The Excitation of Planar Dielectric Waveguide at p-n Junctions, I

Recently there has been great interest in the guiding of light by the p-n junction region in certain piezoelectric semiconductors, for it has been noted that the Pockcls effect clue to the electric field within the p-n junction can be used to modulate light which propagates parallel to the junction plane. 1-4 This effect was first observed, and has been most intensively studied, with visible light in GaP junctions, 1 but it has also been observed with infrared light in GaAs junctions. 1,4 All treatments of the effect so far have assumed that the p-n junction region, which has a higher dielectric constant than the surround1491 1492 T H E BELL SYSTEM TECHNICAL J O U R N A L , SEPTEMBER l ! ) ( i 7 ing, normal GaP, behaves like a dielectric waveguide.1-5 A detailed analysis of this waveguide would require a knowledge of the optical properties in the neighborhood of the junction. However, since these properties change significantly in a fraction of a wavelength, it is extremely difficult to investigate them individually by experimental means. In order to get around this difficulty it has been necessary to adopt an indirect approach based on analyzing a number of different mathematical models and comparing their predictions with experiment. As part of this program Nelson and McKenna 0 have investigated the possible discrete modes which can propagate in a number of different models and have studied in considerable detail the properties of the lowest-order mode of each polarization.