Patent attributes
In order to operate a single photon detector in communication wavelength band at a high speed, a DC bias voltage 2 lower than the breakdown voltage is applied to an InGaAs/InP avalanche photodiode (APD) 1. A 500 MHz sine wave gating signal 3 is superimposed with the DC bias voltage 2 and applied to the APD 1 so as to exceed the breakdown voltage by about 4V in a fractional time of each period. The sine wave gating signal 3 passed through the APD 1 is substantially completely removed by a filter 4, thereby improving S/N and enabling to detect a single photon even if the avalanche multiplication time is shortened to reduce the after pulse and the detection period. As a result, it achieves to detect a single photon in the 1550 nm communication band at a high speed.
