Research On Enhancement Of Kerr Nonlinearity And Pi Phase Shift Based On Electromagnetically Induced Transparency

Since the invention of laser,many novel optical phenomena have emerged,such as saturation absorption,photon echo,stimulated Brillouin scattering,parametric oscillation,self-sensing transparency and four-wave mixing.These phenomena can no longer be explained by the theory of linear optics.Therefore,nonlinear optics emerged to explain these phenomena.Electromagnetically induced transparency is caused by the quantum coherence effect,which has weak absorption near the resonance frequency and sharp changes in polarizability,making it of great application value in many aspects,such as frequency conversion,light velocity reduction Slow and nonlinear enhancements.Using electromagnetically induced transparency,people can achieve relatively strong nonlinear polarizabilities under low light conditions.As a result,many proposals for nonlinear enhancement based on electromagnetically induced transparency have been proposed,and people have focused more on how to obtain strong nonlinear polarizability under weak absorption or even no absorption.One important task in this paper is to investigate the enhancement of the Kerr nonlinearity in a four-level tripod-type atomic system completely without absorption.We use density matrix method to add incoherent pumping rate into the motion equation of density matrix.Through theoretical calculation and numerical simulation,it is found that under the proper parameter condition the Kerr nonlinearity can be enhanced with completely suppressed absorption at two different probe frequencies.Thus,we can get a symmetrical enhanced Kerr nonlinearity.By comparison with existing paper,it is found that the change of particle population and its influence on the coherence of atomic states causes Kerr nonlinearity enhancement.Another important task in this paper is to investigate the phase shift of reflected probe field in an asymmetric optical cavity,based on the electromagnetically induced transparency.In this task,we theoretically calculate the transmission spectrum and reflection spectrum equation of the cavity containing atomic medium,and found that in the reflective channel,the cross phase modulation can be realized by using the transmission and reflection properties of the mirror.And electromagnetically induced transparency here acts as an optical switch,when the electromagnetically induced transparency is formed,the probe field can experience an accurate ? phase shift,when the electromagnetically induced transparency is not formed,there is no phase shift.Compared with the scheme of electromagnetic induced transparency and the scheme of the high-finesse optical cavity,the proposed scheme for cross-phase modulation is easier to implement under existing experimental conditions.Moreover,the accurate ? phase shift can be obtained without strictly controlling the optical length of the medium.