Integrated Fresnel lens on thermally oxidized silicon substrate

Thin film Fresnel lenses have been achieved on SiO(2)/Si substrates covered with a waveguide layer of Si(3)N(4) grown by low pressure chemical vapor deposition (LPCVD). The phase shift between the different zones is induced by a SiO(2) top layer chemically etched. The use of this additional layer having a smaller refractive index than the waveguide results in a saturation of the lens characteristics vs the thickness of the SiO(2) layer; this feature associated with the good reproducibility of the LPCVD technology allows good control of the lens characteristics.