Song Minhyup, Song Minje, Lim Seungyoung, Choi Hyunjong, Lee Taehyun, Choi Gyudong, Jung Youngjin, Ahn Joon Tae
Photonic/Wireless Devices Research Division, Electronics and Telecommunication Research Institute, Daejeon, 34129, South Korea.
School of Electronics Engineering, Kyungpook National University, Daegu, 41566, South Korea.
Sci Rep. 2022 Oct 27;12(1):18036. doi: 10.1038/s41598-022-22463-y.
In this study, we presented flat-topped coherent supercontinuum lasers with tunable repetition rates and programmable spectral bandwidths. Supercontinuum sources with ultra-broadband and high-repetition-rate coverage can be achieved by merging nonlinearly broadened electro-optic optical frequency combs with optical line-by-line spectrum shaping. Spectral bandwidth programming is implemented by iterative spectrum shaping and input power control of highly nonlinear stages, whereas repetition rate tuning is performed by modulation speed control in optical frequency combs. Herein, we implemented a programmable and tunable flat-topped supercontinuum with a maximum bandwidth and repetition rate of 55 nm at 10 dB and 50 GHz, respectively. To clarify the coherence of the supercontinuum during tuning and programming, we performed a phase-noise analysis. We proposed a remarkably modified self-heterodyne method to measure the phase noise of each mode precisely by filtering specific supercontinuum taps in a Mach-Zehnder interferometer. With this method, it has been proved that the single-sideband spectra in each mode are almost similar to that of the RF clock, indicating that our programmable and tunable supercontinuum generation process added minimal degradation to the phase noise properties. This study shows possibilities for generating hundreds of programmable and tunable flat-topped optical carriers with robustness and coherence.
在本研究中，我们展示了具有可调重复频率和可编程光谱带宽的平顶相干超连续谱激光器。通过将非线性展宽的电光光学频率梳与逐行光谱整形相结合，可以实现具有超宽带和高重复频率覆盖的超连续谱源。光谱带宽编程通过高度非线性阶段的迭代光谱整形和输入功率控制来实现，而重复频率调谐则通过光学频率梳中的调制速度控制来执行。在此，我们实现了一种可编程且可调谐的平顶超连续谱，其在10 dB时的最大带宽为55 nm，重复频率为50 GHz。为了阐明调谐和编程过程中超连续谱的相干性，我们进行了相位噪声分析。我们提出了一种经过显著改进的自外差方法，通过在马赫-曾德尔干涉仪中过滤特定的超连续谱抽头来精确测量每个模式的相位噪声。通过这种方法，已证明每个模式中的单边带光谱几乎与射频时钟的单边带光谱相似，这表明我们的可编程且可调谐超连续谱产生过程对相位噪声特性的降解最小。这项研究展示了生成数百个具有稳健性和相干性的可编程且可调谐平顶光载波的可能性。
