Today, the realm of micro-optics comprises quite an impressive range of optical elements, which will be described in the next six chapters.
This chapter focuses on refractive micro-optics, a sub-field of micro-optics [1–3] that considers refraction/reflection and/or the waveguide phenomenon rather than diffraction/diffusion. Therefore, we consider here structures that are much larger than the wavelength, from about 20 times the operating wavelength up to 1000 times that wavelength. Figure 4.1 shows that refractive micro-optics are actually at the interface between the realms of macro-optics and micro-optics.
Refractive and reflective micro-optics have found many applications in today's industry, and both fields are growing at a rapid pace.
While traditional macroscopic optics are fabricated by conventional polishing and grinding techniques, micro-optics are fabricated by lithographic techniques [4–6]. The physical aspects of such optical elements as well as the three major fabrication techniques are shown in Figure 4.2.
Salt diffusion for GRIN lenses and resist reflow process followed by dry proportional etching  are simple tools that provide most of the requirements for refractive micro-optics. Gray-scale lithography is a more complex lithographic technique, which can provide arbitrary surface-relief elements in a single lithography step. For more insight into such fabrication techniques and related processes, including mass replication , see the ...
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