薄膜光学是光学的一个分支，处理各种很薄的光学材料（薄膜）。和薄膜光学有关的材料，其厚度需要在可见光波长的等级内（约500 nm）。此厚度范围的薄膜因为光的干涉，以及薄膜、空间及物质间的折射率差异，可以有显著的折射特性，这些效应称为薄膜干涉，会影响光学材料折射及传输光的特性，像在肥皂泡及水上的油渍就会看到这类的情形。

更广义具有类似光学性质，但不是平面层状结构的周期性结构称为光子晶体。

在制造上，薄膜层可以由在基质（一般是玻璃）上沉积一层至多层薄膜而产生，一般会用像蒸发或溅射淀积等物理气相沉积方式，或是化学气相沉积法。

Thin-film optics is the branch of optics that deals with very thin structured layers of different materials. In order to exhibit thin-film optics, the thickness of the layers of material must be on the order of the wavelengths of visible light (about 500 nm). Layers at this scale can have remarkable reflective properties due to light wave interference and the difference in refractive index between the layers, the air, and the substrate. These effects alter the way the optic reflects and transmits light. This effect, known as thin-film interference, is observable in soap bubbles and oil slicks.