Waveguides

1. A waveguide apparatus, comprising:

a substrate of light transmissive material;

at least one layer arranged within the substrate of material, the layer being arranged to define separate channels within the substrate of material, each channel configured to transmit light of different predefined wavelengths under total internal reflection; and

a grating associated with each channel, wherein each grating is arranged to diffract a portion of light incident thereon out of the substrate of material and to allow the remainder of the light incident thereon to be transmitted in its associated channel under total internal reflection.

2. A waveguide apparatus, as claimed in claim 1 , wherein two layers are arranged within the substrate of material to define three separate channels, and wherein a first channel is arranged to carry light in a red wavelength, a second channel is arranged to arranged to carry light in a green wavelength and a third channel is arranged to carry light in a blue wavelength.

3. A waveguide apparatus, as claimed in claim 1 , wherein at least one filter is arranged to separate light dependent on wavelength prior to transmission within a channel.

4. A waveguide apparatus, as claimed in claim 3 , wherein at least one filter is carried on or within the substrate of material.

5. A waveguide apparatus, as claimed in claim 1 , wherein light is separated dependent on wavelength prior to injection into the substrate of material.

6. A waveguide apparatus, as claimed in claim 1 , wherein each grating is arranged to diffract light out of the substrate of material, and wherein the light is substantially parallel with light diffracted out of the substrate of material by each other grating within another channel.

7. A waveguide apparatus, as claimed in claim 1 , wherein the channels have respective optical elements for injecting image bearing light into the channels, and wherein the optical elements are configured for injecting image bearing light only within respective said predefined wavelengths into the channels and allowing image bearing light outside of those respective predefined wavelengths to pass therethrough.

8. A waveguide apparatus, as claimed in claim 1 , wherein the grating is a holographic optical element.

9. A projection display, for displaying an image to an observer, comprising:

a first waveguide element arranged to be light transmissive;

an image-providing light source device arranged to generate an image and to inject image bearing light into the first waveguide element;

the first waveguide element being arranged to direct the image bearing light internally along the first waveguide element and through which the image bearing light is outputted from the first waveguide element;

a second waveguide element arranged to be light transmissive and transparent and is arranged to receive the image bearing light from the first waveguide element and to direct the image bearing light along the second waveguide element;

the second waveguide element is further arranged to output image bearing light from the second waveguide element towards an observer; and

wherein the first waveguide element includes a substrate of material having at least one layer arranged within the substrate of material, the layer being arranged to define separate channels within the substrate of material, each channel configured to transmit light in different predefined wavelengths and a first grating associated with each channel, wherein each first grating is arranged to diffract a portion of light incident thereon out of the substrate of material and to allow the remainder of the light incident thereon to be transmitted in its associated channel under total internal reflection;

wherein the second waveguide element includes a substrate of material having at least one layer arranged within the substrate of material, the layer being arranged to define separate channels within the substrate of material, each channel configured to transmit light in different predefined wavelengths under total internal reflection and a second grating associated with each channel, wherein each second grating is arranged to diffract light incident thereon to be transmitted in its associated channel under total internal reflection; and

wherein the second waveguide element also includes a third grating associated with each channel, wherein each third grating is arranged to diffract a portion of light incident thereon out of the substrate of material towards the observer and to allow the remainder of the light incident thereon to be transmitted in its associated channel under total internal reflection.

10. A projection display, as claimed in claim 9 , wherein the first waveguide element is plate-like, the second waveguide element is plate-like and the first and second waveguide elements are arranged substantially parallel to one another.

11. A projection display, as claimed in claim 9 , wherein the first waveguide element and the second waveguide element are arranged substantially in the same plane.

12. A projection display, as claimed in claim 11 , wherein the first waveguide element and the second waveguide element are formed within a single piece of material.

13. A projection display, as claimed in claim 9 , wherein the first waveguide element is rod-like, the second waveguide element is plate-like and the first and second waveguide elements are arranged such the image bearing light exits the first waveguide element along a longitudinal axis of the first waveguide element and enters the second waveguide element to propagate along a propagation axis of the second waveguide element.

14. A Head Up Display, or Helmet Mounted Display, or Head Mounted Display including a projection display as claimed in claim 9 .

15. A Head Up Display, or Helmet Mounted Display, or Head Mounted Display including a waveguide apparatus as claimed in claim 9 .