Low tilt, high gain fiber amplifier

An optical transmission system having an optical transmitter and an optical receiver, the system including an optical amplifier, with an input coupling to the transmitter and an output coupling to the receiver, for amplifying an information signal from the transmitter, the amplifier having:

• a doped fiber amplifying medium having an input coupling to the input of the amplifier and an output coupling to the output of the amplifier and exhibiting a gain characteristic and tilt characteristic as a function of length of the fiber, the tilt characteristic having a minimum value;
• a first pump coupling to the input of the amplifying medium, for generating a co-propagating pump signal of a first wavelength;
• a second pump coupling to the output of the amplifying medium, for generating a counter-propagating pump signal of a second wavelength;
• CHARACTERIZED BY:
• a frequency selective reflector, disposed along the amplifying medium to form first and second portion lengths, the reflector being able to reflect substantially all of the counter-propagating pump signal and the ratio of the first portion length to the second portion length being adjusted to shift the tilt characteristic with respect to the gain characteristic so that the minimum value coincides with a region of high gain.