A wavelength tunable device for operating on at least a portion of energy propagating through a waveguide is disclosed. The locking is caused by at least one tongue element which is connected to one of the elements in an articulated manner and which can be pivoted during the joining motion behind a locking edge of the adjacent element, said locking edge extending essentially in the horizontal direction. Preferred embodiments employ a dual-acting valve selectively to control the flow of gas or suction which valve is capable of simultaneously varying flow from a source and the venting of that flow to atmosphere. In the meantime, since the replacing mode of the cover plate is simple, convenient, and fast, thereby, the invention can improve the users’ working efficiency to meet the humanized requirement.