Fabrication of diffractive optical elements for photonic applications by nanolithography

Abstract

Summary form only given. The present research work is devoted to the realization of an efficient optical coupling between single-mode fiber and rectangular waveguide. The outcoming laser beam exiting from the fiber has a gaussian transversal field distribution. On the contrary, the single-mode waveguide has an asymmetric transversal field distribution in X and Y-axis. The problem of transforming the outcoming circular laser beam onto a rectangular, size adjusted, spot can be solved realizing directly on the top of the fiber a diffractive optical element. This optic element 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 plate lenses. Phase modulation is obtained by a multilevel profiling of a polymeric material coating the top of the fiber by means of e-beam lithography. The design of diffractive optical elements has been realized using our own algorithm and code. Focalization experiments have been made with the use of a 1550nm wavelength laser. Description of the lithography and fabrication processes are shown as well.