Ultrafast modulation of semiconductor lasers at a rate higher than the relaxation-oscillation limited frequency is important for millimeter wave photonics and many other applications. Edge-emitters of compound cavities and other multi-section devices have been employed for such generation in the past. We demonstrate in this paper two methods of modulating VCSELs in the frequency range between 20GHz and 130GHz through a detailed numerical simulation. The first method employs two coupled VCSELs and high frequency oscillation is provided by inter-VCSEL coupling, while the second method utilizes multi-transverse mode beating in a large VCSEL. We show that the mode beating is greatly enhanced by collecting laser output from part of the output facet, providing a relatively easy laser modulation at a frequency larger than 100GHz.