Metasurface-controlled holographic microcavities

Optical microcavities confine light to wavelength-scale volumes and are a key component for manipulating and enhancing the interaction of light, vacuum states, and matter. Current microcavities are constrained to a small number of spatial mode profiles. Imaging cavities can accommodate complicated modes but require an externally pre-shaped input. Here, we experimentally demonstrate a visible-wavelength, metasurface-based, holographic microcavity that overcomes these limitations. The micron-scale metasurface cavity fulfills the round-trip condition for a designed mode with a complex-shaped intensity profile and thus selectively enhances light that couples to this mode, achieving a spectral bandwidth of 0.8 nm. By imaging the intracavity mode, we show that the holographic mode changes quickly with the cavity length, and the cavity displays the desired spatial mode profile only close to the design cavity length. When placing a metasurface on a distributed Bragg reflector and realizing steep phase gradients, the correct choice of the reflector's top layer material can boost metasurface performance considerably. The applied forward-design method is readily transferable to other spectral regimes and mode profiles.