详细介绍了磁流体的光学性质，包括磁流体的热透镜效应、磁光效应、磁流体折射率的可控性以及磁致分色效应。由于磁流体的光学性质具有可调谐性，这为磁流体在新型光子器件与光纤传感器的设计和研究提供了新原理、新材料。论述了应用磁流体设计的多路复用器、光开关、光纤调制器、可调谐磁流体光栅与可调谐滤波器，以及基于磁流体的光纤电流传感器原理和结构。

Magnetic fluid is a new type function material which has unique optical properties, including the thermal lens effect, magneto-optical effect, tunable refractive index and magneto-chromatic effect. Magnetic fluid provides new principle and material to the design and research of the novel photonic devices and optical fiber sensors. Wavelength-division multiplexing, optical switch, optical fiber modulator, tunable grating and filter based on the magnetic fluid are presented. Finally, the principle and structure of the optical fiber current sensors based on the magnetic fluid are analyzed.