Index confinement is studied experimentally and through modelling for lithographic vertical-cavity surface-emitting lasers (VCSELs) and contrasted with other types of VCSELs. Modelling shows that the index confinement is set by the height of a shallow internal mesa that produces the optical mode confinement. Overgrowth with a semiconductor mirror enables a range of index confinement from zero (no index guiding) similar to proton-implanted VCSELs to much higher confinement than viable for oxide VCSELs. Lasing spectra are studied for side-mode-suppression ratio and beam patterns are compared for high and low indexes confined VCSELs of different sizes.
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