Light Modulation by Reflection
The possibility of modulating a light beam by reflecting it from the surface of a crystal whose surface dielectric constant is modulated by an electric field is investigated theoretically. Since the dielectric constant may depend on distance in from the surface of the crystal it was necessary to develop a computer program which calculates the reflectivity of a medium with a non-uniform dielectric constant. To get an idea of the effect of spatial variations in the dielectric constant, the program is first used to calculate the reflectivity of media with simple ramps in their dielectric constant. The results show that a dielectric constant whose ramp extends at least one-third of a wavelength of light into the medium looks homogeneous to the light.
To estimate the effectivensss of a reflection modulator, the surface dielectric constant of CdS near a band edge is simulated both with and without a perturbing electric field and the reflectivity program is used to compute both the perturbed and unperturbed reflectivity. The best results, for a field of 106 volt/cm, are that a contrast ratio (ratio of reflectivities) of 17 can be obtained at an efficiency (largest reflectivity) of 1.7 percent.
KeywordsDielectric Constant Band Edge Light Modulation Contrast Ratio Brewster Angle
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