Vertical-cavity surface-emitting laser (VCSEL)-by-VCSEL optical injection locking to obtain high cutoff frequencies of 1.3-mum VCSELs is demonstrated. A detailed physical explanation of the underlying mechanism is presented. VCSELs from the same wafer have been used in a master-follower configuration. Two probe stations are used in this experiment to power-up two VCSELs simultaneously. Polarization insensibility of the injection locking is demonstrated and a novel architecture is proposed to achieve cutoff frequency doubling. For the first time, a high cutoff frequency is achieved through optically injection locking the satellite mode of a long wavelength VCSEL. Injection-locking spectra with variable injection powers and variable detuning values have been obtained and methods have been proposed to obtain high cutoff and/or resonance frequencies. A rate-equation-based model is presented. Simulations have been carried out using this model. Finally, a linear increases in the follower VCSEL cutoff frequency with increasing injected power is demonstrated by using a semiconductor optical amplifier.