There are several advantages in using plastic optical fiber in automobiles. Plastic optical fiber for automotive applications can be classified according to two types of applications: those for the passenger compartment and those for the engine room. The two types can be distinguished by their heat resistance and transmission loss properties. The two types of fiber should be installed in places where they would be suitable. In the passenger compartment, a 85°C to 105°C PMMA optical fiber should be used. In the engine room, fiber made of heat-resistant material such as polycarbonate would be ssstable. This paper will describe the properties of optical fibers which can be supplied commercially. It will also describe the properties of optical couplers made through photolithography. In order to incorporate LAN into automobiles, optical components, such as optical couplers, are becoming applicable.