Frequency domain signal and noise analysis of optoelectronic oscillators under the effects of modulator frequency chirping and fiber dispersion

摘要

The effects of the Mach-Zehnder modulator-induced frequency chirping and optical fiber dispersion on the signal transmission in a microwave photonic link (MWPL) have already been investigated. Here, a more general signal/noise transmission model for MWPLs is introduced. Then a new frequency domain approach utilizing the mentioned model is proposed for analyzing the combined effects of fiber delay line dispersion and modulator frequency chirping on the signal and noise performance of a single-loop optoelectronic oscillator (OEO). It is shown that the dispersion of the fiber delay line and the modulator chirp can largely affect the open-loop gain of the OEO. Consequently they affect the oscillation amplitude such that neglecting them may result in inappropriate adjustment of the small signal gain. Although dispersion of the fiber delay line is the main mechanism through which the laser frequency noise (LFN) contributes to the output phase noise, it is shown that dispersion can reduce the output phase noise due to the noise of the RF amplifier (RFA) up to about 30 dB. In addition, it is shown that a negative chirp results in about 0.5 dB extra reduction of the contribution of the RFA noise in the output phase noise, but for positive chirp values it results in about 15 dB deterioration of noise compared to the dispersion-only case. The chirp effect is negligible for the LFN-induced phase noise. The validity of the new approach is verified by comparing its results with those from other simulation approaches in the literature. (C) 2019 Optical Society of America