Electrooptic

Among the many applications of LB films, the creation or arrangement of colloidal particles in these films is a unique one. On one hand, colloidal particles such as 10-nm silver sols stabilized by oleic acid can be spread at the air-water interface and LB deposited to create unique optical and electrooptical properties for devices [185]. 

In addition to conventional applications in conducting polymers and electrooptical devices, a number of recent novel applications have emerged. Switching of DNA electron transfer upon single-strand/double-strand hybridization fonns the basis for a new medical biosensor teclmology. Since the number of base pairs of length 20... 

CERAMCS - NONLINEAROPTICAL AND ELECTROOPTIC CERAMICS] (Vol 5) b-Barium borate [13701-59-2]... 

Electron tubes Electron tunneling Electrooptic materials Electrooptics Electroosmosis... 

Perovskites have the chemical formula ABO, where A is an 8- to 12-coordinated cation such as an alkaU or alkaline earth, and B is a small, octahedraHy coordinated high valence metal such as Ti, Zr, Nb, or Ta. Glass-ceramics based on perovskite crystals ate characteri2ed by their unusual dielectric and electrooptic properties. Examples include highly crystalline niobate glass-ceramics which exhibit nonlinear optical properties (12), as well as titanate and niobate glass-ceramics with very high dielectric constants (11,14). 

It is also possible to switch a single picosecond pulse out of the train of mode-locked pulses using an electrooptic switch. It is possible to obtain a single pulse having duration in the picosecond regime or even less. Pulses with durations in the regime of a few hundred femtoseconds (10 s) are also available (Fig. 4e). 

Liquid crystal polymers are also used in electrooptic displays. Side-chain polymers are quite suitable for this purpose, but usually involve much larger elastic and viscous constants, which slow the response of the device (33). The chiral smectic C phase is perhaps best suited for a polymer field effect device. The abiHty to attach dichroic or fluorescent dyes as a proportion of the side groups opens the door to appHcations not easily achieved with low molecular weight Hquid crystals. Polymers with smectic phases have also been used to create laser writable devices (30). The laser can address areas a few micrometers wide, changing a clear state to a strong scattering state or vice versa. Future uses of Hquid crystal polymers may include data storage devices. Polymers with nonlinear optical properties may also become important for device appHcations. 

Lithium Niobate. Lithium niobate [12031 -64-9], LiNbO, is normally formed by reaction of lithium hydroxide and niobium oxide. The salt has important uses in switches for optical fiber communication systems and is the material of choice in many electrooptic appHcations including waveguide modulators and sound acoustic wave devices. Crystals of lithium niobate ate usually grown by the Czochralski method foUowed by infiltration of wafers by metal vapor to adjust the index of refraction. 

Materials are also classified according to a particular phenomenon being considered. AppHcations exploiting off-resonance optical nonlinearities include electrooptic modulation, frequency generation, optical parametric oscillation, and optical self-focusing. AppHcations exploiting resonant optical nonlinearities include sensor protection and optical limiting, optical memory appHcations, etc. Because different appHcations have different transparency requirements, distinction between resonant and off-resonance phenomena are thus appHcation specific and somewhat arbitrary. 

Materials for Electrooptic Modulation. The fundamental phenomenon of Pockel s effect is a phase change, A( ), of a light beam in response to a low frequency electric field of voltage, V. Relevant relationships for coUinear electrical and optical field propagation are as foUows (1 6) ... 

Fig. 1. Representative device configurations exploiting electrooptic second-order nonlinear optical materials are shown. Schematic representations are given for (a) a Mach-Zehnder interferometer, (b) a birefringent modulator, and (c) a directional coupler. In (b) the optical input to the birefringent modulator is polarized at 45 degrees and excites both transverse electric (TE) and transverse magnetic (TM) modes. The appHed voltage modulates the output polarization. Intensity modulation is achieved using polarizing components at the output.

The birefringent (BR) modulator makes use of polarized light and tensorial nature of the electrooptic coefficient. For example, poled organic polymer films are characterized by two nonzero components for the electrooptic tensor and parallel and orthogonal to the poling direction,... 

Two parameters that characterize the performance of electrooptic modulators are k E and the bandwidth given by the following ... 

Table 1. Comparison of Electrooptic Modulator Performance Parameters of NLO Materials ...

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