Method of manufacturing a diffractive grating
The invention relates to a method of manufacturing a diffractive grating. The method comprises providing a first substrate and manufacturing onto the first substrate a first surface profile using temporary grating material. Next, the first surface profile is covered entirely by a layer of final grating material and a second substrate is bonded onto the final grating material. Finally, the first substrate and the temporary grating material are removed for producing on the final grating material a second surface profile, which is a negative of the first surface profile. The invention allows for conveniently producing high quality gratings using e.g. inorganic materials and height and/or fill factor modulation for diffraction efficiency control.
1. A method of manufacturing a diffractive grating, comprising:
providing a first substrate,
manufacturing onto the first substrate a first surface profile using temporary grating material,
covering the first surface profile entirely by a layer of final grating material,
bonding a second substrate onto the layer of final grating material,
removing the first substrate, and
removing the temporary grating material for producing on the final grating material a second surface profile which is a negative of the first surface profile.
2. The method according to claim 1 , wherein the first and second surface profile comprise features of different heights for manufacturing a height modulated diffractive grating.
3. The method according to claim 1 , wherein the first and second surface profile comprise features of different widths for manufacturing a fill factor modulated diffractive grating.
4. The method according to claim 1 , further comprising manufacturing the first surface profile using nanoimprint lithography, electron beam lithography or optical lithography.
5. The method according to claim 1 , further comprising applying the grating material using atomic layer deposition, chemical vapor deposition, physical vapor deposition, spin coating, spraying, or inkjet printing or a variant thereof.
6. The method according to claim 1 , wherein said layer of grating material has an even free surface after deposition, onto which the second substrate is bonded.
7. The method according to claim 1 , wherein the grating material comprises an inorganic material, such as Si 3 N 4 , TiO 2 , SiO 2 , HfO 2 .
8. The method according to claim 1 , further comprising bonding the second substrate to the grating material using an adhesive layer.
9. The method according to claim 8 , wherein the adhesive layer has an index of refraction which deviates not more than 10% from the index of refraction of second substrate.
10. The method according to claim 1 , further comprising bonding the second substrate to the grating material using physical or chemical bonding.
11. The method according to claim 1 , wherein the final grating material has an index of refraction which deviates not more than 10% from the index of refraction of the second substrate.
12. The method according claim 1 , wherein the final grating material has an index of refraction which is at least 10% higher than the index of refraction of the second substrate.
13. The method according to claim 1 , wherein the second substrate is a waveguide or the method further comprises bonding the second substrate onto a waveguide.
14. The method according to claim 13 , wherein the waveguide is a waveguide display element of a near-to-eye display.
15. Use of a method of manufacturing a diffractive grating for manufacturing an in-coupling grating, exit pupil expander grating or out-coupling grating of a diffractive waveguide display, wherein the method of manufacturing a diffractive grating comprises:
providing a first substrate,
manufacturing onto the first substrate a first surface profile using temporary grating material,
covering the first surface profile entirely by a layer of final grating material,
bonding a second substrate onto the layer of final grating material,
removing the first substrate, and
removing the temporary grating material for producing on the final grating material a second surface profile which is a negative of the first surface profile.
16. The method according to claim 1 , wherein the final grating material has an index of refraction which is 10-30% higher than the index of refraction of the second substrate.