Frequency Noise Spectrum Research Articles

Characterization of As Implanted Silicides by Frequency Noise Level Measurements

Silicides belong to a very promising group of materials which are of great interest both in the physics of thin films and in microelectronics. Their low resistivity and expected good temperature stability make them desirable for fabrication of reliable and reproducible electrical contacts. Investigations of this type of contacts include both their experimental development and the development of methods for their characterization such as noise level measurement and RBS analysis. The noise level measurements enable the control of the noise, which is important characteristic of metal-semiconductor (M/S) electrical contacts (especially l/f noise). In our work we compare the RBS spectra and low frequency noise spectra of As + implanted layers of TiN-Ti-Si structures, obtained in different conditions. Low frequency noise spectra are also obtained at different sample temperatures. Results of our measurements and analysis are of interest for solving the problems related to the application of ion implantation of As + ions for the formation of silicides on p-Si, that are discussed by many authors in their investigations recently.

Measurement of frequency noise spectra of frequency-stabilized LD-pumped Nd:YAG laser by using a cavity with separately suspended mirrors

We have developed a frequency stability system for a commercial LD-pumped Nd:YAG laser in a nonplanar ring oscillator geometry (MISER) which is used for our 20-m prototype gravitational wave detector. The frequency of the laser is locked to the rigid cavity resonance frequency, and the relative frequency noise is suppressed down to 3 × 10−4Hz/Hz1/2 the shot-noise limited level at below 1 kHz. We are successful in evaluating the frequency noise level more accurately by means of a separately suspended reirror type cavity (4-m mode-cleaner); the noise level is 2 × 10−2Hz/Hz1/2. As compared to a frequency noise spectrum which is locked to separately suspended mirror type cavities, the frequency noise is lower at a frequency below 400 Hz.

Stability of short, single-mode erbium-doped fiber lasers

We conducted a detailed study of the stability of short, erbium-doped fiber lasers fabricated with two UV-induced Bragg gratings written into the doped fiber. We find that the relative intensity noise of single-longitudinal-mode fiber grating lasers is approximately 3 orders of magnitude lower than that of a single-frequency 1.523-mum helium-neon laser. The frequency noise spectrum contains few resonances, none of which exceeds 0.6 kHz/Hz(1/2) rms; the integrated rms frequency noise from 50 Hz to 63 kHz is 36 kHz. We also demonstrate a simple method for monitoring the laser power and number of oscillating modes during laser fabrication.

Semiclassical model of semiconductor laser noise and amplitude noise squeezing. I. Description and application to Fabry-Perot laser

A semiclassical model of semiconductor laser noise, based on the Green's function method, is used to derive analytical formulas for the amplitude and frequency noise spectra taking into account incoming vacuum fluctuations and noise due to internal loss. This formalism also takes into account phenomena such as gain suppression as well as spatial hole burning (SHB). The amplitude noise squeezing is studied for Fabry-Perot structures pointing out the influence of the laser structural parameters. A complete agreement with already existing quantum mechanical models is found. However, extension of the model to SHB induces limitations in the squeezing performances, which are very important for more complex structures as will be pointed out in detail, in Part II.

Frequency noise and modulation of a four-section DBR laser

A theoretical model is presented to describe the tuning, frequency noise, and modulation characteristics of tunable DBR lasers with two active and two passive sections. Analytical expressions are derived for the intensity and frequency modulation responses, frequency noise spectrum, spectral linewidth, effective linewidth enhancement factor, and spontaneous emission rate. It is shown that a nearly flat red-shifted FM response over several gigahertz can be obtained by nonuniform current injection and modulation of the lower carrier density section in the active region. Increasing the tuning current through the passive sections enhances the FM efficiency. However, a higher FM efficiency is generally accompanied by a larger spectral linewidth. The predictions of our theoretical model are in good agreement with the available experimental data.

Experimental determination of mixing length in the buffer layer of a turbulent boundary layer

A method for determining the value of the turbulent mixing length based on measurements of transverse flow velocity fluctuations is proposed. This method is applicable for the boundary layer buffer layer. The results obtained are used to solve the equation of motion for the flow in this region. A method of calculating and generalizing the frequency spectrum of the aerodynamic noise that is generated in the turbulent boundary layer is proposed.

Flux noise in YBaCuO thin film and BiSrCaCuO single crystal

The low frequency noise spectra originating from the temperature induced flux relaxation in YBa2Cu3O7−x thin film and Bi2Sr2CaCu2O8 single crystal have been recorded using the SQUID magnetometer with the sensitivity of 100 fWb Hz−1/2 at 10 Hz. The simultaneous record of the low field AC magnetisation response (susceptibility) shows that the temperature at which the maximum of the trapped flux relaxation rate occures is shifted below the sharp AC response originating from the superconducting to the normal state transition. The trapped flux starts to relax at considerably lower temperature. The temperature sweep shows that the “equilibrium” trapped flux depends only on temperature.

Low frequency noise in separate absorption, grading,chargeand multiplication (SAGCM) avalanche photodiodes

Low frequency noise spectra of five SAGCM APDs were measured. The experimental noise current spectra were fitted with S/sub I/=A/sub F/I/sub d//sup x//f/sup y/+2qI/sub d/M/sub eff/. Any enhancement in shot noise was included in M/sub eff/. The A/sub F/ factors were found to vary from 10/sup -7/ to 10/sup -5/ and were related to the I-V characteristics of these APDs.

Analysis of noise up-conversion in microwave field-effect transistor oscillators

The conversion process of the low frequency noise into phase noise in field-effect transistors (FET) oscillators is investigated. First, an evaluation of the baseband noise contribution to the oscillator phase noise is provided from the analysis of the baseband noise and the frequency noise spectra. A distinction is made within the different components of the low frequency noise contributions to close-in carrier phase noise. Next, the frequency noise of the oscillator circuit is analyzed in terms of the FET's low frequency noise multiplied by the oscillator's pushing factor. Though this product usually provides a good evaluation of the phase noise, experimental results presented here show the inaccuracy of this method at particular gate bias voltages where the pushing factor decreases to zero. To account for these observations, a new nonlinear FET model involving at least two noise sources distributed along the channel is proposed.

Comparing stress ECG enhancement algorithms

There are two predominant types of noise that contaminate the electrocardiogram (EGG) acquired during a stress test: the baseline wander noise (BW) and electrode motion artifact, and electromyogram-induced noise (EMG). BW noise is at a lower frequency, caused by respiration and motion of the subject or the leads. The frequency components of BW noise are usually below 0.5 Hz, and extend into the frequency range of the ST segment during a stress test. EMG noise, on the other hand, is predominantly at higher frequencies, caused by increased muscle activity and by mechanical forces acting on the electrodes. The frequency spectrum of the EMG noise overlaps that of the ECG signal and extends even higher in the frequency domain. In this article, the authors review some of the published ECG enhancing techniques to overcome the noise problems, and compare their performance on stress ECG signals under adverse noise scenarios. They also describe the filter bank-based ECG enhancing algorithm.

The role of baseband noise and its upconversion in HBT oscillator phase noise

The phase noise spectral density (#(f/sub m/)) of an 11.02-GHz heterojunction bipolar transistor (HBT) dielectric resonator oscillator (DRO) has been investigated in terms of the HBT's low frequency noise and the oscillator's upconversion coefficient. Experimental studies have been used for this purpose and the measured #(f/sub m/) ranged from -89 dBc/Hz to -101 dBc/Hz at a 10-kHz offset frequency (best phase noise spectral density performance was -124 dBc/Hz at 100 kHz). It was shown that, in most test cases, #(f/sub m/) can be described by the upconversion of the HBT's baseband noise. As a result the frequency dependence, of #(f/sub m/), is dictated by the low frequency noise spectrum rather than the upconversion itself. Deviation from pure 1/f frequency dependence found for the HBT's baseband noise at frequencies above 100 Hz resulted in d#(f/sub m/)/d(f/sub m/) deviating from about -30-dB/decade rate. Reduced oscillator phase noise at high collector current is attributed to reduced upconversion in the oscillator. >

Low frequency noise in polysilicon-emitter bipolar junction transistors

This paper describes experimental results on low frequency noise in several types of polysilicon-emitter NPN bipolar junction transistors. The experimental data were modelled using a combination of 1/f noise, generation-recombination noise (g-r), and shot noise, and good agreement between model calculations and experimental measurements were obtained. Observed differences in the experimental low frequency noise spectra of devices with similar geometry and under similar biasing conditions could be explained by the differences in the generation-recombination (g-r) noise contributions. Experiments were performed on devices with emitter areas varying from 1.6 to 144 μm2, and it was found that the magnitude of the flicker noise contribution KF varied inversely with emitter area AE or emitter perimeter PE. The fact that KF∼A−1E or KF∼P−1E is explained by the observation that AE∼PE within fabrication errors/tolerances. Using a set of 3.2 μm2 BJTs with pronounced g-r noise, input current noise was measured at different temperatures and from a deconvolution of the noise spectra, a trap at ∼400 meV and with a capture cross section of ∼4×10−17 cm2 was identified. Finally, the effect of different base implant and rapid thermal annealing conditions, polysilicon emitter thicknesses, and surface etching conditions on the noise magnitude were studied, and these results are also reported.

Optical phase-locked loop (OPLL) for an amplitude modulated communications link using solid-state lasers

Theoretical analysis is formulated for a solid state laser based optical phase-locked loop (OPLL) disturbed by shot noise, amplitude modulated noise, and frequency noise. The frequency noise spectral density of solid state lasers is modeled to contain a white component, a 1/f component, and a strong 1/f/sup 2/ component at the laser output. This model is verified and the spectral content of each component is measured using an open-loop RF frequency discriminator. The choice of loop filter is made by considering the frequency noise components, transient effects, and the loop damping factor /spl zeta/. The total phase error variance as a function of loop bandwidth is displayed for several values of carrier signal-to-noise ratio for the measured frequency noise spectrum. Optimal loop bandwidth is also calculated as a function of carrier signal-to-noise ratio. An OPLL experiment is performed, and measured phase error variance is compared with the theoretical predictions using the measured frequency noise spectrum. The results show that the measured phase error variance closely matches the theoretical predictions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A deconvolution method for evaluating indicator-dilution curves

Characteristics of blood flow in tissue can be measured by administering an intravascular tracer and then deconvolving and analysing the resulting indicator-dilution curves. Existing deconvolution methods are not typically generalizable to a variety of tissues. The authors have developed a more general deconvolution method using simulated indicator-dilution data. This method involves filtering the Fourier transform of indicator-dilution data with a modification of the Wiener filter, an adaptive deconvolution filter. Unlike the Wiener filter, this adaptive filter requires no previous knowledge of the noise frequency spectrum; it is derived by varying the magnitude of the noise spectrum until the oscillations in the deconvolved data fall below an optimal value. The optimal value corresponds to the setting of the noise spectrum that allows the most accurate and precise measurement of vascular characteristics from deconvolved data. Vascular characteristics measured in brain tissues using this deconvolution method on actual indicator-dilution data were similar to established values. It should be possible to use this method on time-concentration data collected from a variety of tissues using a number of different tracer measurement techniques, thereby allowing the accurate characterization of vascular physiology.

Current fluctuations in 1D double - barrier heterostructures

A theoretical formalism to study the current-noise characteristic of one-dimensional double barrier heterostructures taking into account correlation effects is developed within the context of the Keldysh nonequilibrium Green functions. The effects of the Coulomb blockade on the characteristic curve (current versus voltage) and on the current fluctuation are studied in a selfconsistent calculation. For the static case a reduction of the full shot noise is observed. The effects of the barrier characteristics on the transport properties are also analyzed. A connection between the noise frequency spectrum and the transit time of the electron going along the structure is established.

Frequency noise of a Bragg grating fibre laser

The measured frequency noise spectrum of a pair of single-frequency Bragg grating fibre lasers is dominated by noise at audio frequencies peaked near 700 Hz which fades into a white noise floor above ~50 kHz. The measured white noise floor yields an estimated Lorentzian FWHM linewidth of ~61 Hz.

Suppression of the intensity noise in a diode-pumped neodymium:YAG nonplanar ring laser

We investigate the intensity noise properties of a continuous-wave diode pumped Nd:YAG ring-laser system and present results for an active feedback loop that suppresses the relaxation oscillation noise. This system reduces the intensity noise to within 6.1 dB of the quantum noise equivalent level (which is at 1.5/spl times/10/sup -8///spl radic/Hz for 1.5 mA) for frequencies between 10 kHz to 300 kHz and to less than 1/spl times/10/sup -7///spl radic/Hz for frequencies between 300 Hz and 10 kHz. The technical properties of the optimized feedback system are presented. The theoretical limits of performance for the system are discussed and it is shown that the performance is within 3.1 dB of these limits. We also present data from an optical beat experiment demonstrating that the intensity control system does not introduce any new features into the frequency noise spectrum.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Volterra functional series expansions for noise in semiconductor lasers

In this paper, we present a full analysis of noise in semiconductor lasers. Time-covariance and cross-covariance functions of all variables governing single-mode semiconductor laser behavior are given including all Langevin noise sources and considering all terms of the laser rate equations, RIN, carrier noise spectrum, frequency noise spectrum, coherence between the FM and AM noise, variance of the phase change and coupling between amplitude and phase are investigated analytically in their more general form. Spectral line shape has been derived showing dissymmetrical satellite lines centered at multiple integers of relaxation frequency around a central line. It is shown that neglecting the shot noise and considering only the carrier contribution in phase dynamics (common procedure) are too general approximations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Heterodyne optical phase-locking of extended-cavity semiconductor lasers at 9 GHz

In order to stimulate atomic velocity-selective Raman transitions on the 852 nm caesium D 2 line in an atomic fountain clock, two extended-cavity diode lasers have been optically phase-locked at a frequency offset of 9.192 GHz. The measured linewidth (fwhm) of the free-running lasers is 50 kHz. The phase-locked loop bandwidth, evaluated by observing the frequency noise spectrum, is 3.7 MHz and the phase error variance is found to be no more than 4 × 10 -3 rad 2.

Level Crossings of Phase of Sine Wave Plus Gaussian Noise

Theoretical results concerning the level crossings of the phase -π≤θ(t)≤π of the process consisting of a sine wave disturbed by additive Gaussian noise are presented, along with the experimental results supporting the theory. The average number of crossings of the phase angle θ(t), as well as the conditional probability densities for R(t), the envelope of the considered process, and for θ′(t), the time derivative of θ(t), are derived for an arbitrary crossing level θ. These derivations are a generalization of the existing theory to the case of a nonsymmetric (about the sine wave frequency) noise spectrum and an arbitrary crossing level -π≤θ≤π. To verify the derivations, experimental measurement of the considered quantities is performed for the case of a Gaussian noise having the 7th-order Butterworth spectrum. The experimental results are compared with the corresponding theoretical ones, and are found to be in good agreement.