The present invention relates to a single photon detector (SPD) at telecom wavelength of 1.55 μm based on InGaAs/InP avalanche photodiode (APD). In order to operate the SPD at a low after-pulse noise, a DC bias voltage lower than the breakdown voltage is applied to an InGaAs/InP APD. A bipolar rectangular gating signal is superimposed with the DC bias voltage and applied to the APD so as to exceed the breakdown voltage during the gate-on time of each period of the gate signal. The use of the bipolar rectangular gating signal enabling us to operate the APD well below the breakdown voltage during the gate-off time, thereby make the release of the trapped charge carriers faster and then reduces the after-pulse noise. As a result, it permits to increase the repetition rate of the SPD.