Performance evaluation for 64-ary and 16-ary optically pre-amplified PPM systems with Fabry-Pérot filters and finite extinction ratio

In this study, we compare the end-to-end performance of optically pre-amplified 16-ary and 64-ary pulse position modulation (PPM) systems for the use in free-space optical communications. Simulations were carried out to evaluate the bit-error-ratio (BER) versus E_b/N₀ for several scenarios where E_b is the energy per bit and N₀ is the effective single-sided power spectral density of the noise at the amplifier input. For the optimum full width half maximum (FWHM) of the Fabry-Pérot filter combined with the optimal 3-dB bandwidth of the butterworth electrical filter in the presence of dual polarized amplifier noise and no extinction ratio, the required E_b/N₀ = 8.37 dB for 16-ary and E_b/N₀ = 7.1 dB for 64-ary at BER=10^-4. At extinction ratio of 15 dB, the 16-ary PPM system outperforms the 64-ary PPM system with E_b/N₀ = 10.8 dB for 16-ary and E_b/N₀ = 12.64 dB for 64-ary since the orthogonality of the M-ary PPM is not maintained any further. The results also indicate that 16-ary PPM systems are more suitable than 64-ary PPM systems for 10 Gbps inter-satellite optical links.