Hafnia-based platform for high-index visible and UV integrated photonics

可见光和紫外波长的集成光子学支持基于单个原子、离子和固体缺陷、生物化学光谱学以及神经刺激和探测的量子系统的应用。与相对成熟的近红外相比，可见光和紫外波长的操作需要不同的材料平台和器件架构，近红外的通信应用已经推动了显著的发展。缺乏传输这些高能光子的宽带隙材料平台一直是这些短波长的集成光子学发展的主要限制。该项目开发了一种新的cmos兼容的紫外和可见光光子学平台，该平台基于薄膜沉积半氧化铝，其相对较高的折射率是目前替代紫外集成光子学氧化铝的关键优势。本计划探索抑制铪的结晶的策略，这是实现低光学损耗的主要障碍，通过控制其他元素加入到薄膜中。所得到的复合薄膜在折射率方面保持了大部分铪的优势，同时减少了数量级的损失。这项工作进一步探索和发展了材料加工和制造技术，将这种材料模式化成低损耗光子器件，并利用原子量子系统应用的新平台开发了新的光子器件概念。这项工作将在蓝/紫外波长下实现更高性能的光子学，并且由于所提出的平台的CMOS兼容性，可以快速集成到最先进的制造平台中。本科教育和参与研究是该计划的关键组成部分，同时也是让K-12学生接触光学和原子科学与技术领域前沿工作的延伸努力。该项目探索了通过原子层沉积形成的HfO2/Al2O3复合材料的材料损耗和指数优化路线，开发了这些复合材料的纳米制造工艺，以实现光刻定义的纳米光子学，并对开发的平台进行了详细的表征。与目前最好的替代品纯Al2O3相比，复合材料的高折射率是多种光子元件的重要优势，包括光栅耦合器，光子晶体，微谐振器以及有源电光器件和声光器件。此外，本工作引入了利用平台功能的新型器件架构，以解决原子量子系统应用中的关键挑战。特别是，介绍了一个新的概念，使鲁棒，宽带产生纯圆极化辐射（相对强度纯度为99.9%）从被动集成光子学。这一概念利用了高折射率对比度所开发的平台，并将继续在理论和实验中证明。这项工作还探索了新的混合方案，通过与体硼酸钡集成，利用HfO2的高指数实现蓝/紫外平行电光控制。这项工作开辟了高效集成短波非线性光学的未来方向，以及蓝/紫外集成声光学的架构。该计划解决了缩放量子系统的关键挑战，跨越光子材料/加工，以及被动和主动光学功能。由于材料与CMOS制造的兼容性，这项工作将迅速影响原子量子系统和更广泛的蓝/紫外波长的集成光子学。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。

Integrated photonics at visible and ultraviolet wavelengths stand to enable applications spanning quantum systems based on individual atoms, ions, and defects in solids, bio-chemical spectroscopy, and neural stimulation and probing. Operation at visible and ultraviolet wavelengths requires different material platforms and device architectures as compared to the comparatively mature near infrared, where communications applications have spurred significant development. The lack of wide-bandgap materials platforms transmissive to these high energy photons has been a major limitation on development of integrated photonics at these short wavelengths. This program develops a new CMOS-compatible platform for ultraviolet and visible photonics based on thin-film deposited hafnia, whose relatively high refractive index is a critical advantage over the current alternative for ultraviolet integrated photonics, alumina. This program explores strategies to inhibit crystallization of hafnia, which has been a major obstacle to realization of low optical losses, by controlled incorporation of other elements into films. The resulting composite films maintain the bulk of hafnia's advantage in refractive index, while reducing losses by orders of magnitude. The work further explores and develops materials processing and fabrication techniques to pattern this material into low-loss photonic devices, and develops novel photonic device concepts leveraging the new platform motivated by application in atomic quantum systems. This work will enable significantly higher performance photonics at blue/UV wavelengths, and due to the CMOS compatibility of the proposed platform, enables rapid integration into state-of-the-art manufacturing platforms. Undergraduate education and participation in the research is a key component of the program, as are outreach efforts exposing K-12 students to cutting-edge work happening in optical and atomic science and technology. The program explores routes to optimizing material loss and index in HfO2/Al2O3 composites formed by atomic layer deposition, develops nanofabrication processes for these composites to enable lithographically defined nanophotonics, and pursues detailed characterization of the developed platform. The high refractive index of the composite material as compared to the current best alternative, pure Al2O3, is a significant enabling advantage for multiple photonic components including grating couplers, photonic crystals, microresonators, and active electro- and acousto-optic devices. Furthermore, this work introduces novel device architectures leveraging the platform capability to address key challenges in application to atomic quantum systems. In particular, a novel concept is introduced to enable robust, broadband generation of pure circularly polarized radiation (99.9% purity in relative intensity) from passive integrated photonics. This concept takes advantage of the high refractive index contrast enabled by the developed platform, and will be pursued in theory and demonstrated in experiment. The work also explores novel hybrid schemes for blue/ultraviolet parallel electro-optic control enabled by HfO2’s high index, via integration with bulk beta barium borate. This work opens future directions in efficient integrated short-wavelength nonlinear optics, as well as architectures for integrated acousto-optics in the blue/ultraviolet. The program addresses key challenges in scaling quantum systems, with advances spanning photonic materials/processing, as well as in passive and active optical functionalities. Due to the material's compatibility with CMOS fabrication, this work stands to rapidly impact integrated photonics for atomic quantum systems and at blue/ultraviolet wavelengths more broadly.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.