Noncircular Refractive Index Profile and Breakdown of Mode Degeneracy of Vertical Cavity Surface Emitting Lasers

Spatially and spectrally resolved near-field images of the transverse mode patterns of vertical cavity surface emitting lasers (VCSELs) are obtained by confocal microscopy with optical spectrum analyzer. A non-circular internal effective index profile of the VCSEL is inferred from the observed wavelength splitting of the degenerated modes. Using the mode intensity patterns associated with their spectral information, an elliptical parabolic profile superposed to a step-like refractive index profile is extracted by fitting the internal structural parameters of VCSEL. Wavelength splitting of the degenerated LG ₀₁ modes is calculated from the fitting results, and is found to be in reasonable accord with our experiment results.