Research On Optoelectronic Oscillator With Frequency Multiplying

With the development of optoelectronic technology and optical communication in the last decades, microwave photonics as a n emerging discipline has attracted widespread attention. And as one branch of microwave photonics, optoelectronic oscillators(OEOs) have also attracted significant attention because they are considered to be one of the effective ways to break through the limit of electrcs. Compared to traditional crystal oscillators, the OEOs are characterized by higher spectral purity, lower phase noise and better frequency stability. However, in the conventional O EO configurations, the frequency of the generated microwave signals is limited by the bandwidth of the electro-optic modulator and electronic filter. Thus it has significant realistic meaning for us to the research on frequency multiplying OEO.In this paper, we first introduce the background of frequency multiplying OEO and explain the purpose of our research. Then we analyze the principle of conventional O EO and study the spectrum and phase noise of the generated microwave signals. In addition, we briefly introduce the principle of electro-optic phase modulator and electro-optic intensity modulator. At last, we propose and demonstrate two schemes of frequency-doubling O EO. They are listed as follows.1. We propose a novel frequency-doubling OEO based on carrier phase-shifted system. In the proposed system, the phase modulator(PM) and a Mach-Zehnder modulator(MZM) operate in parallel, which implements a carrier phase-shifted double sideband(CPS-DSB) modulation to generate a microwace signal at the second- harmonic frequency via photodetector(PD). Meanwhile, the chirp fiber Bragg grating(CFBG) ensures the oscillation of the fundamental frequency signal by rotating the phase between the optical sidebands and the carrier. The proposed OEO is experimentally demonstrated. A self-starting microwave signal at 2.23 GHz and a frequency-doubled microwave signal at 4.30 GHz are simultaneously generated. Moreover, the phase noises and the long-term stability of the generated microwave signals are also investigated.2. We propose a novel frequency-doubling OEO based on destructive interference. In the proposed system, we utlize a cascaded modulator including a phase modulator and an intensity modulator, which implements a carrier-suppressed double-sideband modulation(CS-DSB) based on destructive interference to generate a frequency-doubled microwave signal. Meanwhile, the phase modulator is connected by a CFBG in the loop, which forms a microwave photonic filter to select the fundamental frequency signal in the OEO loop. As a result, a frequency-doubled microwave signal at 17.9 GHz and 20.5 GHz is generated, respectively. The phase noises and the long-term stability of the generated microwave signals are also investigated.