butt coupler
The concept of the end face coupler is relatively simple. In this optocoupler, the end faces of two output fibers are directly coupled to the end face of the input fiber.
The structure of such an optical coupler is very simple and known as a Y-coupler. Since the end face of the incoming optical fiber only partially covers the outgoing fibers, losses occur, as well as from the light power not coupled into the optical fibers and from the end face coupling between the imperfect end faces of the fibers.