This paper reports the spatial and spectral characteristics of multimode vertical cavity surface emitting laser (VCSEL) emission using near field scanning optical microscopy (NSOM). We have investigated 15 m diameter proton implanted 850 nm devices used in 2 Gb/s multimode fiber optic links. We have studied their near field spatial distribution of intensity and the lasing wavelengths of their transverse modes. False colored images were created to portray relative intensity, and spatial distribution information for each transverse mode. Correlation with shear force data allowed mapping of the optical distributions to topographical features of the device. Lasing filaments were observed at high drive currents. Spatially overlapping transverse modes were observed to compete for available gain while spatially isolated modes coexisted.
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