Research On Electromagnetic Induction Grating And Dual-cavity Optical Bistability In Quantum Coherent Media

In recent decades,laser-induced atomic coherence and quantum interference effects have attracted the attention of researchers.When a coherent light couples the transition between two energy levels in atomic system,Autler-Townes split can appear so that the interaction between light and matter will experience multiple transitional channels,and the quantum interference effect between multiple transitional channels results that the absorption,dispersion and nonlinearity of medium exhibit new physical properties.Therefore,quantum coherence effects have potential applications in many fields,such as nonlinear optics,laser physics,quantum optics,quantum information,and precision measurement.In this paper,we ues the semiclassical theory for the interaction between light and matter to investigate electromagnetically induced grating and double-cavity optical bistability in quantum coherence medium.1.The electromagnetically induced grating in different multi-level coherent atomic medium studied.It is found that,in the electromagnetically induced grating,the phase modulation determined by the refractivity of medium can diffract the light into different spatial directions easily,while the amplitude modulation depened on the absorption of medium affects the transmission energy of grating.Therefore,the way to obtain an efficient electromagnetic ally induced grating is to achieve the enhancement of refractivity accompanied with zero-absorption or gain.In an N-type four-level atomic system,by adjusting the resonance states of optical fields,enhanced nonlinear refractivity along with suppressed linear absorption or gain can be realized.In a hybrid system consisting of two A-type three-level atomic systems,two Raman resonances,which result in absorption and gain,can be induced when the atoms are driven by two far-detuned control fields.By controlling the two-photon detuning,we can obtain enhanced refractivity with tunale absorption.In a double-A four-level atomic system,the incoherent pump field helps in generating Raman inversion and the occurrence of gain.At the same time,the coherent coupling field can introduce the atomic coherence effect.Owing to the effects of these two mechanisms,we achieved high refractivity accompanied with vanishing absorption or gain.Since the optical response of atoms strongly depends on the intensity of external optical field,a two-dimensional standing-wave field coupling these three kinds of atomic systems helps in obtaining an efficient two-dimensional electromagnetically induced grating.In addition,we obtained a blazed grating and a blazed gain grating by using a sawtooth-wave to couple a double-? four-level atomic system and further proposed a scheme for all-optical beam splitter and router.Investigation implies that the diffraction order and diffraction energy of the grating can be modified effectively via the intensity and detuning of optical fields,this is in favour of all-optical devices such as optical switching,optical splitting,and optical routing.Therefore,our schemes have potential applications in all-optical communication and networking.2.Based on an N-type four-level atomic system,the double-cavity optical bistability and all-optical bistable switches are studied.Compared with a three-level atomic system,using an N-type atomic system can achieve the enhancement of two-photon absorption or Kerr nonlinearity under low-light conditions,as a result,a double-cavity optical bistability with low-threshold can be realized.It was found that by adjusting the detuning and intensity of the optical field,the threshold and width of the bistable curve can be manipulated effectively.And optical multistability can be obtained for specific intensity and detuning of optical fields.Compared with the traditional single-cavity optical bistability,the double-cavity optical bistability can control the output of the two optical signals in optical cavities simultaneously.Based on this feature,a new type of all-optical switch can be realized when modifying the input of either of the cavity fields,this has potential applications in all-optical calculation and communication.