Fabrication of gratings and design of diffractive optical elements embossed on sol-gel films

Ion exchange, plasma deposition and flame hydrolysis are typically employed techniques for fabricating glass waveguides and gratings. These techniques have several drawbacks such as involvement of expensive instruments, multi-step procedure and high temperature treatment. These drawbacks make it difficult for their adoption in mass production. The sol-gel process is a simple and inexpensive way for making glass, and embossing into sol-gel films provides a simple alternative for fabricating surface profile gratings and other integrated optical devices. In this paper, we report the usage of the embossing technique to fabricate gratings and diffractive optical elements (DOEs) in the sol-gel cladding layer of a waveguide. The designed DOEs manipulate out-coupled light from a slab waveguide and form 3 lines of equal intensity at a stipulated distance. The DOEs were designed as two-level optics by the direct binary search method based on the scalar diffractive theory, and the master molders used in the embossing were fabricated by ultraviolet laser writing on photoresist combined with reactive ion etching. We chose organic modified silane in the sol-gel process and no baking was needed, greatly minimizing possible shrinkage of the thin film.