Research On Long-term Stability Of Optoelectronic Oscillator

With the development of information technology, optical communication technology plays an important role in the fields of electronic radar, aerospace, instrument measurement and sensors and so on. Optoelectronic Oscillator (OEO) has the advantages of high Q value, high spectrum purity and low phase noise, is gaining extensive attention of scholars in various countries. The long fiber and radio-frequency filter of OEO are sensitive to the external environment. Improving the frequency stability has important implications for the practical application of OEO.In this paper, the basic principle of OEO is firstly introduced. We analyze the initial conditions, frequency, amplitude, frequency spectrum and phase noise of OEO. The working principles and the characteristics of OEO with different structures are introduced. Meanwhile, the definition and standard of frequency stability of OEO are introduced. Considering the influence of temperature on refractive index of optical fiber and optical fiber length, we analyze the relationship between the OEO’s frequency and temperature. The commonly used methods to improve long-term stability of OEO are introduced, including method of controlling temperature, measuring optical fiber delay time and using principle of phase-locked loop. The basic principle and characteristics of each method are introduced in detail.Finally, a new method for the long-term stability improvement of an OEO is introduced, which is based on a feedback control loop. To achieve the long-term stability, the frequency of OEO is measured with a frequency dividing circuit. Then the length of OEO loop is adjusted with a fiber delay line. The structure of the systems and the basic principle of frequency measurement are introduced in detail. The accuracy of dividing method to measure the frequency of OEO is discussed in theory. An experiment based on a single loop structure shows that the phase noise performance does not deteriorate while the long-term stability of optoelectronic oscillator is effectively improved, and the frequency stability of OEO with feedback control loop is ±0.8ppm over 7 hours.