Filter made of metamaterials

1. A method of fabricating a filter for filtering ultraviolet to infrared electromagnetic radiation, said filter combining:

a first metamaterial having sub-wavelength properties and arranged to provide first filtering of electromagnetic radiation incident at a first angle in a first range of angles; and

a second metamaterial having sub-wavelength properties and arranged to provide second filtering of electromagnetic radiation at a second angle in a second range of angles, wherein the first and second angles are different and the first and second ranges of angles partially overlap and wherein the first metamaterial and second metamaterial are configured as stacked layers of the filter,

wherein the first filtering comprises blocking electromagnetic radiation at a first frequency bandwidth about a first wavelength and the second filtering comprises blocking electromagnetic radiation at a second frequency bandwidth about the first wavelength, wherein the second frequency bandwidth is substantially similar to the first frequency bandwidth and wherein the first and second frequency bandwidths are within the ultraviolet to infrared spectrum, while each of the first and second metamaterials transmit ultraviolet to infrared electromagnetic radiation that is not in the first or second frequency bandwidth about the first wavelength;

wherein the filter is comprised in a film; and

wherein the first metamaterial is a Bragg reflector or a photonic crystal and the second metamaterial is a Bragg reflector or a photonic crystal, the method comprising:

selecting the size, shape, material or configuration of the structural features of the first and/or second metamaterial to provide the correct material properties to achieve said blocking of electromagnetic radiation within the electromagnetic spectrum, wherein the selecting comprises optimising the filter, to improve multi-angle performance, by monitoring optical properties of the combined filter at multiple angles of incidence whilst adjusting the sub-wavelength properties of the first and second metamaterials.

2. A method as claimed in claim 1 wherein the filter is comprised in or on a windscreen.

3. A method as claimed claim 1 wherein the filter is comprised in or on an aircraft cockpit.

4. A method as claimed in claim 1 wherein the filter is passive.

5. A method as claimed in claim 1 wherein the filter appears substantially transparent to the human eye.

6. A method as claimed in claim 1 wherein the first bandwidth and the second bandwidth are 5-10 nm.

7. A method as claimed in claim 1 , wherein the first metamaterial comprises a plurality of structural features having a size in one dimension no greater than the second wavelength of the electromagnetic radiation.

8. A method as claimed in claim 7 , wherein the first and/or the second metamaterial comprises a plurality of dielectric layers and the structural features are the respective thicknesses of the dielectric layers.

9. A method as claimed in claim 7 , wherein the first and/or the second metamaterial comprises an array of material elements and the structural features are the material elements.

10. A method as claimed in claim 8 , wherein a first dielectric layer of the plurality of the plurality of dielectric layers has a first refractive index n 1 and a second dielectric layer in the plurality of dielectric layers has a second, different, refractive index n 2 wherein said first and second dielectric layers form a Bragg reflector.

11. A method as claimed in claim 9 , wherein the material elements are located in or on a surface of a host medium.

12. A method as claimed in claim 11 , wherein the host medium comprises a dielectric material having a relative permittivity of less than or equal to 5.

13. A method as claimed in claim 9 , wherein the plurality of material elements are arranged in a periodic structure in at least two dimensions.