Guiding the Evolution of Microresonator Frequency Combs

非技术光学频率梳是一种革命性的宽带光形式，由大量的颜色组成，这些颜色在频率上精确间隔。自本世纪初发展以来，光学梳在精确测量时间和频率方面取得了显着进步，这对位置和惯性制导至关重要，并且在高速光谱学中对环境传感和呼吸分析等应用非常有用。然而，这些梳子是由专门的激光器产生的，这些激光器相当笨重，这仍然阻碍了它们在许多现实世界中的应用。此外，它们发射的脉冲被限制在相对较低的重复率。其他有前途的应用需要更高的重复频率，如光通信、基于光子学的射频信号处理和某些天文仪器的校准。最近，一种产生光学频率梳的新选择已经出现，基于光与集成光子芯片上的微小“微谐振器”结构的相互作用。这些基于微谐振器的梳状发生器基本上非常小，这为低成本部署提供了新的机会，并提供了更高的重复率，从而提供了与新应用的兼容性。普渡大学的研究将探索克服挑战的方法，将微谐振器产生的光学梳引导到应用所需的稳定和可重复的低噪声状态，并将为研究生和本科生提供与高科技和科学职业相关的高级培训。高质量因数微谐振器的连续波泵浦可以产生间隔几十到几百千兆赫的光频率梳状结构。这种梳状结构是由于光学克尔效应介导的非线性波混合而产生的，通常被称为克尔梳状结构。在一种特别有趣的状态下，梳状结构由腔孤子（更正式地称为耗散克尔孤子）组成，这是一种超短的光脉冲，由于损耗和参数增益之间以及色散和非线性之间的双重平衡，它在微谐振器中传播，具有显著的稳定性。然而，控制非线性动力学以达到期望的稳定运行状态是复杂的。一个复杂的问题是，梳状体在可能转变为稳定的腔孤子状态之前，会经历一个混沌状态；通过混沌导致生成的状态具有很强的不确定性。在跃迁到孤子态时发生的功率瞬变加剧了热光学非线性，这与热光学非线性的竞争带来了进一步的挑战。虽然已经取得了进展，但处理这些问题的控制策略对于理想的芯片级微谐振器设备来说尤其具有挑战性。该项目提出探索两种新方法来指导梳状体在丰富的非线性动态相空间中向所需状态的演化，包括单孤子状态。一种方法研究了所谓的避免混沌轨迹的想法，包括协调操纵泵浦激光功率和频率，以达到稳定的孤子状态，而不经过通常遇到的混沌运行状态。第二种补充方法将探讨最近提出的基于模式相互作用获得单孤子的被动方案。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

NontechnicalOptical frequency combs are a revolutionary form of broadband light consisting of a large number of colors that are precisely spaced in frequency. Since their development in the early part of the new century, optical combs have enabled remarkable advances in precision measurement of time and frequency, which are critical to position and inertial guidance, and in high-speed spectroscopy useful for applications such as environmental sensing and breath analysis. However, these combs are generated from specialized lasers, which are rather bulky, which still hinders their deployment for many real world applications. Furthermore, the pulses they emit are limited to relatively low repetition rates. Substantially higher repetition rates are needed for other promising applications, such as optical communications, photonics-based radio-frequency signal processing, and calibration of certain astronomical instruments. More recently, a new choice for generating optical frequency combs has emerged, based on the interaction of light with tiny "microresonator" structures on integrated photonic chips. These microresonator-based comb generators are fundamentally very small, which offers new opportunities for low cost deployment, and provide much higher repetition rate, which offers compatibility with new applications. Research at Purdue University will explore methods to overcome challenges in guiding the optical combs generated from microresonators into stable and repeatable low-noise states desirable for applications and will provide advanced training to students at the graduate and undergraduate level relevant to careers in high technology and science.TechnicalContinuous-wave pumping of a high quality factor microresonator can give rise to formation of combs of optical frequencies spaced by tens to hundreds of GHz. Such combs arise due to nonlinear wave mixing mediated by the optical Kerr effect and are frequently termed Kerr combs. In a particularly interesting state, the comb comprises cavity solitons (more formally called dissipative Kerr solitons), ultrashort pulses of light that propagate in the microresonator with remarkable stability, thanks to a double balance between loss and parametric gain and between dispersion and nonlinearity. However, controlling the nonlinear dynamics to achieve the desired stable states of operation is complex. One complication is that the comb evolves through a chaotic regime before it potentially switches into a stable cavity soliton state; the passage through chaos leads to strong indeterminacy in the state generated. Competition with thermo-optic nonlinearities that are exacerbated by power transients that occur upon transition into the soliton state cause further challenges. Although progress has been made, control strategies to deal with these issues are particularly challenging for desirable chip-scale microresonator devices. This project proposes to explore two new approaches to guiding the evolution of the comb to desired states, including single soliton states, within the rich, nonlinear dynamical phase space. One approach investigates the idea of a so-called chaos-avoiding trajectory involving coordinated manipulation of pump laser power and frequency to reach stable soliton states without passing through the chaotic operating regime usually encountered. A second complementary approach will explore a recently proposed passive scheme toward obtaining single solitons based on mode interactions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.