The general field of the invention is that of devices for focusing light to subwavelength dimensions including at least one focusing structure having a metal film provided with a first aperture that penetrates the film, the aperture having dimensions an order of magnitude smaller than the working wavelength of the focusing device. In the devices according to the invention, the focusing structure has at least one optical cavity placed around the aperture so that, when the structure is illuminated with a radiant flux at the working wavelength of the device, a large part of this flux is concentrated on the aperture by said cavity. Several embodiments are described using various cavities that may comprise plasmon reflectors.