High-speed single-photon detection for quantum key distribution

• Main Author: Yu, Timothy Shenrong.
• Other Authors: Shum Ping
• Format: Final Year Project
• Language: English
• Published: 2011
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: http://hdl.handle.net/10356/45846
• Institution: Nanyang Technological University

The integrity of conventional cryptographic systems is placed upon the assumption of the inability of current computational power to generate the reversal of the cryptographic key generation algorithm. However, quantum key distribution utilises the principles of quantum mechanics to ensure secrecy. This is independent of any mathematical algorithm of any mathematical algorithm and hence its security will not be compromised with the improvement of computational power. Nevertheless, current quantum key distribution systems are limited by the detection rate of single photons. Several mega-hertz clocking rate of existing commercially available single-photon detector systems restricts the speed of cryptographic key generation significantly. Therefore, the aim of the final year project was to utilise a commercially available single-photon avalanche diode to enhance the key generation rate of quantum key distribution systems. Conventional rectangular-wave gating allows only approximately 1MHz gate repetition rate due to the long lifetime of trapped carriers. In 2006, a sinusoidal gated scheme was demonstrated, attaining up to 500MHz gating rate. It was subsequently improved to 2.23GHz in 2010. In the final year project, the gated passive quenching circuit required to operate the SPAD was studied extensively and fabricated. Various essential components to realise the detection scheme were integrated with the considerations of high frequency/speed operations.