The digital signal-processing method of fringe pattern extremal curves generation is presented. The method is based on 3D wavelet map computation. The correspondence between features of fringe pattern and 3D wavelet map of the same fringe pattern is described. For analysis, the Symmetrical Morlet wavelet is used. Wavelet map ridge detection algorithm is proposed. Fringe extremal curves obtained are used for fringe phase recovery that leads to possibility of 3D relief
Low frequency noise characteristics of light-emitting diodes with InAs quantum dots in GaInAs layer are investigated. Two noise components were found in experimental noise records: RTS, caused by burst noise, and 1/f Gaussian noise. Extraction of burst noise component from Gaussian noise background was performed using standard signal detection theory and advanced signal-processing techniques. It was found that Hooge's empirical relation applied to diodes by Kleinpenning is applicable to the electric 1/f noise of quantum dot diodes as well. Two different spectra decomposition techniques are used to obtain burst noise spectra. Bias dependences of burst and 1/f noise are compared. It is concluded that the RTS noise and 1/f noise have different physical origins in light-emitting diodes with quantum dots.
The bispectrum of the 1/f noise is investigated in the present work. For the Gaussian noise it equals zero. LEDs on self-organized InAs/GaAs quantum dots and laser diodes on In0.2Ga0.8As/GaAs/InGaP quantum wells made in Russia were tested. The voltage noise was analyzed in a wide interval of currents through the diodes. Estimates of the probability density function and semi-invariants of the noise have not revealed any appreciable deviations from the Gauss law. Noise spectra Sv(f)in the range 1 Hz - 20 kHz were analyzed. In most cases the frequency exponent γs of the spectrum is close to one, the Hooge’s parameter αH has magnitude of the order 10-4. The bispectrum Bv(f1,f2of the noise is a complex function of frequencies f1 and f2. Its absolute value is decreasing while moving from the beginning of the frequency plane Of1f2. The decrease along the bisector (f1 = f2 = f) follows the power law characterized by the frequency exponent γB ≈ 1.5 γs. The dependence of the "height" of |Bv(f,f)| on the current through the diode is qualitatively similar to this one for the spectrum. The power law describes these dependences, however the exponents are essentially different.