Embodiments herein describe optical interposers that utilize waveguides to detect light. For example, in one embodiment, an apparatus is provided that includes an optical detector having a first layer. The first layer includes at least one of polysilicon or amorphous silicon. The first layer forms a diode that includes a p-doped region and an n-doped region. The apparatus further includes a waveguide optically coupled to the diode and disposed on a different layer than the first layer.