Optimal Photon Counting Receiver for Sub-Dead-Time Signal Transmission

In many practical scenarios, single-photon avalanche diodes (SPADs) are good solutions to improve the performance of optical communication systems due to their high sensitivity to photon arrival. SPAD receivers can be implemented in large arrays to achieve higher data rates and additional protection against background light; however, they suffer from a significant intersymbol interference (ISI) if the SPAD dead time is comparable or larger than the symbol duration, i.e., sub-dead-time signal transmission. This work proposes a novel detection scheme designed for high-speed SPAD-based systems to effectively mitigate the degradation induced by ISI. Different from traditional receivers, in the proposed scheme, the information extracted from both the counts and arrival times of photons are utilised for the optimal symbol detection in the presence of the non-linear and random ISI effect due to dead time. Our extensive numerical and experimental results demonstrate the superiority of the proposed photon time information based detection (PTID) scheme in terms of both BER performance and background light tolerance of the communication link. In addition, a linear approximation of the SPAD-based channel is investigated, which illustrates that the traditional equalization methods are effective under some specific circumstances.