Development and Testing of DSP Based Format Flexible Coherent Optical Receiver

Abstract: This thesis discusses the digital signal processing techniques used for the demodulation of 4-dimensional optimized optical constellations. Digital signal processing techniques were implemented to develop a receiver for the offline processing of these constellations. Major receiver tasks included chromatic dispersion compensation, polarization de-multiplexing, phase estimation and de-mapping of symbols to bits. After frequency domain blind chromatic dispersion compensation the polarization de-multiplexing was achieved by a 10-tap butterfly filter, which was preset through LMS based adaptation using a training sequence. For the phase error correction, data-aided feedback phase estimation was used. And finally, the bit decisions were made on the principle of Maximum Likelihood Detection. The performance of the receiver was investigated with the help of simulated signals before applying it to the actually received signals: obtained from the experimental setup in the lab. The optical ber link in the experimental setup consisted of 6 spans of 80 kilometers long Standard Single Mode Fiber (SSMF): providing in total 480 km of dispersion uncompensated link. The attenuation of each span was compensated by an Erbium Doped Fiber Amplier (EDFA); which in turn also degrades the OSNR. The receiver performance was optimized for advanced 4D constellations including Polarization Multiplexed QPSK (PM-QPSK), Optimized PM-QPSK (Opt16) and Polarization Multiplexed QAM (POLQAM).