Patent ID: 6839161

Claim:
An optical gain adjuster which receives an optical wavelength multiplexed signal, said optical gain adjuster comprising: i) a rare earth added optical fiber amplifier including a rare earth added optical fiber propagating said optical wavelength multiplexed signal, an excitation light source outputting light for exciting said rare earth added optical fiber and an excitation light source exciting optical combiner for introducing light outputted from said excitation light source to said rare earth added optical fiber; and ii) an adjusting light source, and an adjusting light combiner for said adjusting light source, for introducing light outputted from said adjusting light source into said rare earth added optical fiber amplifier in a direction opposite to a propagating direction of said received optical wavelength multiplexed signal; said rare earth added optical fiber amplifier changing an amplification factor of a light signal in a wavelength band of said light outputted by said adjusting light source included in said optical wavelength multiplexed signal in accordance with an intensity of said light outputted by said adjusting light source.