Song Yunxiang, Hu Yaowen, Zhu Xinrui, Yang Kiyoul, Lončar Marko
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA.
Quantum Science and Engineering, Harvard University, Cambridge, MA, USA.
Light Sci Appl. 2024 Sep 2;13(1):225. doi: 10.1038/s41377-024-01546-7.
Dissipative Kerr solitons from optical microresonators, commonly referred to as soliton microcombs, have been developed for a broad range of applications, including precision measurement, optical frequency synthesis, and ultra-stable microwave and millimeter wave generation, all on a chip. An important goal for microcombs is self-referencing, which requires octave-spanning bandwidths to detect and stabilize the comb carrier envelope offset frequency. Further, detection and locking of the comb spacings are often achieved using frequency division by electro-optic modulation. The thin-film lithium niobate photonic platform, with its low loss, strong second- and third-order nonlinearities, as well as large Pockels effect, is ideally suited for these tasks. However, octave-spanning soliton microcombs are challenging to demonstrate on this platform, largely complicated by strong Raman effects hindering reliable fabrication of soliton devices. Here, we demonstrate entirely connected and octave-spanning soliton microcombs on thin-film lithium niobate. With appropriate control over microresonator free spectral range and dissipation spectrum, we show that soliton-inhibiting Raman effects are suppressed, and soliton devices are fabricated with near-unity yield. Our work offers an unambiguous method for soliton generation on strongly Raman-active materials. Further, it anticipates monolithically integrated, self-referenced frequency standards in conjunction with established technologies, such as periodically poled waveguides and electro-optic modulators, on thin-film lithium niobate.
光学微谐振器产生的耗散克尔孤子，通常称为孤子微梳，已被开发用于广泛的应用，包括精密测量、光频合成以及超稳定微波和毫米波产生，所有这些都可在芯片上实现。微梳的一个重要目标是自参考，这需要倍频程跨度的带宽来检测和稳定梳状载波包络偏移频率。此外，梳状间隔的检测和锁定通常通过电光调制进行分频来实现。薄膜铌酸锂光子平台具有低损耗、强二阶和三阶非线性以及大普克尔效应，非常适合这些任务。然而，在该平台上展示倍频程跨度的孤子微梳具有挑战性，很大程度上是由于强拉曼效应阻碍了孤子器件的可靠制造。在此，我们展示了在薄膜铌酸锂上完全连通且倍频程跨度的孤子微梳。通过对微谐振器自由光谱范围和耗散光谱进行适当控制，我们表明抑制孤子的拉曼效应得到了抑制，并且孤子器件的制造良品率接近100%。我们的工作为在强拉曼活性材料上产生孤子提供了一种明确的方法。此外，它预示着结合薄膜铌酸锂上的周期性极化波导和电光调制器等现有技术，实现单片集成的自参考频率标准。
