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飞秒光学频率梳的出现使对未知激光的绝对频率测量成为可能，极大地简化了激光绝对频率的量值溯源和比对工作.为了保证测量数值的准确性，飞秒光学频率梳与未知激光的拍频信号fb的信噪比要求大于30 dB.针对碘稳频532 nm激光绝对频率测量的特定需求，以532 nm激光的基频光1064 nm激光的绝对频率测量为着眼点，本文采用303 MHz重复频率的掺Er光纤光学频率梳，首先通过激光放大和光谱展宽技术使光谱覆盖到1 μm波段，然后采用级联掺Yb增益光纤技术，将扩谱后1 μm波段的激光功率进行放大，提高了掺Er光纤光学频率梳扩谱后1 μm波长附近的激光强度.采用碘稳频532 nm激光的基频光作为待测光源与飞秒光学频率梳进行拍频.实验表明，与未经过光谱增强的激光相比，光谱增强后的激光与1064 nm激光拍频信号的信噪比提高了5 dB，保持在35 dB附近.该技术有效地缓解了采用掺Er光纤光梳测量1064 nm激光绝对频率时对直接扩谱所获得的1 μm波长激光的强度要求.
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关键词:
- 掺Er光纤飞秒激光器 /
- 光谱增强 /
- 拍频信号 /
- 光纤光学频率梳
The harmonic optical frequency chain is the only tool for measuring optical frequency till the advent of a femtosecond optical frequency comb (FOFC). However, its disadvantages are obvious, such as high cost, difficult construction, complex usage, and complicated maintenance. The emergence of femtosecond optical frequency combs (FOFCs) makes it possible to measure the absolute frequency of a laser, which greatly simplifies the quantity traceability of the absolute frequency value and comparison, and allows the length unit “m” to be directly traced back to the time unit “s”. The beat note (fb) between an FOFC and a test laser is one of the most important data in measuring absolute frequency of the test laser. In order to ensure the accuracy and reliability of the measurement, the signal-to-noise ratio (SNR) of fb should be above 30 dB at 300 kHz resolution bandwidth. Among the wavelength standards recommended to replicate “meter” (SI), iodine-stabilized 633 nm lasers and iodine-stabilized 532 nm lasers have been widely used. Compared with iodine-stabilized 633 nm lasers, iodine-stabilized 532 nm lasers have the advantages of high stability, high output power, no modulation and fiber coupled output. Therefore, it is of great importance to measure and monitor the absolute frequency of an iodine-stabilized 532 nm laser. Aiming at the specific requirements for absolute frequency measurement of an iodine-stabilized 532 nm laser, the absolute frequency measurement of its fundamental 1064 nm laser has been studied. In this paper, a high-repetition-rate Er-doped femtosecond fiber laser is adopted as an optical source in the system. The repetition rate of the fiber laser is 303 MHz, the output power in the continuous-wave state is 130 mW and the average output power in the mode-locking state is 80 mW. The highest SNR of fb between the comb light and a 1064 nm laser generated by an iodine-stabilized 532 nm laser is only 30 dB due to the low intensity at 1 μm wavelength in the supercontinuum, which just reaches the SNR threshold meeting the counter's working condition. In order to improve the accuracy and reliability of absolute frequency measurement, the technique of cascading an Yb-doped fiber amplifier after spectral broadening is adopted to enhance the spectral intensity at 1 μm wavelength. The experimental results indicate that the SNR of fb between a 1 μm laser after spectral enhancement and a 1064 nm laser is increased by 5 dB and kept at 35 dB for several days, meeting requirements for long-term continuous monitoring. This method can effectively reduce the intensity requirements at 1 μm wavelength when the spectrum is directly broadened in the Er-FOFC.-
Keywords:
- Er-doped fiber femtosecond laser /
- spectral enhancement /
- beat note /
- fiber optical frequency comb
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[15] Chen W, Song Y, Jung K, Hu M L, Wang C Y, Kim J 2016 Opt. Express 24 1347
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[17] Wang S J, Liu B W, Gu C L, Song Y J, Qian C, Hu M L, Chai L, Wang C Y 2013 Opt. Lett. 38 296
[18] Ycas G, Osterman S, Diddams S A 2012 Opt. Lett. 37 2199
[19] Kieu K, Jones R J, Peyghambarian N 2010 Opt. Express 18 21350
[20] Kim Y, Kim Y J, Kim S, Kim S W 2009 Opt. Express 17 18606
[21] Alder F, Diddams S A 2012 Opt. Lett. 37 1400
[22] Klose A, Ycas G, Cruze F C, Maser D L, Diddams S A 2016 Appl. Phys. B 122 77
[23] Liu H, Gong M L, Cao S Y, Lin B K, Fang Z J 2015 Acta Phys. Sin. 64 114210 (in Chinese)[刘欢, 巩马理, 曹士英, 林百科, 方占军2015 64 114210]
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[1] Ma L S, Zucco M, Picard S, Robertsson L, Windeler R S 2003 IEEE J. Sel. Top. Quantum. Electron. 9 1066
[2] Ma L S, Robertsson L, Picard S, Chartier J M, Karlsson H, Prieto E, Windeler R S 2003 IEEE. Trans. Instrum. Meas. 52 232
[3] Millo J, Boudot R, Lours M, Bourgeois P Y, Luiten A N, Coq Y L, Kersalé Y, Santarelli G 2009 Opt. Lett. 34 3707
[4] Peng J L, Ahn H, Shu R H, Chui H C, Nicholson J W 2007 Appl. Phys. B 86 49
[5] Klose A, Ycas G, Maser D L, Diddams S A 2014 Opt. Express 22 28400
[6] Washburn B R, Diddams S A, Newbury N R, Nicholson J W, Yan M F, Jørgensen C G 2004 Opt. Lett. 29 250
[7] Liu H, Cao S Y, Meng F, Lin B K, Fang Z J 2015 Acta Phys. Sin. 64 094204 (in Chinese)[刘欢,曹士英,孟飞,林百科,方占军2015 64 094204]
[8] Liu H, Cao S Y, Meng F, Lin B K, Fang Z J 2015 Laser Phys. 25 075105
[9] Lea S N, Rowley W R C, Margolis H S, Barwood G P, Huang G, Gill P, Chartier J M, Windeler R S 2003 Metrologia 40 84
[10] Eickhoff M L, Hall J L 1995 IEEE Trans. Instrum. Meas. 44 155
[11] Diddams S A, Jones D J, Ye J, Cundiff S T, Hall J L, Ranka J K, Windeler R S, Holzwarth R, Udem T, Hänsch T W 2000 Phys. Rev. Lett. 84 5102
[12] Lin B K, Cao S Y, Zhao Y, Li Y, Wang Q, Lin Y G, Cao J P, Zang E J, Fang Z J, Li T C 2014 Chinese J. Lasers 41 0902002 (in Chinese)[林百科,曹士英,赵阳,李烨,王强,林弋戈,曹建平,臧二军,方占军,李天初2014中国激光41 0902002]
[13] Kharenko D S, Podivilov E V, Apolonski A A, Babin S A 2012 Opt. Lett. 37 4104
[14] Li C, Ma Y X, Gao X, Niu F Z, Jiang T X, Wang A M, Zhang Z G 2015 Appl. Opt. 54 8350
[15] Chen W, Song Y, Jung K, Hu M L, Wang C Y, Kim J 2016 Opt. Express 24 1347
[16] Xie C, Liu B W, Niu H L, Song Y J, Li Y, Hu M L, Zhang Y G, Shen W D, Liu X, Wang C Y 2011 Opt. Lett. 36 4149
[17] Wang S J, Liu B W, Gu C L, Song Y J, Qian C, Hu M L, Chai L, Wang C Y 2013 Opt. Lett. 38 296
[18] Ycas G, Osterman S, Diddams S A 2012 Opt. Lett. 37 2199
[19] Kieu K, Jones R J, Peyghambarian N 2010 Opt. Express 18 21350
[20] Kim Y, Kim Y J, Kim S, Kim S W 2009 Opt. Express 17 18606
[21] Alder F, Diddams S A 2012 Opt. Lett. 37 1400
[22] Klose A, Ycas G, Cruze F C, Maser D L, Diddams S A 2016 Appl. Phys. B 122 77
[23] Liu H, Gong M L, Cao S Y, Lin B K, Fang Z J 2015 Acta Phys. Sin. 64 114210 (in Chinese)[刘欢, 巩马理, 曹士英, 林百科, 方占军2015 64 114210]
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