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The invention relates to a detector comprising a multiple quantum well structure operating on interband or intersubband transitions by absorption of radiation having a wavelength λ having a polarization comprising a component perpendicular to the plane of the multiple quantum well structure, a

The invention relates to a detector comprising a multiple quantum well structure operating on interband or intersubband transitions by absorption of radiation having a wavelength λ having a polarization comprising a component perpendicular to the plane of the multiple quantum well structure, and comprising optical coupling means for coupling said radiation, wherein the coupling means comprise a set of first diffractive lamellar features that are distributed along at least a first direction and a set of second diffractive lamellar features that are distributed along at least a second direction, said first and second directions being mutually perpendicular and lying in a plane parallel to the plane of the multiple quantum well structure.

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The invention claimed is: 1. A detector comprising: a multiple quantum well structure operating on interband or intersubband transitions by absorption of radiation having a wavelength λ each quantum well structure comprising: optical coupling means for coupling said radiation, wherein the cou

The invention claimed is: 1. A detector comprising: a multiple quantum well structure operating on interband or intersubband transitions by absorption of radiation having a wavelength λ each quantum well structure comprising: optical coupling means for coupling said radiation, wherein the coupling means comprise a set of first elongate, narrow diffractive lamellar features that are distributed along at least a first direction and a set of second elongate, narrow diffractive lamellar features that are distributed along at least a second direction, said first and second directions being mutually perpendicular and lying in a plane parallel to the plane of the multiple quantum well structure; wherein the first lamellar features and the second lamellar features are distributed so as to form concentric rectangles or squares, the electromagnetic wave detector comprising a multilayer stack produced on a surface of a substrate, said stack comprising the multiple quantum well structure and external layers, the lamellar features being etched within one external layer. 2. The electromagnetic wave detector as claimed in claim 1, wherein the first lamellar features and the second lamellar features have areas of similar dimensions. 3. The electromagnetic wave detector as claimed in claim 1, wherein the first lamellar features and the second lamellar features are distributed about a center of symmetry with a distribution in the form of four quadrants. 4. The electromagnetic wave detector as claimed in claim 1, wherein the etch depth of the lamellar features is around λ/4. 5. The electromagnetic wave detector as claimed in claim 1, wherein the multilayer stack is a stack of layers of the doped GaAs or GaAlAs type, the substrate being of the undoped GaAs type. 6. The electromagnetic wave detector as claimed in claim 5, wherein the multiple quantum well structure is made up of an alternation of doped GaAs layers and doped GaAlAs layers, the external layers being ohmic contact layers based on GaAs more highly doped than the constituent layers of the multiple quantum well structure. 7. The electromagnetic wave detector as claimed in claim 1, wherein it comprises a substrate that is transparent at the wavelength of the incident radiation and a layer that is reflective at said wavelength, said reflective layer being on the surface of the lamellar features so as to make the detector operate in reflection. 8. A matrix detector comprising a matrix of individual detector elements as claimed in claim 1, each individual detector element having a multilayer stack, said stack comprising the multiple quantum well structure and external layers, the lamellar features being etched within one external layer, said individual detector elements being produced on the surface of a common substrate. 9. The electromagnetic wave detector as claimed in claim 2, wherein the first lamellar features and the second lamellar features are distributed about a center of symmetry with a distribution in the form of four quadrants. 10. The electromagnetic wave detector as claimed in claim 2, comprising a multilayer stack produced on the surface of a substrate, said stack comprising the multiple quantum well structure and external layers, the lamellar features being etched within one external layer. 11. The electromagnetic wave detector as claimed in claim 1, comprising a multilayer stack produced on the surface of a substrate, said stack comprising the multiple quantum well structure and external layers, the lamellar features being etched within one external layer. 12. The electromagnetic wave detector as claimed in claim 3, comprising a multilayer stack produced on the surface of a substrate, said stack comprising the multiple quantum well structure and external layers, the lamellar features being etched within one external layer. 13. The electromagnetic wave detector as claimed in claim 4, wherein the multilayer stack is a stack of layers of the doped GaAs or GaAlAs type, the substrate being of the undoped GaAs type. 14. The electromagnetic wave detector as claimed in claim 4, wherein it comprises a substrate that is transparent at the wavelength of the incident radiation and a layer that is reflective at said wavelength, said reflective layer being on the surface of the lamellar features so as to make the detector operate in reflection. 15. The electromagnetic wave detector as claimed in claim 5, wherein it comprises a substrate that is transparent at the wavelength of the incident radiation and a layer that is reflective at said wavelength, said reflective layer being on the surface of the lamellar features so as to make the detector operate in reflection. 16. The electromagnetic wave detector as claimed in claim 6, wherein it comprises a substrate that is transparent at the wavelength of the incident radiation and a layer that is reflective at said wavelength, said reflective layer being on the surface of the lamellar features so as to make the detector operate in reflection. 17. A detector comprising a multiple quantum well structure operating on interband or intersubband transitions by absorption of radiation having a wavelength λ and comprising optical coupling means for coupling said radiation, wherein the coupling means comprise a set of first diffractive lamellar features that are distributed along at least a first direction and a set of second diffractive lamellar features that are distributed along at least a second direction, said first and second directions being mutually perpendicular and lying in a plane parallel to the plane of the multiple quantum well structure; wherein the first lamellar features and the second lamellar features are contiguous so to form spaced concentric rectangular or square annuli.