An optical coupling efficiency detection assembly includes a first housing accommodating a beam splitter and a fiber port, a second housing accommodating a ferrule enclosing a monitoring fiber, and an attachment block attaching the first housing to the second housing to establish a parfocal arrangement among the beam splitter, the fiber port, and the ferrule. Further, an assembly method for the optical coupling efficiency detection assembly is disclosed. The assembly method may include providing a beam splitter and a fiber port in a first housing, providing a ferrule enclosing a monitoring fiber in a second housing, and attaching the second housing to the first housing via an attachment block to establish a parfocal arrangement among the beam splitter, the fiber port, and the ferrule.
