Non-periodic grating reflectors with focusing power and methods for fabricating the same
Aspects of the present invention are directed to flat sub-wavelength dielectric gratings that can be configured to operate as mirrors and other optical devices. In one aspect, a grating layer ( 102 ) has a planar geometry and is configured with lines ( 206,207 ). The lines widths, line thicknesses and line period spacings ( 208 ) are selected to control phase changes in different portions of a beam of light reflected from the grating such that the phase changes collectively produce a desired wavefront shape in the beam of light reflected from the grating.
1. A device comprising:
a grating layer having a planar geometry and comprising a plurality of different grating sub-patterns, each of the plurality of different grating sub-patterns oriented in a same direction; and
a substrate, wherein the grating layer is disposed on the substrate and the grating layer is composed of a material having a relatively higher refractive index than the refractive index of the substrate;
wherein each of the plurality of different grating sub-patterns comprises a unique pattern of periodically spaced lines to control a phase change in a respective portion of a reflected light beam to produce a target wavefront shape and to form a mirror to focus the reflected light beam to a focal point.
2. The device of claim 1 , wherein the unique pattern comprises at least one of: line widths, line thicknesses, and line period spacings.
3. The device of claim 1 , wherein the lines within each unique pattern of periodically spaced lines of each of the plurality of grating sub-patterns having a selected period and a line width selected to control a phase change in a different portion of the reflected light beam.
4. The device of claim 2 , wherein the line period spacings and the line thicknesses are substantially constant in the plurality of grating sub-patterns and the line width is varied in the plurality of grating sub-patterns to form the mirror to focus the reflected light beam to the focal point.
5. The device of claim 1 , wherein the target wavefront shape corresponds to a target phase change across the grating layer.
6. The device of claim 5 , wherein the each of the plurality of grating sub-patterns corresponds to a different target phase change.
7. An optical device comprising:
a grating layer having a planar geometry and comprising a grating pattern to control phase changes in different portions of a reflected light beam to produce a target wavefront shape; and
a substrate, wherein the grating layer is disposed on the substrate and the grating layer is composed of a material having a relatively higher refractive index than the refractive index of the substrate;
wherein the grating pattern comprises a plurality of periodically spaced, different one-dimensional grating sub-patterns, each oriented in a same direction, each comprising a unique pattern of periodically spaced lines to control a phase change in a respective portion of a reflected light beam to produce a target wavefront shape and to form a mirror to focus the reflected light beam to a focal point.
8. The optical device of claim 7 , wherein each of the grating sub-patterns comprises line widths, line thicknesses, and line period spacing selected to control the phase changes in the different portions of the reflected light beam.
9. The optical device of claim 7 wherein the target wavefront shape corresponds to a target phase change across the grating pattern.