ABSTRACT
This chapter introduces the types of lenses which are used in building optic and optical fibre devices and instruments. Lenses are classified in two categories: thin lenses and thick lenses. Each category has its applications and equations for calculations. Lenses have two refraction surfaces; each surface is a segment of either a sphere or a plane. Graded-index (GRIN) lenses are often specified in terms of their pitch lengths and operating wavelengths. GRIN lenses are used to focus and collimate light within a variety of fibre optical components. Lenses are commonly used to form images by the refraction of light. GRIN lenses are coated with anti-reflection (AR) coatings to reduce Fresnel losses occurring between two parallel optical surfaces. AR coatings also help protect the lens surfaces from humidity, chemical reaction, and other types of physical damage. Ball lenses couple fibres from micro-optic components to light sources, from laser diodes to fibre cables, and from fibre cables to detectors.
