A novel, all-optical feedback scheme that allows remote optical gain switching in Er-doped fibre amplifiers is demonstrated. A selected wavelength of the amplified spontaneous emission (ASE) at the output of the amplifier is fed back to the input through an unpumped Er-doped fibre acting as a saturable absorber. Off and on switching of ring lasing (and hence, respectively, on and off switching of the amplifier gain) is achieved by remotely injecting optical control signals at appropriate wavelengths over the transmission fibre. A gain bistability (on-off ratio) of 26 dB at 1530 nm is demonstrated. A switching time of 10-50 ms was observed, inherent to the erbium fluorescence lifetime. This scheme could be useful in directing traffic flow in optical networks.
