Effect of input impedance mismatch on the large-signal noise figure of microwave photonic links

Abstract

In this paper the effect of mismatch and loss of the input lossy impedance matching network on the noise figure (NF) of microwave photonic links (MWPLs) operating under large radio frequency (RF) signal modulation is theoretically investigated. An intensity-modulation with direct-detection (IMDD) MWPL in which the external modulator is a Mach-Zehnder modulator (MZM) is studied here. The nonlinear input-output relationship of the MZM under large RF signal modulation can lead this link to operate in the nonlinear large-signal regime. The main goal of this paper is to investigate and find the input impedance mismatch conditions for minimizing large-signal NF of MWPLs. To the best of our knowledge, this is the first study on this subject. It is found that large-signal NF of an IMDD MWPL depends on the input impedance mismatch factor and input applied RF power. It is shown that for M≃0.39 the NF can be minimized that is approximately 0.95dB lower compared to the NF at the perfect match (M=1). Regarding a generic optoelectronic oscillator (OEO) containing a MWPL at saturation, the value of this analytical approach is to study the effect of such large-signal NF on the OEO phase noise performance.