Doppler broadening

About: Doppler broadening is a research topic. Over the lifetime, 5509 publications have been published within this topic receiving 92552 citations.

Digital nonlinearity compensation in high-capacity optical communication systems considering signal spectral broadening effect

Abstract: Nyquist-spaced transmission and digital signal processing have proved effective in maximising the spectral efficiency and reach of optical communication systems. In these systems, Kerr nonlinearity determines the performance limits, and leads to spectral broadening of the signals propagating in the fibre. Although digital nonlinearity compensation was validated to be promising for mitigating Kerr nonlinearities, the impact of spectral broadening on nonlinearity compensation has never been quantified. In this paper, the performance of multi-channel digital back-propagation (MC-DBP) for compensating fibre nonlinearities in Nyquist-spaced optical communication systems is investigated, when the effect of signal spectral broadening is considered. It is found that accounting for the spectral broadening effect is crucial for achieving the best performance of DBP in both single-channel and multi-channel communication systems, independent of modulation formats used. For multi-channel systems, the degradation of DBP performance due to neglecting the spectral broadening effect in the compensation is more significant for outer channels. Our work also quantified the minimum bandwidths of optical receivers and signal processing devices to ensure the optimal compensation of deterministic nonlinear distortions.

Measurements of density fluctuations by modulation spectroscopy

Abstract: Theoretical and experimental results describing the application of wavelength modulation spectroscopy to density fluctuations are given. The effects of concurrent amplitude modulation, which often occurs when such experiments are performed with diode lasers are accounted for. It is shown that the characteristics of the signal magnitude at line center as a function of density include the expected increase with density, n, in the Doppler regime. In the effective collision broadened regime the signal magnitude at line center falls approximately as n−N, where N is the order of the harmonic at which detection is performed. This result incorporates the well‐known result for direct absorption (N=0) in which the signal magnitude at line center stays constant while the linewidth increases in the collision broadened regime. It is shown that the sensitivity to density fluctuations measured by wavelength modulation spectroscopy around any ambient value depends strongly on the order of the detection harmonic employed,...

Dual-Polarization Spectral Analysis for Retrieval of Effective Raindrop Shapes

Abstract: Dual-polarization radar observations of precipitation depend on size–shape relations of raindrops. There are several studies presented in literature dedicated to the investigation of this relation. In this work a new approach of investigating raindrop size–shape relation on short time and spatial scales from radar observations is presented. The presented method is based on the use of dual-polarization Doppler power spectral analysis. By measuring complete Doppler spectra at a sufficiently high elevation angle at two polarization settings, namely, horizontal and vertical, it is possible to retrieve drop size distribution (DSD) parameters, ambient air velocity, spectral broadening, and the slope of the assumed linear dependence of raindrop size–shape relation. This paper is mainly focused on the development of the retrieval algorithm and analysis of its performance. As a part of the proposed method an efficient algorithm for DSD parameter retrieval was developed. It is shown that the DSD parameter ...

Diode Laser-Induced Fluorescence of Xenon Ion Velocity Distributions

Abstract: Comparison of a deconvolved ion energy distribution taken in a 500 V ion beam with retarding potential analyzer data showed bulk ion energy agreement within 1%, but only qualified similarity between the distributions Grid misalignment during the LIF experiment may be responsible for the usually broad Doppler broadening As a result, we are presently unable to reliably validate our deconvolution method at 8347 nm