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

可见光和紫外光波长的集成光子学使基于单个原子、离子和固体缺陷的量子系统、生物化学光谱学以及神经刺激和探测的应用成为可能。与相对成熟的近红外相比，在可见光和紫外光下运行需要不同的材料平台和设备架构，近红外通信应用已推动了重大发展。缺乏传输这些高能光子的宽禁带材料平台一直是这些短波长集成光子学发展的主要限制因素。该项目开发了一种新的基于薄膜沉积的Hafnia薄膜的紫外和可见光光子学与CMOS兼容的平台，其相对较高的折射率是相对于当前紫外线集成光子学的替代产品氧化铝的关键优势。这一计划探索了通过在薄膜中控制地掺入其他元素来抑制Hafnia结晶的策略，Hafnia结晶一直是实现低光学损失的主要障碍。得到的复合膜保持了哈夫尼亚公司在折射率方面的大部分优势，同时减少了数量级的损失。这项工作进一步探索和开发了材料加工和制造技术，以将这种材料形成低损耗光子器件，并利用原子量子系统中的应用推动的新平台开发了新的光子器件概念。这项工作将使蓝/紫外光波长下的光子学性能显著提高，并且由于所建议平台的CMOS兼容性，能够快速集成到最先进的制造平台中。本科生教育和参与研究是该计划的一个关键组成部分，外展工作也是让K-12学生接触到光学和原子科学和技术方面的前沿工作。该计划探索了优化原子层沉积形成的HfO2/Al_2O_3复合材料的材料损耗和折射率的途径，为这些复合材料开发了纳米加工工艺，以实现光刻定义的纳米光子学，并对所开发的平台进行了详细的表征。与目前最好的替代材料纯Al_2O_3相比，复合材料的高折射率是包括光栅耦合器、光子晶体、微谐振器和有源电声光器件在内的多种光子组件的显著优势。此外，这项工作引入了新的设备架构，利用平台能力来解决应用于原子量子系统的关键挑战。特别是，引入了一种新的概念，使被动集成光子学能够产生健壮的、宽带的纯圆偏振辐射(相对强度99.9%的纯度)。这一概念利用了所开发的平台实现的高折射率对比度，并将在理论上进行追求，并在实验中得到验证。这项工作还探索了利用氢氧化氢的S高指数，通过与块状贝塔硼酸钡的集成，实现蓝光/紫外光并行电光控制的新型混合方案。这项工作为高效集成短波长非线性光学以及蓝光/紫外光集成声光的结构开辟了未来的方向。该计划解决了在扩展量子系统方面的关键挑战，取得了跨越光子材料/加工以及被动和主动光学功能的进步。由于该材料与CMOS制造的兼容性，这项工作将迅速影响用于原子量子系统和更广泛的蓝/紫外线波长的集成光子学。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.