We present the study of a proof-of-concept integrated device that can be used as a nonlinear broadband isolator. The device is based on the asymmetric loading of a highly-confining silicon-slot photonic coupler with graphene layers, whose ultrafast and low-threshold saturable absorption can be exploited for nonreciprocal transmission between the cross-ports of the coupler. The structure is essentially a non-Hermitian system, whose exceptional points are briefly discussed. The nonlinear device is modeled with a coupled Schrödinger equation system whose validity is checked by full-vector finite element-based beam-propagation method simulations in CW. The numerically computed performance reveals a nonreciprocal intensity range (NRIR) in the vicinity of 100 mW peak power with a bandwidth spanning tens of nanometers, from CW down to ps-long pulses. Finally, the combination of saturable absorption and self-phase modulation (Kerr effect) in graphene is studied, indicating the existence of two NRIR with opposite directionality.

中文翻译：

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基于石墨烯饱和吸收的非互易响应非对称硅槽耦合器


我们提出了可用作非线性宽带隔离器的概念验证集成器件的研究。该器件基于具有石墨烯层的高约束硅槽光子耦合器的不对称负载，其超快和低阈值可饱和吸收可用于耦合器交叉端口之间的不可逆传输。该结构本质上是一个非厄米系统，简要讨论了其特殊之处。该非线性装置采用耦合薛定谔方程组进行建模，其有效性通过连续波中基于全矢量有限元的光束传播方法模拟进行检查。数值计算的性能揭示了 100 mW 峰值功率附近的不可逆强度范围 (NRIR)，带宽跨越数十纳米，从 CW 到 ps 长脉冲。最后，研究了石墨烯中可饱和吸收和自相位调制（克尔效应）的结合，表明存在两个方向性相反的NRIR。