Optical systems including an optical amplifier and a narrow bandwidth optical filter for removing undesired spontaneous emission. An in-fiber Bragg grating reflector reflects substantially only the input amplified signal back to a circulator port of an optical circulator where the desired amplified signal is coupled from the next circulator port. The undesired emission exits from the grating reflector and is removed from the system. Cascaded grating reflectors are used in a wavelength division multiplexing (WDM) system. A two section narrow band transmission filter with cascaded gratings.
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