Reduction of spectral noise density in p-i-n-HEMT lightwavereceivers

The spectral noise density of a lightwave receiver is computed from known physical parameters of the photodiode and the high-electron-mobility transistor (HEMT). Low noise is achieved for an appropriate choice of device parameters. The results are applied to circuits built with readily available commercial HEMTs and p-i-n photodiodes. They also predict the superior noise performance of cooled receivers which cannot be readily derived from previous work     

Reduction of musical noise in spectral subtraction method usingsubframe phase randomisation

A subframe phase randomisation method is proposed and applied to the enhanced speech with spectral subtraction method to reduce musical noise in the nonvoicing region. The musical noise in the spectral subtraction method is largely due to narrowband tonal components appearing somewhat periodically in the spectrogram of unvoiced and silence regions. Thus, each synthesis frame in a nonvoicing region is divided into several subframes to broaden the narrowband spectrum, and then phases of silence and unvoiced regions are randomised to disrupt the tonal spectrum structure     

Automated decomposition of intramuscular electromyographic signals

We present a novel method for extracting and classifying motor unit action potentials (MUAPs) from one-channel electromyographic recordings. The extraction of MUAP templates is carried out using a symbolic representation of waveforms, a common technique in signature verification applications. The assignment of MUAPs to their specific trains is achieved by means of repeated template matching passes using pseudocorrelation, a new matched-filter-based similarity measure. Identified MUAPs are peeled off and the residual signal is analyzed using shortened templates to facilitate the resolution of superimpositions. The program was tested with simulated data and with experimental signals obtained using fine-wire electrodes in the biceps brachii during isometric contractions ranging from 5% to 30% of the maximum voluntary contraction. Analyzed signals were made of up to 14 MUAP trains. Most templates were extracted automatically, but complex signals sometimes required the adjustment of 2 parameters to account for all the MUAP trains present. Classification accuracy rates for simulations ranged from an average of 96.3% +/- 0.9% (4 trains) to 75.6% +/- 11.0% (12 trains). The classification portion of the program never required user intervention. Decomposition of most 10-s-long signals required less than 10 s using a conventional desktop computer, thus showing capabilities for real-time applications.     

Ensemble empirical mode decomposition based fluorescence spectral noise reduction for low concentration PAHs

A new noise reduction method based on ensemble empirical mode decomposition (EEMD) is proposed to improve the detection effect for fluorescence spectra. Polycyclic aromatic hydrocarbons (PAHs) pollutants, as a kind of important current environmental pollution source, are highly oncogenic. Using the fluorescence spectroscopy method, the PAHs pollutants can be detected. However, instrument will produce noise in the experiment. Weak fluorescent signals can be affected by noise, so we propose a way to denoise and improve the detection effect. Firstly, we use fluorescence spectrometer to detect PAHs to obtain fluorescence spectra. Subsequently, noises are reduced by EEMD algorithm. Finally, the experiment results show the proposed method is feasible.     

Reduction of FM noise in impatt oscillators by optical illumination

Experiments are described in which laser illumination of the active device has reduced the FM noise output by up to 5 dB for a GaAs impatt oscillator and 2 dB for a Si impatt oscillator. A qualitative explanation of the observed results is given, and the effect of laser amplitude noise on the maximum noise reduction obtainable is shown.     

Sampling frequency of the electrocardiogram for spectral analysisof the heart rate variability

The R-R interval measurement from digitized electrocardiograms (ECG) contains an error due to the finite sampling frequency which may jeopardize the beat-to-beat analysis of the heart rate. In this paper, we develop a model to describe and quantitate this error. The "measured" R-R interval is modeled as the sum of the "true" R-R interval and of the error of measurement. The first and second order statistics of the error are computed in order to investigate its influence on the heart rate variability (HRV) power spectrum. They are found to be only functions of the ECG sampling frequency and, in particular, the power spectrum of the error contributes an additive high-pass filter-like term (colored noise) to the power spectrum of the HRV. The accuracy of the model is tested via a simulation procedure. The model indicates that the relative balance between the HRV and the error power spectra is important and should be checked before any variability analysis on the heart rate. This balance may be favorable to the error when 1) the sampling frequency of the ECG is too low, and/or 2) the variability of the heart rate is too little. In these cases, the HRV spectrum analysis may not give reliable results. Two tests are proposed in order to evaluate the error influence either in specific frequency bands or in the total frequency range.     

On estimating spectral moments in the presence of colored noise

Let{q^(1) (t)}, the signal, be a complex Gaussian process corrupted by additive Gaussian noise{q^(2) (t) }. Observations onp(t)q(t)andp(t) q^(2) (t)are assumed to be available wherep(t)is a smooth weighting function andq = q^(1) + q^(2). Using the Fourier transform of the samples ofp(t)q(t)andp(t) q^(2) (t), estimators are derived for estimating the mean frequency and spectral width of the unknown power spectrum of the unweighted signal process. The means and variances of these statistics are computed in general, and explicitly for nontrivial practical examples. Asymptotic formulas for the moment estimators as a function of the number of realizations, frequency resolution, signal-to-noise ratio and spectral width, and consistency of the estimators are some of the results that are discussed in detail.     

FM noise and spectral linewidth reduction by incoherent opticalnegative feedback

An all-optical, stable, external feedback method, the incoherent optical negative feedback method, is proposed and demonstrated for spectral linewidth reduction and optical-frequency stabilization of distributed-feedback (DFB) lasers. The power-spectral density of frequency modulation (FM) noise is shown to be reduced in a wide range of up to several hundreds of megahertz. The linewidth and the optical-frequency drift are simultaneously experimentally reduced to about 140 kHz and less than 17 MHz, respectively. The frequency range of the effective FM noise reduction and the reduction ratio of the FM noise are up to 1 GHz and 22 dB, respectively     

Reduction of popcorn noise in integrated circuits

Popcorn (burst) noise continues to deteriorate the operation of linear IC devices. Reduction of popcorn noise by a few simple modifications in the manufacturing process is reported in this paper. Annealing in an HC1 atmosphere to getter metal impurities and slow pulling after emitter deposition to diminish stress-induced junction defects appear to reduce the popcorn noise significantly.     

Reduction of flicker noise in transistor amplifiers

An amplifier has been built using the chopper technique suggested by Baxandall. A low-frequency noise figure of 6dB has been obtained, but in the region of 1 Hz upwards, a simple bipolar or f.e.t. circuit will give a better performance.     

数字全息再现像的激光散斑消除的研究

由于数字全息图受到激光散斑影响,使得其再现像产生较为严重的噪音。通过详细分析激光散斑形成的原因,并提出了用同一物体的多幅全息图的强度再现像叠加来减小激光散斑的干扰。具体分析了该方法的原理：在记录全息的物体照明光路中加入一散射体,在散射体的M个不同位置记录M张同一物体的全息图,然后将M幅数字全息的再现像叠加,激光散斑噪音下降为M~(-1/2)。最后给出了实验结果。     

Reduction of noise in high-power crossed-field amplifiers

The letter describes a method of reducing the broadband noise of a high-power injected-beam crossed-field amplifier by means of a nonuniform magnetic field in the electron-gun region. The noise reduction achieved is some tens of decibels, and also results in improvements in other characteristics of the tube.     

Zero-crossing based spectral analysis and SVD spectral analysis forformant frequency estimation in noise

The authors discuss a method for spectral analysis of noise corrupted signals using statistical properties of the zero-crossing intervals. It is shown that an initial stage of filter-bank analysis is effective for achieving noise robustness. The technique is compared with currently popular spectral analysis techniques based on singular value decomposition and is found to provide generally better resolution and lower variance at low signal to noise ratios (SNRs). These techniques, along with three established methods and three variations of these method, are further evaluated for their effectiveness for formant frequency estimation of noise corrupted speech. The theoretical results predict and experimental results confirm that the zero-crossing method performs well for estimating low frequencies and hence for first formant frequency estimation in speech at high noise levels (~0 dB SNR). Otherwise, J.A. Cadzow's high performance method (1983) is found to be a close alternative for reliable spectral estimation. As expected the overall performance of all techniques is found to degrade for speech data. The standard autocorrelation-LPC method is found best for clean speech and all methods deteriorate roughly equally in noise     

Reduction of optical phase noise in semiconductor lasers

There are several applications of highly coherent semiconductor lasers, especially in coherent optical-fibre communications systems and optical-fibre sensors. Optical phase noise is extremely important in these applications. Here we report preliminary results from a simple technique whereby phase noise in semiconductor lasers may be reduced. Initial results demonstrate a phase-noise reduction of typically 20 dB. Developments of the technique should permit reduction towards the shot noise limit.     

A spectral Lanczos decomposition method for solving 3-Dlow-frequency electromagnetic diffusion by the finite-elementmethod

A very efficient three-dimensional (3-D) solver for the diffusion of the electromagnetic fields in an inhomogeneous medium is described. The proposed method employs either the node-based or the edge-based finite-element method (FEM) to discretize Maxwell's equations. The resultant matrix equation is solved by the spectral Lanczos decomposition method (SLDM), which is based on the Krylov subspace (Lanczos) approximation of the solution in the frequency domain. By analyzing some practical geophysical problems, it is shown that the SLDM is extremely fast and, furthermore, the electromagnetic fields at many frequencies can be evaluated by performing the SLDM iteration only at the lowest frequency     

Reduction of modal noise in high-speed short-distance computer datalinks by an electrical signal

Measured and calculated data on the tradeoffs between modal noise reduction and intermodulation penalty are presented. The authors quantify how a high modulation bandwidth and optical power can be obtained using conventional high-speed semiconductor lasers, by combining a sinusoidal auxiliary microwave signal with the normal data signal. How the characteristics of the laser diode determine the optimum values of the auxiliary carrier parameters is shown. Some results of optical data link simulations are presented. A 2.4-Gb/s transmission experiment shows an improvement of the bit error rate due to the microwave signal     

Recovering of autoregressive spectral estimates of signals buried in noise

In this paper, we propose a noise modeling that does not destroy AR structure of buried signals in noise independently of its nature (white or colored, Gaussian or not) and its variance. Expression of perturbed AR coefficients is derived and proposed restoration does not use any a-priori information on the nature of noise and its variance. It is shown that AR coefficients are closer to nominal ones (noise-free) in the presence of noise for lower frequency contents with respect to the sampling frequency of corresponding continuous-time processes from which samples are taken for AR estimation. For unknown frequency contents, denoising of AR coefficients is obtained by decreasing the time interval separating samples used by AR estimation. A model order selection adapted to degraded signal-to-noise ratios is proposed. Performances of the proposed recovering of original AR spectra are demonstrated via signals buried in white and colored noise. Observed results are in accordance with the developed theory.     

Phase noise and spectral line shape in semiconductor lasers

Experimental results concerning the study of phase noise in single-mode semiconductor lasers are reported, which show a strict connection between phase and intensity noise. In particular, phase-noise spectrum is found to present a sharp peak at the same peak frequency of intensity-noise spectrum, a fact which is proven to be responsible for the appearance of satellite peaks in the emission line shape. Direct measurements of the line shape, performed by means of a Fabry-Perot interferometer, are in agreement with the line shape evaluated by using phase-noise spectrum measurements.     

Reduction of semiconductor laser intensity noise by feedforwardcompensation: experiment and theory

The authors have recently demonstrated that an optical feedforward compensation technique can be used to reduce distortion and intensity noise in semiconductor laser transmitters. In the present work, an experimental demonstration of noise reduction by feedforward compensation and a theoretical estimation of noise limitations of the optical feedforward system are described. It is shown that in an optimized feedforward system using state-of-the-art components the relative intensity noise (RIN) can be as low as -160 dB/Hz     

Reduction of noise and distortion in amplifiers using adaptivecancellation

Application of adaptive cancellation techniques to feed-forward networks for amplifier linearization is discussed. Results of a test showing over 25 dB reduction in third order intermodulation products are presented