Display comprising an optical waveguide and switchable diffraction gratings and method of producing the same

An apparatus for producing an optical display comprising:

• an optical waveguide;
• a first switchable diffractive part arranged adjacent to an external front surface of an input portion of said optical waveguide, said first switchable diffractive part switchable between a diffractive state for diffracting light of a first wavelength and a non-diffractive state, and arranged to receive light and selectively to diffract the light into said optical waveguide;
• a second diffractive part formed on an external rear surface of said input portion of said optical waveguide, said second diffractive part arranged to receive from the first switchable diffractive part diffracted light of said first wavelength and non-diffracted light of a second wavelength other than the first wavelength and to diffract said light of either wavelength to a common angle for guided propagation along the optical waveguide;
• a third diffractive part formed on said external rear surface of an output portion of said optical waveguide, said third diffractive part optically coupled to the second diffractive part via total internal reflection along the optical waveguide and arranged to receive and to diffract light of said first wavelength from the second diffractive part to a first angle for output from the optical waveguide and to receive and to diffract light of said second wavelength from the second diffractive part to a second angle for output from the optical waveguide;
• and
• a fourth switchable diffractive part arranged adjacent to said external front surface of said output portion of said optical waveguide, said fourth switchable diffractive part switchable between a diffractive state for diffracting light of the first wavelength and a non-diffractive state, and arranged to receive and selectively to diffract said light from the third diffractive part into a common angle such that light of the first and second wavelengths occupy the same field of view.