Dissertation > Industrial Technology > Radio electronics, telecommunications technology > General issues > Basic theory > Microwave and UHF

Tunable Microwave Source Based on Microwave Photonics

Author QiaoYunFei
Tutor ZhangXianMin
School Zhejiang University
Course Electronic Science and Technology
Keywords Microwave photonics Generation of tunable microwave Microchiplaser Optoelectronic oscillator Optical frequency multiplication
Type PhD thesis
Year 2013
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Microwave photonics is an emerging interdisciplinary research area which studies the interaction of microwave and optical signals for applications such as photonic generation, distribution, processing and measurement of microwave/millimeter-wave signal; radio-over-Fiber (RoF) system; optically controlled phased array radar, and so on. As a key technique for microwave photonic system, generation of wideband and tunable microwave signal has attracted great interests in the past few years. With briefly introducing the historical development and main application areas of microwave photonics, this thesis is mainly concerned on the generation of widely tunable microwave/millimeter-wave signal based on microwave photonics, and propose several novel methods both theoretically and experimentally, including microwave source based on optical frequency multiplication (OFM); tunable microwave source based on frequency-doubling optoelectronic oscillator (OEO) and microwave source based on microchip laser.The OFM generation of millimeter wave signal based on optical self-heterodyning, generating high frequency millimeter wave signal through processing low frequency signal in optical domain, has low requirement for device and high cost performance. By configuring a fiber ring resonator combined with an tunable optical filter, a60GHz millimeter wave with six-time frequency multiplication of a lOGHz microwave signal is obtained, while the frequency tenability can be realized by adjusting the frequency of driven signal.The tunable microwave source based on frequency-doubling OEO has excellent phase noise performance. After fully studying the principle of OEO, we first propose a simple realization of frequency-doubling optoelectronic oscillator using a phase modulator and a chirp fiber Bragg grating (CFBG). In this OEO configuration, a phase modulator in combination with an optical filter is working as doubled-sideband phase modulation to produce a frequency-doubling microwave signal, while the CFBG ensures the oscillation of feedback driving signal at fundamental frequency with its dispersion effect. As a result, high quality fundamental signal at8GHz and frequency-doubling signal at16GHz are simultaneously obtained. Furthermore, on the basis of frequency-doubling optoelectronic oscillator mentioned above, removing the CFBG, we introduce Stimulated Brillouin Scattering effect to provides the narrowband filtering and ensure the oscillation of the feedback driving signal at fundamental frequency. By varying the Brillouin pump signal introduced via double sideband-carrier suppression (DSB-CS) modulation, the frequency tunability of the frequency-doubling OEO is realized over a wide range. In experiment, a continuous tunable frequency-doubling signal from21.4GHz to25GHz is generated when the diving signal applied on the intensity modulator is tuned from200MHz to2GHz.The tunable microwave source based on microchip laser, which has the advantages of low cost, compact size, high performance and wideband tenability, and can effectively meet the need of integration for future communication system, is not only a hot spot for research, but also a focus of this thesis. We fully investigating the principle of microchip laser, design and fabricate a composite cavity microchip laser, which consists of Nd.YAG crystal acting as active medium and LiNbO3acting as electro-optical tuning component. Varying the controlling voltage applied on the LiNbO3, a continuously tunable microwave signal can be easily obtained by beating the dual-frequency laser with two orthogonal polarization modes that generated by the intra-cavity birefringence. Because the two optical modes share the same cavity and experience the same phase fluctuations, a good phase noise performance heterodyning signal is expected due to the good phase coherence. This configuration has several unique advantages, such as compact size, flexible integration, wideband tunability, high respond speed and excellent signal quality. In experiment, a widely electrically tunable microwave source with tuning range of14GHz and tuning sensitivity of3.02MHz/V is demonstrated, while the phase noises of14GHz signals is about-82dBc/Hz.

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