Time-domain balanced homodyne detection for measuring ultra-weak light

A homodyne detector was constructed for use in the balanced homodyne detection of light. In the frequency domain, the detector had an approximately 95 MHz 3 dB bandwidth and showed a 10 dB difference with regard to the electronic noise level at a local oscillator power of approximately 14 mW. With the detector, mean photon numbers in the signal light were measured in the time domain. The minimum mean photon number was about a few photons during the detector’s integration time of approximately 5.3 ns.