Optical devices/switches

Although by far nematics are the most extensively used ones, other phases (smectic, cholesteric, etc.) of hquid crystals and mixed systems such as polymer-dispersed liquid crystals capable of field-induced reorientation have also been employed for electro-optical studies and applications. They are basically based on the same basic mechanism of field-induced director axis reorientation similar to nematic hquid crystals i.e., the response is Kerr like in that it is independent of the direction of the electric field. In general, nematic liquid crystal electro-optics devices switch at a rate of several terrs of hertz, corresponding to response times from a few to tens of microsecorrds. 

The random laser is a simple optical system in which the strong optical scattering in the random medium forms an optical recurrent path. Recent reports on random lasers have described the emission of laser light by metal-oxide polycrystalline and micrometer-sized particles [46]. Because of its structural simplicity and small size, the single random laser is a promising miniature light source for optical devices, such as waveguides and optical switches. 

In recent years advances in the chemistry of leuco dyes have taken place particularly in the areas of structural identification by means of H- and 13C-NMR and selective syntheses of aminoquinones, etc. New applications of leuco quinones such as in electro-optical devices and information recording media have enhanced their importance. In these applications, the chemistry of leuco quinones is interesting mainly due to switching from a colored to a colorless system by a redox process. 

Losses still occur in the fibres developed for commercial use. Nonetheless, these have been reduced to a point where transmission over kilometres is possible. Along with transmission of information in telephone systems and similar applications, it has been suggested that optical devices may replace conventional electronics in more advanced applications such as computers. For such applications, it will be necessary to develop optical switches, amplifiers, and so on. In the last two decades, new materials have been developed that may form the basis of integrated optical circuits. These materials are photonic crystals. 

Until recently a general drawback of this passive Q-switching scheme was the difficulty of obtaining an exact synchronization of the giant pulse with other events in more complex experiments. This difficulty does not exist with active Q-switching in which an electro-optic device, e.g. a Kerr-cell or Pockels-cell, is used instead of a dye cell, and one is able to determine exactly the time at which... 

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... 

Photochemical bistability is a conditio sine qua non, but a number of other requirements are essential for application of chiral switches in photonic materials or optical devices 11,4,101... 

Nonlinear optical activity reflects the nonlinear response of /r, (f- ) to electromagnetic radiation, which Eq. (7) shows to be governed by the first and second hyperpolarizabilities, p and y. A high level of such activity can have important applications in a variety of electro-optical devices,82,86,87 such as frequency converters, modulators, switches, etc. 

Q-switched laser A laser in which the state of the device introducing important losses in the resonant cavity and preventing lasing operation is suddenly switched to a state where the device introduces very low losses. This increases rapidly the Quality factor of the cavity, allowing the build-up of a short and very intense laser pulse. Typical pulse durations are in the ns range. The Q-switching may be active (a rotating mirror or electro-optic device) or passive (a saturable absorber). 

Microfabricated devices capable of switching optical light beams, also termed MOEMS, have gained attention about a decade ago for applications like optical fiber switches, microscanners, or digital micromirror arrays. Particularly, the latter devices have found widespread application in video projection systems for office presentations, home cinema, and very recently, the replacement of classical projectors in movie theaters. Other applications, for example, for head-up displays on auto windscreens are in development. In all cases, arrays of small micromirrors are used for the modulation of light. 

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