Pulse Generation Scheme Research Articles

Interference fading suppression with a multi-subcarrier pulse in a distributed acoustic sensor

A low-complexity multi-subcarrier pulse generation scheme is proposed to suppress the interference fading in a phase-sensitive optical time-domain reflectometer (Φ-OTDR) based distributed acoustic sensor (DAS) with heterodyne coherent detection. The multi-subcarrier pulse is generated in the digital domain based on the proper clipping operation of a sine signal. The localization and recovery of the disturbance signal are realized by the spectrum extraction and rotated vector sum (SERVS) method. The experimental results show that the occurrences of interference fading can be significantly reduced. The intensity fluctuation is reduced from ∼75 dB to ∼25 dB. Multiple disturbance signals are successfully demodulated to verify the effectiveness of the proposed method.

A novel scheme for ultrashort terahertz pulse generation over a gapless wide spectral range: Raman-resonance-enhanced four-wave mixing

Ultrashort energetic terahertz (THz) pulses have created an exciting new area of research on light interactions with matter. For material studies in small laboratories, widely tunable femtosecond THz pulses with peak field strength close to MV cm−1 are desired. Currently, they can be largely acquired by optical rectification and difference frequency generation in crystals without inversion symmetry. We describe in this paper a novel scheme of THz pulse generation with no frequency tuning gap based on Raman-resonance-enhanced four-wave mixing in centrosymmetric media, particularly diamond. We show that we could generate highly stable, few-cycle pulses with near-Gaussian spatial and temporal profiles and carrier frequency tunable from 5 to >20 THz. They had a stable and controllable carrier-envelop phase and carried ~15 nJ energy per pulse at 10 THz (with a peak field strength of ~1 MV cm−1 at focus) from a 0.5-mm-thick diamond. The measured THz pulse characteristics agreed well with theoretical predictions. Other merits of the scheme are discussed, including the possibility of improving the THz output energy to a much higher level.

Experimental Generation of Reconfigurable Ultra-Wideband Signal Based on the Pulse Difference by Using Optical Polarization Synthesis

A reconfigurable optical ultra-wideband (UWB) pulse generation scheme based on the pulse difference by using polarization synthesis is proposed and demonstrated experimentally. The Gaussian pulses with an appropriate time delay are modulated via the two sub-MZMs of the DPol-MZM, and the optically carried signals are combined via orthogonal polarization multiplexing, avoiding the optical interference. By setting the DC bias voltages of the sub-MZMs and the time delay, a pair of polarity-reversed Gaussian monocycle, doublet, triplet and quadruplet signals are generated with the central frequency of 3.37, 4.79, 4.5, 5.05 GHz and the fractional bandwidths of 166%, 129%, 124%, 89% accordingly. The signals of pulse shape modulation, binary phase shift keying modulation and on-off keying modulation are generated with the experimental system.

The role of asymmetry in few-cycle, mid-IR pulses during THz pulse generation

The efficiency of terahertz (THz) pulse generation improves at longer driving wavelengths. For this reason, the use of mid-infrared (MIR) sources is more advantageous compared to visible or near-infrared systems. In this work, we investigate how single-color and two-color schemes of MIR pulses with few-cycle pulse durations compare in producing THz pulses. The results reveal that as the duration of the driving pulses decreases, the second harmonic generation crystal can be omitted from the system. Our numerical study pinpointed three regions where the optimal pulse parameters are fundamentally different for the most efficient THz pulse generation. The first is the two-color approach, where the two-color scheme is dominant at 3.2 optical cycles and over. The second is the single-color approach, where the single-color scheme becomes dominant at 1.7 optical cycles and below. Therefore, it simplifies the traditional two-color scheme for THz pulse generation. There is also a third transitional region where the two-color scheme still prevails, but the sign of the relative phase between the input pulses becomes important. Considering the effect of the relative phase and the carrier to envelope phase (CEP) effect on the THz pulse generation, the results have shown that as the pulse duration become shorter, the role of the CEP becomes important for efficient THz generation. By measuring the efficiency of the THz generation in this optical arrangement, quantifying the CEP becomes possible, which could become an important experimental tool for few-cycle, MIR laser technology.

Fully FPGA‐based implementation of a modified control strategy for power electronic transformer in railway traction applications

AbstractDue to its several advantages (especially low volume and weight), power electronic transformer has gained notable attraction in railway applications. The main focus of this work is devoted to development a fully filed programmable gate array (FPGA)‐based control platform for power electronic transformer in the aforementioned application. Due to the parallel processing of FPGAs that results in a faster control algorithm execution, reliable operation (which is of major importance in traction applications) is guaranteed. For this purpose, an input series output parallel power electronic transformer structure is built, and various considerations for reliable and stable operation of the power electronic transformer in traction applications, such as safe start‐up and bidirectional power flow, along with the required control and pulse generation schemes, have been designed and implemented in a Xilinx FPGA control platform. Moreover, a modified control algorithm is proposed for controlling the power electronic transformer in a simple and more reliable manner. This control scheme is developed based on the output voltage of the DC–DC–LLC resonant converter, and can effectively control the sum of rectifier DC‐link voltages and track the input sine reference current, with a lower number of required sensors. Finally, the effectiveness of the proposal has been tested from various aspects by experimental tests.

Investigation of optical short pulse generation using intensity modulation for LiDAR and free-space communications

A simple optical pulse generation scheme for pulsed light detection and ranging (LiDAR) and free-space communications is proposed and experimentally and numerically demonstrated, in which continuous-wave light emitted by a distributed feedback-laser diode (DFB-LD) is modulated by a lithium-niobate Mach–Zehnder intensity modulator to generate optical short pulses, and an Er-doped fiber amplifier (EDFA) is used to boost transmitting light power. Possibilities of intensity modulators for high speed communications being used to generate optical short pulses for low speed pulsed LiDAR are investigated. The influences of bias voltage of intensity modulator and bit rate of modulation signal on the generated optical pulses are discussed. The pulse width obtained by using the return to zero signal with 33% duty cycle on bit rate of 2.5 and 5 Gbit/s is respectively 128.0 and 63.2 ps, and the corresponding nominal accuracy of pulsed LiDAR is respectively 19.2 and 9.5 mm, and low repetition frequency required by pulsed LiDAR is achieved by coding to high-speed modulation signal. The system performance for free-space communications and pulsed LiDAR is evaluated, respectively. We believe that the proposed scheme is suitable for the integrated system of pulsed LiDAR and free-space communications.

Performance analysis of clock pulse generators and design of low power area efficient shift register using multiplexer based clock pulse generator

Shift registers are the essential elements that are capable of storing and transmitting the data in sequential mode in digital circuits. It consists of D flip-flops, which are connected in a successive manner and share the common clock pulse applied to each Flip-flop. However, the clock distribution network consumes the major portion among the whole power consumption. In this paper a novel clock pulse generation scheme, called as Multiplexer based Clock Pulse Generator (MCPG) is proposed to minimize the power consumption and reduce the silicon area occupation of the shift register by reconstructing the clock distribution network using MCPG. It generates multiple non overlapped clock pulses with minimum power utilization, less area and also resolves the inequality between arrival of clock pulse and data to the consecutive Flip-flops at different time. The proposed clock distribution method reduce area and overall power consumption up to 22% and 31% respectively, compared with shift registers implemented using conventional clocking methods. The optimized MCPG with Conditional Pass Logic Dynamic D Flip-flop(CPLDDFF) is also implemented in 256-bit arrayed shift register via an 8- bit Serial In Serial Out(SISO) sub shift register, save power up to 12%. The proposed system is realized using SPICE with CMOS 0.13 μm technology.

Cross Connected Compact Switched-Capacitor Multilevel Inverter (C3-SCMLI) Topology With Reduced Switch Count

In this brief, a new cross-connected compact switched capacitor (C3SC) cell is introduced for multilevel inverter applications. The proposed CCS cell uses four switches and two diodes for interconnecting the input dc source and floating capacitors (FCs). A nine-level inverter is derived with the proposed C2SC cell requiring only ten switches and two FCs. The proposed C3SC cell-based MLI is self-balancing and has a voltage gain of two. All the switches of the proposed topology have a maximum blocking voltage within the input dc voltage ( v $_{in}$ ) value. The operating principle is detailed, and a simple logic gate based gate pulse generation scheme is presented. Detailed simulations and experimental results obtained from an 850 W prototype with several test cases are presented to validate the operation of the proposed topology. Finally, a detailed comparative assessment is performed with other recent SCMLIs to demonstrate the merits and superiority of the proposed topology.

Common-Ground-Type Five-Level Transformerless Inverter Topology With Full DC-Bus Utilizaton

Transformerless inverters (TIs) are widespread in photovoltaic (PV) applications due to their low cost and high efficiency. However, TIs suffer due to leakage current as a consequence of PV parasitic capacitance, and high-frequency common-mode voltage, which has resulted in the emergence of several topological and control scheme modifications. In this article, a switched-capacitor (SC) based inverter capable of synthesizing a five-level voltage is proposed. In the devised structure, the negative pole of the dc bus is directly connected to the grid neutral, thereby resulting in zero leakage current. In addition, industrial standard half-bridge modules can be employed directly for implementing the proposed inverter without modifications, making it more practically feasible. The proposed topology has the capability of self-voltage balancing of SC, reactive power processing, and full dc-bus utilization as opposed to half-bridge topologies. The principle of operation and a simple logic-gate-based pulse generation scheme is presented in detail. Simulation and experimental results confirming the practical viability of the proposed topology are presented. Finally, the superior features and the merits of the proposed topology are shown through a detailed comparison against state-of-the-art topologies.

Highly flexible Nyquist pulse generation based on multi-wavelength control

By controlling the wavelength and power of multiple light sources, we have realized a highly flexible Nyquist pulse generation scheme, in which the pulse repetition frequency, pulse multiplication factor, waveform envelope shape, and duty cycle are all tunable. By modulating the 3.2 GHz RF signal, we experimentally generated Nyquist pulses with repetition rates of 6.4 GHz and 9.6 GHz, a rectangular wave with a duty cycle of 0.26, and a sawtooth wave with a duty cycle of 0.52.

High-efficiency ultrafast optical-to-electrical converters based on InAs nanowire-plasmonic arrays.

There has been a growing interest in developing high-efficiency ultrafast optical-to-electrical converters for advanced imaging and sensing applications. Here, we propose a three-dimensional (3D) plasmonic platform based on InAs nanowire arrays with self-assembled gold gratings, which converts a telecom-wavelength (1550nm) optical beam to sub-picosecond current pulses with quantum efficiency up to 18.3%, while operating in photovoltaic mode, i.e., at zero bias. Using a comprehensive 3D photoresponse model, we reveal that the incident photons form tightly confined fields near the gratings at nanowire tips, and thus a majority of the photogenerated carriers are efficiently routed to the metal within a few tens of nanometers distance, resulting in ultrafast current pulses. In addition, we show that the amplitude of current pulses is robust to the nanowire surface quality and can be effectively tuned by varying the doping levels in nanowires. This work paves a way to realizing a low-power, highly compact, and low-cost device scheme for ultrafast pulse generation.

Strategies for the characterization of partially coherent ultrashort pulses with dispersion scan

Established characterization methods for repetitive pulse trains tend to fail in the presence of degraded coherence properties. Partial coherence is present in several pulse generation schemes but is not yet properly addressed in many pulse characterization techniques. Full coherence is a common assumption in most techniques, and failing to detect and account for it can lead to erroneous measurements that can be easily overlooked. While some techniques can indicate the presence of a coherence degradation, no method is known that can simultaneously retrieve the enveloping pulse width as well as the coherence time within a pulse train. Here we propose different pertinent strategies to deal with partially coherent ultrashort pulses measured using dispersion scan. The effect of partial coherence in dispersion scan is first investigated, and the three strategies, namely fidelity measurement, mixed-states reconstruction, and self-calibrating dispersion scan, are subsequently demonstrated and compared. The demonstrated retrieval algorithms can be readily adapted to existing dispersion scan hardware. Therefore, this study leads the way toward a more holistic approach to pulse characterization, dealing with fewer assumptions on the pulse trains and resulting in more accurate measurements.

A Self-Balancing Five-Level Boosting Inverter With Reduced Components

Two-Stage boosting multilevel inverters (MLIs), which are highly suitable for photovoltaic power plants, are known to suffer because of the high voltage stress on the switches of second stage. One of the ways to confront this issue is through eliminating the front-end booster. However, this leads to increased structural and control complexity of the resulting integrated boosting MLI. This letter presents a single-stage boosting MLI requiring lesser number of switches, diodes, and capacitors for renewable power generation applications. It requires nine switches and only one capacitor for five-level voltage generation. The topology has inherent self-balancing capability, thereby does not need additional balancing circuitry. The proposed topology has a uniform peak inverse voltage stress on the switches of value equal to the input dc voltage. A less complicated logic-form-equations-based gating pulse generation scheme is designed for enabling the proposed MLI to maintain its capacitor voltage. Further, a comparative study with state-of-the-art topologies is carried out to demonstrate the superior performance of the proposed topology. Finally, the feasibility of the proposed topology is validated through experimental tests and the corresponding results are elucidated.

Simulation of a concept for a compact ultrafast X-ray pulse source based on RF and THz technologies

We study through simulations a layout mixing RF and THz technologies for a compact ultrafast X-ray pulse source based on Inverse Compton Scattering (ICS), aiming to deliver few femtoseconds to sub-femtosecond pulses. The layout consists of an S-band gun as the electron source and a dielectric-loaded circular waveguide driven by a multicycle THz pulse to accelerate and longitudinally compress the bunch, before X-ray generation via ICS with a laser pulse. We detail several schemes allowing the optimization of the electron bunch properties. This optimization leads to a preliminary layout and various working points able to deliver 0.1–5 pC bunches, ranging from 15 to 18 MeV average kinetic energy, 0.4 to 5 fs rms length, 0.1% to 2.6% rms energy spread, and 5 to 13 μm rms transverse size. Simultaneously, the beamline is kept compact (≈1.3 m up to the ICS point), which has not yet been achieved using only conventional RF technologies. The properties of the X-ray pulse are investigated with simulations, showing the possibility to tune its energy between 2.9 and 11.5 keV. For 400 mJ of laser energy, 1.5 × 104–7.7 × 104 photons/pulse in 1.5% rms bandwidth or 6.2 × 103–3.5 × 104 photons/pulse with lower bandwidths (0.56%–1.5% rms along the energy range) can be expected. The properties of the DLW and of the THz pulse driving it, the state-of-the-art of the THz pulse generation schemes, and the influence of various jitters and the limits that they should not exceed for a reasonably stable operation are finally given.

Electron Beam Driven Generation of Frequency-Tunable Isolated Relativistic Subcycle Pulses.

We propose a novel scheme for frequency-tunable subcycle electromagnetic pulse generation. To this end a pump electron beam is injected into an electromagnetic seed pulse as the latter is reflected by a mirror. The electron beam is shown to be able to amplify the field of the seed pulse while upshifting its central frequency and reducing its number of cycles. We demonstrate the amplification by means of 1D and 2D particle-in-cell simulations. In order to explain and optimize the process, a model based on fluid theory is proposed. We estimate that using currently available electron beams and terahertz pulse sources, our scheme is able to produce millijoule-strong midinfrared subcycle pulses.

Exploration of VCSEL ultra-low biasing scheme for pulse generation

The generation of optical pulses at ultra low bias level, thus low energy cost, is explored in a commercial microcavity semiconductor laser in view of testing the principle of energy efficient information encoding in potential integrated schemes. Sequences of regular, highly nonlinear pulses with acceptable amplitude stability are obtained from a commercial device as potential sources of bits where the information is added by post-treatment (pulse removal). A discussion on the energy expenditure per bit is offered, together with the optimal frequency for pulse generation, which is found to lie slightly below the above-threshold value declared by the manufacturer.

Phase-Difference Compensation and Nonuniform Pulse Transmission for Accurate Real-Time Moving Object Tracking

This paper presents a radio-based real-time moving object tracking method based on Kalman filtering using a phase-difference compensation technique and a non-uniform pulse transmission scheme. Conventional Kalman-based tracking methods often require time, amplitude, phase information and their derivatives for each receiver antenna; however, their location estimation accuracy does not become good even with many transmitting pulses. The presented method employs relative phase-difference information and a non-uniform pulse generation scheme, which can greatly reduce the number of transmitting pulses while preserving the tracking accuracy. Its performance is evaluated in comparison with that of conventional methods.

A 1-Gb/s 6–10-GHz, Filterless, Pulsed UWB Transmitter With Symmetrical Waveform Analysis and Generation

This paper presents a fully integrated, regulation-aware pulsed ultra wideband (UWB) transmitter (TX) for low-cost, high-data-rate applications. Waveform nonidealities have been systematically analyzed for the first time, demonstrating that envelope asymmetry may cause spectrum regulation violations. In order to generate regulation-compliant UWB pulses without costly filters, the proposed high-data-rate TX employs an intrinsically symmetrical carrier-based pulse generation scheme. The prototype was fabricated using a 130-nm CMOS process, occupying 0.37 mm2. This biphase-modulated TX can support a measured maximum data rate of 1 Gb/s with a pulsewidth of 0.5 ns and a power efficiency of 14.4 pJ/b. Without filters, the output spectrums are not only compliant with the regulations but also consistent with the theoretical results.

Pulse generation scheme for flying electromagnetic doughnuts

Transverse electromagnetic plane waves are fundamental solutions of Maxwell's equations. It is less known that a radically different type of solutions has been described theoretically, but has never been realized experimentally, that exist only in the form of short burst of electromagnetic energy propagating in free-space at the speed of light. They are distinguished from transverse waves by a donut-like configuration of electric and magnetic fields with a strong field component along the propagation direction. Here, we report that such 'Flying Donuts' can be generated from conventional pulses using a singular metamaterial converter designed to manipulate both the spatial and spectral structure of the input pulse. The ability to generate Flying Donuts is of fundamental interest, as they shall interact with matter in unique ways, including non-trivial field transformations upon reflection from interfaces and the excitation of toroidal response and anapole modes in matter, thus offering new opportunities for telecommunications, sensing, and spectroscopy.

Pedestal-free 25-GHz subpicosecond optical pulse source for 16 × 25-Gb/s OTDM based on phase modulation and dual-stage nonlinear compression.

An optical pulse generation scheme based on an ultra-short chirped seed pulse generator followed by a dual-stage fiber-based nonlinear pulse processing stage is proposed and demonstrated experimentally. After phase modulation and linear-chirp compensation, optical seed pulse with a duty cycle of 9.8% and an obvious pedestal is obtained. By soliton compression and Mamyshev reshaping, a pedestal-free optical pulse with a duty cycle of 2% and an extinction ratio of 27dB is achieved. The optical pulse source is further applied in a 16×25-Gb/s on-off keying optical time-division multiplexing transmitter.