When most people think of “optics,” the first component that is likely to spring to mind is the lens. Whereas opticians know that the field is much broader than this, and the heft of this book reminds micro-opticians that their field is equally diverse, lenses are nevertheless essential optical elements in most optical systems. Mirrors are even older, but lenses have also experienced considerable historical development, and indeed much of the story of optics concerns lenses and their combinations. As creators of images, lenses are used to project the world as we perceive it, from the television camera to the human eye.

We consider in this chapter the domain of what is known as geometric or refractive optics, which relies on the refraction of light, to which we were introduced in Section 4.1.3, to achieve a desired optical function. In geometric optics we can consider light propagating as rays; interference effects are (mostly) ignored, as these form the basis of diffractive optics, the subject of Chapter 8.

The physics of macroscopic lenses is identical to that of their microscopic brethren, so that much of the following discussion is not a function of size. Because of their dimensions, however, microlenses are much more susceptible to diffraction phenomena, and are fabricated using very different manufacturing techniques than classical optical elements. Since the optical physics needed to understand refractive lenses applies to both regimes, we will initially present lenses independent of their size, and consider micro-optical aspects and special considerations in the case studies at the end of the chapter.