Collaborative Research: All-Optical Fabrication of Low-Loss, High-Index-Contrast, Silicon-in-Silicon Waveguides

职务名称：硅中硅波导的全光制作本项目的目标是开发一种直接激光写入方法，以制作低传播损耗的嵌入硅中的三维（3D）光波导。虽然低损耗的3D波导已经在玻璃内部得到了证明，但到目前为止，硅内部写入的波导的典型损耗要高出一个数量级以上。研究团队面临的两个主要挑战是能量沉积不足和硅内部的随机材料变化，这是通过新的光束传输和对强激光照射下材料响应的基本理解来解决的。在这个项目中开发的直接激光写入方法简化了硅光子器件的制造过程，增加了通信带宽，促进了器件的小型化，并显着增强了片上和芯片到芯片的数据处理能力。该方法具有与选择性湿法蚀刻集成以制造微流体通道的能力，从而能够在单个芯片中集成光子、电子和流体功能。该团队与当地和国家光子行业的紧密联系，通过加快实验室到工厂的过渡，增强了该项目的社会影响力。该研究通过本科生和研究生培训，课堂教学模块和K-12外展活动与教育紧密结合，以促进未来的劳动力发展。该基金支持在受限环境中激光诱导相变的基础研究，目标是在硅（“Si in Si”）内部深处创建低损耗，高折射率对比度，三维（3D）波导。目前的硅中硅波导具有大的损耗和低的折射率对比度，使得它们不适合用于大多数光子学应用中。差的性能是由于在激光聚焦区域中的局部温度驱动的混合Si相组成的微米和纳米尺度的不均匀性。在该项目中，飞秒-纳秒激光脉冲将用于实现向非晶相和高压相转变所需的能量密度。将进行建模、模拟和实验以确定导致结晶稳定的Si相的过渡途径。将制作一个三维分束器作为测试结构，测量其光学性能，并与理论和仿真进行比较。本计画将增进对下列问题的了解：（1）超短激光脉冲在矽中的时空限制，矽具有高度的非线性和强双光子吸收;（2）矽的压力诱导相变，特别是朝向不常见的高压相;以及（3）具有3D结构的波导的光学性能，该奖项反映了NSF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。

Title: All-optical fabrication of “silicon-in-silicon” waveguidesThe goal of this project is to develop a direct laser writing method to produce three-dimensional (3D) optical waveguides embedded inside silicon with low propagation loss. Although low-loss 3D waveguides have been demonstrated inside glass, the typical loss for waveguides written inside silicon so far is more than one order of magnitude higher. Two main challenges faced by the research team are insufficient energy deposition and random material change inside silicon, which are tackled through novel beam delivery and fundamental understanding of material response under intense laser irradiation. The direct laser writing method developed in this project simplifies fabrication procedures for silicon photonic devices, increases communication bandwidth, facilitates device miniaturization, and significantly enhances on-chip and chip-to-chip data processing capabilities. This method has the capability to be integrated with selective wet etching to fabricate microfluidic channels, enabling the integration of photonic, electronic and fluidic functionalities in a single chip. The team’s strong connection with local and national photonics industries enhances the societal impact of the project by expediting lab-to-fab transition with the proposed technology. The research is tightly integrated with education through undergraduate and graduate student training, classroom teaching modules, and K-12 outreach events for future workforce development. This grant supports basic research on laser-induced phase transformation in confined environment, with the goal to create low-loss, high-index-contrast, three-dimensional (3D) waveguides deep inside silicon (“Si-in-Si”). Current Si-in-Si waveguides have large loss and low contrast of refractive indices, making them unsuitable to be used in most photonics applications. The poor performance is due to micro- and nano-scale inhomogeneities consisting of mixed Si phases driven by local temperature in the laser focal region. In this project, femtosecond-nanosecond laser pulses will be used to achieve energy density required for the transition to amorphous and high-pressure phases. Modelling, simulation and experiments will be conducted to identify transition pathways leading to thermodynamically stable Si phases. A 3D splitter will be fabricated as a testing structure and its optical performance will be measured and compared with theory and simulation. This project will advance the understanding of (1) space-time confinement of ultrashort laser pulses in Si which exhibits high nonlinearity and strong two-photon absorption; (2) pressure-induced phase transition of Si, especially toward uncommon high-pressure phases; and (3) optical performance of waveguides with 3D architecture, such as bending radius and mode quality.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.