Low frequency fluctuations and the stabilization in semiconductor laser diodes

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A system for analyzing low frequency light fluctuation is set up with amonochromator (MC50N) and multi-channel detector (Hamamatsu C2326). The multi-channel detector includes a PCD Image Sensor which has 256 sensing elements. The light output of a laser diode is divided into various wavelengths and the light spectral intensities are obtained at various wavelengths. The current noise is also measured. The noises show 1/f spectra. This can explained by the superposition of the Lorentzian spectra. The correlation coefficient between the light and the driving current was calculated from the measured values in single- and multi-mode operations. The optical feedback was carried out to the laser diode and the noise reduction was demonstrated. The mode-hopping noise and mode partition noise would often occur in multi-mode operation on the light output of laser diodes. Employing this analyzing system, more detailed study including the current dependence of the noise will be carried out and the 1/f noise problem should be studied more intensively in the low ferquency range including the other semiconductor devices.