Polarization control coding method coder and quantum key distributing system

Abstract

The present invention relates to a polarization control coding method, its coder and quantum key distribution system. It is characterized by that in the coder interior it adopts polarization retaining light path or 90-degree rotation Faraday mirror reflection to make output light pulse polarization states be identical; the quantum key distribution system is formed from polarization control coder as kernel, the light pulse outputted from transmitting end can be passed through quantum channel and unidirectional transferred into the receiving end, according to the superimposed interference result of light pulses and according to the quantum key distribution protocol the quantum key distribution can be implemented.

Description

Technical field: [0001] The invention belongs to the technical field of optical transmission secure communication, in particular to an encoding method and device in quantum key distribution. Background technique: [0002] Early quantum key distribution was encoded with photon polarization, which is suitable for free space communication but not for optical fiber communication system. Because the symmetry of ordinary optical fibers is not very good, and the interference in the transmission path is manifested as the influence on the polarization state of light, it cannot maintain the polarization state of light propagating in it, and polarization coding is not suitable for use in optical fibers. U.S. Patent No. 5,307,410 discloses a phase-encoded quantum key distribution scheme based on a pair of unequal-arm Mach-Zehnder (Mach-Zehnder) interferometers. Different arms of the special interferometer, because the interference received by different arms cannot be completely consist...

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Problems solved by technology

In fact, this kind of stability is only effective when the transmission distance is not too long and the interference frequency is not too high. When the transmission distance increases, the time difference of the light pulse going back and forth to experience the same position increases, and the anti-interference ability decreases accordingly; , because the optical pulse has to go back and forth twice in the quantum channel, the total loss of the channel is equal to the loss when the actual quantum channel is twice the length. Usually, the method of going strong light and returning single photon is used to make up for this defect, but this compensation method is only applicable to In the current situation of simulating a single-photon source with strongly attenuated laser pulses, the light source for ideal quantum key distribution should be a single-photon source, but the ideal single-photon source is not yet practical. Once the ideal single-photon source is used, the limit transmission of this scheme The distance is only half of the current distance; a more serious defect is that this scheme has potential safety hazards: eavesdroppers may attenuate the strong signal before entering the receiving area in proportion, and then supplement it with a Trojan horse signal with a wavelength very close to the working wavelength, making the reception The total monitoring signal strength in the area remains unchanged, that is, the signal strength monitoring fails. When the signal returns, the Trojan horse signal can be separated by the eavesdropper and the information it carries can be detected, and then the original signal photon is sent back through the "super low loss channel" Or, as long as the eavesdropper properly controls the signal attenuation ratio, the receiving code rate of the system can be unaffected, so that the sender cannot detect it.

For information security technology, this hidden danger of eavesdropping is fatal

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