Research And Development Of Single-Photon Detector Used In Quantum Communication And Issues Related

Quantum communication performs quantum key distribution (QKD) based on quantum mechanics for safe key exchange. It provides an ideal solution for traditional cryptography key exchange.1310nm,1550nm, which have the least loss of optical fiber, is the main band used in quantum communications.But the infrared photon signal is very weak and hard to detect. Development of stable and efficient infrared single-photon detectors is of great significance.Firstly, QKD protocols and their security are studies and discussed. Key technologies and the latest experimental progress of quantum communication are introduced. The SPD R&D includes five modules: SPD bias voltage, pre-amplification, avalanche signal extraction, temperature control and digital control circuit. InGaAs/InP avalanche photodiode (APD) which is the best single-photon detector for L-band as our research.A stable APD driver circuit, the passive mode and active suppression gated mode bias voltage circuit were designed. It is shown that the gate-pulse mode reduces the dead time and improves the count rate. Since avalanche APD output is extremely weak,80 to 100 times pre-amplification is achieved by high-precision wideband amp OP37. Precision comparator AD8561 is used to design window discriminator for effectively filtering interference. It is shown that detection sensitivity is improved significantly. Temperature is an important factor of APD work. APD is cooled by sophisticated controller MAX1978,which performs a precise control the operating temperature of APD.Air-cooled system is used for reducing the size of temperature-controller and makes it easier to move and maintain. In order to adapt to different APD and different detection requirements,MCS-51 microcontroller and precise time delay chip DS1023 series is used to design digital control circuit, parameters and working conditions can be set by a small keyboard on the machine which makes the single-photon detector has broader applicability.Finally, dark counts,behind-pulse, gate-pulse width are preliminary discussed. It is shown that a reasonable gate-pulse width can effectively reduce the interference caused by a variety of factors and improve detection performance. Single-photon detector as faint optical detection equipment, not only has important application in quantum communication, but also has further applications in space science, biology, medicine and other fields which are introduced in the end.