Spontaneous Raman scattering in [100], [110], and [11-2] directional GaP waveguides

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Abstract
Spontaneous Raman scattering in GaP waveguides with micrometer size cross sections has been investigated for [100], [110], and [11-2] directions. For backward scattering, the result is the same as for the GaP bulk crystals, which depends exactly on the Raman selection rule. However, it is found that mode changes from longitudinal optical (LO) phonon to transverse optical (TO) phonon mode and TO phonon to LO phonon mode occur when the waveguide cross section is of micrometer size for forward scattering. The mode change is determined by the relationship of the waveguide width, thickness and wave vector of phonons. The Raman scattering intensity ratios for different waveguide directions as well as for different light polarization directions obtained from the forward scattering experiments show good agreement with the calculations for this waveguide effect. In particular, the highest LO intensity is obtained for forward scattering in a [11-2] directional waveguide. This effect should be taken into account for the design of semiconductor Raman amplifiers and lasers with micrometer size waveguides.

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