In a device (100) for continuously varying the extinction ratio, ER, a laser diode (102) is connected to a first end of a PZ fiber (108). At a second end, the PZ fiber is connected to a connector (110). At the other end of the connector a PM fiber (106) is connected. The two fibers meet in the connector, which means that opposite end facets of the fibers are located at a very close distance of each other. A rotation is produced by a rotator (104), mechanically coupled to the connector. The device can be used for: selecting a desired ER of the PM fiber; achieving high accuracy of angular alignment between the principal axes of two PM fibers (106, 506); evaluating the quality of angular alignment of a splice between two PM fibers made by a splicer; and setting the adjustment/calibration of a PM fiber.