Influence of optical amplifier on inter-satellite microwave photonics links employing a low-biased Mach-Zehnder modulator

An exact analytical expression of signal-to-noise ratio (SNR) for inter-satellite microwave photonics links using a low-biased Mach-Zehnder modulator, and with both an optical booster amplifier and a preamplifier, is derived with the method of Bessel expansion and Graf's addition theorem. It is observed that the most limitative noise is changed from the thermal noise to the signal-amplifier spontaneous emission beating noise that arises from the optical preamplifier, and the signal power is seen to increase more compared with the power of noise because of optical preamplifier. Thus, the SNR of system configurations with both an optical booster amplifier and an optical preamplifier can be improved compared with the SNR of system configurations with only an optical booster amplifier. For the preamplifier gain of 20 dB and noise figure of 3 dB, an increase of about 19.7 dB in optimum SNR is accessible. In addition, the effect of optical booster amplifier and preamplifier parameters on the optimum DC bias phase shift and SNR is also investigated.