The Mechanical 3-Paddle Polarization Controller is made by the principle of optical fiber induced  birefringence under the action of external force. The three paddles are equivalent to three kinds of wave  plates ë/4, ë/2, ë/4. The light waves are converted into linearly polarized light through the ë/4 wave  plate, and then the polarization direction is adjusted by the ë/2 wave plate, and finally passes through  the ë/4-wave plate changes the polarization state of linearly polarized light into an arbitrary polarization  state.