互易波导模式耦合理论

Reciprocal waveguide coupled mode theory

波导中模式耦合是一种普遍的现象.在光纤通信中不同导模之间的耦合会引起串扰,导模和辐射模的耦合会降低导模的功率.另一方面,利用模式耦合现象能设计出具有特定功能的耦合器和分束器等光学器件.模式耦合在光纤通信和光纤传感中也具有广泛应用.因此,分析研究波导模式如何耦合具有重要的应用价值.模式耦合理论是研究波导中模式耦合的常用方法,不仅提供了一种直观的物理图景来描述光学模式如何杂化,而且还对相关模式如何杂化给出定量评估.近年来,以宇称时间对称性结构为代表的非厄米波导成为研究热点,但传统模式耦合理论在这种情况下不再适用.本文简述了模式耦合理论的发展历史,详细介绍了构造互易波导模式耦合理论的关键概念和方法,进一步回顾了在波导模式耦合理论方面的一系列代表性工作,尤其是手征对称模式耦合理论以及广义模式耦合理论,总结了这些模式耦合理论和传统模式耦合理论之间的联系,最后简单介绍了它们在宇称时间对称波导及各向异性波导中的应用.

Mode coupling is a common phenomenon in waveguides.The mode coupling among different guided modes in fiber-optic communication can cause crosstalk,and the mode coupling of guided mode and radiated mode can reduce the power of the guided mode.Application of mode coupling can guide the design of optical devices such as couplers and beam splitters with specific functions,which have been widely used in fiber optic communication and fiber sensing.So it is important to analyze how waveguide modes are coupled.The coupledmode theory is a common method of studying mode coupling in waveguides.It provides not only an intuitive picture of how the photonic modes are hybridized,but also a quantitative assessment of how the hybridization among those relevant modes evolves.In recent years,non-Hermitian waveguides,represented by parity-time symmetrical structures,have become a research hotspot.However the conventional coupled-mode theory no longer works in this case.In this review,we briefly summarize the development history of coupled-mode theory and introduce the representative work in reciprocal waveguide coupled-mode theory in detail.Then the relationship among several coupled-mode theories is analyzed and their applications are briefly introduced.