Optical systems, which provide much convenience to our lives and industries,
manipulate light to satisfy the particular requirements of end users. For end users and optical engineers, understanding optical systems is of fundamental importance for using, designing, or manufacturing optical systems. In order to better understand optical systems, it is essential to be familiar with the behavior and properties of light. In history, the behavior and properties of light have been gradually discovered in the process of explaining some optical phenomena, and validated by many experiments. However, the nature of light is still difficult for many people to understand, especially for beginner students of optics. In this chapter, we give readers a very brief description of light and optical systems. The question “What is light?” is firstly addressed. The generation of light and the three basic theories of light—geometrical optics, wave optics, and quantum optics—are then briefly discussed, after which, the concept of statistical optics is mentioned. Finally, an overview of optical systems is presented, and some examples are also provided to give readers a sense of what is entailed in such systems.
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