Avalanche photo-detection for high data rate applications

Avalanche photo-detection is commonly used in applications which require single-photon sensitivity. We examine the limits of using avalanche photodiodes (APD) for characterizing photon statistics at high data rates. To identify the regime of linear APD operation, we employ a ps-pulsed diode laser with variable repetition rates between 0.5 MHz and 80 MHz. We modify the mean optical power of the coherent pulses by applying different levels of wellcalibrated attenuation. The linearity at high repetition rates is limited by the APD dead time and a nonlinear response arises at higher photon-numbers due to multiphoton events. Assuming Poissonian input-light statistics we ascertain the effective mean photon-number of the incident light with high accuracy. Time multiplexed detectors (TMD) allow us to accomplish photon-number resolution by ‘photon chopping’. This detection setup extends the linear response function to higher photon-numbers and statistical methods may be used to compensate for nonlinearity. We investigate this effect, compare it to the single APD case and show the validity of the convolution treatment in the TMD data analysis.