Characterization of wavelength tunable lasers for use in wavelength packet switched networks

Abstract

The telecom industry's greatest challenge, and the optical systems and components vendors' biggest opportunity is enabling providers to expand their data services. The solution lies in making optical networks more responsive to customer needs, i.e., making them more rapidly adaptable. One possible technique to achieve this is to employ wavelength tunable optical transmitters. The importance of tunability grows greater every year, as the average number of channels deployed on DWDM platforms increases. By deploying tunable lasers it is much easier to facilitate forecasting, planning and last minute changes in the network. This technology provides with solution for inventory reduction. It also offers solution for fast switching at packet level. The conducted research activities of the project was divided in two work packages: 1. Full static characterization-the laser used in the experiment was a butterfly-packaged Sampled Grating DBR laser with four electrically tunable sections. LabView programme was developed for distant control of the equipment and the laser itself. The parameters required for creating a look-up table with the exact currents for the four sections of the laser, namely wavelength, side mode suppression ratio and output power, were transferred to tables. Based on those tables the currents were defined for each of the 96 different accessible channels. The channel allocation is based on the 50 GHz spacing grid. A detailed analysis of the tuning mechanisms is provided. 2. Dynamic characterization and BER performance in wavelength packet switched WDM systems-a commercially available module was used supplied with the software package for controlling the wavelength channels and setting the laser to switch between any accessible channel. The laser is DBR laser without SOA integration so the dynamic tunability can be investigated. As the switching in the nanosecond regime is executed in the electrical domain, analysis of the switching parameters concerning the electrical circuit as well as laser structure is provided. The actual switching time was defined. The degradation in system performance due to spurious wavelength signals emitted from the tunable module during the switching event and their interference with other active channels was demonstrated by examining the presence of an error floor in the BER rate against received power measurements