An optical coupling efficiency detection assembly includes a first housing (520) accommodating a beam splitter (304) and a fiber port (404), a second housing (530) accommodating a ferrule (424) enclosing a monitoring fiber (306), and an attachment block (510) 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 (304) and a fiber port (404) in a first housing (520), providing a ferrule (424) enclosing a monitoring fiber (306) in a second housing (530), and attaching the second housing to the first housing via an attachment block (510) to establish a parfocal arrangement among the beam splitter, the fiber port, and the ferrule.
