MANUFACTURING OF GLASS DIFFRACTIVE OPTICS BY USE OF MOLDING PROCESS

Growing demands on high-speed data, voice and video signals transmissions depend on low cost and reliable optical components to convert optical signals to electrical signals or vice versa. Microlenses, diffractive optical elements (DOE) and micromirrors are increasingly playing an important role in these applications [1-2]. The basic concept of a DOE relies on constructive and destructive interference of spherical sources to produce the desired illumination geometry. For example, in the simplest design, two parallel slits illuminated by a collimated beam (planar wave front) such as a laser. As the light propagates from the slits, both slits act as independent light sources and the light from each propagates in a spherical shape, see figure 1. At some distance, the two spherical waves Figure 1: Schematic of a DOE design interact with each other. In order to produce 2-dimensional patterns, such as the square depicted in figure 1. In this setup the line pattern is replaced by a 2-dimensional pattern, which appears to be very complicated. In order to design this pattern, an Inverse Fast Fourier Transforms (iFFT) of complex arrays is used. More specifically, in order to design a mask to produce a square, the image is constructed as a bitmap graphics based on the intensity mapping of the image. The image is then inverted from the center to the corners, and an inverse (iFFT) is performed on the inverted image based on equation 1 [3]. +− = dxdyeyxfffF yfxfjyx yx)(2),(), ( π (1) where f(x,y) is a function that includes the complex values of the original bitmap image (inverted) at the index locations x and y, and F(fx,fy) is the phase domain of the image (complex amplitudes) of the bitmap at index locations x and y. fx, and fy are the spatial frequencies. The details of the DOE design can be found in reference [4]