On the structure and the adjustment of the all-fiber isolator

The working principle of the all-fiber isolator and the decrease of isolation degree caused by some imperfections in real devices are discussed. If the polarization rotating angle of a Faraday rotator is 45° exactly, the maximum isolation degree of the isolator equals the extinction ratio of the polarizer. The authors simplify the analysis by assuming the extinction ratio of the polarizer is infinite, attempting to approach this limit of maximum isolation degree as closely as possible. Analysis and experiment prove that by using two polarization controllers the highest isolation ratio and the smallest insertion loss can be obtained simultaneously. The adjusting principle of the device is also explained