An ultra-sensitive optical detector with large time resolution, using a surface plasmon. The optical detector is configured to detect at least one photon, and including a dielectric substrate, and on the substrate, at least one bolometric detection component, that generates an electrical signal from the energy of received photon(s). Additionally, at least one coupling component is formed on the substrate, distinct from the detection component and including a metal component, and generates a surface plasmon by interaction with the photon(s) and guiding the plasmon right up to the detection component, which then absorbs the energy of the surface plasmon.