Abstract Optical add-drop multiplexers (OADMs) will play an important role enabling greater connectivity and flexibility in dense wavelength-division multiplexing (DWDM) networks. In this paper, we first, to the best of our knowledge, utilize the Mach–Zehnder fiber Bragg grating (MZ-FBG) based devices with associated optical switches to construct large-dimension OADMs without the need for wavelength demultiplexers and multiplexers at the drop and add ports, respectively. The single- and cascaded-stage MZ-FBGs as the add-drop elements separately in a total of one fixed and two reconfigurable OADM architectures are considered. We investigate the required constitutive elements, and examine the relevant characteristics of system insertion loss and differential system loss for the added, dropped, and passed-through channels. The system power penalty induced by both inter- and intra-band crosstalks, and the required spectral characteristics for the MZ-FBG devices are analyzed. The add-drop dimension limits of these MZ-FBG-based OADMs are estimated. Other related issues such as multiwavelength amplification and bandwidth narrowing for the cascaded OADM chain in DWDM networks are also addressed. These proposed MZ-FBG-based OADMs may find important applications in DWDM systems and networks.