FIELD: optical frequency changing. SUBSTANCE: circuit incorporates input-filter change-over device with input fiber connected through fiber switch passed by input signal in effective direction of multiplexing to wavelength channel filter of wavelength multiplexing/demultiplexing device built up of set of such channel filters, frequency changer passing input signal and laser pumping signal in reverse direction, output filter built up of wavelength channel filter of wavelength multiplexing/demultiplexing device passing output signal in effective direction of demultiplexing which is connected on output end to output fiber. EFFECT: reduced cost of optical frequency changing. 2 cl, 2 dwg
