Sampled grating DBR lasers for WDM systems

WDM systems tend to be limited to a small number of channels (four to eight), primarily in point to point communication applications. WDM is a very elegant solution for the implementation of new, high capacity optical networks, but even with a small number of WDM channels, the selection of single frequency lasers with the correct wavelengths is a very laborious and costly approach, so the use of optical transmitters that are accurately tuneable over the entire gain spectrum of the EDFA, offers new and exciting possibilities. Sampled grating-DBR (SG-DBR) lasers offer tuning ranges of 50 nm-100 nm, and have as a result received much attention. The SG-DBR laser is operated by current injection into four different sections: the output power level is controlled by the current in the gain section, the wavelength tuning is achieved by the independent control of currents in each of two sampled grating sections, and the additional control of a fourth current in the phase section allows the maximisation of the side mode suppression ratio (SMSR) for each wavelength