence relationship, other leagues show little or no relationship, and some leagues, particularly, the English Premier League and top-tier divisions in Belgium and Netherlands, have a strong negative dispersion–persistence relationship. The key policy implication for leagues is the importance of understanding the direction and impact of dispersion and persistence effects on the demand for league products.Originality/valueThe variability in the strength and direction of the dispersion–persistence relationship across leagues is an important result that undermines the “one-size-fits-all” approach to designing league regulatory mechanisms.

Photonic crystal fiber with high nonlinearity and extremely negative dispersion

Photonic crystal fiber with high nonlinearity and extremely negative dispersion

Investigation of defective hybrid cladding with silicon nanocrystal PCF for supercontinuum generation

Defective hybrid cladding through a silicon nanocrystal-core-structured photonic crystal fiber intended for high pump power supercontinuum proliferation is discussed in this paper. The cladding comprehends a hybrid approach of a hexagonal air hole in the outer section and a petal-structured air hole in the inner layer with a twisted pattern. Such a procedure with an air hole in the cladding section with a silicon nanocore displays high nonlinearity and negative dispersion at the communication window for varying pulse widths with 20 kW pump power. The impact of structural parameters of the proposed structure on the optical constraints is discussed, namely, dispersion, nonlinearity and group-velocity dispersion for wavelengths ranging from 0.45 µm to 1.85 µm. The proposed structure with optimized structural parameters provides high nonlinearity of about 6.38 × 106 W−1 km−1 with negative dispersion of −70.19 ps (nm km)−1 at 1550 nm.

Anomalous spin exciton with a magnetoroton minimum in a quantum Hall ferromagnet at a filling factor ν=2

In ZnO-based two-dimensional electron systems with strong Coulomb interaction, the anomalous spin-exciton branch is revealed. As probed by inelastic light scattering, in a ferromagnetic quantum-Hall state with the filling factor $\ensuremath{\nu}=2$, a spin exciton has a negative momentum dispersion with steepness dependent on the electron density. The negative dispersion of the spin exciton is associated with its interaction with higher-energy spin-flip modes that exist near $\ensuremath{\nu}=2$. Surprisingly, the anti-Stokes light scattering on spin excitons at ferromagnetic state $\ensuremath{\nu}=2$ is amplified by orders of magnitude, indicating the macroscopic accumulation of these excitations. The experimental findings are confirmed by the exact diagonalization method---these calculations show a magnetoroton minimum in the dispersion of spin excitons and also the attractive interaction between magnetoroton spin excitations.

On propagation characteristics of Rayleigh wave in saturated porous media based on the strain gradient nonlocal Biot theory

Based on the strain gradient nonlocal Biot theory, the semi-analytical solution of Rayleigh wave fields is obtained using the wave function expansion method. The influence of nonlocal pore size (characterized by nonlocal parameter) and heterogeneity structure effect (characterized by scale factor) on the propagation of Rayleigh wave are numerically implemented and then discussed in detail. The results show that the nonlocal parameter and scale factor have an ignorable influence on the propagation of Rayleigh wave in low frequency region while a significant influence within high frequency range by comparing with the results obtained from the classical Biot theory. A critical ratio of scale factor to nonlocal parameter defining the transition of negative dispersion to positive dispersion is observed. The Rayleigh wave velocity in saturated porous media increases with increasing nonlocal parameter and decreases with the increase of the scale factor. The length of the principal axis and minor axis of the ellipse formed by the displacement fields strongly depends on the ratio of nonlocal parameter to scale factor and the depth of the observation point. Furthermore, the displacement amplitude is intensified by increasing the nonlocal parameter and weakened by increasing the scale factor.

Asymptotic behavior of solution of Whitham–Broer–Kaup type equations with negative dispersion

Abstract In this work, we discuss the long time behavior of solutions of the Whitham–Broer–Kaup system with Lipschitz nonlinearity and negative dispersion term. We prove the global well-posedness when α + β 2 < 0 {\alpha+\beta^{2}<0} as well as the convergence to 0 of small solutions at rate 𝒪 ⁢ ( t - 1 / 2 ) {\mathcal{O}(t^{-1/2})} .

Wave Steering by Relaying Interface States in a Valley-Hall-Derived Photonic Superlattice

Topological notions in physics have become a powerful perspective that leads to the discoveries of topological interface states (TISs). In this work, we present a scheme to achieve negative refraction by leveraging the properties of TISs in a valley photonic crystal (VPC). Due to the chiral characteristics, one type of the TISs deterministically possesses negative dispersion relation, which can cause an obliquely incident wave to undergo a negative lateral shift. By stacking multiple VPC interfaces, the TIS-induced lateral shifts can relay in the transmitted wave towards the far side of incidence. The resultant outgoing wave appears to have undergone negative refraction. This finding is verified in microwave experiments. Our scheme opens new application scenarios for topological systems in bulk wave manipulations.

Enhanced 850-nm SM VCSEL transmission by favorable chirp interaction with fiber dispersion

Single-mode (SM) vertical-cavity surface-emitting lasers (VCSELs), especially those operating around 850 nm, have been studied intensively in recent years for short distance transmission. Despite the demonstrations of increased data rate and system distance, the impact of frequency chirp that is commonly present in directly modulated lasers is an area that needs more detailed studies for 850 nm VCSEL-based systems. In this paper, we explore the interaction between a laser chirp and fiber chromatic dispersion using an 850-nm SM VCSEL over a standard SM fiber that is two-mode at the operating wavelength. Our transmission experiments show that the system can enjoy a benefit from negative fiber dispersion instead of a penalty compared to the back-to-back case, due to the favorable chirp–dispersion interaction, which is also supported by our system bandwidth measurements. Furthermore, we measure the chirp value of the SM VCSEL and conduct modeling using the time-domain pulse concept to illustrate the impact on the chirp–dispersion interaction and explore the optimal chirp parameters for different transmission data rates. Our study indicates a significant system benefit of using 850-nm SM VCSELs with a high bandwidth single-mode fiber around 850 nm due to the favorable chirp–dispersion interaction. Such a benefit can enable high data rate and longer distance system transmission for modern data center applications.

Post-compression of long-wave infrared 2picosecond sub-terawatt pulses in bulk materials.

We have experimentally demonstrated the post-compression of a long-wave infrared (9.2 μm) 150 GW peak power pulse from 2 ps to less than 500 fs using a sequence of two bulk materials with negative group velocity dispersion (GVD). The compression resulted in up to 1.6-fold increase of the peak power and up to 2.8-fold increase of the intensity in the center of a quasi-Gaussian beam. The partial decoupling of the self-phase modulation and chirp compensation stages by using two materials with significantly different ratios of nonlinear refractive index to GVD provides accurate optimization of the compression mechanism and promises a viable path to scaling peak powers to supra-terawatt levels. During the preparatory study, we measured, for the first time to our knowledge, the nonlinear refractive indices of NaCl, KCl, and BaF2 for picosecond pulses in the long-wave infrared region.

Natural Hyperbolic Dispersion with Anisotropic Epsilon‐Near‐Zero and Epsilon‐Near‐Pole in Squaraine Molecular Film

AbstractEpsilon‐near‐zero (ENZ) optical material has been employed in a number of novel linear and nonlinear optical applications, owing to the vanishing polarization upon an incident optical wave. In a uniaxial medium possessing hyperbolic energy–momentum dispersion of optical wave, ENZ can take place at ordinary and extraordinary permittivities. Organic thin films presenting a lamellar structure have been reported to exhibit a transverse negative hyperbolic dispersion with ENZ at ordinary permittivity. Here, organic thin film with ENZ at extraordinary permittivity is demonstrated. Newly synthesized polymethine dye (i.e., squaraine indolenine triethyleneglycol molecule) self‐organizes to form a layered structure in a pristine film, and both transverse negative and positive hyperbolic dispersions are observed at visible wavelengths. Analysis of tens‐nanometer‐thick pristine film shows that both ENZ and epsilon‐near‐pole (ENP) occur at longitudinal as well as transverse component of dielectric permittivity. Optical characterization of squaraine pristine film is presented, and the importance of transverse positive hyperbolic dispersion in such monolithic thin film is discussed.

Pulse evolution and multi-pulse state of coherently coupled polarization domain walls in a fiber ring laser.

Pulse evolution and multi-pulse state of coherently coupled polarization domain walls (PDW) is experimentally demonstrated in a novel fiber ring laser. Versatile pulse shapes benefit by wide range moving of PDW in the weakly birefringent fiber. The 8.6 m short-cavity structure is more compact and accessible based on a 976 nm pump with nearly zero negative dispersion (-0.0002 ps2). Besides, multi-pulse patterns such as PDW splitting, harmonic mode-locking, and periodic soliton collision are also observed under larger net negative dispersion (-3.09 ps2) and 151m-longer cavity. This is the first demonstration of coherently coupled PDW in a fiber laser using a bandpass filter and the formation of coherently coupled PDW is ascribed to the BPF's force filtering.