| Popis: |
The main purpose of this work was to investigate electrical, optical noise and cross-correlation coefficient of visible light laser diodes and to compare the noise characteristics of LDs of different materials. The experiment was conducted on four multi-mode Fabry–Perot laser diodes: two AlGaInP laser diodes, and two InGaN based laser diodes. All tested semiconductor laser diodes in stable lasing generation have 1/f type of electrical and optical noise in low frequencies. When the mode-hopping occurs, additional Lorentzian type noise adds to the spectrum of fluctuations. In low currents, the non-ideality factor of laser diodes and characteristics of electrical fluctuations can expose defectiveness of diode structure. The analysis shows, that InGaN laser diodes have more defects in the active region and its interface because of In impurities, which help to produce light of shorter wavelength. The cross-correlation coefficient between electrical and optical fluctuations helps us to describe the device quality and proceses in devices structure without destructive methods. For all tested laser diodes positive correlation coefficient occurs in threshold region and is negative in lasing operation. Negative coefficient is related with the defects in the interface of the active layer. AlGaInP laser diodes had peaks of correlation coefficient in all currents above the threshold, InGaN had these peaks only on high currents, these peaks show the occuring mode hopping noise. The results of this experiment reveals that analysis for low frequency spectroscopy of electrical and optical noise is a safe and informative way to describe the quality of laser diodes and their defectiveness. |
