Photodetector having a near field concentration

A photodetector comprising:

• an active zone for detecting optical radiation;
• and
• a structure arranged on said active zone, intended for optically coupling the optical radiation, said structure combining the properties of coupling gratings and Bragg gratings and having a defect which, from an incident wave, makes it possible to obtain a plasmon wave which is both coupled and localized in the active zone, said active zone having dimensions which are small compared to those of said structure,
• wherein said active zone has an elongate share and said structure is composed of grooves which are mutually parallel and parallel to the length of the active zone;
• wherein said structure is produced in a layer of at least one dielectric material which is transparent in the spectral range of the optical radiation, said layer comprising a substantially plane lower face in contact with the active zone and an upper face comprising the grooves of the structure, said face being covered with a metal film, and in that the optical thickness of said layer separating the lower face from the upper face along an axis (Ox) perpendicular to the direction of the grooves and parallel to the plane of the lower face varies as the superposition of a coupling grating whose pitch has a first spatial frequency and a second grating whose pitch has a second spatial frequency that is two times the first spatial frequency and which has a central spatial defect.