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提出了一种新型的基于波长双环路结构的光电振荡器方案. 在此方案中, 利用两个激光器产生两束波长不同的连续光, 分别通过两段长度不同的光纤构成双环路结构, 利用光学游标效应可以获得单一的起振模式. 通过理论分析可知, 不同波长的两束光载波在耦合时, 几乎不会产生随机拍噪声. 实验中, 获得了X波段(8-12 GHz)内频率可调谐的高质量微波信号. 通过测量, 信号的边模抑制比达到60 dB, 相位噪声为-132.6 dBc/Hz@10 kHz. 同时, 利用锁相环技术, 通过光纤拉伸器有效补偿系统的腔长漂移, 因此振荡频率的稳定性得到极大改善. 系统的频率漂移在2 h内小于±84.3 mHz. 另外, 测得的微波线宽为5.3 mHz, Q值在1012量级, 具有很高的谱纯度.Microwave generator is the foundation of all the applications in the area in microwave. It is widely used in electronic systems. Note that, the phase noises in microwave sources them are so important that if the phase noises in them are reduced, the performance of many electronic systems will be significantly improved, such as radar and so on. Optoelectronic oscillators, with a characteristic of ultra-low phase noise, have attracted great attention in recent years. In this paper, a novel scheme of optoelectronic oscillator based on dual-loop structure with different wavelengths is demonstrated. In this structure, two beams of continuous-wave light at different wavelengths, emitted by two lasers separately, are combined together by a wavelength division multiplexer and then are injected into an electro-optical modulator. After injection, the optical carriers at different wavelengths are divided into two paths again by using a second wavelength division multiplexer. The two optical beams at different wavelengths go through two optical fibers of different lengths, and then the two paths are combined together by a third wavelength division multiplexer. This constitutes the dual-loop structure. According to Vernier effects, this dual-loop structure can achieve effective side-mode suppression, since only the modes that satisfy the oscillation conditions of the two loops will be selected. Theoretical work has demonstrated that there are few beating noises when the two optical carriers at different wavelengths are combined. Compared with the scheme of dual-loop optoelectronic oscillator with orthogonal states of polarizations (SOPs), the interference between the two beams with different wavelengths in a wavelength division multiplexer system is much less than those with orthogonal SOPs in polarization-beam splitter/polarization-beam combiner devices. Therefore, the scheme in our experiment can reduce the beating noise due to random interference. Meanwhile, the stability in the dual-loop structure with different wavelengths could be achieved by using ordinary single-mode fiber, instead of adopting polarization maintaining fiber in the dual-loop structure with orthogonal SOPs. Hence, the cost of the system is reduced. In this experiment, the high-quality and tunable microwave signal within the X-band (8-12 GHz) is achieved. The measurement results indicate that the side-mode suppression ratio of the signal is 60 dB and the phase noise is -132.6 dBc/Hz@10 kHz. The loop drift of the system is compensated effectively by a fiber stretcher using phase-loop locked technology and the stability of the RF has been improved greatly. Then the frequency drift in terms of the loop drift in the system becomes less than ±84.3 mHz within 2 h. In addition, the linewidth is measured as 5.3 mHz and the Q-factor is on the order of 1012. Therefore, the signal is of a high spectral purity.
[1] Driscoll M M, Hazzard A C, Opdycke D G 1994 Proceedings of the 48th IEEE International Symposium on Frequency Control Boston, MA, June 1-3, 1994 p647
[2] Wallin T, Josefsson L, Lofter B 2003 Proceedings from the Seventh Symposium on GigaHertz Linkoping, Sweden, November 4-5, 2003 p1
[3] Sun B, Yu J L, Wang J, Miao W, Meng T H, Wang W R, Yang E Z 2012 Chin. J. Lasers 39 0305010 (in Chinese) [孙斌, 于晋龙, 王菊, 苗旺, 孟天晖, 王文睿, 杨恩泽 2012 中国激光 39 0305010]
[4] Pei L, Liu G H, Ning T G, Gao S, Li J, Zhang Y J 2012 Acta Phys. Sin. 61 064203 (in Chinese) [裴丽, 刘观辉, 宁提纲, 高嵩, 李晶, 张义军 2012 物理学报 61 064203]
[5] Wang T, Sang X Z, Yan B B, Ai Q, Li Y, Chen X, Zhang Y, Chen G X, Song F J, Zhang X, Wang K R, Yuan J H, Yu C X, Xiao F, Kamal A 2014 Chin. Phys. B 23 064217
[6] Yao X S, Maleki L 1996 J. Opt. Soc. Am. B 13 1275
[7] Kengo K, Masato Y, Masataka N 2010 IEEE Photon. Technol. Lett. 22 293
[8] Sakamoto T, Kawanishi T, Izutsu M 2006 Opt. Lett. 31 811
[9] Yao X S, Maleki L 2000 IEEE J. Quantum Electron. 36 79
[10] Jiang Y, Yu J L, Wang Y T, Zhang L T, Yang E Z 2007 IEEE Photon. Technol. Lett. 19 807
[11] Gallion P B, Debarge G 1984 IEEE J. Quantum Electron. 20 333
[12] Fan Z F, Dagenais M 1997 IEEE Trans. Microw. Theory Techn. 45 1296
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[1] Driscoll M M, Hazzard A C, Opdycke D G 1994 Proceedings of the 48th IEEE International Symposium on Frequency Control Boston, MA, June 1-3, 1994 p647
[2] Wallin T, Josefsson L, Lofter B 2003 Proceedings from the Seventh Symposium on GigaHertz Linkoping, Sweden, November 4-5, 2003 p1
[3] Sun B, Yu J L, Wang J, Miao W, Meng T H, Wang W R, Yang E Z 2012 Chin. J. Lasers 39 0305010 (in Chinese) [孙斌, 于晋龙, 王菊, 苗旺, 孟天晖, 王文睿, 杨恩泽 2012 中国激光 39 0305010]
[4] Pei L, Liu G H, Ning T G, Gao S, Li J, Zhang Y J 2012 Acta Phys. Sin. 61 064203 (in Chinese) [裴丽, 刘观辉, 宁提纲, 高嵩, 李晶, 张义军 2012 物理学报 61 064203]
[5] Wang T, Sang X Z, Yan B B, Ai Q, Li Y, Chen X, Zhang Y, Chen G X, Song F J, Zhang X, Wang K R, Yuan J H, Yu C X, Xiao F, Kamal A 2014 Chin. Phys. B 23 064217
[6] Yao X S, Maleki L 1996 J. Opt. Soc. Am. B 13 1275
[7] Kengo K, Masato Y, Masataka N 2010 IEEE Photon. Technol. Lett. 22 293
[8] Sakamoto T, Kawanishi T, Izutsu M 2006 Opt. Lett. 31 811
[9] Yao X S, Maleki L 2000 IEEE J. Quantum Electron. 36 79
[10] Jiang Y, Yu J L, Wang Y T, Zhang L T, Yang E Z 2007 IEEE Photon. Technol. Lett. 19 807
[11] Gallion P B, Debarge G 1984 IEEE J. Quantum Electron. 20 333
[12] Fan Z F, Dagenais M 1997 IEEE Trans. Microw. Theory Techn. 45 1296
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