Optoisolators (also referred to as optical couplers, photocouplers, and optocouplers) are optical passive devices that allow light to be transmitted in one direction along the optical path. They are primarily used to suppress reflected waves in optical communication networks. Optoisolators are widely employed in the emission, amplification, and transmission of optical signals. Many optical devices, such as laser diodes and optical amplifiers, are highly sensitive to reflected light from connectors, splices, and filters. If these reflected lights are not mitigated, the performance of the device can deteriorate significantly. Optoisolators are therefore necessary to prevent reflected light from returning to the system. The two main parameters of Optoisolators are insertion loss and isolation. The smaller the insertion loss of forward incident light, the better, and the larger the isolation of reverse reflected light, the better. Currently, the typical value of insertion loss is around 1 dB, and the typical value of isolation is between 40 and 50 dB.