LED已经成为头盔液晶显示的主流背光光源，为了提升LED主视角亮度，减小背光模块的体积，对双自由曲面透镜进行了扁平化设计，形成透镜薄膜，仿真结果表明光线透过透镜薄膜后，存在中心亮度升高、光斑缩小的问题。采用反馈优化方法修改了双自由曲面透镜设计时的能量分布，并重新设计了透镜薄膜，仿真结果表明优化后的光斑尺寸从2.3 mm增加到7.1 mm。采用无掩模直写光刻技术制备了两层透镜薄膜，分别包含一个扁平化后的自由曲面。对包含和不包含透镜薄膜的背光模块进行了测试，测试结果表明：包含透镜薄膜的背光模块平均亮度比不包含的提升了18.1%，设计的透镜薄膜可有效提升LED背光亮度，减小背光模块体积。

LED has become a mainstream light source in helmet liquid crystal (LC) display. To increase luminance and decrease backlight unit volume, a flatening design of double free-form surface lens was carried out to form the lens film. The simulation results show that the central luminance increases and the spot size decreases after lights passing through the lens film. The feedback optimization was performed to redefine the power distribution when designing the double free-form surface lens, and the lens film is redesigned. The simulation results illustrate that the spot size increases from 2.3 mm to 7.1 mm after optimization. The designed lens films were prepared by maskless direct-writing lithography, and each film contained a free-form surface. The backlight units with and without the lens films were measured, and the measured results show that the average luminance with the lens film increases by 18.1%. The designed lens film can effectively increase the luminance and decrease the backlight units volume.