We simulate the injection-locking performance of a 1% antireflection coated Fabry-Perot laser amplifier (AR-FPLA) and demonstrate the 2.5-Gbit/s DWDM-PON application with the directly modulated AR-FPLA based ONU transmitter under side-mode injection-locking condition. The effect of the AR-FPLA front-facet reflectivity on the injection locking range detuning and the Q-factor are interpreted from theoretical simulations and are experimentally characterized. A 25-channel locking capacity is reported for such a side-mode injection-locked AR-FPLA with corresponding wavelength locking range of 30 nm, the minimal requested power of -7 dBm and gain extinction ratio of <;7 dB by reducing its front-facet reflectivity to 1%. At bit rate of 2.5 Gbit/s, the BER of 10 -12 is achievable for the nearest 17 channels of AR-FPLA at receiving power of -21 dBm, and all of the 25 injection-locked channels with SMSR of > 35 dB can guarantee the BER of <; 10 -9 with their worst receiving sensitivity degrading to -19 dBm.