In this work, two different multi-wavelength fiber ring laser configurations have been proposed and experimentally demonstrated. The aim of this paper is to show the versatility of the MUX/DMUX device for designing fiber lasers. That was carried out by enhancing the performance of two intrinsically different fiber lasers: an EDF in single longitudinal-mode (SLM) operation and an ultra-long cavity multi-wavelength Raman laser for remote sensing applications. The main objective of the first experimental setup is to generate SLM emission lines with linewidths as narrow as possible. That was carried out by using the interaction between the reflected signals from the FBGs and the transmitted signal from the corresponding PS-FBG in each transmission band. The second topology consists of a multi-wavelength fiber laser for remote sensing applications by using Raman amplification where sensors located 100 km away from the receiver have been measured. As a remarkable improvement from other remote sensing systems, the sensors can be located at any place of the fiber length and can be monitored simultaneously.