Metasurfaces for optical detection of tissue and fibrous material anisotropy
A metasurface optical device composed of three stacked dielectric layers which form an anti-reflective structure for wavelengths in a predetermined operational wavelength range within the visible spectrum. The anti-reflective structure contains a rectangular lattice of rhombohedral perturbations that produce guided-mode resonances within the predetermined operational wavelength range. The guided-mode-resonant dielectric metasurface device is capable of detecting by colorimetric readout the presence and orientation of a linearly birefringent anisotropic medium, such as a fibrous tissue, positioned above the stacked dielectric layers.
1. A metasurface optical device comprising:
a first layer composed of a first dielectric material, a second layer composed of a second dielectric material, and a third layer composed of a third dielectric material;
wherein the first layer, the second layer, and the third layer are stacked to form an anti-reflective structure for wavelengths in a predetermined operational wavelength range within the visible spectrum;
wherein the anti-reflective structure contains a rectangular lattice of rhombohedral perturbations that produce guided-mode resonances within the predetermined operational wavelength range;
wherein each of the rhombohedral perturbations breaks reflection and/or rotation symmetry sufficient to induce at least a 10% difference in a colorimetric response of the metasurface optical device within the predetermined operational wavelength range within the visible spectrum compared to a colorimetric response of a device with symmetric perturbations.
2. The metasurface optical device of claim 1 wherein each of the rhombohedral perturbations has a size less than wavelengths in the predetermined operational wavelength range.
3. The metasurface optical device of claim 1 wherein the rectangular lattice of rhombohedral perturbations has lattice periodicity less than wavelengths in the predetermined operational wavelength range.
4. The metasurface optical device of claim 1 wherein the guided-mode resonances have sub-10 nm bandwidth within the predetermined operational wavelength range.
5. The metasurface optical device of claim 1 wherein the first dielectric material has a first refractive index, the second dielectric material has a second refractive index, and the third dielectric material has a third refractive index.
6. The metasurface optical device of claim 1 wherein the second refractive index is larger than the first refractive index and larger than the third refractive index.
7. The metasurface optical device of claim 1 wherein the first dielectric material, the second dielectric material, and the third dielectric material each have negligible loss within the predetermined operational wavelength range.
8. The metasurface optical device of claim 1 wherein the anti-reflective structure has a substantially flat spectral background for wavelengths in a predetermined operational wavelength range of the metasurface optical device.
9. The metasurface optical device of claim 1 wherein the second layer and the third layer each have a thickness less than 1 μm.
10. The metasurface optical device of claim 1 wherein the predetermined operational wavelength range is within the visible spectrum.
11. The metasurface optical device of claim 1 wherein the first layer is a silicon dioxide (SiO 2 ) substrate.
12. The metasurface optical device of claim 1 wherein the second dielectric material is silicon nitride (Si 3 N 4 ) or titanium dioxide (TiO 2 ).
13. The metasurface optical device of claim 1 wherein the third dielectric material is silicon dioxide (SiO 2 ).