[论文解读] Self-referencing of an on-chip soliton Kerr frequency comb without external broadening

Victor Brasch, Erwan Lucas+3 more|arXiv (Cornell University)|May 9, 2016

Advanced Fiber Laser Technologies参考文献 49被引用 45

一句话总结

该论文展示了无需外部光谱展宽的片上孤子克尔光频梳自参考技术，利用时间域耗散克尔孤子形成及孤子切伦科夫辐射，实现了三分之二倍频程的相干带宽。作者通过连续波转移激光实现2f-3f方案，实现稳定自参考，精确测量并追踪本振激光的光频与频率梳的频偏，证明了片上集成微波至光频梳系统的可行性。

ABSTRACT

Self-referencing turns pulsed laser systems into self-referenced frequency combs. Such frequency combs allow counting of optical frequencies and have a wide range of applications. The required optical bandwidth to implement self-referencing is typically obtained via nonlinear broadening in optical fibers. Recent advances in the field of Kerr frequency combs have provided a path towards the development of compact frequency comb sources that provide broadband frequency combs, exhibit microwave repetition rates and that are compatible with on-chip photonic integration. These devices have the potential to significantly expand the use of frequency combs. Yet to date self-referencing of such Kerr frequency combs has only been attained by applying conventional, fiber based broadening techniques. Here we demonstrate external broadening-free self-referencing of a Kerr frequency comb. An optical spectrum that spans two-thirds of an octave is directly synthesized from a continuous wave laser-driven silicon nitride microresonator using temporal dissipative Kerr soliton formation and soliton Cherenkov radiation. Using this coherent bandwidth and two continuous wave transfer lasers in a 2f-3f self-referencing scheme, we are able to detect the offset frequency of the soliton Kerr frequency comb. By stabilizing the repetition rate to a radio frequency reference the self-referenced frequency comb is used to count and track the continuous wave pump laser's frequency. This work demonstrates the principal ability of soliton Kerr frequency combs to provide microwave-to-optical clockworks on a chip.

研究动机与目标

• 实现无需依赖外部光纤光谱展宽的片上孤子克尔光频梳自参考。
• 证明可通过氮化硅微腔中的孤子动力学实现足够用于自参考的相干光谱展宽。
• 建立完全集成的片上微波至光频梳系统，实现精确光学频率计数。
• 通过与商用频率梳的环外比对，验证频偏频率测量的准确性。
• 利用稳定化的光频梳实现对连续波本振激光频率的精确追踪。

提出的方法

• 将连续波激光耦合进氮化硅微腔，激发时间域耗散克尔孤子，通过孤子切伦科夫辐射生成宽带光频梳。
• 生成的光频梳覆盖三分之二倍频程，带宽足以实现自参考而无需外部展宽。
• 采用两台相位锁定的连续波转移激光（频率分别为150 THz和225 THz）实现2f-3f自参考方案。
• 通过双频与三频转移激光的混频拍频检测测量频偏频率。
• 重复频率被稳定至射频参考源，实现从微波到光频域的相位相干频率计数。
• 通过环外测量将从克尔光频梳推导出的本振激光频率与商用自参考频率梳进行比对，验证精度。

实验结果

研究问题

• RQ1 能否在不依赖外部光谱展宽的前提下实现片上克尔光频梳的自参考？
• RQ2 通过孤子动力学与切伦科夫辐射生成的光谱带宽是否足以支持2f-3f自参考？
• RQ3 能否仅通过集成器件与外部转移激光，实现对片上光频梳频偏频率的高精度测量与稳定？
• RQ4 能否利用自参考光频梳精确追踪连续波本振激光的频率？
• RQ5 该片上系统性能是否可与传统光纤基光频梳相媲美？

主要发现

• 作者成功实现仅依赖内在孤子动力学、无需任何外部光谱展宽的片上集成孤子克尔光频梳自参考。
• 生成的光频梳具有三分之二倍频程的相干带宽，足以支持2f-3f自参考。
• 光频梳的频偏频率测量值约为159.71 GHz，其漂移通过f2f3f拍频信号持续监测。
• 与商用频率梳的环外比对显示极佳一致性，160秒测量中差值呈高斯分布，中心为172 Hz。
• 系统可通过将本振激光的频率漂移映射至光频梳的频偏频率，实现其频率的精确追踪。
• 结果证实了在芯片上实现完全集成、自参考光频梳的可行性，适用于光学计量与微波至光频合成应用。