Zhang Xin, Zhang Jianghua, Yin Ke, Li Yiming, Zheng Xin, Jiang Tian
Opt Express. 2020 Nov 9;28(23):34761-34771. doi: 10.1364/OE.409838.
A sub-100 fs all-fiber broadband optical frequency comb seeded from a 12.5 GHz electro-optic modulated pulse is presented. Combining pulse reshaping, nonlinear mixing with dispersion compensation processes, a frequency comb with the main pulse width of 86 fs was achieved. The frequency comb has a 6 dB spectral bandwidth spanning over 150 nm which corresponding to more than 1500 comb tones. The measured average power of the broadband comb is over 550 mW, and the calculated average power of each comb line is roughly -4 dBm. To illustrate the whole spectral broadening process, a numerical investigation was also brought out, showing a very good match with the experiments. With a delayed self-heterodyne interferometer, the evolutions of the seed comb linewidths and the broadened comb linewidths were measured revealing the same parabolic trend. Specifically, the linewidths of the 20 seed comb lines are less than 10 kHz, while the linewidths of the 400 broadened comb lines are less than 1 MHz. The results also indicate that the nonlinear mixing led to an accumulation of the phase noise with respect to the comb line number, indicating that a low phase noise RF source or phase locking technique is essential to produce ultra-low phase noise broadband electro-optic combs.
本文展示了一种由12.5 GHz电光调制脉冲作为种子源的亚100 fs全光纤宽带光学频率梳。通过结合脉冲整形、非线性混频与色散补偿过程，实现了主脉冲宽度为86 fs的频率梳。该频率梳具有6 dB的光谱带宽，跨度超过150 nm，对应1500多个梳状谱线。测量得到的宽带梳平均功率超过550 mW，计算得出的每条梳状谱线平均功率约为-4 dBm。为了说明整个光谱展宽过程，还进行了数值研究，结果与实验非常吻合。利用延迟自外差干涉仪，测量了种子梳状谱线宽度和展宽后的梳状谱线宽度的演变，揭示了相同的抛物线趋势。具体而言，20条种子梳状谱线的线宽小于10 kHz，而400条展宽后的梳状谱线的线宽小于1 MHz。结果还表明，非线性混频导致相位噪声相对于梳状谱线数量累积，这表明低相位噪声射频源或锁相技术对于产生超低相位噪声宽带电光梳至关重要。
