Optical Switch And Field-intensity Correlation Based On Intra-cavity Electromagnetically Induced Transparency

Optical switch,as one of the most important elements in optical communication,has lots of advantages on solving wavelength competition,improving wavelength reusing,optical path management and network distribution.Moreover,optical switch is the basic unit for optical quantum computer in future.Comparing with the logic elements in electric computer,optical logic elements built by optical switch can implement parallel action.Therefore,the running speed and information storage capacity of computer can be improved a lot.All-optical switch based on light controlling light can realize all-optical communication and all-optical computing,and is an essential subject to build all-optical network.Many researches have been carried out in atomic media,nanostructure and optical fiber system to realize optical bistable switch,wide-band optical switch and interaction-free optical switch et al.Among these researches,switching field is often applied between a ground level and an excited level thus strong switching field must be used to control weak signal,which influences the efficiency and response time of optical switch.In the thesis,we take advantage of intra-cavity electromagnetically induced transparency(EIT)technology on more sophisticated and efficient light manipulation in four-level atom-cavity system.This includes the manipulation on output field intensity,field phase and field-intensity correlation(quantum correlation)of output channels.By combining optical cavity technique with EIT technology,the output efficiency of system has been improved.This kind of optical switch has drawn a lot of attention in recent ten years.It can not only reduce optical loss and improve optical nonlinearity of the system,but also compress output linewidth and improve the switching efficiency of optical signal in high-speed information network.Firstly,a four-level atom-cavity system is utilized to fulfill a low-light-level high-efficient optical switch,where switching field couples two ground levels.It is much easier to realize splitting of intra-cavity dark state and observe double EIT windows by this way,and this overcomes the disadvantage of reducing switching power in previous works with three-level atom system.Therefore,an optical switch based on the splitting of intra-cavity dark state rather than single EIT window has higher efficiency.Owing to much smaller decay rate of ground levels(several orders smaller than the decay rate of excited levels),outputs can be switched on and off with much lower intensity of switching field(in our system,the Rabi frequency is 0.6MHz,similar order with decay rate of ground levels).Even with two control fields in our system,high switching efficiency for two output channels(98% for transmitted field and 94% for reflected field)has been obtained,which is a great improvement comparing with other optical switches based on EIT technology.Motivated by predecessors' works,a closed-loop interaction contour is introduced in above model leading to more sophisticated manipulation of light.The difference is that three ground levels and one excited level are utilized in our system instead of two ground levels and two excited levels.Thus,output linewidth can be much narrower,which provides advantage for optical switch in multichannel optical information network.Meanwhile,the closed loop induces phase-dependent EIT phenomenon,which realizes the continuously tunable transfer from single EIT window to double EIT windows as well as output intensity control.Besides,phase-dependent EIT has advantages on cross phase modulation(XPM),and it leads to the phase shift-? ??,which is believed to has potential application on quantum phase gate.In our next work,phase-dependent EIT technology is utilized on manipulation of output field-intensity correlation.Combining phase-dependent EIT technology with the driving method of two-sided coherent probe fields in four-level atom-cavity system,we use closed-loop phase and driving-field phase to control quantum coherence and quantum correlation of the system.Output properties and evolution of correlation function of two output channels are analyzed,and the main results are as following.(1)With driving-field phase equal to zero and closed-loop phase equal to odd order of ?2,coherent perfect absorption(CPA)of probe field appears at probe laser resonance.With driving-field phase equal to ?,the system is at total-reflection state.Therefore,making two kinds of phase as switching parameters,an optical switch with perfect efficiency(100%)can be operated.(2)With different closed-loop phase,manipulation on stable correlation of two output channels can be realized(at probe laser resonance: 0.27 ?0.46,at non-resonance of probe laser: 0.31 ?0.70).(3)Driving-field phase affects the coherence and capacity of noise resistance in this system.When two phases are both ?2,the stable intensity correlation of two output channels is the weakest and the noise resistance is fragile.When driving-field phase is ?,the intensity correlation of two output channels achieves maximum stable value 1 and the noise resistance is robust.The study on field-intensity correlation has potential application on correlated imaging,image encryption transmission and the improvement of noise resistance in quantum network.