片上跨倍频程克尔光频梳与时域腔孤子特性的研究

氮化硅微腔结构简单，与CMOS工艺兼容，其通过级联四波混频效应产生的克尔光频梳梳齿间距大、单梳齿功率高，在光通信、光谱分析、微波光子学等领域具有广泛的应用，然而如何获得高相干的跨倍频程克尔光频梳和稳定的时域腔孤子是目前面临的难题。本项目拟研究氮化硅微腔中的跨倍频程克尔光频梳的产生和稳定，研究时域腔孤子形成的机理。设计和加工反常色散氮化硅微腔，改善加工工艺使其Q值达到10^6量级。研究光频梳带宽、相位噪声、振幅噪声与腔色散、泵浦光参数之间的关系。着重研究1-2 μm的跨倍频程高相干的克尔光频梳的产生和时域腔孤子锁模的机理。利用色散波增强光频梳中的长波长分量和f-2f自参考方法实现克尔光频梳偏置频率f0探测，并进行前向反馈锁定。利用电光调制光学分频方法实现200 GHz 重频的探测，并将其锁定至微波频率标准。利用平衡光学互相关技术对腔孤子的时间抖动进行全面的表征。

Kerr frequency comb, generated from the cascaded four-wave-mixing in high-Q microresonators has been extensively studied in recent years, as it has various advantages such as CMOS compatibility, compactness, large comb line spacing and high power per mode etc.. Kerr frequency comb has great prospects in applications for e.g., spectroscopy, WDM communication, microwave photonics etc. However, obtaining coherent octave spanning, self-reference stabilized Kerr frequency comb remains a challenge currently. In this proposal, we will investigate the mode-locking mechanism for cavity soliton and self-reference locking of octave-spanning Kerr frequency comb based on a high Q SiN microresonator. We will design geometry of the waveguide to obtain flattened anomalous dispersion and improve the fabrication quality to make microresonators with Q-factor exceeding 10^6. The dependence of bandwidth, phase noise, amplitude noise of the Kerr frequency comb on the pump condition and cavity parameters will be carefully studied. Then we expect to achieve soliton mode-locking in the microresonator by fine tuning the pump wavelength, while obtaining a coherent Kerr frequency comb spanning from 1 to 2 μm, with comb lines around 2 μm enhanced by dispersive wave emission. The carrier-envelope offset frequency f0 of the Kerr frequency comb will be detected by f-2f self-referencing and locked to an arbitrary microwave frequency through feed-forward locking method. The 200 GHz repetition rate fr will be divided via electro-optical modulation, and locked to a microwave reference by controlling the pump power. As timing jitter affects the stability of the Kerr frequency dramatically, we will fully characterize the timing jitter of the cavity soliton by balanced optical cross-correlation (BOC). We expect to get a self-reference stabilized on-chip Kerr frequency comb, as well as gain insights into the formation and pulse dynamics of few-cycle cavity soliton from this project.