Semiconductor optical amplifier (SOA) can be used to generate narrow optical pulse with steady high extinction ratio and has been widely used in the field of optical fiber sensing. However, most of current schemes only employ SOA in unidirectional modulation for pulse generation. Based on the feature that SOA can work in both directions, this paper proposes a bidirectional narrow pulse modulation of SOA to further enhance the extinction ratio of optical pulse. A fiber optic mirror is used to reflect the optical pulse generated by unidirectional modulation back to the SOA for the second pulse modulation. The experimental results show that compared with unidirectional modulation, bidirectional modulation achieves a maximum extra gain of 6.18 dB at low input optical power. For pulsed light with an input peak power of 6 dBm, the bidirectional absorption can further weaken the leakage light intensity by more than 30 dB, and the overall absorption rate reaches more than 72 dB.