We have investigated the spectral characteristics of semiconductor lasers locked to the external light injected from a modulated laser. study on FM sideband injection locking has shown that when SLs are locked to the target sidebands of the directly modulated ML, the presence of the unselected sidebands influences the resulting microwave signals. The unselected signals can produce the unwanted beat signals around the desired beat signal, which degrade the overall system performance. This analysis way to generate Giga HZ signal generation.