Enhancing Nonlinear Kerr effect in Silicon Nitride Waveguides

通过新兴的CMOS兼容硅光子平台，该平台可以提供更复杂的功能，并将满足需求。克尔非线性是一种可用于各种光信号处理应用的效应，如光采样、参数放大、波长转换等。到目前为止，这种效应已用于光纤，但集成克尔非线性也可以在不久的将来用于信号处理目的。硅波导已经为此目的进行了初步研究，但由于硅中的双光子吸收（TPA）很强，累积的非线性相移仅限于几个弧度。虽然氮化硅的Kerr非线性系数比硅低，但由于其TPA系数要低得多，因此具有提供更多累积非线性相移的潜力。在本项目中，计划最大限度地提高氮化硅波导中克尔效应引起的累积非线性相移。我们将研究慢光结构，以增强结构内部的光场，并提供一个会加剧克尔非线性的减速因子。在各种慢光结构中，我们将考虑波纹波导（一维光子晶体），带线缺陷的二维光子晶体和耦合环形谐振器。此外，还将研究硅和氮化硅的混合组合（因为两者都可以很容易地在CMOS晶圆厂的绝缘体晶圆上使用），以进一步提高Kerr非线性系数。基于大量文献综述的分析模型将用于慢光结构的设计，并进行密集的数值模拟来分析所设计的结构并找出其对制造公差的鲁棒性。设计将准备好并送出胶带，最后将对装配式结构进行表征。我们试图找到结构的最终限制，为在氮化硅波导中使用克尔非线性光信号处理铺平道路。

By emerging CMOS compatible silicon photonics platform, more complex functionalities in this platform can be offered and will be demanded. Kerr nonlinearity is an effect which can be used for various optical signal processing applications like optical sampling, parametric amplification, wavelength conversion, etc. So far, this effect has been used in optical fibers, but integrated Kerr nonlinearity can also be exploited in the near future for signal processing purposes. Silicon waveguides have been initially investigated for this purpose but since two photon absorption (TPA) is strong in silicon, accumulated nonlinear phase shift is limited to a few radians. Although, silicon nitride has lower Kerr nonlinear coefficient than silicon, since it has much lower TPA coefficient, it has the potential to provide more accumulated nonlinear phase shift. In this project, it is planned to maximize the accumulated nonlinear phase shift caused by Kerr effect in silicon nitride waveguides. Slow light structures will be investigated to enhance the optical field inside the structure and provide a slowdown factor which would intensify the Kerr nonlinearity. Among the various slow light structures, we will consider corrugated waveguides (one dimensional photonic crystal), two dimensional photonic crystals with line defect and coupled ring resonators. Also a mixed combination of silicon and silicon nitride (since both can be used easily on silicon on insulator wafers in a CMOS fab) will also be investigated to further enhance Kerr nonlinearity coefficient. Analytical models based on an intensive literature review will be used to prepare the design of the slow light structures and intensive numerical simulations will be performed to analyze the designed structures and find their robustness to fabrication tolerance. The designs will be prepared and sent for tape out and finally the fabricated structures will be characterized. We try to find the ultimate limitations of the structures to pave the way for optical signal processing using Kerr nonlinearity in silicon nitride waveguides.