Optical structure for augmented reality display

A method, comprising:

• receiving light at a first input diffractive optical element of a first waveguide;
• diffracting the received light, by the first input diffractive optical element, so that diffracted wavelengths of the light in a first one or more colours are coupled into the first waveguide;
• totally internally reflecting the diffracted wavelengths of the light in the first one or more colours within the first waveguide, so that diffracted wavelengths of the light in a second one or more colours are coupled out of the first waveguide in a direction towards a second waveguide;
• receiving and diffracting, by a first output diffractive optical element of the first waveguide, the totally internally reflected light within the first waveguide in order to couple the totally internally reflected light out of the first waveguide towards a viewer;
• receiving, at a second input diffractive optical element of the second waveguide, diffracted light that is coupled out of the first waveguide by the first input diffractive optical element;
• diffracting, by the second input diffractive optical element, the received light so that diffracted wavelengths of the light in a second one or more colours are coupled into the second waveguide;
• totally internally reflecting the diffracted wavelengths of the light in the second one or more colours within the second waveguide;
• and
• receiving and diffracting, by a second output diffractive optical element of the second waveguide, the totally internally reflected light within the second waveguide in order to couple the totally internally reflected light out of the second waveguide towards a viewer;
• wherein the diffractive optical elements have a period which is a separation of diffractive optical features, and wherein the inverse of the period of the second output diffractive optical element is equal to an inverse of the period of the first input diffractive optical element plus the inverse of the period of the second input diffractive optical element.