Patent ID: 8503075

Claim:
An optical focusing device comprising at least one focusing structure including: a metal film provided with at least one aperture that penetrates the film, said aperture having dimensions an order of magnitude smaller than a working wavelength of the focusing device, the at least one focusing structure comprising at least one optical cavity that opens into the aperture or apertures, wherein lateral walls of the aperture being formed by the metal film, wherein the cavity is a hole produced in a thickness of the metal film so as to open into the at least one aperture, the diameter of the cavity being at least three times greater than the dimensions of said aperture and a depth of the cavity being less than the thickness of the metal film, wherein plasmons generated in the cavity by the working wavelength having a wavelength called the plasmon wavelength λ sp , the width of the cavity is substantially equal to an integral number p of half plasmon-wavelengths, and wherein the metal lateral walls of the cavity have a lateral thickness greater than the plasmon wavelength so as to reflect the plasmons present inside the cavity.