Chirp Parameter Research Articles

Modulation bandwidth enhancement in monolithic integrated two-section DFB lasers based on the detuned loading effect

Modulation bandwidth enhancement in a directly modulated two-section distributed feedback (TS-DFB) laser based on a detuned loading effect is investigated and experimentally demonstrated. The results show that the 3-dB bandwidth of the TS-DFB laser is increased to 17.6 GHz and that chirp parameter can be reduced to 2.24. Compared to the absence of a detuned loading effect, there is a 4.6 GHz increase and a 2.45 reduction, respectively. After transmitting a 10 Gb/s non-return-to-zero (NRZ) signal through a 5-km fiber, the modulation eye diagram still achieves a large opening. Eight-channel laser arrays with precise wavelength spacing are fabricated. Each TS-DFB laser in the array has side mode suppression ratios (SMSR) > 49.093 dB and the maximum wavelength residual < 0.316 nm.

Enhancing harmonic brightness near the cutoff region by using laser pulses with a small positive chirp.

Efficient enhancement of harmonic brightness near the cutoff region is achieved by employing laser pulses with a small positive chirp in theory, where the laser intensity and frequency near the peak of the laser pulse are almost unchanged relative to the chirp-free field. The improvement of harmonic brightness is achieved under the condition that the ionization probability is almost unchanged. Through the analysis of the harmonics contributed by the rising and falling parts of the laser pulse, we have uncovered a "frequency compensation" mechanism that leads to an enhanced harmonic brightness near the cutoff region. Under appropriate chirp parameters, the harmonics contributed by the rising and falling parts can be constructively interfered in a smaller frequency range with greater intensity, thereby obtaining harmonics with good monochromaticity and high brightness. This study explains the mechanism of harmonic brightness enhancement from a new perspective, and provides a new idea for harmonic regulation without changing the ionization.

Auditory brainstem response to different chirp (based on cochlear partition) stimulation rates

All through the last decades, hearing thresholds have been estimated by audiologists by different means, such as pure-tone assessments, auditory steady state response, auditory brainstem response, etc. Objective EEG-based measurements have been applied, such as the auditory brainstem response (ABR), which measures neural synchrony along the brainstem auditory pathway. Through ABR waves’ amplitude and latency due to a stimulus level, hearing thresholds can be estimated. Considered a short-latencyauditory evoked potential (1–20 ms), very short transient stimulus (0.1–10 ms) is needed to evoke ABR. Chirp is a stimulus that has demonstrated to evoke better response, compared with clicks (aprox twice responses amplitude). Chirp is a transient auditory stimulus designed that considers delay in basilar membrane tonotopic gradient inside the cochlea. Chirp auditory response has been suggested to represent higher amplitudes, lower latency and lower time to identify thresholds. Characterization of ABR morphology due to chirp stimulus is something that has still been studied since multiple chirp designs have been proposed to identify changes in response due to chirp parameters differences. In the present work a description of Chirp design and detailed ABR extraction is presented, looking for a comparison between 4 Chirp stimulation rates as described in literature.

Focusing characteristics of chirped phase-modulated Lorentz-Gaussian vortex beams.

This work presents a thorough investigation of the focusing characteristic of chirped phase modulated Lorentz-Gaussian (LG) vortex beams based on the vector diffraction theory. The results show that changing the first-order chirp parameter c 1 can effectively adjust the size of the focusing spot, and the distance between focusing spots can also be controlled. The second-order chirp parameter c 2 can control the up-and-down movement of the optical chain in the focusing region. Simultaneously, the length of the focusing spots can be accurately changed by modulating the waist width ω. In addition, the influence of integer topological charge number m on controlling the size of an optical dark trap is discussed in detail. And fractional topological charge number m can control the rotation of focus peak and the number of optical dark traps. Potential applications of these findings include optical shape and capture, optical particle transmission, and contemporary medical care.

Ballistic dynamics of emergent soliton from Airy pulse in a medium with linear optical potential

We numerically investigate the propagation dynamics of Airy pulse in dispersive and nonlinear medium with time-dependent external optical potential. These time-dependent optical potentials are created by the co-propagating strong pump wave. In the presence of linear optical potential, soliton shedding from signal Airy pulse is observed, which demonstrates ballistic motion. However, emergent soliton can either be advanced or delayed depending upon the sign of the potential and the extent of temporal advancement or delay is directly proportional to the magnitude of the potential strength. In addition, the temporal shift of the emergent soliton is found to be dependent on the input pulse power. Moreover, we show ballistic motion of the emergent soliton by incorporating an initial linear phase as well as linear chirp (quadratic phase) parameters in the input Airy pulse. Furthermore, the effect of truncation factor on the propagation dynamics is explored. These results provide new insights on the manipulation of the signal Airy pulse dynamics in dispersive and nonlinear media.

On refinements to QMFD based chirp parameter estimation

Commuting matrix methods furnish a full basis of orthogonal eigenvectors for the discrete Fourier transform or its centered version needed for computing the discrete fractional Fourier transform and multicomponent chirp signal analysis. However, these approaches suffer from ill-conditioning issues at higher matrix sizes, and require a computationally expensive eigenvalue decomposition.In this paper, ill-conditioning issues associated with the QMFD approach developed previously by the authors are addressed via diagonal modification. Further symmetries of the eigenvectors are used to reduce the size of the underlying eigenvalue problem. These modifications are then incorporated into the real-arithmetic implementation of the QMFD approach that is shown to be significantly superior to the conventional implementation and the corresponding MSE of the chirp parameter estimates are shown to approach their Cramer–Rao lower bounds.

Improvement on stability of direct modulation laser with integrated active feedback by partial corrugated gratings.

Researchers have developed a uniform grating DFB with an integrated active optical feedback waveguide (UG-AFDFB) to enhance the modulation speed of direct modulation lasers (DMLs) while reducing costs based on identical active layer designations. However, this design has difficulties in obtaining high single mode yield (SMY) and low relative intensity noise (RIN) as a result of the strong optical feedback caused by the integrated active feedback waveguide (AFW) and the random phase of the facet phase. In this paper, a partial corrugated grating DFB with an integrated active optical feedback waveguide (PG-AFDFB) is proposed to address this issue. Comparison of SMY, S21, RIN, modulation eye pattern, and frequency chirp parameters between UG-AFDFB and PG-AFDFB based on time-domain transmission line laser mode reveals that PG-AFDFB with an optimized grating couple parameter κ performs significantly better than UG-AFDFB under the same conditions. Furthermore, the performance of PG-AFDFB is not sensitive to the random phase of the rear facet phase. Even when κ ranges from 6000 /m to 12000 /m, the current in the AFW is between 0 mA and 20 mA, and the length of the AFW ranges from 50 µm to 100 µm; the SMY of PG-AFDFB remains above 80%.

Spiraling Laguerre-Gaussian solitons and arrays in parabolic potential wells.

Controllable trajectories of beams are one of the main themes in optical science. Here, we investigate the propagation dynamics of Laguerre-Gaussian (LG) solitons in parabolic potential wells and introduce off-axis and chirp parameters (which represent the displacement and the initial angle of beams) to make solitons sinusoidally oscillate in the x and y directions and undergo elliptically or circularly spiraling trajectories during propagation. Additionally, LG solitons with different orders and powers can be combined into soliton arrays of various shapes, depending on the off-axis parameter. Moreover, the soliton arrays can exhibit periodic converging, rotating, and other evolution behaviors, by the proper choice of the chirp parameter. A series of interesting examples demonstrate typical propagation scenarios. Our results may provide a new perspective on and stimulate further investigations of multisoliton interactions in potential wells and may find applications in optical communication and particle control.

Propagation dynamics of (3+1)-dimensional self-accelerating sinh-Gaussian and cosh-Gaussian wave packets in a harmonic potential

In a harmonic potential, the propagation properties of self-accelerating sinh-Gaussian and cosh-Gaussian wave packets are investigated. Analytical results from a (3+1)-dimensional evolution equation are derived. Changing the distribution factor allows these wave packets to present different forms, including dipoles, elliptic vortex, hollow rings, horizontal figure eight, and elliptic Gaussian. These spatiotemporal wave packets rotate periodically, and the period depends on the potential depth. Their shapes are strongly determined by the distribution factor and the cross-phase factor while propagating. Further, the wave packets with negative chirp parameters can reverse their self-accelerating direction. We also investigate these wave packets’ energy flow and angular moment density to explore their dynamic rotating features. The spatiotemporal self-accelerating sinh-Gaussian and cosh-Gaussian wave packets have distinctive characteristics, which may provide a novel platform for the realization of joint control of the optical field in the spatiotemporal domain.

Protecting the fidelity of a pulsed-driven harmonic oscillator

The temporal fidelity of a non-dissipative quantised harmonic oscillator (QHO) driven by two types of pulsed laser; namely, rectangular and train of n-chirped Gaussian pulses is investigated. The computational results are presented for two initial states of the HO, namely, the superposition of coherent states (Schrödinger cat states type) and squeezed coherent state. Quantum interference between the two component states |α〉 and |−α〉 of the initial cat state in the non-resonance case induces oscillatory behaviour in the fidelity. The case of initial squeezed coherent state shows profound maximum bounds of the fidelity or lesser maximum peaks, depending on the pulse shape and other system parameters (squeezing, chirp and pulse number parameters).

Analytical and numerical study of chirped optical solitons in a spatially inhomogeneous polynomial law fiber with parity-time symmetry potential

This work studies the dynamical transmission of chirped optical solitons in a spatially inhomogeneous nonlinear fiber with cubic-quintic-septic nonlinearity, weak nonlocal nonlinearity, self-frequency shift and parity-time () symmetry potential. A generalized variable-coefficient nonlinear Schrödinger equation that models the dynamical evolution of solitons has been investigated by the analytical method of similarity transformation and the numerical mixed method of split-step Fourier method and Runge–Kutta method. The analytical self-similar bright and kink solitons, as well as their associated frequency chirps, are derived for the first time. We found that the amplitude of the bright and kink solitons can be controlled by adjusting the imaginary part of the -symmetric potential. Moreover, the influence of the initial chirp parameter on the soliton pulse widths is quantitatively analyzed. It is worth emphasizing that we could control the chirp whether it is linear or nonlinear by adjusting optical fiber parameters. The simulation results of bright and kink solitons fit perfectly with the analytical ones, and the stabilities of these soliton solutions against noises are checked by numerical simulation.

High-Output-Power 1358-nm-Wavelength SOA-Integrated EADFB Laser (AXEL) for 25-Gbit/s 100-km Transmissions

We developed a 1358-nm-wavelength semiconductor optical amplifier (SOA)-assisted extended-reach electroabsorption modulator integrated distributed feedback laser (AXEL) as a high-power light source for 25G-class passive optical networks (PONs) to ensure sufficient power margin in the transmitter and extend the transmission reach to 100 km. We investigated the effect of the integrated SOA length on the light output power and modulation performance of the AXEL. We found that there was no significant degradation in modulation performance at 25 Gbit/s even for an AXEL with a 175-μm-long SOA. Using this AXEL chip, we fabricated a transmitter by using a commercially available package. The transmitter attained sufficient modulated light output power of 10. 5 dBm and had a high-quality eye diagram for 25-Gbit/s operation. In addition, we found that the measured chirp parameter of the AXEL transmitter was almost 0. This alleviates the transmission distance limitation due to chromatic dispersion and enables the transmission distance to be extended. The loss budget for 20-km transmission, as determined from the measured bit error rate, was 38.4 dB, which is much larger than the value specified for 25G-EPONs. Moreover, the transmission reach was extended to 100 km for the first time, thanks to the AXEL transmitter's high output power. Finally, the possibility of incorporating the AXEL in 100-Gbit/s-ZR4 (80 km) applications using four wavelength channels was considered. The estimated power penalties using the measured chirp parameter were significantly smaller than the measured penalty for 1358 nm. This suggests that the AXEL can also be used for 100-Gbit/s over 80-km transmissions using four channels in a LAN-WDM grid.

Analytical light bullet solutions in diffraction-decreasing media with inhomogeneous parameters

We obtain exact analytical light bullet solutions to the (3+1)-dimensional generalized nonlinear Schrödinger equation with inhomogeneous parameters. We study three types of diffraction-decreasing media to show the broadening and compression properties of the light bullet solutions. The influence of chirp parameter on the propagation of solutions is discussed in details. Furthermore, a comparison with these three different media indicates that the light bullet solutions with Logarithmic profile are compressed to a higher degree. Stability analysis reveal that the light bullet solutions can maintain their structures against small withe noise and are insensitive to disturbance under the constraint condition.

Modulation Bandwidth Enhancement and Frequency Chirp Suppression in Two-Section DFB Laser

We demonstrate a two-section distributed feedback (DFB) laser for direct modulation based on the reconstruction equivalent chirp (REC) technology. The two-section DFB laser exhibits a stable single-mode characteristic. Utilizing the photon-photon resonance (PPR) effect and detuned-loading effect, the 3-dB modulation bandwidth of the two-section DFB laser is improved from 8 GHz to 23 GHz. A 25 Gb/s non-return to zero (NRZ) signal is applied to the two-section DFB laser and eye diagrams with large open extent are obtained. In addition, the relative intensity noise is reduced to below −143 dB/Hz. The frequency chirp is also suppressed. The chirp parameter is reduced from 5.67 to 1.37, which is a small value in directly modulated DFB laser. We compared the eye diagrams after transmitting different distances, the results show that the two-section structure reduces the frequency chirp significantly. The modulation of the two-section DFB laser also has good linearity, with a 1-dB compression point of more than 18 dBm.

Assessment of Complex Signal Parameters Effect on the Energy Concealment Degree

The article deals with the problem of obtaining a qualitative assessment of the energy concealment degree of radio signals. Energy concealment is regarded as the most significant form of signal concealment, since a designer of radio transmitting devices has the most influence and the greatest freedom in defining these properties. The purpose of the article is to systematize the available knowledge about the methods of assessment of energy concealment in order to conduct a mutual comparison of the characteristics of various signals. The authors describe and analyze a number of methods for assessment of energy concealment of signals based on the number of necessary measurements of the signal level range of the signal reconnaissance, as well as probabilistic assessment of signal disclosure. The results of the analysis showed that described methods are not suitable for obtaining a comparative assessment. Based on the conclusions made in the study energy concealment assessment methods, the author's method for assessment the degree of energy concealment of signals in terms of transmitted symbol energy is proposed. The article clarifies the application of the method to assess the parameters of chirp signals, narrowband and wideband FM, BPSK, QPSK, as well as quadrature signals. A comparative assessment of the chirp, FM, BPSK, QPSK and QAM-16 signal parameters for the decimeter VHF band is obtained, taking into account the transmission speed and power. Assessment of energy concealment of signals were obtained at typical information transfer rates. On the basis of the results, some regularities were described that make it possible to evaluate the effect of changing individual parameters of a radio transmitting device on final energy concealment.

Precise control of the ionization channel in strong-field ionization by a few-cycle chirped laser pulse

We investigate theoretically the photoelectron holography in strong-field ionization by a few-cycle chirped laser pulse. It is shown that the numerical results by solving the two-dimensional (2D) time-dependent Schr\"odinger equation (TDSE) are in agreement with that by using the semiclassical two-step (SCTS) model. The opening and the closing of the ionization channel can be controlled precisely by a few-cycle chirped laser pulse and the holographic interference structure can be isolated by adjusting the chirp parameters. This holographic interference structure is related to the rescattered electron wave packet (EWP) which released within an attosecond timescale. We demonstrate that the chirped laser pulse can be used to coherently control the recollision process. By analyzing the rescattered trajectory, we illustrate that the travel time of the rescattered electron is increased and the rescattered electron can obtain high return energy in a negatively chirped laser pulse. In addition, we also illustrate that the photoelectron momentum distributions (PMDs) are very sensitive to the carrier-envelope phase.

Effect of chirp on pulse reflection and refraction at a moving temporal boundary.

The reflection and refraction of chirped Gaussian pulse at a moving step refractive-index boundary are investigated. When a chirped Gaussian pulse crosses a temporal boundary, the shape of the reflected spectra is distorted by adjusting chirp parameters. However, the transmitted spectra retain the Gaussian shape. The shape of the final output spectra is the same if the absolute values of the chirp are the same. By changing the chirp values, we can control the energy of the reflected and transmitted pulses, and the splitting distance of the pulse at the temporal boundary. By adjusting the time-dependent refractive index, chirped Gaussian pulses can experience total internal reflection at the temporal boundary. When pulse splitting occurs in an anomalous dispersion region, the velocity of the transmitted pulse decreases.

Ultrashort light bullet solutions in dual-core dispersion-decreasing media

The ultrashort light bullet solutions to a (3+1)-dimensional generalized nonlinear Schrödinger equation with inhomogeneous coefficients and a varying source are obtained. This model can describe the wave propagation in the dual-core dispersion-decreasing media. Two types of dispersion, the hyperbolic and the Gaussian profiles, are discussed in the media to show the different propagation properties of light bullet solutions. We find that the chirp parameter can control whether the solution is broadened or compressed, and the light bullet solutions in the dispersion-decreasing media with Gaussian profile can be compressed to a predictable degree. Our results may be useful to the pulse compression in dual-core diffraction-decreasing media when associate with the generation of ultrashort pulses.

Towards high photon density for Compton scattering by spectral chirp

Scattering of intense laser pulses on high-energy electron beams allows one to produce a large number of X and gamma rays. For temporally pulsed lasers the resulting spectra is broadband which severely limits practical applications. One could use linearly chirped laser pulses to compensate that broadening. We show for laser pulses chirped in the spectral domain that there is the optimal chirp parameter at which the spectra has the brightest peak. Additionally, we use catastrophe theory to analytically find this optimal chirp value.

The effect of chirp parameter on laser propagation in collisional quantum plasma

This manuscript investigates the effect of the chirp factor on the relativistic self-focusing of a Gaussian chirped pulse laser in collisional quantum plasmas. Nonlinear equations are derived to describe the propagation of a linear chirped laser frequency; afterward, by considering dielectric function obtained by quantum kinetic equation and BGK collision integral in coordinate space, evolution differential equations of laser beam width are found; and numerically solved by the fourth-order Runge-Kutta method. It studies oscillations of the beam width along the propagation direction for different values of collision frequency, chirp parameter, plasma density, and laser intensity. Numerical analyses show that a laser beam is defocused after focusing on a definite value; nonetheless, the positive chirp parameter could reduce the defocusing and strengthen the self-focusing in collisional quantum plasma. Also, the higher chirp value leads to a smaller oscillation amplitude and a greater oscillation rate. Furthermore, the self-focusing effect becomes stronger by increasing plasma density and laser intensity. These consequences could be beneficial in the improvement of fast ignition experiments.