In this work we present the design, fabrication and characterization of a variable Sagnac Loop Interferometer that can be employed as a tunable mirror. This is a key building block to be included in the implementation of folded devices in order to reduce their footprint. The improvement on the power consumption of variable couplers based on standalone Mach-Zehnder interferometers (MZIs) or MZIs with Sagnac Loop Reflectors is discussed as well. To assess the feasibility of the designed components, several configurations have been implemented in a Silicon Nitride platform and the results obtained are in good agreement with the theoretical developments carried out.