A variety of theoretical techniques have been developed to describe the generation, propagation, and detection of light. Geometrical-optics, also known as ray-optics, is primarily concerned with image formation from lenses and mirrors. Wave-optics describes light as a scalar sinusoidal lightwave and is adequate to explain many interference and diffraction effects. Electromagnetic-optics introduces a vector form for the lightwave, which allows the explanation of polarization effects and propagation in dielectric media. Quantum-optics is the most complete and fundamental technique and allows the prediction of virtually all observed phenomena, including the details of interactions between lightwaves and atoms.
A complete treatment of quantum-optics is beyond the scope of this text. Fortunately, a perfectly adequate theory of photodetection can be developed by combining some of the simpler concepts from quantum-optics with conventional electromagnetic and wave-optic descriptions of light. This âsemi-classicalâ approach takes advantage of what has been termed the wave-particle duality of light and will be the technique used in this text. Light will be modeled both as an electromagnetic lightwave and as a stream of incident âparticlesâ known as photons.
3.1 The Detection of Optical Signals
The ability to respond to light is a fundamental requirement of all optical receivers. Several methods to detect the presence of an optical signal have been developed, with photographic film probably being the most widely manufactured âdetector.â In communication applications, the photodetection method employed must convert the received optical signal into an electrical signal that is then processed by conventional electronics to recover the information being transmitted. Table 3.1 lists the techniques that are those most often associated with the detection of optical signals .
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