Research On New Optoelectronic Oscillator

In the middle of20century, with the rapid development of wireless communications, optical communications, radar and electronic warfare, aerospace, sensor etc., frequency stability and spectral purity of the microwave source have been more and more important. Therefore, the research on new technologies of the microwave source has drawn great attention around the world. Compared with the conventional microwave oscillator, by utilizing the high-Q of long fibers and selected model characteristic of the filter, optoelectronic oscillator (OEO) not only can generate optical pulse signal with low jitter, but also generate microwave signal with low phase noise.Firstly, the basic principles, structure and performance of the optoelectronic oscillator (OEO) is theoretically analyzed. At the same time, the theoretical analysis and experimental research of coupled optoelectronic oscillator (COEO) is presented. The experimental result shows the oscillation frequency is decided by the length of optical ring cavity. Secondly, a frequency multiplying optoelectronic oscillator (FM-OEO) with nonlinearly-coupled double loops based on two cascaded Mach-Zehnder modulators is proposed, and its theoretical analysis is demonstrated. The phase noise of base band signals and frequency doubling signals are measured. In the experiments, microwave signals at10GHz with-121dBc/Hz phase noise at10kHz offset and20GHz with-112.8dBc/Hz phase noise at10kHz offset are generated. Meanwhile, their side-mode suppression ratios are also evaluated and the maximum ratio of70dB is obtained.Finally, the phase noise improvement program of OEO is designed. By increasing the optical power of the laser source, the input optical power of photodetector (PD) is saturated to prevent influence of the relative intensity noise. Therefore, the phase noise of the microwave signal is reduced because of the relative intensity noise has litter influence on PD.