ABSTRACT
This chapter examines the optical front-end requirement of wireless infrared (IR) receivers for indoor and outdoor applications. It describes different options of optical filters and presents a variety of imaging and non-imaging concentrators. The chapter introduces the main characteristics of Fresnel lenses and explains the principal features of hemispherical lenses, compound parabolic concentrators (CPCs), and dielectric totally internally reflecting concentrators (DTIRCs). It also explains the way in which different concentrators can be used in combination with a variety of filters. High-speed wireless IR communication systems require transmitters whose emitted energy presents a narrow linewidth. The hemispherical lens is one of the most popular non-imaging concentrators currently employed in indoor and mobile wireless IR communication equipment. CPCs present an alternative to hemispherical concentrators for wireless IR communication applications. DTIRCs can incorporate planar thin-film optical filters to reduce background noise. DTIRCs can incorporate either bandpass or longpass filters.
