Optical communication devices

Optical networks require a variety of active and passive devices to accomplish connectivity. The purpose of these devices is to allow generation, routing and detection of photons. The light can be affected by the device in several ways, e.g., by light absorption, light scattering, light diffraction, wave 

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H. Yonezu, Optical Communications Device Engineering, Kogakutosho, Tokyo, 1984,... 

The chalcogenides of Be, Zn, Cd, and Hg are often referred to as II-VI semiconductors. They all have a zinc blende-type structure. The band gap decreases with increasing size of the metal from 3.0 eV in beryllium to 0.02 eV in mercury. The II-VI semiconductors find applications in solar cells, IR detectors, and optical communication devices. 

J.S. Patel, Liquid crystals for optical communication devices, in Handbook of Liquid Crystal Research, Ch. 12., Ed. P.J. Collings, J.S. Patel, Oxford University Press, New York (1997), and references therein. 

In additions to improvements in Si, a variety of devices based on compound semiconductors can be expected. Blue lasers witli high brightness and long operating lifetimes already exist in tlie laboratory. LEDs are likely to be used for all lighting purjDoses. The bandwidtli of optical communications will continue to increase witli ever faster semiconductor lasers. 

The supplanting of germanium-based semiconductor devices by shicon devices has almost eliminated the use of indium in the related ahoy junction (see Semiconductors). Indium, however, is finding increased use in III—V compound semiconductors such as indium phosphide [22398-80-7] for laser diodes used in fiber optic communication systems (see Electronic materials Fiber optics Light generation). Other important indium-containing semiconductors include indium arsenide [1303-11-3] indium antimonide [1312-41 -0] and copper—indium—diselenide [12018-95-0]. 

Communications. The advent of the laser improved prospects for optical communications enormously. The coherence of the laser meant that techniques developed in the radio portion of the electromagnetic spectmm could be extended to the optical portion of the spectmm. Because lasers operate at frequencies near 10 Hz, they offer a potentially wide bandwidth, equal to about 10 television channels of width (ca 10 Hz). It has not proved possible to take advantage of this full bandwidth because devices such as modulators capable of operating at 10 Hz are not available. 

The relevance of photonics technology is best measured by its omnipresence. Semiconductor lasers, for example, are found in compact disk players, CD-ROM drives, and bar code scaimers, as well as in data communication systems such as telephone systems. Compound semiconductor-based LEDs utilized in multicolor displays, automobile indicators, and most recendy in traffic lights represent an even bigger market, with approximately 1 biUion in aimual sales. The trend to faster and smaller systems with lower power requirements and lower loss has led toward the development of optical communication and computing systems and thus rapid technological advancement in photonics systems is expected for the future. In this section, compound semiconductor photonics technology is reviewed with a focus on three primary photonic devices LEDs, laser diodes, and detectors. Overviews of other important compound semiconductor-based photonic devices can be found in References 75—78. 

Light wave technologies provide a number of special challenges for polymeric materials. Polymer fibers offer the best potential for optical communications in local area network (LAN) applications, because their large core size makes it relatively cheap to attach connectors to them. There is a need for polymer fibers that have low losses and that can transmit the bandwidths needed for LAN applications the aciylate and methacrylate polymers now under study have poor loss and bandwidth performance. Research on monomer purification, polymerization to precise molecular-size distributions, and weU-controlled drawing processes is relevant here. There is also a need for precision plastic molding processes for mass prodnction of optical fiber connectors and splice hardware. A tenfold reduction in the cost of fiber and related devices is necessaiy to make the utilization of optical fiber and related devices economical for local area networks and tlie telecommunications loop. 

In the past few years, erbium doped materials gained much attention in the field of optical communications, since the Er ion shows a broad optical emission at 1540 nm [111], within the main wavelengths window in the telecommunication technology. For this reason Er can be suitable as an active element for the generation and amplification of light in optical devices [112,113], also if limitations for the realization of an efficient planar amplifier are related to the small cross section for Er excitation (typically 10 -10 cm according to the matrix). In order to enhance Er ion pumping efficiency, a possible... 

Polymers that have been already found to offer NLO behavior include polydiacetylenes and a number of polymers with liquid crystal side chains. Polymers are also employed as carriers of materials, which themselves are NLO materials. Applications include communication devices, routing components, and optical switches. 

Our communications infrastructure relies heavily on advanced materials chemistries. From the manufacturing processes used to fabricate optical fiber cables to molecular beam epitaxy techniques for the creation of nanoscale heterostructures that enable many optical devices, innovations in materials chemistry have played a role. An example of a recent technological achievement that relates to optical communications systems is the MEMS-based (microelectromechanical system) Lambda Router. The Lambda Router is an optical system developed at Lucent Technologies for switching narrowly focused... 

Arrayed microlenses are widely used in a variety of applications that involve miniaturized optical components.172 For example, they can be found at the heart of optical communication systems, facsimile machines, laser printers, and many other kinds of digital information storage or processing devices. In all these applications, the arrayed microlenses simply serve as diode laser correctors, fiber-optic couplers or connectors, and optical scanners. In a set of recent publications, Whitesides and coworkers have also demonstrated that arrayed microlenses could be used as a new platform for photolithography, through which submicrometer-sized structures could be conveniently fabricated as patterned arrays by reducing mm to cm scale features on a photomask.157... 

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