Volumetric Optical Integrated Circuit Elements (VOICE)

该研究项目的基本目标是开发一种在硅片体积内形成高性能光子器件的方法，而不是像通常情况下那样在其表面形成高性能光子器件。在电信、计算、数据存储和传输以及消费电子等许多重要应用中，光子器件是不可或缺的。硅光子学使电路小型化和集成化成为可能。如果这些技术能够以足够高的密度成功地集成成多平面光子集成电路(PIC)，那么它们将在速度、密度和能效方面得到显著提高。预计的两个关键社会影响是(1)在下一代计算机内使用在芯片内或芯片之间以3D方式传送光的通道进行超高速数据传输，以及(2)使用具有多个执行操作的平面的PIC进行先进的全光信号处理。该项目还包括对本科生和研究生进行光子器件/电路理论、微制造、计量学和数值模拟方面的培训。研究和教学将通过PI的三门课程紧密结合在一起：纳米技术材料、集成光电子学和实验研究原理。来自代表性不足群体的学生的参与将通过本科生研究和利用现有的大型K-12外展计划来扩大，这些计划将影响超过1000名学生。PI提出了一个概念验证项目，以在硅晶片的体积内实现多个平面的互连的微型光学元件、波导和无源光子器件。亚表面梯度折射率(GRIN)器件将通过双光子光刻技术在多孔硅(PSI)或二氧化硅(PSiO_2=氧化态PSI)中制备，以选择性地聚合多孔硅中的光致抗蚀剂。这种直接激光写入(DLW)方法能够在每个体素处实现索引控制(NPSI=1.4-1.9，nPSiO=1.15-1.3)。复杂的GRIN元件(例如，复合消色差透镜、光子纳米射流发射器、衍射和光子带隙结构、螺旋相位板和折射率/模式匹配竹形锥体)加上传统的硅光子元件(例如，干涉仪、光栅、微环复用器和滤光器)都可以在4英寸晶片上以1微米临界尺寸的自对准方式制造。这项研究旨在推进亚表面制造和光子集成领域的知识。这个由2名PI、2名研究生和2名本科生组成的跨学科团队将利用他们在GRIN PSI和PSiO光学、DLW、光学器件/电路理论和设计、计算电磁学、成像、计量学和纳米制造方面的经验和培训，通过五个主要目标回答关于复杂光学制造的基本科学问题：1.研究和应用基于聚合的折射率控制和光学特性在介孔支架启用的双光子光刻中。测量写入过程的折射率和吸收系数(400-1700 nm)的光谱依赖性以及三维点扩散函数。开发软件工具以：(A)优化3D折射率分布以实现给定的光学功能和(B)确定实现所述分布所需的双光子光刻曝光条件。设计、制造、表征新型梯度折射率元件和亚表面三维光波导，并建立其模型。展示上述单片集成的8平面PIC和光学插入器。演示以前无法实现的光子几何和功能不仅将为未来的PIC架构创建新的范例，还将导致新的科学应用，如芯片实验室、干涉测量、计量学、成像和量子光学。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。

The fundamental goal of this research project is to develop a route to form high performance photonic devices within the volume of a silicon wafer rather than on its surface, as is generally the case. Photonic devices are integral to many important applications in telecommunications, computing, data storage and transfer, and consumer electronics. Silicon photonics has enabled circuits that are miniaturized and integrated. These technologies will dramatically improve in speed, density, and energy efficiency if they can be successfully integrated at a high enough density as a multi-plane photonic integrated circuit (PIC). Two key projected societal impacts are (1) ultra-high speed data transfer within next generation computers using channels that route light in 3D within a chip or between chips and (2) advanced all-optical signal processing using a PIC that has numerous planes for performing operations. The project also includes the training of undergraduate and graduate researchers in photonic device/circuit theory, microfabrication, metrology, and numerical simulation. Research and teaching will be closely integrated through three of the PI's courses: Materials in Nanotechnology, Integrated Optoelectronics, and Principles of Experimental Research. Participation of students from underrepresented groups will be broadened through undergrad research and by leveraging large existing K-12 outreach initiatives that will impact greater than a thousand students.The PIs propose a proof-of-concept project to realize multiple planes of interconnected micro-optic elements, waveguides, and passive photonic devices within the volume of a silicon wafer. Subsurface gradient refractive index (GRIN) devices will be fabricated within porous silicon (PSi) or silica (PSiO2 = oxidized PSi) via two-photon lithography to selectively polymerize photoresist within the porous host. This direct laser writing (DLW) approach enables index control (nPSi = 1.4-1.9, nPSiO2 = 1.15-1.3) at each voxel. Complex GRIN elements (e.g., compound apochromatic lenses, photonic nanojet emitters, diffractive and photonic bandgap structures, spiral phase plates, and index/mode matching bamboo-shaped tapers) plus conventional silicon photonic elements (e.g., interferometers, gratings, and microring multiplexers and filters) can all be fabricated in a self-aligned manner with 1 micron critical dimensions across a 4" wafer. The research seeks to advance knowledge in the fields of subsurface fabrication and photonic integration. The interdisciplinary team of 2 PIs, 2 grad students, and 2 undergrad students will leverage their experience and training in GRIN PSi and PSiO2 optics, DLW, optical device/circuit theory and design, computational electromagnetics, imaging, metrology, and nanomanufacturing to answer fundamental scientific questions about the fabrication of complex optics by addressing five major goals:1. Investigate and apply polymerization-based index control and optical characteristics in mesoporous scaffold-enabled two-photon lithography.2. Measure the spectral dependence of the refractive index and absorption coefficient (400 - 1700 nm) as well as the 3D point spread function of the writing process.3. Develop software tools to: (a) optimize the 3D index profile to achieve a given optical functionality and (b) determine the necessary two-photon lithography exposure conditions to realize said profile.4. Design, fabricate, characterize, and model novel GRIN elements and subsurface 3D waveguides.5. Demonstrate the aforementioned monolithically integrated 8-plane PIC and optical interposer.Demonstration of previously unachievable photonic geometries and functionalities will not only create a new paradigm for future PIC architectures but will also lead to new scientific applications such as lab-in-chip, interferometry, metrology, imaging, and quantum optics.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.