Showing papers on "Noise (radio) published in 1986"

Random walk of coherently amplified solitons in optical fiber transmission

Abstract: In an optical-communications system using soliton pulse transmission, periodic amplification is needed to maintain the energy of the solitons. We show that amplifier noise causes a soliton's group velocity to undergo a random-walk process. The resultant timing errors at the receiver limit the system's product of length times bit rate, in one example, to about 24 000 GHz-km.

Theory of spontaneous emission noise in open resonators and its application to lasers and optical amplifiers

Abstract: A theory of spontaneous emission noise is presented based on classical electromagnetic theory. Unlike conventional theories of laser noise, this presentation is valid for open resonators. A local Langevin force is added to the wave equation to account for spontaneous emission. A general expression is found relating the diffusion coefficient of this force to the imaginary part of the dielectric function. The fields of lasers and amplifiers are found by solving the wave equation by the Green's function method. The lasing mode is a resonant state associated with a pole in Green's function. In this way, noise in lasers and amplifiers is treated by a unified approach that is valid for either gain guiding or index guiding. The Langevin rate equations for the laser are derived. The theory is illustrated with applications to traveling wave and Fabry-Perot amplifiers and Fabry-Perot lasers. Several new results are found: optical amplifier noise increases inversely with quantum efficiency; spontaneous emission into the lasing mode is enhanced in lasers with low facet reflectivities; and the linewidth of a Fabry-Perot laser with a passive section decreases as the square of the fraction of the cavity optical length that is active.

High-frequency noise measurements on FET's with small dimensions

Abstract: A low-noise high-frequency transresistance amplifier has been used to accurately measure broad-band noise in MOSFET's with small widths and submicrometer channel lengths The technique allows noise characterization up to frequencies of 100 MHz of the small devices available as process test arrays from different fabrication lines The noise in the different portions of the I-V characteristics of submicrometer MOSFET's has been characterized and shown to be greater by factors of 2 to 4 than the noise expected from long-channel noise theory

Low-frequency 1/f noise in the interplanetary magnetic field

Abstract: Spacecraft observations of the interplanetary magnetic field at 1 AU are shown to have frequency spectra with a 1/f dependence in the range 2.7-80 microHz. It is suggested that the 1/f spectrum results from the superposition of uncorrelated samples of solar surface turbulence that have log-normal distributions of correlation lengths corresponding to a scale-invariant distribution of correlation times over an appropriate range of parameters.

Neural networks with nonlinear synapses and a static noise

Abstract: The theory of neural networks is extended to include a static noise as well as nonlinear updating of synapses by learning. The noise appears either in the form of spin-glass interactions, which are independent of the learning process, or as a random decaying of synapses. In an unsaturated network, the nonlinear learning algorithms may modify the energy surface and lead to interesting new computational capabilities. Close to saturation, they act as an additional source of a static noise. The effect of the noise on memory storage is calculated.

Noise analysis of injection-locked semiconductor injection lasers

Abstract: The noise of injection-locked semiconductor lasers is analyzed by rate equations including the spontaneous emission noise. The side mode suppression and the relative intensity noise (RIN) of the locked laser (slave laser) are given for different wavelengths detuning between the master and slave laser and for different linewidth enhancement factors α. For large α, locking is difficult to achieve, whereas extremely low noise may be obtained for injection-locked lasers with a low linewidth enhancement factor.

Radiowave Propagation in Satellite Communications

Abstract: 1 Introduction.- 1.1 Purpose and Objectives.- 1.2 Developments and Trends in Space Communications.- 1.3 Frequency Allocations and Regulatory Aspects.- 1.3.1 Frequency Allocations for Satellite Communications.- References.- 2 Fundamentals of Radiowave Propagation.- 2.1 Transmission Principles.- 2.2 Antenna Gain and Free Space Attenuation.- 2.3 Polarization.- 2.4 Radiowave Frequency and Space Communications.- 2.5 Radiowave Propagation Mechanisms.- 2.6 Major Radiowave Propagation Factors in Space Communications.- 2.6.1 Propagation Factors Above About 3 GHz.- 2.6.2 Propagation Factors Below About 3 GHz.- References.- 3 Attenuation by Atmospheric Gases.- 3.1 Oxygen and Water Vapor Attenuation 25.- 3.2 Total Slant Path Atmospheric Attenuation.- 3.2.1 Multiple Regression Analysis Procedure.- 3.3 Summary of Atmospheric Attenuation Procedure.- References.- 4 Hydrometeor Attenuation on Satellite Paths.- 4.1 Classical Development for Rain Attenuation.- 4.1.1 Attenuation and Rain Rate.- 4.1.2 Slant Path and Elevation Angle Dependence.- 4.2 Rain Attenuation Measurements.- 4.3 Cloud and Fog Attenuation.- 4.3.1 Cloud Attenuation Prediction Model.- 4.3.1 Fog Attenuation on Earth-Space Paths.- References.- 5 Rain Attenuation Prediction Methods.- 5.1 Rice Holmberg Rain Model.- 5.2 Dutton-Dougherty Attenution Prediction.- 5.3 Lin Rain Attenuation Model.- 5.4 Crane Global Rain Attenuation Model.- 5.5 CCIR Rain Attenuation Model.- 5.6 Summary.- References.- 6 Depolarization on Satellite Paths.- 6.1 Depolarization Caused By Rain.- 6.1.1 Depolarization Prediction.- 6.1.2 Depolarization Measurements.- 6.2 Ice Depolarization.- 6.2.1 Ice Depolarization Measurements.- 6.2.2 Ice Depolarization Prediction.- 6.2.3 Summary.- 6.3 Multipath Depolarization.- 6.3.1 Multipath Depolarization Characteristics.- References.- 7 Radio Noise in Satellite Communications.- 7.1 Noise From Atmospheric Gases.- 7.2 Noise From Clouds.- 7.3 Noise From Rain.- 7.4 Noise From Surface Emissions.- 7.5 Noise From Extra-terrestrial Sources.- References.- 8 Scintillation, Bandwidth Coherence, and Other Propagation Factors.- 8.1 Scintillation.- 8.1.1 Ionospheric Scintillation.- 8.1.2 Tropospheric Scintillation.- 8.1.3 Amplitude Scintillation Measurements in Earth-Space Paths.- 8.2 Bandwidth Coherence.- 8.3 Antenna Gain Degradation and Angle of Arrival Effects.- References.- 9 Propagation Effects on Communications Satellite Link Performance.- 9.1 Communications System Parameters.- 9.1.1 Noise Temperature and Noise Figure.- 9.1.2 Figure of Merit.- 9.1.3 Carrier-to-Noise Ratio.- 9.1.4 Effective Isotropic Radiated Power.- 9.1.5 Percent-of-Time Performance Specifications.- 9.2 Link Performance in the Presence of Propagation Effects.- 9.2.1 Frequency Translation Satellite.- 9.2.2 On-board Processing Satellite 171.- 9.2.3 Effects of Path Attenuation on System Performance.- References.- 10 Restoration Techniques for Overcoming Severe Attenuation.- 10.1 Site Diversity.- 10.1.1 Diversity Gain and Diversity Improvement.- 10.1.2 Diversity Measurements.- 10.1.3 Diversity System Performance and Design.- 10.1.4 Diversity Processing.- 10.2 Power Control.- 10.2.1 Uplink Power Control.- 10.2.2 Downlink Power Control.- 10.3 Orbital Diversity.- 10.4 Spot Beams.- 10.5 Signal Processing Restoration Techniques.- 10.5.1 Frequency Diversity.- 10.5.2 Bandwidth Reduction.- 10.5.3 Transmission Delay.- 10.5.4 Adaptive Forward Error Correction.- 10.6 Summary.- References.- Appendix A Elevation Angle Dependence for Slant Path Communications Links.- Appendix B Interpolation Procedure for Atmospheric Attenuation Coefficients.- Appendix D Crane Global Rain Attenuation Model Calculation Procedure.- Appendix E CCIR Rain Attenuation Model Calculation Procedure.- Appendix F CCIR Tropospheric Scintillation Model Procedure.

Phase noise and linewidth in an InGaAsP DFB laser

Abstract: Measurements and calculations of interferometrically demodulated phase noise in an InGaAsP DFB laser are reported. The results led to a novel method of laser linewidth measurement. The effect of this noise on a DPSK coherent system is considered.

Reflection noise in index-guided InGaAsP lasers

Abstract: We report a detailed study of the excess noise induced in index-guided InGaAsP laser structures by reflection feedback. The phenomena of high-frequency noise (1-5 GHz), low-frequency noise (< 100 MHz), and intensity fluctuations are shown to have a common physical origin in the unusual instability of the coupled laser-external cavity system. After a randomly occurring light intensity drop, the light output recovers in 10-15 steps, each corresponding to an external cavity roundtrip (high-frequency noise); the total recovery time corresponds to the low-frequency noise. The instability, and the subsequent noise, can be suppressed under conditions of very strong feedback such as obtained for lasers with anti-reflection-coated facets. The reflection noise characteristics are shown to be largely independent of the laser structure and structure modifications such as distributed feedback.

Theory of mode competition noise in semiconductor injection lasers

Abstract: A theoretical analysis of the mode-competition noise in semiconductor injection lasers is given. The source of the noise is supposed to be fluctuations of the number of photons and electrons on optical emission, and is amplified by optical gain in which the mode-competition phenomena are taken into account. When a lasing mode jumps to another mode, noise becomes largest and shows 1/f^{\alpha} characteristics on its frequency spectrum, where the index of \alpha = 2 is theoretically obtained based on a perturbation analysis of the noise. The noise of an individual mode is in general larger than that of the overall lasing modes. The noise reduces to the level of the quantum noise when the laser operates either in single mode or in stable multimodes.

Frequency and intensity noise in injection-locked semiconductor lasers: Theory and experiments

Abstract: Analytical expressions for the power spectral densities of intensity and frequency noise of single-mode semiconductor lasers operating in a regime of injection locking are derived by appropriately taking into account the spontaneous emission processes into the lasing modes of both the master and slave lasers. They show how the noise spectra of the slave are influenced by the value of the injected power, by the difference between the emission frequencies of the master and slave optical cavities, and how they are correlated to the noise properties of both the master and the free-running slave. In particular, the very low frequency part of the frequency noise of the slave turns out to coincide with that of the master within a certain frequency region whose range increases as the values of the injected signal does, too. We also present measurements of the power spectral densities obtained by means of an experimental apparatus similar to that described in [1] and show how the experimental results are accounted for by the present theory.

The generation of broadband electrostatic noise by an ion beam in the magnetotail

Abstract: The results of a theoretical investigation of the generation of broadband electrostatic noise (BEN) by an ion beam in the earth's magnetotail are presented. It is shown that at low beam temperatures an ion beam can generate BEN at wave normal angles (theta) between zero and 80 deg with the maximum growth occurring at theta - 0 deg when the beam velocity is small and at large theta (about 70 deg) for higher beam velocities. It is also shown that two types of instability are responsible for the wave amplification. One is the ion acoustic instability associated with the electron-ion beam relative drift, and the other is the ion-ion instability. The broad frequency and angular spectra of BEN can be explained by the presence of the two instabilities. These instabilities are shown to be insensitive to the presence of a background magnetic field.

Noise characteristics in longitudinal thin-film media

Abstract: The noise of longitudinal thin metal film media is experimentally investigated using a new method: the reverse DC erase media noise measuring method. The reverse DC erase noise of thin metal film shows a sharp peak at the field around coercive force Hc. The maximum reverse DC erase noise has a strong correlation to the signal recorded noise. Media with large noise has low D 50 and also low Overwrite S/N.

Theory and simulations of broadband electrostatic noise in the geomagnetic tail

Abstract: The excitation mechanism for broadband electrostatic noise (BEN) and the effects of BEN particles in the geomagnetic tail are examined using the linear analysis theory and particle simulations. The linear theory for electrostatic instabilities is discussed. The plasma sheet particle population is simulated using counter-streaming cold ion beams, and warm ions and electrons. The ion-ion instability, ion-acoustic mode, and the electrostatic ion cyclotron harmonic waves are studied. The velocity distributions, electric field intensity, and electron plasma waves for the plasma sheet boundary layer are evaluated. The frequency wave spectrum and particle distributions are computed and analyzed. The conditions for the two simulations, which differ only in beam ion drift speed, are described; it is observed that in the first simulation the dominate modes propagate parallel to the magnetic field and in the second simulation the propagation modes are oblique. The simulation data reveal that when beam temperature is smaller than plasma sheet temperature ion-acoustic and ion-ion instabilities grow to large amplitudes heating both electrons and ions. The data are compared to ISEE-1 observations and good correlation is obtained.

Vortex creep and the internal temperature of neutron stars : timing noise in pulsars.

Abstract: Vortex creep theory is used to construct model noise power spectra for three physically distinct types of events which might give rise to pulsar timing noise These are 'pure' events, in which vortex unpinning is the source of the initial frequency jump; 'mixed' events, in which the initial frequency jump is produced by some physical process other than vortex unpinning but leads to the unpinning of some vortices; and 'external' events, in which the initial frequency jumps responsible for noise do not involve any vortex unpinning For the first two types of events, it is found that relaxation processes in the region responsible for the noise will give rise to structure in the observed power spectra, while for external events, the resulting noise spectra will not be influenced by vortex creep The theoretical results are compared with observed power spectra for 25 pulsars The absence of structure in the observed power spectra of the Crab and Vela pulsars within the range of time scales which characterize their postglitch behavior indicates that the pinning regions which play a role in postglitch behavior do not experience the small unpinning events leading to timing noise

A method relating to three dimensional measurement of objects

Abstract: A method for three dimensional measurement of objects (1) being conveyed through or moved relative to a measurement frame (4) for, by incremental measurements of height, width and length of the object to calculate cubical and circumscribed volume of the object. Each transmitter/receiver element pair of the measurement frame (4) is calibrated by controlling the amount of the light emitted from the transmitter and the threshold level of the receiver, such that the signal/noise ratio of the receiver lies above a specific limit, simultaneously with the illumination time being kept the shortest possible. By incremental measurements at least one pair consisting of transmitter element and directly opposite receiver element in the measurement frame (4) is activated at time, and an external signal being a function of the movement of the object relative to the measurement frame is compared with the registered signals from the receiver elements for calculation of the said volumes. The measurement frame is constructed in the form of horizontal and vertical transmitter- and receiver modules (6.1, 6.2; 8.1, 8.2; 7.1, 7.2; 9.1, 9.2) consisting of said transmitter elements and receiver elements, respectively. A computer is connected to the measurement frame for calibration of the respective transmitter- and receiver elements of the measurement frame (4) and for calculation of said volumes being derived as a result of shadow images of the object on the receiver elements. A display (22) is associated with the computer for display of the volume magnitude of the object. Utilization for e.g. calculation of freight charges of objects.

Bit-Error-Rate Degradation in a Multimode Fiber Optic Transmission Link Due to Modal Noise

Abstract: A review is given of the statistics of modal noise and of the expressions for the signal-to-noise ratio for the cases of a monochromatic and a nonmonochromatic light source including the effects of source frequency fluctuations. Using the results, a quantitative analysis is made of how modal noise degrades the bit-error-rate performance of a digital transmission link with multimode fiber. Plots of the bit-error rate versus the received optical power show the characteristic asymptotic behavior (BER floor); expressions are derived for the asymptotic BER. The power penalty due to modal noise can be considerably reduced by suitable system modifications, e.g., by optimization of the decision threshold setting or by application of a low coherent light source such as an LED or a laser diode operating with several spectral emission lines of low coherence and low partition noise.

Electron acoustic instabilities in the geomagnetic tail

Abstract: Electron acoustic waves present in a two temperature electron plasma can be driven unstable when ion beams propagate along the magnetic field. Both linear theory and numerical simulations indicate that this instability contributes to the generation of broadband electrostatic noise (BEN) in the geomagnetic tail.

High-frequency-modulation spectroscopy with a lead-salt diode laser

Abstract: High frequency modulation (FM) spectroscopy, (1,2,3) is a promising tool for high speed and ultrasensitive atmospheric trace gas monitoring. Based on a measured wideband noise characteristics (4) of a lead-salt diode-laser emitting in the mid IR a sensitivity improvement of 2 orders of magnitude in comparison to conventional derivative (2f) spectroscopy is expected. This improvement can be achieved by moving in modulation and detection frequency space from the 1/f noise dominated region (10 kHz) into a shot noise limited frequency domain above 100 MHz. Optical densities of 10−4 were measured on a µsec timescale with a 200 kHz detection bandwidth. Using digital averaging techniques (5) a detection limit of 2.5.10−6 has been demonstrated with the actual measurement bandwidth of 1.5 kHz. Up to this sensitivity no limitations due to etalons or laser intrinsic parameters could be observed. Further bandwidth reduction is currently being investigated and requires digital background subtraction techniques as well as etalon suppression schemes.

Electromagnetic touch sensor input system in a cathode ray tube display device

Abstract: A cathode ray tube display device has conductive plates mounted adjacent the four sides of the CRT faceplate. These plates are positioned to sense electromagnetic noise radiation generated by the CRT. The plates are coupled to differential circuits so that normally the noise signals generated in the plates cancel. However when a finger or other object is placed at or near the CRT faceplate, the noise radiation field is disturbed, and the changed signals generated in the plates are sensed by the circuits to provide output signals indicative of the coordinate position of the object at the faceplate. The plates are preferably mounted in the front bezel of the display cabinet.

Low-frequency noise and discrete charge trapping in small-area tunnel junction dc SQUID's

Abstract: We present measurements of the noise properties of very small‐area, high current density tunnel junction dc superconducting quantum interference devices (SQUID’s). The low‐frequency noise spectra display broad curves and bumps consistent with the presence of individual Lorentzian features superimposed on a background which is always much flatter than 1/f. When these features are most prominent, the voltage across the SQUID exhibits discrete switching behavior which we attribute to the trapping and untrapping of single electrons within the tunneling barrier. This observation, along with other evidence presented, suggests that critical current fluctuations displaying tunneling kinetics dominate the low‐frequency noise of these ultrasmall devices.

Magnetic equilibrium noise in spin-glasses: Eu0.4Sr0.6S.

Abstract: Mesure simultanee, par une nouvelle technique magnetometrique, du bruit lie aux fluctuations magnetiques et de la susceptibilite ac comme fonctions de la temperature; mise en evidence de la validite du theoreme de fluctuation-dissipation au-dessus et au-dessous de la temperature de gel; particularites des variations dans le domaine des basses frequences

Analysis and interpretation of the shocklike electrostatic noise observed during the AMPTE solar wind lithium releases

Abstract: During the AMPTE (Active Magnetospheric Particle Tracer Explorers) solar wind lithium release on September 11, and again on September 20, 1984, an intense burst of electrostatic noise was observed near the upstream edge of the ion cloud. Comparisons with measurements by the IMP-6 and ISEE-1 spacecraft show that the spectrum and overall features of this noise are very similar to electrostatic noise observed at the Earth's bow shock. A stability analysis using realistic parameters shows that the electrostatic noise can be accounted for by an ion beam-plasma instability caused by the solar wind proton beam streaming through the nearly stationary lithium cloud. The growth rate of this instability is largest when the ion density and solar wind proton density are similar, which explains why the noise only occurs near the outer edge of the ion cloud. The similarity to the noise in the Earth's bow shock suggest that a shock may exist in the solar wind plasma flow upstream of the ion cloud. If the noise is associated with a shock, then it must be an electrostatic shock, since the ion cyclotron radii are too small for the existence of a MHD shock. Since the electrostatic instability occurs at phase velocities near the lithium thermal velocity, the electrostatic turbulence may play a role in heating the lithium ions and transferring momentum from the solar wind to the ion cloud.

Waves generated during electron beam emissions from the space shuttle

Abstract: Observations from the SEPAC (Space Experiments with Particle Accelerators) experiment on Spacelab 1 Shuttle mission of waves generated during electron beam emissions are presented. The dependence of the wave intensity on the beam parameters and the Shuttle attitude is outlined, and the shape of the wave spectra are discussed. It is found that the noise in the 0.75- to 10 kHz band has a spectral shape that can be characterized by an f exp -n law, and that the VLF signal level depends on the beam angle to the magnetic field, the strongest emissions being observed for parallel beams. These features are found to be consistent with a drift wave instability.

Environmental correlates of pack ice noise

Abstract: Low‐frequency ambient noise under pack ice of the central Arctic Ocean has long‐term variations (periods greater than 1 h) which correlate highly with composite measures of stress applied to the ice by wind, current, and drift. These composites are the horizontal ice stress and the stress moment, and are derived from meteorological and oceanographic data observed simultaneously with the noise. Atmospheric cooling, a known high correlate of midfrequency noise under the ice, is not important at low frequencies.

Spatial structure of media noise in film disks

Abstract: Measurements of the spatial structure of media noise across the track direction are made using new techniques involving computer processing of digitized transient read signal waveforms. Images of media noise having spatial resolution much finer than available head widths are obtained, and are used to study the scaling of media noise with read head width. Results are presented for two types of metal film disks and a particulate disk. Uniformly DC erased media noise is found to decrease less rapidly with decreasing head width for the metal film disks than for the particulate disk, in which it scales approximately as the square root of head width. A strip of excess noise is found at the edges of written tracks on the metal film disks but not the particulate disk.