Injection locking properties of a single loop optoelectronic oscillator have been re-visited with particular emphasis on injecting an external microwave signal to the stationary microwave signal present in the loop shining on the Mach–Zehnder modulator. This approach has made it possible to investigate the behavior of the normalized amplitude and frequency with the fiber delay. Detailed theoretical calculations have been carried out to investigate the dependence of the locking characteristics on the loop parameters. Also presented are experimental results in support of the theoretical findings.