Zero-index photonic crystals for visible and near infrared applications
A two dimensional (2D) photonic crystal (PhC) structure includes a substrate and a periodic grating structure formed on the substrate. The periodic grating structure includes a plurality of gratings having a grating period, a. Each pair of adjacent gratings is separated by air. Each grating has a grating width, d, and includes a plurality of alternating layers of a first material and a second material. The first material corresponds to a high index material. The second material corresponds to a low index material. A ratio of a first refractive index of the first material to a second refractive index of the second material is greater than or equal to two. Each first material layer has a first thickness, t1. Each second material layer has a second thickness, t2. The 2D PhC structure has a structure refractive index at or near zero for a range of frequencies.
1. A two dimensional (2D) photonic crystal (PhC) structure comprising:
a substrate; and
a periodic grating structure formed on the substrate, the periodic grating structure comprising a plurality of gratings having a grating period, a, each pair of adjacent gratings separated by air, each grating having a grating width, d, and comprising a plurality of alternating layers of a first material and a second material, the first material corresponding to a high index material, the second material corresponding to a low index material, a ratio of a first refractive index of the first material to a second refractive index of the second material greater than or equal to two, each first material layer having a first thickness, t1, each second material layer having a second thickness, t2, wherein the 2D PhC structure has a structure refractive index at or near zero for a range of frequencies.
2. The 2D PhC structure of claim 1 , wherein the first material is TiO 2 (titanium dioxide) and the second material is SiO2 (silicon dioxide).
3. The 2D PhC structure of claim 1 , wherein the periodic grating structure is configured to receive TE (transverse electric)-polarized light.
4. The 2D PhC structure of claim 1 , wherein the plurality of layers are formed using oblique angle deposition.
5. The 2D PhC structure of claim 4 , wherein the first material is TiO 2 (titanium dioxide), the second material is SiO 2 (silicon dioxide), a first deposition angle during formation of the layers of TiO 2 is at or near 30° and a second deposition angle during formation of the layers of SiO 2 is at or near 89°.
6. The 2D PhC structure according to claim 1 , wherein the periodic grating structure comprises five first material layers and four second material layers.
7. The 2D PhC structure according to claim 1 , wherein the grating period is 600 nanometers (nm), the grating width is 270 nm, the first material is dense TiO 2 , the second material is porous SiO 2 , the first refractive index is 2.45, the second refractive index 1.05, the first thickness is 270 nm and the second thickness is 330 nm.
8. The 2D PhC structure according to claim 1 , wherein the substrate comprises silicon.
9. The 2D PhC structure according to claim 1 , wherein the range of frequencies corresponds to at least one of visible and/or near-infrared wavelengths.
10. The 2D PhC structure according to claim 1 , wherein the 2D PhC structure is C 4v symmetric.