II-VI Semiconductor-Doped Glass: Nonlinear Optical Properties and Devices
II–VI semiconductor doped glass consists of nanocrystallites of semiconductors, such as CdSxSe1-x and CdTe, in a glass matrix. Depending upon the manufacturing process the crystallites can be between 2 and 10 nm in size and up to 0.1% of the total volume. They appear to be randomly orientated in the glass and of a fairly uniform size distribution. Due to the optical absorption characteristics of the semiconductor crystallites these glasseshave a sharp cut off in their transmission for photon energies larger than the band-gap. The wavelength of the cut off can be altered primarily according to value of x in CdSxSe1-x and the range 500 to 695 nm. This feature makes the glasses particularly useful as wavelength filters and they are commercially available in this form. Recent investigations (Yao et al., Olbright et al. and Roussignol et al.) of the nonlinear optical properties of these semiconductor doped glass (SDG) have revealed a significant nonlinear refractive index which recovers on a picosecond time-scale. It has also been possible to manufacture both optical waveguides and optical fibres using SDG. The advantage of guided wave configurations for nonlinear optics is that high intensities can be maintained over longer distances than bulk optics and interaction distances can be absorption rather than diffraction limited. In summary SDG is attractive as nonlinear optical material primarily because it offers a rapid recovery time and room temperature operation; it is also commercially available, inexpensive and has an available guided wave technology. The combination of a material with à fast nonlinear refractive index and waveguide technology opens up the possibility of high speed all-optical logic devices utilising guided wave geometries.
KeywordsNonlinear Optical Property Nonlinear Refractive Index Photoexcited Carrier Couple Wave Equation British Telecom
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