Multiphoton discrimination at telecom wavelength with charge integration photon detector

We present a charge integration photon detector (CIPD) that enables the efficient measurement of photon number states at the telecom-fiber wavelengths with a quantum efficiency of 80% and a resolution less than 0.5 electrons at 1Hz sampling. The CIPD consists of an InGaAs pin photodiode and a GaAs JFET in a charge integration amplifier, which is cooled to 4.2K to reduce thermal noise and leakage current. The charge integration amplifier exhibits a low noise level of 470nV∕Hz1∕2. The dark count is as low as 500electrons∕h.