| 摘要 |
A modulator is formed of a semiconductor material which utilises the electro-optic effect to achieve a change in the refractive index Deltan of the material under the influence of an applied electrical field F (251), in accordance with the equation: Deltan=-½ n<SUB>0</SUB><SUP>3 </SUP>[rF+sF<SUP>2</SUP>]≡Deltan<SUB>L</SUB>+Deltan<SUB>Q </SUB>where n<SUB>0 </SUB>is the refractive index of the material at zero field, and Deltan<SUB>L </SUB>and Deltan<SUB>L </SUB>and Deltan<SUB>Q </SUB>are the linear and quadratic contributions to the change in refractive index respectively, r is the linear electro-optic coefficient of the material and s is the quadratic electro-optic coefficient of the material incorporating a plurality of quantum dots and operating in a wavelength region where the value of rF is sufficiently greater than the value of sF<SUP>2 </SUP>so as to operate with the dominant effect on the refractive index Deltan being contributed by the linear effect. In this way, a device with a wide bandwidth is achieved by appropriately separating the band-gap wavelength (lambda<SUB>g</SUB>) and the operating wavelengths (lambda).
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