Structure and method for manufacturing surface relief diffractive

Abstract

A structure and method for manufacturing surface relief diffractive optical elements are disclosed in the invention, which combines surface relief grating structure and gradient refractive index. Unlike the prior art, the invention does not require control of grating profile structure to modulate the optical path difference of incident light beam. Furthermore, control of grating profile makes the fabrication process more complicated and difficult. This method according to the invention comprises the following steps. A refractive index distribution layer is formed on a substrate by a thin film coating technology with controlled refractive index distribution, thereby the optical path difference is introduced when a incident light beams impinges the refractive index distribution layer. Then a spinning coated photoresist layer on the refractive index distribution layer. In addition, the distribution specification of the refractive index layer can be calculated and/or designed by a rigorous coupled wave theory with parameters, such as depth of the fringe pattern and required diffraction efficiency. Thereafter, a required interference fringe pattern can be transferred into the photoresist layer using a photolithography technique, laser direct writing or two laser beam interference techniques. Next, the required fringe pattern is formed on the photoresist layer via developing and fixing. Finally, the required fringe pattern is fabricated in the refractive index distribution layer by a dry ion beam etching technique, then removing the photoresist layer. In comparison with the prior art, the invention has advantages of easy fabrication of grating profile, feasibility of diffraction efficiency control, suitability for high-volume production and low cost.