Holographic optical element
A holographic optical element (HOE) is a thin film of material that diffracts light according to a certain shape and pattern. It can be used for augmented reality.
A holographic optical element can replicate a lens in an abitrarily thin piece of substrate.[1]
A holographic optical element can replicate a microlens array, and be used to make a much thinner light field display than by using a traditional microlens array.
They have been used in AR glasses by Intel on the Vaunt project and by North for the Focals.[2]