Guided mode resonance device for optical beam tapping and imaging without rainbows
View Patent ↗Waveguide enhanced resonant diffraction is provided in grating structures having negligible non-resonant diffraction by the grating. This is done by making the grating thickness much less than any relevant wavelength, and by having the grating in proximity to a waveguide for diffractive coupling to and from a mode of the waveguide. Material absorption in the grating material can be used to suppress undesired diffraction orders. The resulting structures can provide rainbow-free diffractive optical sampling.
1. Optical apparatus comprising:
an optical waveguide;
a diffraction grating disposed in proximity to the optical waveguide such that incident light on the diffraction grating can also diffractively couple to the optical waveguide;
wherein a first diffraction process is non-resonant diffraction of the incident light by the diffraction grating without coupling to the optical waveguide;
wherein a second diffraction process is resonant diffraction of the incident light via 1) diffractive coupling of the incident light to a guided mode of the optical waveguide to provide guided light, followed by 2) additional diffraction of the guided light into diffracted radiation;
wherein an efficiency of the second diffraction process is substantially larger than any efficiency of the first diffraction process at a predetermined incidence angle and frequency of the incident light.
2. The apparatus of claim 1 , wherein the efficiency of the second diffraction process is 10× or more greater than any efficiency of the first diffraction process.
3. The apparatus of claim 1 , wherein a combined efficiency of parasitic diffraction processes is 0.1% or less.
4. The apparatus of claim 1 , wherein a thickness of the diffraction grating is between 0.6 nm and 10 nm.
5. The apparatus of claim 1 , wherein a ratio of grating line width to grating period is selected to enhance diffraction efficiency into a selected diffraction order.
6. The apparatus of claim 1 ,
wherein the waveguide is a planar waveguide formed by a core layer sandwiched between a substrate and a capping layer;
wherein the diffraction grating is disposed at an interface between the core layer and the capping layer.
7. The apparatus of claim 1 , wherein the diffraction grating is formed in a material selected from the group consisting of: Si, Ge, InP, GaAs, MoS 2 , WS 2 , and WSe 2 .
8. An augmented reality display comprising:
the optical apparatus of claim 1 ;
further comprising an infrared source emitting at a source wavelength between 800 nm and 1500 nm;
wherein the optical apparatus is configured to have zero order transmittance of 90% or more in a wavelength range from 400 nm to 750 nm;
wherein the optical apparatus is configured to provide selective redirection of light at the source wavelength via the second diffraction process.
9. The apparatus of claim 8 , wherein a thickness of the diffraction grating is between 0.6 nm and 10 nm.
10. The apparatus of claim 8 , wherein an efficiency of the selective redirection of light at the source wavelength is 10% or more.
11. The apparatus of claim 8 , wherein a combined efficiency of parasitic diffraction processes is 0.1% or less.
12. The apparatus of claim 8 , wherein the diffraction grating is formed in a material that is opaque in a wavelength range from 400 nm to 750 nm.
13. The apparatus of claim 12 , wherein the diffraction grating is formed in silicon.