Microwave signal generator is the key component of modern Radio-Frequency (RF) systems, such as navigation, radar, communications,and electronic warfare. Optoelectronic Oscillator (OEO), a new type of microwave oscillator,is able to directly generate a high-frequency microwave signal with low phase noise. Therefore, OEO is considered a promising solution for high-performance microwave signal generation. Phase noise is one of the vital parameters to evaluate the performance of microwave signal sources,including OEO. To date,a number of Phase Noise Measurement(PNM)methods have been designed and carried out to accurately measure the phase noise of microwave signal sources,including direct spectrum method,phase detector method, and frequency discriminator method. Among these methods,the frequency-discriminator-based PNM method is more attractive since it can eliminate the requirement of a low phase noise reference oscillator. However,the measurement sensitivity of this method is related to the time delay,which is limited by the large loss of electrical cables. Fortunately,a photonic delay line PNM method has been proposed with a high measurement sensitivity, where a section of optical fiber is applied to provide a long-time delay with negligible loss. In recent years,a lot of efforts have been devoted to improving the overall performance of the photonic delay line PNM system. For instance,a microwave photonic phase shifter and microwave photonic mixer have been employed to replace the electrical phase shifter and mixer of a traditional photonic delay line PNM system to extend the operation bandwidth. In addition,digital phase demodulation is adopted to eliminate the calibration procedure. Nevertheless, a problem with most previous photonic delay line-based schemes is that too many discrete electrical and optical components are used, which makes them bulky and leads to considerable coupling loss. Furthermore, the functionality of current photonic delay line PNM systems is relatively homogeneous, with only phase noise measurement,and few solutions with dual-or multi-functionality have been reported. However,during the development,optimization and operation of OEO-based RF systems,especially signal generation systems,it is necessary to develop a low-cost, simple and compact phase noise measurement solution to evaluate the quality of the signal source in time and make corresponding parameter adjustments to optimize its performance. In this paper,we propose a photonics-based dual-functional system that can achieve both microwave signal generation and phase noise measurement using an Electro-absorption Modulated Laser(EML). In this system,an EML-based optoelectronic oscillator module and a phase noise measurement module based on a photonic delay line method are implemented simultaneously. By replacing the laser source and intensity modulator with a single EML,the proposed photonics-based dual-functional system achieves a low cost and simple structure,as well as maintaining high performance. In the proof-of-concept experiment, a 9.952-GHz signal generated by the EML-based OEO has a side mode suppression ratio of 66 dB and a phase noise of -116.53 dBc/Hz@10 kHz, which is over 25 dB lower than that of Anritsu-MG3692B. In addition, the PNM module has a phase noise floor reaching -133.71 dBc/Hz@10 kHz, which is lower than that of the commercial signal source analyzer R&S FSV40. The experimental results show that the dual-functional system is capable of simultaneously generating a highperformance microwave signal and providing a high-sensitivity phase noise measurement solution for both internal and external microwave signals. This solution will facilitate the development,optimization and operation of OEObased RF systems,especially signal generation systems,by evaluating the quality of the signal source in time and making the corresponding parameter adjustments to optimize its performance. Therefore,the proposed scheme is suitable for occasions where a high-performance microwave signal is required,and the phase noise performance of different microwave signals within the system can be monitored at the same time.
