With the rapid development of information technology, the security problem of network communication becomes more and more obvious. With the increasing computational power of computers, traditional encryption methods are faced with great risks and will be vulnerable to decoding by quantum computers. Therefore, scientists developed the Quantum Key Distribution (QKD) technology based on Quantum mechanics and cryptography, which is called Quantum secret communication and provides a strong guarantee for information security.

        The principle of quantum secret communication is the use of quantum states cannot be measured and replication, at opposite ends of the communication line with quantum key for information encryption, information if intercepted or copy, the original quantum state will be destroyed, so that the transmission side know the existence of the eavesdropper, so also known as quantum communication completely safe data transmission scheme.

       However, quantum security technology faces many challenges in ultra-long distance communication. The single photon of quantum state is indivisible and cannot be duplicated, so it cannot be duplicated and amplified like traditional communication, which greatly limits the distribution distance of quantum key in optical fiber. Therefore, the transmission distance of quantum secret communication based on single photon technology largely depends on the loss in the line, and the optical fiber with lower attenuation is an effective way to extend the transmission distance.

     Therefore, the application of ultra-low loss optical fiber in quantum communication will become very important.

      So, what is ultra-low-loss fiber?

      The loss of optical fiber mainly comes from Rayleigh scattering loss and absorption loss of core material. The traditional optical fiber needs to be doped in the core to improve the refractive index of the core, but it will lead to high Rayleigh scattering and optical fiber attenuation. In ultra-low-loss optical fiber, pure silica is used in the core and cladding doping reduces the refractive index, which not only reduces the attenuation caused by Rayleigh scattering of the core, but also realizes the transmission of total reflection of signal light.

     Application of ultra-low loss optical fiber in quantum communication