一、引言单模光纤定向耦合器是一种重要的无源光器件。它在光纤通信系统的相干光检测、波分复用以及光纤传感器中,都得到了广泛的应用。定向耦合器可分三端(T型和Y型)耦合器,四端(X型)耦合器及多端(星型)耦合器。本文主要讨论X型耦合器。制造X型耦合器的常见方法有光学冷加工法,即磨抛光纤然后横向拼接粘合;光纤扭 I. Introduction Single-mode fiber directional coupler is an important passive optical device. It is widely used in coherent optical detection, wavelength division multiplexing and optical fiber sensors in optical fiber communication systems. Directional couplers are available in three-way (T and Y) couplers, four-way (X-type) couplers and multi-port (star) couplers. This article focuses on the X-type coupler. Common methods of manufacturing X-type coupler are optical cold-working method, that is, grinding and polishing fiber and horizontal splicing and bonding;