Research For Generating Optical Pulse Based On Regeneratively Mode-Locked Fiber Laser

The highly requirements of the future radar gives rise to several challenges of generation of large bandwidth waveforms and high processing speed and bandwidth. Photonic radar is established based on the microwave photonics technologies, which overcome the electronic bottleneck of traditional microwave systems in processing speed and bandwidth, and also have the advantages of low loss and immunity to electromagnetic interference. Thus photonic radar is an important development direction of the future radar. Stable optical pulses with high quality are important basement of the optical sampling and multi-band signal generation in photonic radar. The optical pulses generated based on the regeneratively mode-locked fiber laser(RMLFL) is a key research topic and well fits with the demand of photonic radar, due to the ability of high coherence, high repetition frequency and low time jitter.The research topic of this paper is optical pulse generation based on stable regeneratively mode-locked fiber laser. Main works are focused on the following aspects:1. Stable pulse trains generation with greatly improved SMSR from a RMLFL by using a polarization maintained dual-loop structure is proposed. The polarization maintained dual-loop structure stabilizes the polarization state in the fiber laser loop and suppresses the side modes simultaneously.The effect of the polarization noise with the system is studied. The RMLFL using the polarization maintained dual-loop structure is experimentally demonstrated. 10-GHz stable optical pulse train is successfully generated and a SMSR as high as 62.2 dB is realized for the modulated output. A phase noise of-107.59 dBc/Hz at 10-kHz offset is realized.2. A stable regeneratively mode-locked fiber laser(RMLFL) using an unpumped erbium-doped fiber(EDF) is proposed. A new structure is designed to form strong standing waves in the unpumped EDF, which enables large spatial hole burning(SHB) effect to improve the side-mode suppression and ensure stable operation.The principle of enhancing the SHB effect based on the unpumped EDF is theoretically and experimentally analyzed. The theoretical model of the optical pulse generation based on the RMLFL is also studied, and the main noise source of the system is analyzed. Based on these, the experimental system of the RMLFL using an unpumped EDF is established. 10-GHz stable optical pulse train is successfully generated and a SMSR of 72.5 dB is achieved for the modulated output. A phase noise of-123.6 dBc/Hz at 10-kHz offset is realized with the modulated RF output.3. A stable regeneratively mode-locked fiber laser based on the loop control technologies. Optical pulses with high quality are generated by controlling the key parameters of the fiber laser loop, such as the loop length.The effects of the key parameters of the fiber laser loop with the quality of the generated optical pulses are theoretically studied. The regeneratively mode-locked fiber laser with the loop length controlled is experimentally demonstrated. Both 10-GHz and 40-GHz stable optical pulse trains are generated with the side mode suppression ratio of 90 and 80 dB, respectively. The phase noise is achieved with-114 dBc/Hz and-102 dBc/Hz at 10-kHz offset for the 10-GHz and 40-GHz modulated RF output, respectively.