• 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)

   
  a)                                 b)
  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.

Fig. 4. Imagine SEM- detaliu al elemntului difractiv (unitatea de masura- 2 mm)
The far field image obtained with this DOE is given in fig. 5

Fig. 5 Far field recostruction image

1.3. Photonic Crystals

Experiments for the fabrication of Photonic crystals for IR radiation and integration with optical waveguides. Structures with feature size in the range 27 nm-365 nm heve been obtained.

Fig. 6. SEM image of a hexagonal PhC, period  600nm  and feature size 365 nm

Fig. 7. SEM image of a hexagonal PhC, period  600nm  and feature size27 nm

Fig. 8. Optical image of the optical waveguide to be integragted with the PhC)