Investigation of spectral properties of a DFB laser source

We determine the linewidth characteristic of a DFB laser source by conducting experiments employing a coherent detection setup. We use an instrument grade external semiconductor laser device as the local oscillator and the DFB laser as the signal. We analyze the photocurrent using real-time oscilloscope and RF spectrum analyzer.;We compute the auto-correlation and the power spectral density of the photocurrent. We model the natural width of the DFB and compare the simulated plot with the experiment data. We determine the intrinsic linewidth of the DFB laser source with this plot.;We design a LabView program to record the beat center frequency as a function of time while both the lasers are not modulated. With this data, we determine the slow moving drift and the fast fluctuations of the beat frequency.;With these values, it is possible to improve the stability of the DFB laser by designing a feedback loop that would mitigate the drift in the laser source.