The influence of residual facet reflection on the high-frequency response of distributed feedback semiconductor laser(DFB-LD)/electroabsorption(EA) modulator integrated light sources and its suppression are studied.To explain the peaks observed in the low frequency range of the modulation response of the integrated light sources,we measured the relative intensity noise spectra of the DFB LD and the modulation response of the EA modulator at different reverse biases.It is found that the key factor influencing the modulation response of integrated light sources comes from the residual reflection at the EA facet rather than the microwave signal crosstalk.In order to suppress the facet reflection,improved anti-reflection coating was applied to EA modulator facet,and efficient improvement in high-frequency performance has been demonstrated.