Third harmonic generation of terahertz radiation is expected to occur in monolayer graphene due to the nonlinear relationship between the crystal momentum and the current density. In this work, we calculate the terahertz nonlinear response of graphene inside a parallel-plate waveguide including pump depletion, self-phase, and cross-phase modulation. To overcome the phase mismatching between the pump field and third-harmonic field at high input fields due to self-phase and cross-phase modulation, we design a waveguide with two dielectric layers with different indices of refraction. We find that, by tuning the relative thicknesses of the two layers, we are able to improve phase matching, and thereby increase the power efficiency of the system by more than a factor of two at high powers. With this approach, we find that dispite the loss in this system, for an incident frequency of $2$ THz, we are able to achieve power efficiencies of $75 \%$ for graphene with low Fermi energies of $20$ meV and up to $35\%$ when the Fermi energy is $100$ meV.
Near-Field Coupling of Polypropylene Dielectric Waveguide Routed Near PCB Board at Terahertz Frequencies
School of Integrated Circuits and Electronic, Beijing Institute of Technology（北京理工大学集成电路与电子学院）；State Key Laboratory of Environment Characteristics and Effects for Near-space（临近空间环境特性及效应国家重点实验室）；School of Electronic and Information Engineering, Hebei University of Technology（河北工业大学电子信息工程学院）；Advanced Laser Technology Research Center（先进激光技术研究中心）
Adiabatic following of terahertz surface plasmon-polaritons coupler via two waveguides structure
最近，两篇引人注目的论文[New J. Phys. 21，113004（2019）; IEEE J. Sel. Top. Quantum Electron 27，1（2020）]提出了通过应用相干量子控制的宽带完全转移太赫兹（THz）表面等离子体激元（SPP）波导耦合器-受激拉曼绝热通道（STIRAP）。然而，以前的研究需要三个SPP波导耦合器。本文提出了一种新的宽带全转移太赫兹表面等离子体耦合器的设计，它采用了一种新颖的双波导结构，采用了两态绝热跟随。为了实现这一设计，我们首次在表面等离子体光波导的耦合方程中引入了失谐量。我们相信，这一发现将改善太赫兹通信领域。
