Light-emitting diodes are the light source of choice for local area low and medium bit rate optical communication. Owing to the spontaneous emission lifetime of about 1 ns in highly excited semiconductors, the maximum bit rates attainable with LEDs are limited to rates < 1 Gbit/s. Thus, multi-Gbit/s transmission rates are not feasible with LED […]

Free-space communication LEDs are commonly made with GaAs or GaInAs active regions and are grown on GaAs substrates. The GaInAs layer is pseudomorphic, i. e. sufficiently thin that it is coherently strained, and no dislocations are generated. The emission wavelength of GaAs and coherently strained GaInAs LEDs is limited to wavelengths in the IR ranging […]

LEDs can be used for either free-space communication or for fiber communication applications. Free-space communication applications include the remote control of appliances such as television sets and stereos, and data communication between a computer and peripheral devices. LEDs used in optical fiber communication applications are suited for distances of a few km and bit rates […]

Free-space optical communication (Carruthers, 2002; Heatley et al., 1998; Kahn and Barry, 2001) is suitable for low to medium bit rates. The most common application of free-space optical communication is the remote control of consumer appliances such as stereos and television sets. Other applications are the remote control of automobile door locks and the cordless […]

Owing to the requirement of total internal reflection, the only light rays that can propagate losslessly in the core of an optical fiber are those that have a propagation angle smaller than the critical angle for total internal reflection. Light rays for which the propagation angle is too large will consequently not couple into the […]

Material dispersion is another mechanism limiting the capacity of optical fibers. Material dispersion is due to the dependence of the refractive index on the wavelength. Figure 22.5 shows, as a function of wavelength, the phase refractive index and the group refractive index of silica. The indices are defined as c (22.4) n= (phase refractive index) […]

Modal dispersion occurs in multimode fibers that have a larger core diameter or a larger index difference between the core and the cladding than single-mode fibers. Typical core diameters range from 50 to 1 000 |im for multimode fibers and 5 to 10 |im for single-mode fibers. In the ray optics model, different optical modes […]

Silica (SiO2) has excellent optical properties including great long-term stability. A large variety of glasses and fibers are available. The attenuation of silica fibers is shown in Fig. 22.2. Inspection of Fig. 22.2 reveals that a minimum loss of 0.2 dB occurs at a wavelength of 1.55 |im. There are several optical “windows” for communication […]

The cross section of optical fibers consists of a circular core region surrounded by a cladding region. The core region has a higher refractive index than the cladding region. Typically, the core refractive index is about 1% higher than the cladding refractive index. Light propagating in the core is guided inside the core by means […]

LEDs are used in communication systems transmitting low and medium data rates (< 1 Gbit/s) over short and medium distances (< 10 km). These communication systems are based on either guided light waves (Keiser, 1999; Neyer et al., 1999; Hecht, 2001; Mynbaev and Scheiner, 2001; Kibler et al., 2004) or free-space waves (Carruthers, 2002; Heatley […]