Research On Microwave Photonic Oscillator

A microwave photonic oscillator(MPO), as a novel microwave signal generator, consists of a laser source and an optoelectronic feedback loop system. In the oscillator, it utilizes the work characteristics of modulator and optical devices to convert light energy into high stability, high spectral purity and low phase noise microwave signals and their phase noise performance independence of oscillation frequency, and can be applied in the fields of radio-over-fiber system, optical signal processing, radar, sensor, electronic warfare systems and modern instrumentation. Therefore, the study of related theories and technical schemes for the MPO are of significance for guidance.In this dissertation, we first analyze the operation principles of the MPO(Yao-Maleki model) and the optical domain dual-loop MPO. Then, through research on the mechanisms of the reconfigurability, frequency tunability and frequency multiplier, several novel schemes are proposed and verified by experiments. The major works and innovations are as follows:1. The work characteristics of the MPO(Yao-Maleki model) are discussed in detail and the relationships between performance indexes(the mode spacing and phase noise) and loop length are given by theoretical analysis and experimental setup. Subsequently, considering the improvement of the side-mode suppression performance and the requirement of future work, we study the optical domain dual-loop MPO and its feasibility of the performance improvement is verified by experiments.2. According to the work mechanism of recirculating delay line(RDL), two reconfigurable MPOs based on double-coupling RDL are presented. Firstly, a reconfigurable MPO using a double-coupling single RDL(DC-RDL) is proposed and demonstrated. In the oscillator, a two-tap microwave photonic filter(MPF), formed by employing the filter response of the DC-RDL and an optical domain dual-loop system which is constructed between dual outputs of the RDL and PBS, is used to realize the selection of the oscillation mode. By changing the loop lengths of the DC-RDL, the MPF can be reconfigurabled and the oscillation frequency of MPO is tuned. Then, on the basis of the first one, a series-coupled double recirculating delay lines(SC-DRDLs) is formed by cascaded a DC-RDL, and the large free spectrum range(the least common multiple of the two DC-RDLs) of the system can be obtained by series characteristics of the SC-DRDLs. Therefore, the side-mode suppression performance can be improved by comparision of the first one. Lastly, the two schemes are verified and compared by experiments3. Through research on the tuning mechanism of MPO, several novel widely tunable MPOs are proposed and the flexible tuning mechanisms of the MPO are further improved. Firstly, a frequency tunable MPO, which employs stimulated Brillouin scattering(SBS) effect from joint operation of an upper single sideband modulated signal and a pump laser, is proposed. By simply adjusting the Brillouin pump wavelength, the oscillation frequency of MPO can be tuned. However, the stability and phase noise performance of the MPO are limited by the SBS effect. Therefore, we propose a frequency tunable MPO based on an all-optical microwave photonic filter(MPF) with dispersion-induced transmission fading. The MPF implemented by using two laser sources and a chirped fiber Bragg grating(CFBG). By changing the wavelength spacing between the two laser sources, a microwave signal with a frequency-tuning range of 4.057 to 8.595 GHz is generated, and its phase noise and stability have greatly enhance. To eliminate the expensive tunable laser, the third scheme, which incorporates a carrier phase-shifted double-sideband modulation(CPS-DSB) system, is presented. Through designing a CPS-DSB system, and combined with a dispersive element, a microwave signal with a frequency-tuning range from 7.235 to 14.05 GHz is generated by simply adjusting the tunable optical delay line. In this scheme, only a wavelength-fixed laser is required and the tuning element is a passive device—tunable optical delay line, and have characteristics of low cost and electricity-friendly.4. Through research on the frequency-multiplying mechanism of MPO, several novel frequency-multiplying MPOs are proposed. Firstly, a frequency-sextupling MPO with joint operation of a MZI(consisting of an optical coupler, a ?-bias Mach-Zehnder modulator, and a polarization beam splitter) and a fiber Bragg grating(FBG) is presented. Therefore, a high-quality frequency-sextupled microwave signal is generated without any electronic microwave filters. Then, a frequency- multiplying MPO with a tunable frequency-multiplication factor is proposed by using the optical domain dual-loop MPO and fiber ring. A detail theoretical analysis is provided, which is verified by experiment. By cascading the fiber ring and carefully adjusting their loop length, a high quality frequency-multiplied microwave signal can be generated and its frequency-multiplication is 2n, where n is the cascade number. The approach features high stability, simple structure and high signal quality.