Performance Evaluation of Optically Preamplified PPM Systems With Dual-Polarized ASE Noise and Finite Extinction Ratios

Pulse position modulation (PPM) presents several advantages in free-space optical systems, unrepeatered fiber transmission, and passive optical networks. In this paper, we study the error performance in direct-detection optically preamplified M-ary PPM optical communication systems. We consider the impact of the amplifier spontaneous emission noise, as well of the finite extinction ratio of the transmitter, on the probability of bit error at the receiver. We derive expressions for the probability of bit error under both assumptions of noise polarization, namely, single- and dual-polarized amplifier noise, and compute it numerically for different symbol sizes M and extinction ratios. In addition, we present the power penalty due to the transmitter finite extinction ratio for systems with and without forward error correction. Our findings show that, in the cases of practically achievable finite extinction ratios, systems with smaller M may perform equally well when compared to those using higher values of M. We also show that there is little benefit, if any, associated with using a polarization filter in the receiver since the additional size, weight, and power consumption requirements outweigh the error performance improvement.