Ultra-wideband achromatism compensator

The invention discloses an ultra-wideband achromatism compensator which comprises a magnesium fluoride crystal waveplate, a quartz crystal waveplate and a sapphire crystal waveplate. According to the assembling structure, the magnesium fluoride crystal waveplate is clamped between the quartz crystal waveplate and the sapphire crystal waveplate, and the optical axes of the three crystal waveplates are all parallel to the light-permeable face. During assembling, the optical axis of the sapphire crystal waveplate and the optical axis of the magnesium fluoride crystal waveplate are parallel to each other and perpendicular to the optical axis of the quartz crystal waveplate. By means of the calculation formula of the waveplates, optimized design is conducted through a mathematic model, thickness parameters of the three crystal waveplates can be obtained, and therefore the effect of the compensator is achieved in the whole waveband from 410 nm to 2600 nm.