The present thesis has been devoted to the study of optical transmissions at 100 Gbps with coherently detected QPSK signals taking advantage of polarization multiplexing. Two di erent systems have been investigated: single carrier and orthogonal double carrier. Numerical simulations have been carried out in order to gain knowledge about the nature and the general behavior of the systems. The performance of both schemes have been systematically compared, detailing the advantages and drawbacks of each system in front of many di erent scenarios. As a starting point, the implementation of a DQPSK system has been accomplished with a twofold objective. First the validation of the models of optical and electrical devices created. Second, the validation of the proper application of the Montecarlo error counting method. The mentioned calibration tests have enabled the author to investigate the novel systems assuring that both the physical models and the performance estimation method were correct.