Pulse Propagation Characteristics Research Articles

Ultrafast pulse propagation in direct gap semiconductor quantum well waveguide structures

Using the Luttinger formulations, we have analysed the propagation characteristics of an ultrashort (femtosecond) coherent radiation pulse in the transverse plane of a direct gap semiconductor quantum well waveguide structure (QWWS). The semiconductor QWWS is considered to possess degenerate valence subbands near the centre of the Brillouin zone. The photoinduced resonant transitions below the band edge to both 1s and 2s excitonic states from the light hole (lh) and heavy hole (hh) subbands have been considered. The cross-over between the lh and hh bands occurs in the case of the transverse plane where the light holes are found to play a more dominant role than the heavy holes. Efforts have been directed towards analysing the transient pulse propagation characteristics such as pulse break-up and optical nutation. We have also studied the transverse electric mode propagation in the QWWS assuming the same to behave as a three-layer asymmetric optical planar waveguide. Numerical analysis made for GaAs/AlGaAs QWWS illuminated by a 150 fs Ti : sapphire laser shows good qualitative agreement of the present results with those available in literature.

Chirp-induced splitting of pulses in optical fibers

An investigation is made of the effects of initial or dynamically induced chirping on the linear propagation characteristics of pulses in optical fibers. It is shown that under certain conditions the chirping will give rise to a splitting of the initial pulse into two separating subpulses. The necessary conditions for pulse splitting to occur are established analytically and corroborated by numerical computations.

相互相関周波数分解光ゲート法を用いた光ファイバにおける超短パルス光の伝搬特性の解析

Characteristics of ultrashort pulse propagation in optical fibers at the wavelength region of 1.55 μm are experimentally analyzed using the cross-correlation frequency resolved optical gating (X-FROG) technique. In the anomalous dispersive fibers, widely wavelength tunable femtosecond soliton pulse is generated. The spectrogram of almost transform limited soliton pulse around 2 μm is observed. In the dispersion shifted fibers, the wavelength tunable soliton pulse and anti-stokes pulse are generated. As the results of X-FROG measurement, it is clarified that the anti-stokes pulse is overlapped with the soliton pulse and trapped by the soliton pulse. In the highly nonlinear optical fibers, 1.2-2.1 μm ultra-widely broadened super continuum and 1.46-1.68 μm linearly chirped one are generated. The spectrograms of generated super continuum are observed. The phenomenon of pulse trapping is also observed in generated super continuum.

FDTD analysis of propagation characteristics of terahertz electromagnetic pulses

A three dimensional finite difference time domain (FDTD) technique is applied to analyze the propagation characteristics of terahertz (THz) antenna whose dimension is smaller than the wavelength. A diffraction theory is also utilized with the FDTD technique for observing the far-field dispersion and attenuation of radiation from the THz antenna with a hyper-hemispherical silicon lens which is much larger than the wavelength. The signal degradation effects due to misalignment between the antenna and silicon lens are also characterized.

Development of an on-line partial discharge monitoring system for gas insulated substations

This paper describes the results of tests and discussions carried out to develop a system for partial discharge monitoring in GIS. They include the propagation characteristics of partial discharge pulses in each GIS component, as well as the test results obtained using an actual 300-kV GIS. We also report the results of verification test on the GIS partial discharge monitoring and location system developed by the authors. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 40–50, 1999

Investigation of PD pulse propagation characteristics in GIS

Concentrating on the TEM mode, the damping characteristics of partial discharge (PD) pulses propagating through each gas-insulated switchgear (GIS) component were investigated. As a result, it was discovered that frequency components above 500 MHz were remarkably damped by spacers, T-shape branches, and L-bends. Quantitative studies were undertaken on the frequency dependency of these damping characteristics. Then the equivalent circuits for analyzing the propagation characteristic of PD pulses were proposed. Furthermore, the validity of concentrating on the TEM mode was denoted by tests at a substation in service.

単一応力波によるエネルギ反射率の測定

In order to study the propagation characteristics of stress pulses in various structures, the reflection wave reflected from a fillet part is measured. The part is made of same material as the structure. A semiconductor strain gauge is used for the detection of stress waves. The reflection coefficient is obtained as the summation of the transfer function. The reflection coefficient is calculated by changing the duration of stress pulse and the curvature of fillet. As the result, it becomes clear that the reflection coefficient can be obtained from strain energy without using Discrete Fourier Transform if a single pulse is used.

Influence of resonant absorption on the propagation of femtosecond pulses in an Er-doped optical fibre

By making numerical simulations the influence of resonant absorption in Er-doped fibres on the propagation characteristics of femtosecond pulses has been examined. It is shown that when the fibre background dispersion is relatively small compared to the dispersion caused by absorption, the pulses propagating in an unpumped Er-doped fibre can be either compressed or broadened, depending on whether the spectrum of the launched pulse is on the longer or shorter wavelength side of the absorption center. The phase distortion due to absorption has a more severe impact on the temporal profile of a propagating pulse than the corresponding amplitude attenuation. A switching of the sign of the actual fibre dispersion on one side of the absorption center occurs and this can lead to a change of pulse propagation characteristics from a soliton regime to a non-solitonic regime.

Pulse propagation characteristics at 2.4 GHz inside buildings

The growing use of unlicensed wireless systems has spurred interest in the 2.4-GHz ISM band. In order to facilitate the design of such systems, measurements of the pulse response characteristics have been made inside commercial buildings. From the measured pulse response, the statistical properties of the amplitude variation for individual pulses was determined, in addition to the path loss, mean excess delay, root mean square (RMS) delay spread, and the coherence bandwidth of the indoor channel.

Analysis of spatial‐time characteristics of broadband pulse propagation through ocean sound channels by using shallow water acoustical mode propagation model

Broadband pulse propagation through an oceanic sound channel is investigated to characterize some important oceanic properties, namely, the vertical sound profile, bottom structure, and also source localization. Examples of waveguides with surface and bottom ducting are considered. The new fast normal mode method (SWAMP) based on a new expansion method allows one to study the high frequency range in which large numbers of modes can be excited. In this situation the complicated structure of the wavefront that is the result of the interference of the low‐order trapped refractive modes and the high‐order reflected modes is observed in the waveguides. To understand the structure of this informatively rich wavefront, two techniques are presented: The static spatial‐time maps of the sound field intensity distribution in a waveguide and video movies permitting one to observe the time evolution of a pulse through the fixed spatial region. The later technique gives much additional information on the process and can offer additional insight into the nature of pulse evolution along a waveguide. [Work sponsored by the Office of Naval Research.]

Experimental and numerical investigation of short pulse propagation and amplification around 1.3 μm in a Nd 3+-doped fluoride fiber

We have investigated experimentally and theoretically the propagation and amplification characteristics of short optical pulses at λ ≈ 1.3 μm in a neodymium-doped fluorozirconate fiber. We have found that psec pulses (4 ps) with sub-nJ energies can be propagated and amplified without appreciable temporal and spectral reshaping. The propagation and amplification of sub-psec pulses (300 fs) of comparable energy, however, is significantly affected by the dispersive and nonlinear properties of the fiber. The interplay between dispersion and nonlinear effects leads to a power dependent pulse broadening which is more pronounced when the pulses are amplified. The experimental results are in good agreement with numerical simulations based on an extended version of the nonlinear Schrödinger equation. The comparison between experimental and numerical results allows to identify the pulse shaping mechanisms involved which is important in order to assess the potential of Nd 3+-doped fluoride fibers as mode-locked fiber lasers and amplifiers.

Analysis of Optical Pulse Distortion Through Clouds for Satellite to Earth Adaptive Optical Communication

Abstract Clouds, if part of an optical communication channel, cause temporal widening and attenuation of optical pulse power. Space optical communication from satellite to earth (ground or airplane) occasionally involves clouds as part of the optical channel. Here, based upon Monte Carlo simulations, mathematical models are developed for the temporal characteristics of optical pulse propagation through clouds. These include temporal impulse response, transfer function, bandwidth, received energy and bode analysis. The method presented here can be used as an inclusive framework for developing other mathematical models of other characteristics of radiation propagating through clouds, as required. Several conclusions of this work are obtained. One is that simple prediction models can be applied to adaptive methods of optical communication. Another is that using shorter wavelengths such as 0·532 μm yields least temporal widening and maximum received power, and is thus preferable for optical communication. In ...

Coherent pulse propagation in a mode-locked argon laser

An investigation has been carried out on coherent pulse propagation effects in a mode-locked argon-ion laser. It is shown that this laser, when operated in a high-Q-cavity configuration, produces pulses exhibiting characteristics of coherent pulse propagation, including spectral power broadening and coherent ringing on the trailing edge of the pulses. A semiclassical model of the laser predicts results that are in good agreement with our experiment. The exploitation of these coherent effects in improving the performance of the mode-locked argon-ion laser, and of mode-locked lasers in general, is also discussed.

Characteristics of optical pulse propagation in monomode optical fibres at zero-dispersion wavelength

The linear propagation of optical pulses in monomode optical fibres at zero-dispersion wavelength is studied theoretically. From the envelope transmission equation, the root mean square (RMS) pulse width is obtained, and the minimum evolution condition, minimum pulse width and its corresponding distance are given. The case of chirped pulse is discussed in particular detail. It is shown that an arbitrary initial pulse transmitting at a zero-dispersion point has a restoration characteristic, which is entirely a result of the interplay between second-order dispersion and source chirp.

Modal dispersion control and distortion suppression of picosecond pulses in suspended coplanar waveguides

The propagation and dispersion characteristics of picosecond electrical pulses in a suspended coplanar waveguide (SCPW) are investigated, and it is shown that the SCPW is a very promising transmission structure for ultrashort pulses. Numerical results for the modal dispersion of the SCPW are presented and compared to those of the conventional CPW, and a field-coupling theory is used to explain the evolution in the dispersion behavior. An evaluation based on the numerical analysis shows that a SCPW with properly controlled dispersion can exhibit a five times improvement in pulse transmission capability compared to the conventional CPW. Both computer simulations and experimental measurements show a substantial suppression in pulse distortion as well, compared to conventional CPWs. >

Electrical Modelling of Multilevel On-Chip Interconnections for High-Speed Integrated Circuits

A method for the electrical parameters analysis and modelling of lossy-coupled multilayer on-chip interconnection lines at high bit rates is presented in detail. It can be used by the VLSI designer to analyze on-chip interconnections with linear, as well as nonlinear/time varying terminators and to simulate the pulse propagation characteristics in high-speed integrated circuits. First the capacitance, inductance, conductance and resistance matrices per unit length for the given multiconductor geometry is computed. A multiple coupled line model consisting of uncoupled lossy transmission lines and linear dependent current and voltage sources if finally calculated according to the capacitance, inductance, conductance and resistance matrix values computed.

Similar pressure pulse propagation and reflection characteristics in aortas of mammals

Similar pressure and flow waveforms recorded in mammalian aortas suggest that pulse transmission characteristics may also be similar. We examined the validity of this hypothesis, utilizing allometric equations of pertinent hemodynamic parameters and a model of the arterial system. Results show that both the reflection coefficient and the propagation constant times the aortic length are essentially invariant across the mammalian species investigated. Resolved forward and reflected propagating waves are also similar. These findings suggest that the arterial system in these mammals indeed functions in a similar manner.

Electromagnetic pulse transmission on superconducting interconnects

The pulse propagation characteristics of geometrically similar microstrips comprising high-Tc superconductor and aluminium are compared. Bearing in mind applications to high-speed VLSI circuits, the substrate material used is silicon. Loss characteristics for the two types of interconnect are studied and transmission characteristics for gaussian and square pulses are evaluated using fast Fourier transforms. It was found that superconducting interconnects offer a significant advantage over aluminium interconnects in respect or increased bandwidth (in excess of 1 THz), distortion-free transmission and low attenuation.

Propagation characteristics of picosecond electrical pulses on a periodically loaded coplanar waveguide

A theoretical model which was developed to investigate the propagation characteristics of picosecond electrical pulses on a coplanar waveguide capacitively coupled to periodically spaced sampling channels is presented. Various factors which affect the signal waveform are analyzed in both the frequency and the time domains. The results show that in addition to modal dispersion, conductor loss, and radiation loss of the electrical signals, multiple reflections among the sampling gaps constitute another feature of the signal transfer along the waveguide. The authors have measured the picosecond pulse dispersion using the optoelectronic correlation technique. The experimental data are compared with the theoretical results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Propagation characteristics of femtosecond pulses in erbium-doped monomode optical fibers

The spectral and temporal characteristics of femtosecond optical pulses (durations of approximately 120 fs, wavelength of 1.5 mu m) propagating in erbium-doped monomode fibers have been experimentally studied in detail. Distinct spectral broadening and shifting processes have been observed for three types of fibers (two different dopant concentrations and one erbium-free sample for comparison). Whereas only a small amount of spectral broadening occurs in the Er-free fiber, there is a major spectral extension (1.3-1.7 mu m) for the low-doped erbium fiber, in which a self-phase-modulation mediated four-wave-mixing process has been observed. Autocorrelation data for the exiting pulses indicate the existence of strong pulse shaping and breakup effects in the Er-doped fibers.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>