An optical fused coupler is a passive device used in optical fiber systems to combine or split optical signals with high precision. It operates on the principle of light wave interference and is capable of fusing two or more fibers together to form a single, integrated output. Unlike transformers or capacitors, which can only transfer AC signals across the isolation barrier, optocouplers can. Definition: An optocoupler or optoelectronic coupler is an electronic component that basically acts as an interface between the two separate circuits with different voltage levels. For this coupling to take place cumulatively over a substantial length, the light must. 1)The working principle of optical coupler is that the photo-coupler produces optical current due to photoelectric effect, which is induced from the output of the photon and realizes the conversion of electro-light-one-electricity. The objective of this paper is to provide a review of the theory, techniques, and applications of optical.