Digital Optics Fabrication Techniques
The first synthetic grating assembled by man was probably made out of animal hair (binary amplitude transmission gratings). These would diffract direct sunlight faintly into its constitutive spectra (rainbow colors). Later synthetic gratings were probably made from scratches in shiny surfaces, metal or glassy rocks (as binary phase gratings), in order to generate interesting 3D visual effects (for more details on such ‘scratch-o-grams’, see Chapter 2).
Today, industry is becoming a fast-growing user of diffractive and micro-optics, and therefore needs a stable, reliable and cheap fabrication and replication technological basis, in order to integrate such elements in industrial applications as well as in consumer electronics products (Chapter 16), especially when the products and applications using such elements are to be become commercial commodities.
Depending on the target diffraction efficiency and the smallest feature size in the digital optical element, the optical engineer has a choice between a vast variety of fabrication technologies, ranging from holographic exposure and diamond machining to multilevel binary lithography and complex gray-scale masking technology.
The flowchart in Figure 12.1 summarizes the various fabrication technologies as they have appeared chronologically.
For a single optical functionality – for example, a spherical lens – the optical engineer can decide to use various different fabrication technologies [