Applied Digital Optics: From Micro-optics to Nanophotonics

2

Classification of Digital Optics

As defined in Chapter 1, the adjective ‘digital’ in digital optics does not refer, as in the case of digital electronics, to the digital functionality of the element (digital signal processing) but, rather, to the digital way in which the optics are designed (by a digital computer) and fabricated (by a digital or binary microlithography technology – i.e. successive binary photomasks or reticles).

Chapter 1 has shown that the realm of digital optics can be split into two distinctive groups, free-space digital optics and guided-wave digital optics.

The emphasis in this book will be on free-space digital optics, since guided-wave digital optics are a special subdivision of digital optics, and are better described in numerous books dedicated to fiber optics and integrated waveguide optics. However, Chapter 3 will briefly describe guided-wave digital optics and related technologies.

2.1 Early Digital Optics

Mother Nature had developed an infinite variety of high-end refractives, diffractives, waveguides and hybrid optics, and even photonic crystals, long before the first humans were able to carve out the stones with which to smash the skulls of animals that looked reasonably edible. Such examples range from micro-optics to nanophotonics. Figure 2.1 shows a replica of one of the first diffraction gratings (the feather) on the left and one of the first sub-wavelength gratings (or photonic crystals) on the right (morpho-butterfly wings).

While the feather ...