Pulse Compression Performance Research Articles

X‐Parameter Measurement of Pulse‐Compression Nonlinear Transmission Lines

X‐parameters provide a powerful and eminently practical solution for interoperable measurement, modeling, and simulation of nonlinear microwave and RF components. Using X‐parameters to do large‐signal measurements has been brought into the spotlight. This paper introduces a new X‐parameter application: measuring large‐signal behaviour of pulse‐compression nonlinear transmission lines (NLTLs). A specially configured Nonlinear Vector Network Analyzer (NVNA) was used to measure the X‐parameters in the frequency‐domain, and then the measured data was transformed into a nonlinear time‐domain waveform. The results show both rise‐time and fall‐time reduction (double‐edge compression) as expected and indicate that this newly developed X‐parameter method implemented with an NVNA could correctly predict NLTLs′ pulse‐compression performance.

Improving Performance of Pulse Compression in a Doppler Ultrasound System Using Amplitude Modulated Chirps and Wiener Filtering

The use of coded excitation and pulse compression in transcranial Doppler (TCD) ultrasound systems is in the very early stages; the optimal processing scheme has yet to be determined. This study uses linear frequency-modulated (FM) chirps with 0.8-MHz bandwidth and compares the use of pulses with and without amplitude modulation and also matched filtering vs. Wiener filtering. The results demonstrate that using amplitude-modulated pulses vastly improves the axial resolution and provides a more predictable mainlobe-to-sidelobe distance in the radiofrequency (RF) signal. It is also shown that a Wiener filter can provide better performance than a matched filter, in terms of axial resolution and sidelobe level in the RF signal and signal-to-noise ratio in conventional sonograms. Although this study uses a TCD system, the techniques described are equally as applicable in other Doppler ultrasound devices. (E-mail: j.cowe@le.ac.uk)

Amplification, Compression and Shaping of Picosecond Super-Gaussian Optical Pulse Using MZI-SOAS Configuration

We present a numerical investigation to the output waveform of a picosecond super-Gaussian optical pulse from a Mach-Zehnder interferometer (MZI) configuration with semiconductor optical amplifiers (SOAs) on their arms by solving the system equations of the SOAs. The simulation results show that the performance of pulse amplification, compression and shaping can be achieved by using the MZI-SOAs configuration by adjusting the system parameters. Moreover, the dynamic dimension of input pulse power and width is improved.

Multi-stage pulse compression by use of cascaded quadratic nonlinearity

In this paper, the multi-stage compression of picosecond pulses by cascaded quadratic nonlinearity is studied theoretically, and the dependence of pulse compression on phase-mismatch, laser intensity, and crystal characteristics has been discussed in detail. We demonstrate that the multi-stage pulse compression is much more efficient than the single-stage with a same total crystal length. Pulses as short as ∼150 fs can be generated by compressing 30-ps initial pulses in a two-stage configuration under the realistic crystal and laser conditions, and shorter pulses of ∼30 fs may be obtained by three-stage compression. Pulse compression performances with BiBO and BBO crystals are compared and discussed finally.

Generation of pedestal-free ultrashort soliton pulses and optimum dispersion profile in real dispersion-decreasing fibre

In this paper, we study the generation of high-quality ultrashort soliton pulses in dispersion-decreasing fibres with the inclusion of fibre loss in the integrable case. Five closely shaped profiles, namely linear, hyperbolic, exponential, logarithmic, and Gaussian, have been considered. The effects of these dispersion profiles and fibre loss on the performance of pulse compression in dispersion-decreasing fibres have been analysed. The pulse is compressed adiabatically by keeping the soliton property of conservation of pulse area provided the fibre loss is less than the critical value. Both analytical and graphical results show that, out of the five different profiles considered, the Gaussian profile is the optimum profile for achieving maximum pulse compression.

Applying a Mode Selector to Improve the Pulse-Compression Performance of Asymmetric-Coupled-Waveguide-Based Dispersion Compensators

An InGaAsP slab-type asymmetric-coupled-waveguide-based dispersion compensator with a mode selector has been designed and fabricated. The mode selector is necessary to select either a symmetric [with a positive group-velocity dispersion (GVD)] or antisymmetric (with a negative GVD) supermode. These supermodes exist simultaneously in the dispersion-compensation region of the device. Pulse-compression experiments were used to test the dispersion compensator, evaluating the function of the mode selector. A theoretical study of the experimental results shows that the mode selector obtains a very strong selectivity (nearly 100%) for the antisymmetric supermode.

Even-odd transformation with application to multiuser CW radars

An even odd transformation is a linear phase transformation which translates a set of sequences into another set, all of whose absolute even (also called periodic) and odd correlation functions become the respective absolute odd and even correlation functions of the original set. This transformation enables the choice of periodic or odd-periodic sequence sets to simplify the implementation of a multiuser CW radar without sacrificing its pulse compression performance. As an application example, the odd-perfect counterparts of the famous Zadoff-Chu sequence sets are derived. Of particular interest is a pair of odd perfect sequences with optimal odd cross-correlation levels, whose phase alphabet size is only half of that of the well-known P3 code for even lengths.

Performance analysis of pulse compression using phase-coded signals for sparse-array synthetic impulse and aperture radar

Sparse-array Synthetic Impulse and Aperture Radar (SIAR) can isotropically radiate by employing multiple frequencies (synthetic pulse) and multiple antennas (synthetic antenna). According to Ambiguity Function(AF), its range resolution depends only on bandwidth of transmitted signals, however, the distance grating lobes emerge when increasing the time-bandwidth product of transmitted signals. The performance of pulse compression is analyzed with the transmitted signals modulated by phase-coded sequences. It is seen that greater ratio of pulse compression and suppression of range sidelobe in SIAR can be obtained, and its effective range and range resolution is increased as well.

Optimum dispersion profile for compression of fundamental solitons in dispersion decreasing fibers

In this paper, we have investigated the effect of dispersion profile on the performance of pulse compression in a dispersion decreasing fiber (DDF). Four closely shaped profiles, namely linear, Gaussian, exponential, and hyperbolic, have been considered. We have shown that appropriate shaping of the dispersion profile, particularly when higher order effects are accounted for, is quite effective for adiabatic compression of fundamental solitons, producing high-quality compressed pulses in the sense that the soliton pulse is compressed as a single unit and pedestals do not form. It is concluded that the linear and Gaussian dispersion profiles are nearly optimum in regards to the quality of the compressed pulse and the amount of compression achievable, in particular in the case of subpicosecond soliton pulse compression.

Estimation of the effect of oscillator instabilities on signal processing by means of Monte Carlo computer simulation

In this paper, Monte Carlo computer simulation is used to estimate the effect of oscillator instabilities on signal processing. The key link of this method is generating high quality random number sequence simulating the phase noise of the oscillator. The case of the pulse compression performance is discussed as an example in order to clarify: (1) the effect of oscillator instabilities on pulce compression performance, and (2) the requirement of oscillator frequency stability when the tolerance of the system performance is known. Finally, some computer simulation examples are given which will provide as reference data for engineering designers.

Surface-wave dispersion with a time bandwidth of 1000

Experimental results are presented that were obtained in the initial evaluation of a multifunction surface wave delay line designed for a time bandwidth product of 1000. Two types of lines that operate on ST-cut quartz substrates are described. One type utilizes three identical coded 25-Ms transducers symmetrically arranged so that both positive and negative chirp slopes are obtained in addition to zero slope or flat delay. The other type of line provides positive and negative slopes with separate transducer pairs approximately coded. Lines of both types are designed to operate at a center frequency of 60 MHz with a 20-MHz bandwidth and a 50-/spl mu/s time delay. Tests demonstrated time-bandwidth product capabilities of 785 and 900, with time dispersions of 45 and 50 /spl mu/s, respectively, and bandwidths of 18 MHz. Time multiplexing and spectrum inversion were used to measure pulse compression performance. Measured sidelobe levels of -9 to -18 dB indicated nonlinearity and incidential weighting present in these lines. In addition, surface-wave delay-line performance was measured with a 56-/spl mu/ delay, a nominal 10-MHz bandwidth, and -15-dB time sidelobes. The lines were also temperature tested for center frequency time-delay stability. Results indicated time-delay variations of less than 2 ppm//spl deg/C, which is an order of magnitude improvement over those in YX-cut quartz substrates lines.