a high speed optical receiver for receiving a substantially diminished optical signal . an optical amplifier amplifies the diminished optical signal at least several db and an ultra narrow - band filter filters the noise generated in the optical amplifier to produce a filtered amplified optical signal which is detected by a fast response photo detector . in a preferred embodiment the optical amplifier is a semiconductor laser amplifier . in this embodiment a faraday filter provides the ultra narrow - band filtering , virtually eliminating the noise produced by the amplifier . transmitters are described for transmitting information at a wavelength tuned to the ultra narrow - band filters .