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射频调制的脉冲激光是激光雷达探测领域内的一项重要研究内容.根据声光斩波器的强度和频率调制特性，设计了基于频移反馈腔的全光纤射频调制脉冲激光.理论上，建立了基于频移反馈腔的激光外差相干理论模型，并进行了数值仿真.根据理论模型，实验上严格控制频移反馈腔的长度和声光斩波器触发信号的周期，在100 MHz的射频信号驱动下，产生了脉冲宽度110 ns、重复频率约20 kHz的具有最高700 MHz射频调制的脉冲激光（脉内调制激光）；同时微调斩波周期可以实现脉冲前沿或后沿的多样性射频调制.通过改变反馈腔内光纤放大器的输出功率实现了射频调制深度的连续可调，最高达到了0.67.Lidar-radar by using an radio frequency modulated (RF-modulated) laser transmitter is a powerful technique for applications involving remote sensing. The method is based on the use of an optically carried RF signal in order to acquire the merits of both the directivity of the optical beam (lidar) and the accuracy of RF signal processing (radar). Compared with single-frequency coherent lidars, lidar-radars are less sensitive to atmospheric turbulence and the speckle noise induced by target roughness. For long range detection, pulsed operation is usually required because of the high peak power. In order to meet the requirement for long range detection, an RF-modulated pulse train based on an all-fiber frequency shifted feedback loop is proposed in this paper. A continuous-wave single-frequency fiber laser (seed laser) is coupled into a fiber link and an acousto-optic chopper is used as a frequency shifter and beam chopper. A Yb3+-doped fiber amplifier is used to compensate for the loss of the signal in the fiber loop. The pulse duration is determined by the open time of acousto-optic chopper, which is fixed at 110 ns. A square wave generated by an arbitrary waveform generator is used as a trigger signal of the acousto-optic chopper. The RF within the pulse results from the interference of frequency shifed pulse with the seed laser. By inserting a 10 km fiber in the loop and accurately controlling the trigger cycle of the acousto-optic chopper equal to the roundtrip time of the loop, the pulse train generated by acousto-optic chopper can circulate in the loop, leading to the generation of RF-modulated pulse with about 20 kHz repetition rate and 110 ns width. The gain provided by fiber amplifier in the loop partially compensates for the loss. By adjusting the gain of fiber amplifier, the modulation depth of RF within the pulse can be continuously adjusted and the maximum modulation depth is 0.67. We also present an time-delayed scalar interference model which includes the loop length, trigger cycle, frequency-shift, and the gain. According to the theoretical model, the RF-modulated pulse affected by trigger cycle and fiber amplifier is numerically simulated. The experimental results accord well with theoritical predictions. The RF-modulated pulse has the advantage of high pulse-to-pulse coherence, which provides potential applications in lidar-radar detection. Besides, with an additional frequency doubling stage one can obtain a source for underwater detections and communications. Extension of the scheme to the 1.5 μm telecommunication window is straightforwardfor various radio-over-fiber applications.
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Keywords:
- laser with radio frequency-modualtion /
- pulse laser /
- frequency shifted feedback loop /
- modulation depth
[1] Morvan L, Lai N D, Dolfi D, Huignard J P, Brunel M, Bretenaker F, Floch A L 2002 Appl. Opt. 41 5702
[2] Zheng Z, Zhao C M, Zhang H Y, Yang S H, Zhang D H, Yang H Z, Liu J W 2016 Opt. Laser Technol. 80 169
[3] Cheng C H, Lee C W, Lin T W, Lin F Y 2012 Opt. Express 20 20255
[4] Pillet G, Morvan L, Dolfi D, Huignard J P 2008 Proc. SPIE 7114 71140E
[5] Dominicis L D, Collibus M F D, Fornetti G, Guarneri M, Nuvoli M, Ricci R, Francucci M 2009 J. Eur. Opt. Soc. Rapid Pub. 5 10004
[6] Diaz R, Chan S C, Liu J M 2006 Opt. Lett. 31 3600
[7] Ghelfi P, Laghezza F, Scotti F, Serafine G, Capria A, Pinna S, Onori D, Porzi C, Scaffardi M, Malacarne A, Vercesi V, Lazzeri E, Berizzi F, Bogoni A 2014 Nature 507 341
[8] Kao D C, Kane T J, Mullen L J 2004 Opt. Lett. 29 1203
[9] Vallet M, Barreaux J, Romanelli M, Pillet G, Thévenin J, Wang L, Brunel M 2013 Appl. Opt. 52 5402
[10] Brunel M, Vallet M 2008 Opt. Lett. 33 2524
[11] Thenenin J, Vallet M, Brunel M, Gilles H, Girard S 2011 J. Opt. Soc. Am. B 28 1104
[12] Zhang H Y, Brunel M, Romanelli M, Vallet M 2016 Appl. Opt. 55 2467
[13] Kowalski F V, Shattil S J, Halle P D 1988 Appl. Phys. Lett. 53 734
[14] Phillips M W, Liang G Y, Barr J M R 1993 Opt. Commun. 100 473
[15] Sabert H, Brinkmeyer E 1994 J. Lightwave Technol. 12 1360
[16] Guillet d C H, Jacquin O, Hugon O, Glastre W, Lacot E, Marklof J 2013 Opt. Express 21 15065
[17] de Chatellus H G, Lacot E, Glastre W, Jacquin O, Hugon O 2013 Phys. Rev. A 88 033828
[18] Chatellus H G D, Cortés L R, Azaña J 2016 Optica 3 1
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[1] Morvan L, Lai N D, Dolfi D, Huignard J P, Brunel M, Bretenaker F, Floch A L 2002 Appl. Opt. 41 5702
[2] Zheng Z, Zhao C M, Zhang H Y, Yang S H, Zhang D H, Yang H Z, Liu J W 2016 Opt. Laser Technol. 80 169
[3] Cheng C H, Lee C W, Lin T W, Lin F Y 2012 Opt. Express 20 20255
[4] Pillet G, Morvan L, Dolfi D, Huignard J P 2008 Proc. SPIE 7114 71140E
[5] Dominicis L D, Collibus M F D, Fornetti G, Guarneri M, Nuvoli M, Ricci R, Francucci M 2009 J. Eur. Opt. Soc. Rapid Pub. 5 10004
[6] Diaz R, Chan S C, Liu J M 2006 Opt. Lett. 31 3600
[7] Ghelfi P, Laghezza F, Scotti F, Serafine G, Capria A, Pinna S, Onori D, Porzi C, Scaffardi M, Malacarne A, Vercesi V, Lazzeri E, Berizzi F, Bogoni A 2014 Nature 507 341
[8] Kao D C, Kane T J, Mullen L J 2004 Opt. Lett. 29 1203
[9] Vallet M, Barreaux J, Romanelli M, Pillet G, Thévenin J, Wang L, Brunel M 2013 Appl. Opt. 52 5402
[10] Brunel M, Vallet M 2008 Opt. Lett. 33 2524
[11] Thenenin J, Vallet M, Brunel M, Gilles H, Girard S 2011 J. Opt. Soc. Am. B 28 1104
[12] Zhang H Y, Brunel M, Romanelli M, Vallet M 2016 Appl. Opt. 55 2467
[13] Kowalski F V, Shattil S J, Halle P D 1988 Appl. Phys. Lett. 53 734
[14] Phillips M W, Liang G Y, Barr J M R 1993 Opt. Commun. 100 473
[15] Sabert H, Brinkmeyer E 1994 J. Lightwave Technol. 12 1360
[16] Guillet d C H, Jacquin O, Hugon O, Glastre W, Lacot E, Marklof J 2013 Opt. Express 21 15065
[17] de Chatellus H G, Lacot E, Glastre W, Jacquin O, Hugon O 2013 Phys. Rev. A 88 033828
[18] Chatellus H G D, Cortés L R, Azaña J 2016 Optica 3 1
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