Efficient modulation of electrically injected spin signals that is suitable for modern-day transistor functionality is yet to be established. In this work, we demonstrate in detail the fabrication of a Fe/n-GaAs spin injection device and the experimental setup for an optical gating of the nonlocal spin transport signal. In situ scanning electron microscopy interface imaging reveals more uniform current distribution at the Fe/n-GaAs injector interface at bias voltages higher than the Schottky barrier height. Three- and four-terminal Hanle measurements confirm successful spin injection into n-GaAs, with strong interfacial spin dephasing at high magnetic fields. A time-resolved pump-probe Kerr rotation setup was used to illuminate circularly polarized light in the region of the pure spin current in Fe/n-GaAs lateral spin injection devices, where (0.4±0.3)% modulation of the nonlocal signal depending on the light helicity was observed at 30K.