Smaller Peak Power Research Articles

Modulational instability of truncated Airy pulses in cubic–quintic nonlinear optical waveguides with multiphoton absorptions

In this work we study the modulational instability (MI) phenomenon of truncated Airy pulses in a cubic–quintic nonlinear optical waveguide including nonlinear multiphoton absorptions as the two-photon absorption (TPA) and the three-photon absorption (3PA) in the anomalous group-velocity dispersion (AGVD) regime of chromatic dispersion. The investigation is done through a lossless and dimensionless cubic–quintic nonlinear Schrödinger equation (CQNLSE) where we launch a perturbed truncated Airy pulse. The perturbation is defined through the linear analysis of the steady-state of a continuous-wave (CW) in which we have chosen to operate with the optimal frequencies of the MI gain. The data obtained through this analysis led to generate the destabilization of the pulse through its lobes starting with the dominant peak. This MI is improved by the cooperating nonlinearities while its distance of achievement is reduced in this case growing from the main lobe to secondary sides lobes of tail. The MI is avoided in the competing case of nonlinearities for small peak power because the negative quintic Kerr nonlinearity (QKN) reduces or almost cancels the cubic Kerr nonlinearity (CKN) effect. If the peak power of the pulse increases, the deleterious effect of the competing QKN decreases while the AGVD and the CKN take over to bring the MI into existence breaking the Airy pulse into sub-pulses. This feature becomes more and more noised as the peak power increases. The TPA comes as a limiting factor of the MI for both the cases of cooperating and competing nonlinearities. The introduction of 3PA performs this TPA effect in the case of cooperating nonlinearities while in the competing case, the 3PA surprisingly cancels the TPA, increasing the AGVD effect. Since the same feature has already been observed recently in Ref. Heuteu et al, J. Opt. 23, 095503 (2021) for the supercontinuum generation (SCG) of Airy pulses, it is therefore shown that the 3PA could be used for better control the TPA effect even in the MI of this kind of pulses. Moreover, it is also shown that the increase of the Airy pulse duration drastically enhances its MI occurrence with noised outputs for large values of pulse width. However, reducing the pulse width also reduces its input energy, consequently the Airy pulse does not undergo the MI phenomenon but simply manifests the property of acceleration.

Design of Multifunctional Mesosphere-Ionosphere Sounding System and Preliminary Results.

This paper describes a novel sounding system for which the functions of the medium frequency (MF) radar and the ionosonde are integrated on the same hardware platform and antenna structure, namely the middle atmosphere-ionosphere (MAI) system. Unlike the common MF radar, MAI system adopts the pseudo-random (PRN) phase-coded modulation technology, which breaks the limitation of the traditional monopulse mode. Through the pulse compression, only a small peak power is needed to achieve the signal-to-noise ratio (SNR) requirement. The excellent anti-jamming performance is also very suitable for the ionospheric sounding. One transmitting and six receiving modes are adopted for the MF sounding. While neglecting the structure of the T/R switches, the coupling interference between the transmitter and the receiver may also be avoided. Moreover, by employing a miniaturized antenna array composed of progressive-wave antennas for the MF receiving and ionospheric sounding, the MAI system takes account of the requirements of the inversion algorithms of MF radar and the large bandwidth need for the ionospheric sounding concurrently. Such an antenna structure can also greatly simplify the system structure and minimize the difficulty of deployment. The experiments verified the availability of the system scheme and its engineering application significance. Through further analysis of the sounding data, the wind field of the mesosphere, the electron density of D layer and electron density profile from layers E to F were obtained at the identical location. The capability of MAI system can play an important role in studying the interaction and coupling mechanism between the mesosphere and ionosphere.

Indices to Study the Electrical Power Signals in Active and Passive Distribution Lines: A Combined Analysis with Empirical Mode Decomposition

The broad diffusion of renewable energy-based technologies has introduced several open issues in the design and operation of smart grids (SGs) when distributed generators (DGs) inject a large amount of power into the grid. In this paper, a theoretical investigation on active and reactive power data is performed for one active line characterized by several photovoltaic (PV) plants with a great amount of injectable power and two passive lines, one of them having a small peak power PV plant and the other one having no PV power. The frequencies calculated via the empirical mode decomposition (EMD) method based on the Hilbert-Huang transform (HHT) are compared to the ones obtained via the fast Fourier transform (FFT) and the wavelet transform (WT), showing a wider spectrum of significant modes mainly due to the non-periodical behavior of the power signals. The results obtained according to the HHT-EMD analysis are corroborated by the calculation of three new indices that are computed starting from the electrical signal itself and not from the Hilbert spectrum. These indices give the quantitative deviation from the periodicity and the coherence degree of the power signals, which typically deviate from the stationary regime and have a nonlinear behavior in terms of amplitude and phase. This information allows to extract intrinsic features of power lines belonging to SGs and this is useful for their optimal operation and planning.

Research on the Transient Characteristics of Microgrid with Pulsed Load

Unlike traditional load, pulsed load typically features small average power and large peak power. In this paper, the mathematic models of microgrid consisting of synchronous generator and pulsed load are established. Average Magnitude Difference Compensate Function (AMDCF) is proposed to calculate the frequency of synchronous generator, and, based on AMDCF, relative deviation rate (RDR) which characterizes the impact of pulsed load on the AC side of grid is firstly defined and this paper describes calculation process in detail. Insulated Gate Bipolar Transistor (IGBT) is used as DC switch to control the on/off state of resistive load for simulating pulsed load, the period and duty-cycle of the pulsed load are simulated by setting the gate signal of IGBT, and the peak power of the pulsed load is simulated by setting the resistance. The system dynamic characteristics under pulsed load are analyzed in detail, and the influence of duty-cycle, period, peak power, and filter capacitance of the pulsed load on system dynamic indicators is studied and validated experimentally.

Perfect radar pulse compression via unimodular fourier multipliers

We propose a novel framework for studying radar pulse compression with continuous waveforms. Our methodology is based on the recent developments of the mathematical theory of comparison of measurements. First we show that a radar measurement of a time-independent but spatially distributed radar target is rigorously more informative than another one if the modulus of the Fourier transform of the radar code is greater than or equal to the modulus of the Fourier transform of the second radar code. We then motivate the study by spreading a Gaussian pulse into a longer pulse with smaller peak power and re-compressing the spread pulse into its original form. We then review the basic concepts of the theory and pose the conditions for statistically equivalent radar experiments. We show that such experiments can be constructed by spreading the radar pulses via multiplication of their Fourier transforms by unimodular functions. Finally, we show by analytical and numerical methods some examples of the spreading and re-compression of certain simple pulses.

Two kinds of optical pulse compression approaches based on cross phase modulation

Time lens based on cross phase modulation can realize accurate quadratic phase modulation. However, its application in optical pulse compression is restricted by the pump pulse with a high peak power. The formula of the peak power is deduced. It is proposed to use an output fiber with positive dispersion to lower the high peak power requirement for the pump pulse. It is also proposed to use a 4f system which consists of two time lenses to realize optical pulse compression, thereby more effectively lowering the peak power of the pump pulse. The formulas of the peak power and the resolution of the 4f system are deduced. The optical pulse compression is simulated and analysed. The research results demonstrate that in a 4f system based on cross phase modulation, femtosecond pulses can be generated by using pump pulses with small peak power; With compression factor increasing, the pulse width of the output pulse is restricted mainly by the solution of the 4f system. The method of improving the solution of the 4f system is discussed.

Design of a continuously tunable delay line using vectorial modulational instability and chromatic dispersion in optical fibers

We design an all-optical tunable delay line based on both dispersive and wavelength conversion stages involving modulational instability of a two-frequency pump field propagating in a highly birefringent fiber. More precisely, we numerically show that, by varying the frequency separation between the two orthogonally polarized pump waves, we achieve a controllable and continuous delay of hundreds of picoseconds for signal pulse durations from picoseconds to nanoseconds, without pulse distortion and with only small peak power fluctuations. The proposed method does not require any tunable bandpass filter and can be applied to delay digital data streams at tens of Gbit/s depending on the pump power level.

A Compact 6.5-W PHEMT MMIC Power Amplifier for Ku-Band Applications

A compact 6.5-W AlGaAs/InGaAs/GaAs PHEMT monolithic microwave integrated circuit (MMIC) power amplifier (PA) for Ku-band applications is proposed. This two-stage amplifier with chip size of 8.554mm2 (3.64mmtimes2.35mm) is designed to fully match 50-Omega input and output impedance. Under 8V and 2000mA dc bias condition, the PA deliver 38.1dBm (6.5W) saturated output power, 10.5-dB small signal gain and peak power added efficiency of 24.6% from 13.6 to 14.2GHz. This MMIC also achieved the best power densities (760mW/mm2) at Ku band reported to date

Operation of Hybrid Wind-Turbine Compressed-Air System for Connection to Electric Grid Networks and Cogeneration

This paper describes a storage system that uses wind energy to compress air in a series of high-pressure storage tanks. When needed, the compressed air is expanded through a turbo-expander to generate electricity. The system is designed for the storage of wind energy and utilises above-ground compressed-air storage with 8,278 kPa (1,200-psia) tanks. It is applicable in the operational power region between (1) electrical storage batteries for relatively small peak power and (2) large pressurized underground salt caverns for large peak power. Therefore, it is most economic for between 0.5 and 100 Megawatt electric power systems. The key advantages over these other storage methods are that there is no need to either purchase, maintain and dispose of waste chemicals, or locate large underground caverns. In addition to supplying electrical power, the by-product heat may be utilised as cogeneration. For instance, the multi-stage compressor coolant may heat domestic water and the cooled exhaust air from the turbo-expander may benefit air-conditioning. Accounting 5% benefit from the hot water and 20% from the refrigerated air, the $0.076/kWh cost of delivered electricity decreases to $0.057/kWh. Reducing or eliminating high-pressure tanks and high-voltage power lines by using the volumetrically equivalent of long high-pressure transfer lines, further reduces the unit cost. This is particularly applicable for offshore windfarms.

Quasi-soliton propagation in dispersion-managed optical fibers

Combination of programmed chirp and dispersion profiles produced a solitonlike nonlinear pulse with a stationary structure (quasi-soliton). The quasi-soliton has more attractive properties than those of a soliton because of its reduced interaction and smaller peak power than a soliton and allows ~100-Gbit / s transmission over a 125-dispersion distance with reasonable power.

A 65-ns 4-Mbit CMOS DRAM with a twisted driveline sense amplifier

A 4-Mb word/spl times/1-b/1-Mb word/spl times/4-b CMOS DRAM characterized by a twisted driveline sense-amplifier (TDSA) scheme and a multiphase drive circuit which enable faster access time and a smaller peak power supply current, respectively, is described. The implementation of an initialize mode with CAS-before-RAS (CBR) logic control, which reduces the memory-chip initialization time by almost a thousand times, is also discussed. The chip measures 6.38/spl times/17.38 mm/SUP 2/ and has been fabricated by using double-well CMOS technology with a minimum design rule of 0.8 /spl mu/m. A typical access time of 65 ns and a peak power supply current of less then 150 mA have been obtained.

Rydberg-atom masers. I. A theoretical and experimental study of super-radiant systems in the millimeter-wave domain

The operation of maser devices using highly excited Rydberg atoms as active medium is investigated. These systems, working in a transient regime reminiscent of super-radiance generate few-hundred-ns-long bursts of mm-wave radiation. They are characterized by extremely low inversion density thresholds (${N}_{0}\ensuremath{\sim}{10}^{4}$ atoms typically) and very small peak power outputs (in the ${10}^{\ensuremath{-}11}$- to ${10}^{\ensuremath{-}13}$-watt range). This study is interesting in the context of new tests of super-radiance and electrodynamics theory. It also opens new possibilities in the important domain of mm-wave amplification and detection. In this paper, we present a simple semiclassical theory of transient Rydberg maser operation and we report the experimental observation of a large number of maser emission lines on Na atoms, spanning a wide frequency interval ($60l\ensuremath{\nu}l950$ GHz). The technique used to monitor the emission is the indirect field ionization procedure which reveals fast radiative transfers occurring between Rydberg levels. Another method involving the direct detection of the maser radiation by a heterodyne receiver is described in a subsequent paper, along with a report on the investigation of various effects related to the triggering of the transient maser emission by external radiation.