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A new method to detect infrared single photon using avalanche photodiodes is proposed, which combine the requirements of a single photon detector control circuit and features of the electric pulses generator by transient process of transmission lines. When the terminated boundary conditions of transmission lines are changed quickly, voltage across the switch devices will drop suddenly in the electric pulses generator model and at the same time a signal that can reflect the drive information of the switch device will export from load resistance. So we can replace the switch with avalanche photodiodes who can act as an excellent optoelectronic switch. Then when faint laser pulses enter the avalanche photodiode, resistance of the avalanche photodiode will decrease quickly and with that voltage across avalanche photodiodes will drop simultaneously and a signal that can reflect the single-photon laser pulses will export from the load resistance. The simulation results are given for the new quenching circuit model of avalanche photodiodes and the analyses emphasis on the feasibility of the quenching model and the influence of each electrical component on the performance of the quenching circuit. Finally optimal parameter of the electrical components in the model is demonstrated.

This paper introduces the design of a single photon detector based on the AT89C51 single chip microcontroller for quantum key distribution at telecommunication wavelengths. An avalanche photodiode (APD) is operated in Geiger mode and stabilized at temperature of 228K for translating the single photon signals into electrical pulses. The photon induced avalanche pulses are amplified and converted to digital data. The microcontroller discriminates the data, counting the number of photons, and then displays the photon number and the detection efficiency on a LCD display. The instrument can effectively support the study of quantum key distribution.

Photon cannot keep itself unchanged from emission to absorption. The information encoded on the photon is also changed due to interaction with environment. There has no definitely demonstration that the photon being absorbed is the original one from ideal light source since the quantum mechanics itself is an indeterminate theory that the physical measurement is only the probability. We divide the change of the photon state into two parts that one can be compensated and the other cannot be compensated. A concept of photon reconstruction is introduced to explain every optical phenomena including Raman scattering, multi-photon absorption, nonlinear phenomena, free electron lasing, quantum entanglement, high order coherence, ghost imaging and the de-phase which result in error bits or information loss in the quantum information process. An experimental result is explained to show that the signal photon can modify the background even the energy of the photon is not enough for absorption in the wide-band gap semiconductor material. The photon-current-voltage curve and dark-current-voltage curve of an absorption, grating, and multiplication InGaAs/InP avalanche photodiode is analyzed to show that 1550nm input light modified the dark background even the applied reverse bias voltage is far below the punch-through voltage. This increase of the dark count directly relates to the input photons at the 1550nm wavelength but is not due to absorption in the absorption layer and insensitive to the applied voltage.