Development of micro/nano optical devices: diffractive Fresnel lenses, diffractive optical elements type pattern generator; photonic cryistals
1.1. Fresnel lenses
We obtained diffractive Fresnel lenses with 2 and 4 levels (for the first time in Romania), and minimum feature size 2.4 mm. The chip size is 5x5 mm2, and the lens diameter is 4 mm. The etching depth is 150-160 nm for the 2-level structure (l/4 ) and ~80 nm for the second etching step (for 4 level structures). Lenses with focal length of 3,4,5,6 and 7 cm have been obtained for red radiation (630 nm). The structures were processed using optical lithography and reactive ion etching of SiO2.
Fig. 1. Optical image of a 4-level Fresnel lens with focal length 6 cm (central zone)
Fig. 2. SEM images of Fresnel lens with 2 levels and 4 levels (details)
Fig. 3. Reflected light in the focal plane –fresnel lens with 4 levels (a) and 2 levels (b)
1.2. Diffractive optical element for generation of IMT logo.
The devices is a 2-level diffractive optical element obtained by Electron beam lithography in a PMMA layer 160 nm thick.(first time in Romania). The pixel size is 1 mm . The size of the DOE is 1x1 mm2.