LOW DISTORTION TRANSMISSION OF 802.11a/n SIGNALS IN AMPLIFIED RADIO OVER FIBRE LINKS WITH MODULATOR BIAS OPTIMIZATION

In this work, we study the propagation of an IEEE 802.11a/n compliant signal over an analog optical link employing a Mach-Zehnder modulator, an Erbium doped fibre amplifier and 10 km of standard fibre. We show that, when the bias of the modulator is controlled in order to maximize the received RF power at the end of the link, the link linearity can also be improved. This is due to the interaction between the distortion caused by the Mach-Zehnder and the fibre nonlinearities. We simulate and measure the link intermodulation distortion (ID3) as a function of the modulator bias, showing in which condi-tions it is possible to simultaneously minimize the ID3 and maximize the link gain. Also, we show that the error vector magnitude, an important quality factor of OFDM IEEE 802.11a/n signals, can greatly benefit from the im-proved link linearity. Thus, the bias optimization allows for both higher power and higher quality transmission with respect to standard quadrature biased links. KEY WORDS ROF links, wireless signals on optical link, fibre nonlin-earities, Mach-Zehnder nonlinearities