Real-Time Parallel Optical Sampling

Abstract

Real-time parallel optical sampling shows great promise for overcoming the bandwidth limitation of fiber optical communication systems caused by the analog-to-digital converters in electronic sampling oscilloscopes. The basic concept of parallel optical sampling is to split the signal into multiple branches where the branches are delayed with equidistant sampling times. The signal branches are then sampled in the optical domain with a pulse of a few picoseconds and the branches are then detected in a standard fashion. The signal can then be reconstructed and transmission impairments can be compensated for using digital signal processing. In this project, real-time parallel optical sampling with one sample per symbol synchronously sampled has been demonstrated for 25 Gbaud and 50 Gbaud QPSK signals. Since the bandwidth of the analog-to-digital converters used was 16 GHz, the sampling of 50 Gbaud QPSK signals that has been demonstrated is far beyond the capacity for traditional detection. The bit error rate performance at 10^-3 for a back-to-back configuration was found to have a 2.8 dB penalty from the theoretical limit for 25 Gbaud QPSK signals and 2.6 dB penalty for 50 Gbaud QPSK signals. This penalty was most likely due to optical pulse imperfections such as amplitude noise. At 50 Gbaud the OSNR required for a bit error rate of 10^-3 was roughly 15.4 dB.