Oxide–confined vertical cavity surface emitting lasers (VCSELs) with anti–waveguiding AlAs–rich core presently attract a lot of attention. Anti–waveguiding cavity enables the maximum possible optical confinement of the VCSEL mode (“λ/2 design”), increases its oscillator strength and reduces dramatically the optical power accumulated in the VCSEL mesa regions outside the aperture. VCSEL designs are suggested that favor single transverse mode operation. Modeling including current–induced and absorption–induced overheating shows that the preference for the transverse fundamental mode persists up to 10 mA current at 5 µm aperture diameter. Error–free data transmission is realized up to 160 Gb/s in digital–multitone (DMT) format using single–mode anti–waveguiding VCSELs. The approach to single–mode anti–waveguiding VCSELs is extended over a broad spectral range realizing error–free high–speed data transmission at both 850 nm and 910 nm.