An optical amplification system is described which comprises an optical amplifier and an optical filter. The gain of the optical amplifier is changeable to different gain values. For every one of the gain values, a wavelength-dependent gain curve exists. At least for one of the gain values, the gain curve varies over the wavelength. An apodized long-period grating (LPG) is used as the optical filter. The apodized LPG provides at least one wavelength-dependent attenuation curve which compensates the gain curve varying over the wavelength.