增透膜（英语：Anti-reflective coating，AR）是一种表面光学镀层，它通过减少光的反射而增加透过率。在复杂的光学系统中，它可以通过减少系统中的散射光来提高对比度，例如望远镜，这对天文学十分重要。其他方面，增透膜能减少暗处双筒望远镜的闪光。

很多涂层都包括折射率不同的透明的薄膜结构thin film structures with alternating layers of contrasting. 薄膜的厚度决定了其作用的反射光波长。当光线在增透膜上产生二次反射时，会和原反射光发生干涉，从而减弱反射光。而根据能量守恒，光的能量不变。因此当反射光减少时，透射光便增多。这就是增透膜的原理。一般，选择增透膜时需确定波长，如红外线，可见光以及紫外线。

An antireflective or anti-reflection (AR) coating is a type of optical coating applied to the surface of lenses and other optical elements to reduce reflection. In typical imaging systems, this improves the efficiency since less light is lost. In complex systems such as a telescope, the reduction in reflections also improves the contrast of the image by elimination of stray light. This is especially important in planetary astronomy. In other applications, the primary benefit is the elimination of the reflection itself, such as a coating on eyeglass lenses that makes the eyes of the wearer more visible to others, or a coating to reduce the glint from a covert viewer's binoculars or telescopic sight.