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High-frequency relative intensity noise, mode-suppression ratio and cross-spectra of low-frequency optical and electrical noise were measured in 1.55 /spl mu/m strained-layer multi-quantum-well (MQW) InGaAsP/InP laser diodes, which underwent accelerated aging. The deterioration of the linewidth and side-mode-suppression ratio is accompanied by an increase in the negative correlation between the optical noise and terminal electrical noise in the vicinity of the threshold. This is explained by recombination processes through point defects in some areas of the active layer, which contributes to an intensive Lorentzian noise. An absence of both the Lorentzian noise and negative correlation between optical and electrical fluctuations at threshold indicate higher quality laser operation. It is, therefore, concluded that measurements of the correlation factor could be used as convenient method in laser quality screening.

The optical and electrical low-frequency noise spectra and their correlation factor of multiple quantum well strained-layer Fabry-Perot (F-P) and distributed-feedback (DFB) InGaAsP/InP laser diodes have been investigated as a function of temperature and current. Particular attention has been given to the optical and electrical fluctuations due to mode-hopping effects, which are observed in the F-P lasers at specific currents and temperatures. Both the electrical and optical noise during mode hopping have a Lorentzian type spectrum, and are very strongly correlated and very sensitive to temperature and optical feedback.

The low‐frequency noise characteristics in Bi‐based superconductor thick films have been measured as a function of frequency, temperature, bias current, and applied magnetic field. These results have been compared with the resistance, temperature coefficient of the resistance dependences on temperature, and also with ones of Y‐based thick film superconductor. Our investigation shows that the peak of the voltage noise is not related with the peaks both of the temperature coefficient of the resistance and the voltage‐to‐flux transfer function. We suppose that voltage fluctuations are taking place at grain boundaries (weak Josephson links) between superconducting and normal grains, and that depend on the relative filling of the film by the superconducting grains. We represent a model that explains the resistance fluctuation peak in the superconducting transition temperature region.

We report measurements of low frequency 1/f excess noise for the series of La0.75Sr0.25MnO3 (LSMO) giant magnetoresistive thin epitaxial films with thickness of 42, 50, 100, and 600 Å. Fabricated manganite films experience semiconductor-normal metal (paramagnetic-ferromagnetic) phase transition with the temperature change. The transition manifests itself by the sharp change of resistivity and characteristic peak of magnetoresistivity. Thickness decrease results in lowering the transition temperature and increasing of resistivity. The noise spectra has 1/fa behavior with a ≈ 1± 0.2. The voltage fluctuations spectral density shows quadratic dependence on current indicating that observed noise is caused by the resistance fluctuations. Noise level, temperature coefficient of resisistvity and magnetoresistance increase for thin films. Therefore, the operation point (transition temperature) can be tailored from 330 K to 220 K by changing only the film thickness while the performance of temperature and magnetic field LSMO sensors can be maintained almost constant in thickness range down to 100 Å.