Fabrication of Diffractive Optical Elements On-Fiber for Photonic Applications by Nanolitography

The present research work is devoted to the realisation of efficient fiber-wave-guide optical coupling between single-mode fiber and rectangular wave guide by fabricating a multilevel diffractive phase element on the top of the fiber by nanolitography. This optical arrangement is able to redistribute the diffractive electromagnetic field on a selected area by a suitable phase modulation of the light, in analogy with what happens for Fresnel Zone Plates Lens. The design of diffractive optical elements has been realized using our own algorthim and code. The out-coming laser beam exiting from the fiber has a gaussian transversal field in contrast to single-mode wave-guide which has an asymmetric transversal field distribution in X and Y direction. Phase modulation has been accomplished by multilevel profiling a polymeric material coated on the top of the fiber by means of a specific fabrication process including e-beam lithography and chemical etching. Focalization experiments for a fiber-waveguide coupling with a 20 microns diameter diffractive element were made with the use of 1550 nm wavelength laser are also discussed.