This application note deals with the way we measure and analyze the linewidth of Distributed Feedback Lasers (DFBs). The linewidth of the diode stems mainly from intrinsic optical phase and frequency fluctuations caused by spontaneous emission. However, the measured linewidth depends strongly on the current noise and the quality of the measurement setup, both of which differ from lab to lab. This application note is motivated by the fact that there are different methods to measure linewidth and several ways to interpret it, often leading to varying results. By describing our approach we hope to make clear how we determine linewidth.Since the determination of linewidth is relatively sophisticated and time consuming, we carry out this measurement only randomlyon sample DFBs. If you would like the linewidth of your DFB to be measured before shipment, please let us know ahead of time.
