Single Photon Interference In Fiber System

Phase interferometry is widely used in telecommunications, manufactories and other occasions where require high-precision measurement of ranging and angle. Phase interference means that the interference intensity will vary due to the relative phase between two light waves with same frequency but from different lengths encounter each other in some space. After measuring the interference intensity, we could obtain the corresponding phase information and associated path information. Single photons phase interferometry measurement can obtain the phase information by observe the interference at single photons level. The interferometer of single photons is applied to quantum key distribution, with information coded in the single photon phase, access to key information at the receiver. For single-photon comply with quantum mechanics theorem, indivisibility and non-clone, Quantum key distribution using single-photon carrying information is proved to be absolutely security in theoretically, the application of Vernam one-pad key distribution in the quantum field. Phase-coded key transfer has high practical value in the distribution of fiber-optic quantum cryptography because of its nearly independence of birefringence effect in fiber. The device of single photon sideband phase encoding use an electro-optical phase modulator to encode or decode phase information at the sender and receiver respectively. It is effective to eliminate instability from fiber thermal drift.In this paper, we analysis the entire transmission in the mathematical way of the device single photon sideband phase modulation, then obtain the conclusion that the error is minimal when the visibility is maximal through the study between them. To attain the maximal visibility, the modulus of the two phase modulations is asked to be equal. However, the distribution system is not enough ideal for inconstant external environment, address which we make following research: (1) We have analyzed the optimal modulation factor ratio to the two phase modulators. Considering the random time-dependent phase noise, we present a method to lock the optimal modulation factor ratio by using the fast tracking the relative phase between the two modulators. The final phase fluctuation is±0.0016rad. And the changing to interference visibility is no more than2x10-4.(2) It is significant for single photons transmission to make the FP cavity transmission frequency to the laser frequency. We use wavelength modulated and demodulated techniques for the FP cavity, with mean photon number about0.1, to lock the FP cavity transmission frequency to the laser frequency. The FP transmission band is limited to2MHz after locked.