Method of fabricating all-dielectric flat lens with low refractive index
A method is disclosed of fabricating all-dielectric flat lens with low refractive index comprising: selecting dielectric substrate material and lens structure material; determining incident wavelength; calculating phase modulation corresponding to each pillar unit; periodically sampling circular area of dielectric substrate with radius to obtain plurality of sampling points; calculating phase modulation required at position of each sampling point; obtaining pillar corresponding to each sampling point; arranging different dielectric pillars with low refractive index and same thickness are arranged on dielectric substrate, thereby obtaining all dielectric flat lens with low refractive index. Also disclosed is method of fabricating all-dielectric flat lens with low refractive index that fabricates plane divergent lens with high transmission in wavelength range of visible light, and providing all-dielectric flat lens with low refractive index to improve transmission in visible light region through using dielectric with low refractive index to replace metal and dielectric with high refractive index.
1. A method of fabricating an all-dielectric flat lens with low refractive index, characterized in that, the method comprises steps as follows:
S 1 : selecting a dielectric substrate material and a lens structure material from an all-dielectric material with low refractive index, and this all-dielectric material is composed of dielectric pillars with a low refractive index not less than 2.5;
S 2 : determining an incident wavelength λ in a range of visible light from 390 nm to 780 nm;
S 3 : according to the selected dielectric substrate material and the lens structure material, selecting the pillars with determined thickness and a periodic arrangement, and according to each pillar with the selected periodic arrangement, calculating a phase modulation corresponding to each pillar unit;
S 4 : determining a lens radius R, a lens focal length f, and a lens type, and periodically sampling a circular area of a dielectric substrate with a radius of R to obtain a plurality of sampling points;
S 5 : calculating a phase modulation required at a position r of each sampling point, and a calculation formula thereof is:
for
a
divergent
lens
:
ϕ
(
r
)
=
2
π
λ
(
r
2
+
f
2
-
f
)
for
a
convergent
lens
:
ϕ
(
r
)
=
-
2
π
λ
(
r
2
+
f
2
-
f
)
wherein r is a distance to a center of the plane lens;
S 6 : comparing the obtained phase modulation with the phase modulation corresponding to each pillar unit obtained in the step S 3 to obtain the pillar corresponding to each sampling point;
S 7 : according to the obtained pillars, arranging different dielectric pillars with low refractive index and same thickness on the dielectric substrate, thereby obtaining the all-dielectric flat lens with low refractive index.
2. The method of fabricating the all-dielectric flat lens with low refractive index according to claim 1 , wherein the substrate material with low refractive index and the lens structure material mentioned in the step S 1 are quartz, silicon nitride, titanium dioxide, diamond, silicon dioxide or gallium nitride.
3. The method of fabricating the all-dielectric flat lens with low refractive index according to claim 1 , wherein the thickness of the pillars mentioned in the step S 3 is 0.2λ to 3λ, that is a wavelength or sub-wavelength scale, wherein λ is an incident wavelength.
4. The method of fabricating the all-dielectric flat lens with low refractive index according to claim 1 , wherein said pillars in the step S 3 are seen from a top view as a circle, a square or a plane pattern having a rotational symmetry of 90°.