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Optical Surface Waveguide

IP.com Disclosure Number: IPCOM000077118D
Original Publication Date: 1972-Jun-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Lean, EG: AUTHOR [+2]

Abstract

Fig. 1 shows an optical waveguide which consists of a layer 1 of undoped epitaxial semiconducting film on top of a heavily doped substrate 2 of the same composition as film 1. It is well known that the index of refraction may be lowered by doping due to the interaction of light with carriers (plasma wave-photon interaction). The reasons for the lowering of the index of refraction is because the dispersion curve for the photon-plasmon system has a higher ratio of omega/k, as shown in Fig. 2.

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Optical Surface Waveguide

Fig. 1 shows an optical waveguide which consists of a layer 1 of undoped epitaxial semiconducting film on top of a heavily doped substrate 2 of the same composition as film 1. It is well known that the index of refraction may be lowered by doping due to the interaction of light with carriers (plasma wave- photon interaction). The reasons for the lowering of the index of refraction is because the dispersion curve for the photon-plasmon system has a higher ratio of omega/k, as shown in Fig. 2.

For a good estimate of the refractive index, one may use the dielectric function epsilon(omega) = epsilon(infinity)omega/2/(p)/(omega/2/ + iw upsilon), where epsilon(omega), epsilon(infinity), omega(p), omega and upsilon are, respectively, the dielectric constant, the optical dielectric constant, the plasma frequency, the frequency of light and the collision frequency for the electrons or holes. Calculations have shown that for p-type GaAs, with 1020 cm-3 doping, one may achieve a 3% lowering of the index of refraction in comparison to the undoped case. The undoped epitaxial film having a higher index of refraction provides a guided optical medium for the surface wave. The arrangement of Fig. 1 has the following advantages:

1) The attenuation due to boundary scattering should be low. There is no physical discontinuity such as elastic properties, surface strain, etc., because the medium is an epitaxial growth of a substrate of the same composition and...