Optoelectronic Oscillator And Its Phase Noise Measurements

With the modern photoelectric information technology widely used and rapid development in the fields of aerospace, radar, communications, instrumentation, electronic countermeasures etc., frequency stability and spectral purity of the signal source have been put forward higher and higher requirements. Phase noise measurement plays an increasingly important role in the research and performance measurement of the oscillators. Compared with the traditional microwave oscillator, optoelectronic oscillator(OEO) using low loss of the modulator and optical fiber can not only convert continuous light into microwave signal with very low phase noise, but also can output a stable optical signal.Firstly, this paper studies the structure, the principle and the performance of the OEOs. Then the commonly used OEO schemes are introduced. Secondly, the frequency stability and phase noise performance of the optoelectronic oscillator are analyzed in detail. Finally, the phase noise measurement methods of OEO are summarized and the advantages and disadvantages of each scheme are compared.According to existing phase noise measurement methods, a practical measurement technique and a new system calibration method have been proposed to measure the phase noise of OEOs. By using optical fiber delay-line, the frequency fluctuations of the source are converted to phase fluctuations. After that, the phase fluctuations are converted to voltage fluctuations via a double-balanced mixer. The phase noise can be obtained by measuring the power spectral density of voltage signal. The relationship between the phase separation and amplitude of the voltage signal is measured by adjusting the variable optical fiber delay-line. Parameters of the system are calculated, and the system is recalibrated. The experimental results show its advantages of low cost, fewer devices required and the capability of measuring various optoelectronic oscillators with different structures and frequencies.