Study On Frequency-entangled Two-photon Based On Parametric Instability In Fiber Ring Cavity

High performance frequency-entangled two-photon source has important application in quantum communication,quantum computation et al.Nowdays,the preparation of entangled photon source is mainly based on nonlinear optical medium with second-order or third-order susceptibilities.The efficiency of entangled photon produced by spontaneous parametric down conversion process in second-order nonlinear crystal(such as?-Ba B₂O₄,etc.)is low,and the modulation instability in third-order nonlinear medium(such as fiber,etc.)can produce entangled photon pairs with high efficiency,but the photon pairs fluctuate randomly both in frequency and phase due to quantum noise.Recently,it has been found that the parametric instability gain sidebands generated in a dispersion periodically modulated fiber ring has high coherence and strong quantum correlation,which can be used to high coherent frequency-entangled two-photon source.In this paper,the basic principle and output characteristics of parametric instability in fiber ring cavity are discussed,and the entanglement characteristics of two-photon source based on parametric instability are verified by experiments.The main research contents are as follows:(1)The difference between parametric instability and modulation instability is compared,and a high coherent frequency-entangled two-photon source based on parametric instability is proposed.The evolution mechanism of parametric instability in dispersion periodically modulated fiber is analyzed,and the process of parametric instability in fiber ring cavity is simulated.The simulation results show that when the pump peak power is larger than 5W,parametric instability appears in the ring cavity,the frequency interval of gain sidebands can be tuned by the pump peak power,which provides a theoretical guidance for the subsequent formation of a two-photon source with high coherence parametric instability in the ring cavity.(2)We build an active fiber ring cavity with periodically modulated dispersion,and excite the parametric instability by controlling pump and polarization state.The parametric instability gain sidebands can be tuned effectively by biasing intra-cavity polarization state.A real-time measurement module based on dispersive Fourier transform is built to characterize the single-shot spectral characteristics of the parametric instability sidebands.Through the autocorrelation analysis of the conservative single-shot spectra,it is found that the single-shot spectrum generated by parametric instability is completely identical,and the Stokes and anti-Stokes sidebands have high coherence and consistency.(3)Using the single photon measurement technology,it is found that the average power of each sideband after filtering reaches-49.6dBm,and the single channel photon counting rate reaches 80k/s.Furthermore,we use two-photon coincidence measurement technology to study the photon statistical characteristics of the two-photon source,and compare the coincidence counting rate under different attenuation degrees.When the single channel photon counting rate is reduced to 2000/s by a tunable attenuator,the influence of the system random noise on the single photon can be effectively avoided.Finally,the quantum correlation characteristics of the two-photon source are studied by two-photon interference technology.The Hanbury Brown-Twiss(HBT)interference experiment shows that the coherence time of the two-photon source reaches about 3.8ns,The Hong-Ou-Mandel(HOM)interference visibility of the two-photon source is greater than 84.6%,and the coherence length reaches 4.57mm,The above experimental results shows that the two-photon source based on the parameter instability in the fiber ring cavity has good quantum correlation.