Research On Optoelectronic Oscillator Based On Optical Filter

High-quality microwave signal source is the foundation of the microwave application in a wide range of professional fields, such as civil communication, measuring instruments, aerospace, radar, electronic warfare and so on. Microwave photonics, a developing discipline, is the mutual integration of microwave technology and photonic technologies, which meets the need of high-speed transport link in optical fiber. To generate high frequency microwave signal, the traditional technology would face the complex semiconductor process, but the method of photo-generated can work around this situation. Optoelectronic Oscillator,(OEO) simultaneously produces tunable optical and electrical signal independently. More over the phase noise has no relationship with the oscillation frequency. Generally this device emerges the oscillation frequency from several MHz to hundreds of GHz with high Q(quality) values up to 1010.This paper primarily focuses on using optical filter technology to improve the existing optoelectronic oscillator system. In the first section, threshold conditions of the basic single-loop and dual-loop OEO have been discussed. Then we analyze the characteristics of amplitude and phase of the oscillator frequency signal, as well as the noise of the system.In the second section, there are detailed analysis and simulation about the amplitude and frequency of single-loop optoelectronic oscillator based on optical filter Fabry-Perot(F-P) etalon. The F-P etalon had high quality, less influenced by the surrounding temperature, and it had lower phase noise than the electrical filter. But this structure of OEO requires the etalon with extremely high reflectance, and the optical loss is large, which leads to significant increase gain of the amplifier. In order to solve this problem, we proposed a novel dual-loop OEO based on F-P etalon. Dual-loop system provides the additional frequency selection effectively, so F-P etalon’s plated layer reflectance can be reduced, and it also reduces the length of fiber delay line.The last part completes a study on the experiments of optical oscillator:(1) we achieve the oscillation signal with frequency below 10 MHz by using ceramic filters in the basic single loop OEO system.(2) For increasing the frequency of the oscillation, we choose a bandpass filter with 90 MHz center frequency in the standard structure of OEO. As the theoretical analysis the OEO finally produce the same frequency oscillation signal.(3)Finally we got the stable oscillation signal with the optical filter. According to the comb filtering principle, we use a micro-ring coupler to replace the F-P etalon as filter in the OEO system, which was completely without energy storage long fiber. And by using two cascaded optical filter,the side-mode suppression ratio(SMSR) becomes better.(4) Detailed analysis and comparison of the result of these experiments have been exhibited at last.