The optical models of modern photonic design tools are based on Maxwell’s electromagnetic field theory. The electromagnetic field theory predicts that light can be approximated by an electromagnetic wave. In fact, the concept of light in the wave form was initially introduced a century earlier by Thomas Young. Interestingly, the first theory of light developed in the modern era, namely the geometric optics, predicted that light is not a wave but a stream of corpuscles. This postulate was justified by several experiments that were carried out in the late sixteenth and seventeenth centuries and, even though it was strongly contested by Christiaan Huygens, geometric optics established itself as the theory of light back in the eighteenth

FIGURE 1.1 The schematic of a laser diode on a C-mount.