What is a phase difference film? Phase difference film, also called phase difference film, is also called optical compensation film. Here we are discussing thin film products used in the display polarizer industry. There are different optical compensation methods for different liquid crystal display modes, such as TN/STN/IPS/TFT, etc. Liquid crystal molecules have a variety of appearances, such as rod-shaped and disc-shaped, but they all have an optical property, which is the birefringence property. Learn about the birefringence property of crystals.