Arbitrary Power Levels Research Articles

High-power ultrafast fiber lasers for materials processing

Abstract State-of-the-art fiber-laser systems can deliver femtosecond pulses at average powers beyond the kilowatt level and multi-mJ pulse energies by employing advanced large-mode-area fiber designs, chirped-pulse amplification, and the coherent combination of parallel fiber amplifiers. By using sophisticated coherent phase control, one or even several output ports can be modulated at virtually arbitrary power levels and switching speeds. In addition, an all-fiber setup for GHz-burst generation is described allowing to access an even wider range of laser parameters. The combination of all these approaches together with the robustness, efficiency, and excellent beam quality inherent to fiber-laser technology has the potential to strongly improve existing materials-processing applications.

Design Methodology for Three-Phase Buck-Type and Boost-Type Rectifiers to Comply With the DO-160G Current Distortion Test

The main standard for avionic equipment DO-160G defines a set of tests that require compliance before the employment of a device in aircraft. An important test involves the generator voltage and consequential current distortion of the three-phase load in the variable 360–800 Hz frequency grid. The main purpose of this paper is to present and analyze a systematic design methodology for three-phase boost and buck rectifiers in order to meet with the voltage distortion test requirement. For a given voltage harmonic profile, the current harmonic limits that have to be satisfied are translated into equivalent per-harmonic admittances and a profile of maximum rectifier input admittance versus frequency is obtained. The defined profile, due to normalization, is applicable to arbitrary power level with simple shifting by the base admittance governed by the converter nominal power. It is shown that for boost-type rectifiers there is a tradeoff between current controller bandwidth and input inductor size, while for the buck-type rectifiers main limitation lies in the input LC filter design used for differential electromagnetic interference filtering. The experimental results conducted on an SiC three-phase 10 kW VIENNA rectifier are tightly backing up the proposed theoretical analysis. This paper is accompanied by three videos demonstrating experimental measurement of d -axis open-loop duty cycle to inductor current transfer function, loop-gain of d -axis current controller with 3.8 kHz bandwidth and variable grid frequency 360–800 Hz operation of the converter under 0% and 10% input three-phase voltage total harmonic distortion.

Corrections to “Channel Power Optimization of WDM Systems Following Gaussian Noise Nonlinearity Model in Presence of Stimulated Raman Scattering” [Nov 17, no. 23, 5237-5249

An error in the equations in the Appendix of the above-named work [ibid., vol. 35, no. 23, pp. 5237–5249, Nov. 2017] has been identified. The corrected equations fix a contradiction in the printed statement at the end of the Appendix. The numerical results presented, including optimized power allocations and figures, used the incorrect model as printed. For the significantly tilted optimized power allocations considered and at the relatively low total fiber powers considered, using the correct model yields a negligible change to those results, so the interpretation and conclusions remain unaltered. The model as corrected here yields correct results at arbitrary power levels, including levels much higher than those considered in the paper.

Polynomial time solution to minimum forwarding set problem in wireless networks under disk coverage model

In this paper, we consider a practical problem, called Minimum Forwarding Set Problem (MFSP), that emerges within the context of implementing (energy efficient) communication protocols for wireless ad hoc or sensor networks. For a given node v, MFSP asks for a minimum cardinality subset of 1-hop neighbors of v to cover v’s 2-hop neighbors. MFSP problem is also known as multi-point relay (MPR) problem. It is shown to be an NP-complete problem for its general case that does not consider the coverage characteristics of wireless transmissions. In this paper, we present two polynomial time algorithms to solve the MFSP problem under disk coverage model for wireless transmissions. In our earlier work, we presented a polynomial time algorithm for this problem under unit disk coverage model. In the current work, we present several observations on the geometric characteristics of wireless transmissions under disk coverage model and build two alternative dynamic programming based solutions with different run time and space complexities to the problem. Disk coverage model is a more general model because it allows nodes to use arbitrary power levels for transmissions. As a result, the presented algorithms provide a more practical solution that can be used as a building block for energy efficient communication protocols designed for wireless ad hoc and sensor networks.

Modeling of Arbitrary Power Level PV Array Based on Circuit Equivalent Mechanism

According to the equivalent circuit of single solar cell and the V-I equation of PV cell based on physical mechanism, a simulation model of single solar cell is established. According to this model and structure feature of PV array, the Thevenin circuit equivalent transform theory is used. The control relationship between single solar cell and PV array is given. Then a simple modeling method for arbitrary power level PV array is proposed. To verify the model effectiveness, a Pspice simulation model is established. Output characteristics of the model and its feasibility in PV power generation system are simulated. Simulation results show that the output characteristics of simulation model are in good consistency with actual PV array, and the model can be effectively applied in simulation of PV power generation system. The modeling method is simple and can be used for simulation on some control algorithms of PV power generation system

Heterodyne detection with a weak local oscillator

Heterodyne detection in the limit of weak (a few photons) local oscillator and signal power levels has been largely neglected in the past, as authors almost always assumed that the noise was dominated by the shot noise from a strong local oscillator. We present the theory for heterodyne detection of diffuse and specular targets at arbitrary power levels, including the case where the local oscillator power is only a few photons per coherent integration period. The theory was tested with experimental results, and was found to show good agreement. We show how to interpret the power spectral density of the heterodyne signal and how to determine the optimal number of signal and local oscillator photons per coherent integration.

Exact Average Symbol Error Probability of Optimum Combining With Arbitrary Interference Power

A new expression is derived for the exact average symbol error probability for optimum combining with M-ary phase-shift keying. The expression adds to the significant body of work in this field by handling interferers with arbitrary power levels. The expression involves a single integral with finite limits and finite integrand. A closed-form expression is also derived for the average symbol error probability for binary phase-shift keying.

Dynamic optical transfer function of an acoustooptic modulator with a damped sound wave

Based on a spatially dependent dynamic optical transfer function of an acoustooptic modulator, a dynamic model of light modulation by a sound signal under conditions of acoustic damping is developed. A system of equations describing the dynamics of the acoustooptic interaction is given. Solutions of this equation for arbitrary power level and spatial-time structure of a sound signal are found. It is shown that acoustooptic damping has the strongest effect in a nonlinear modulation regime. Here, the dissipation of an acoustic signal suppresses the higher harmonic of the dynamic optical transfer function. An analytical model of the dynamic optical transfer function for a low level of acoustooptic coupling is given. It is shown that when the pump beam aperture is much greater than the spatial size of an acoustic signal, the time response of the acoustooptic modulator response is identical within a phase factor to the amplitude profile of a pump beam apodized by the exponential dependence of the amplitude of a damped sound wave. Otherwise, the sound damping produces almost no distortions of a plane top of the acoustooptic modulator response to a pulsed signal and shows itself only under phase mismatch conditions. Here, the asymmetry of overshoots at the edges of the acoustooptic modulator response is observed. Calculated plots are presented, which illustrate the aforementioned specific features of the transient process under conditions of acoustic damping in the acoustooptic interaction in paratellurite.

Average inversion level, modeling, and physics of erbium-doped fiber amplifiers

We present a detailed study of a set of models for characterizing the gain, the input and output powers of single erbium-doped fiber amplifiers (EDFAs) and networks of EDFAs. The time dependent gain is described by a single ordinary differential equation for the average inversion level of an EDFA with arbitrary number of signal channels with arbitrary power levels and propagation directions. In steady state, this ordinary differential equation becomes a transcendental equation from which many important parameters are derived. Through perturbation analysis of the time dependent model, the output perturbation can be expressed explicitly in terms of the input perturbations, which is useful for tone calculations. Therefore, this set of models can be applied to the steady state, and to large- and small-signal transient states in wavelength-division multiplexed (WDM) optical communication networks with EDFAs. The models are applied to analyze fast power transients in networks of EDFAs.

Model for gain dynamics in erbium-doped fibre amplifiers

A simple model is presented for characterising the dynamic gain of an erbium-doped fibre amplifier (EDFA). The time dependent gain is described by a single ordinary differential equation for an EDFA with arbitrary number of signal channels with arbitrary power levels and propagation directions. The simulation results agree with experimental data.

A new implementation of the device line measurement technique for accurate microwave oscillator design

In this paper a device line characterization system using a six-port measurement technique is reported for the first time. Device line measurements on a Gunn diode mounted in a coaxial fixture and on a loaded MESFET were performed at C and at L bands, respectively, in order to experimentally optimize the output microwave power and the power efficiency in their respective oscillating modes. Effects of bias conditions on the added power were investigated for both devices. In addition, the effect of the phase of the offset short circuit which terminates the gate-source port of the MESFET was also investigated. Based on these device line measurements, a MESFET oscillator was designed, built, and tested. It was found that the performance of the oscillator was in good agreement with the predicted results obtained from the device line characterization. In addition to its relatively low cost and its ability to perform simultaneous impedance and power flow measurements at an arbitrary power level, the present measurement system has the further advantage of being able to measure the large-signal reflection coefficients of negative resistance devices at the actual power level during oscillation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Plane-wave theory of parametric oscillator and coupled oscillator-upconverter

Previous steady-state plane-wave theory for the singly resonant parametric oscillator has been extended to the case of arbitrary mirror reflectivities using the exact solutions given by Armstrong et al. [3] for the parametric interaction of three traveling waves. Numerical results are obtained for the efficiency, pump power transmission, optimum output coupling, threshold for the second mode, etc., for parametric oscillators with arbitrary mirror reflectivities and operating under arbitrary power levels. The analysis is also applied to the intracavity-coupled parametric oscillator-upconverter.