Experimental analysis of fibre non-linearity on second harmonic optical microwave radio-over-fibre system

In this study, the authors propose an optical microwave (MW) radio-over-fibre system in which an integrated dual-parallel Mach-Zehnder modulator (DP-MZM) is biased at the maximum transmission biasing point. A single drive Mach-Zehnder modulator, in series with the DP-MZM, is used to modulate the 1 GHz radio frequency data onto the optical carrier. They characterise the efficiency of the practical system in terms of power penalty and error vector magnitude. Two modulation schemes are investigated, namely binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) over fibre spans of 10 and 25 km of standard single mode fibre. The results show that the second-order sideband of MW has the potential to provide error free transmission for BPSK and QPSK. The error free communication system is achieved for BPSK at 10 and 25 km fibre spans at optical launch power (OLP) of 7 dBm, whereas for QPSK, the OLP is ~11 and ~12 dBm for 10 and 25 km fibre spans, respectively.