A novel optical inverted bistable switch based on a nonlinear fiber ring resonator (FRR), which contains a semiconductor optical amplifier (SOA) in the loop, have been analyzed and experimentally demonstrated. The optical bistability phenomenon is obtained due to the combined nonlinear effects of the transmission characteristics of the resonator and the SOA's gain property. A complete theoretical analysis and supporting simulations are presented. A working prototype is build using commercial optical components. Experimental results show switching speed in tens of MHz with rising and falling times lower than 10 ns. Limitations in switching speed are caused by the length of the fiber loop. Therefore, improvements in operating frequencies can be increased up to GHz range if the length of the loop is reduced to the order of centimeters.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.