Investigation For Cross-kerr Effect Via Atomic Coherence And All Optical Switching

The enhanced cross-kerr nonlinear refractive index n₂ of a three-level A-type atomic system via electromagnetically induced transparency (EIT) is theoretically analyzed and experimentally investigated. The dependence of the shift of an optical bistability hysteresis curve on the nonlinear phase shift induced by a controlling light is observed in a four-level atomic system of ⁸⁷Rb inside an optical ring cavity. The refractive and absorptive nonlinearities enhanced by atomic coherence provide the physical mechanism of the phenomena. Based on this effect, an all-optical flip-flop and storage of optical pulse signals switching are implemented. Also included in this thesis are some preliminary research work which relevant to the designing and construction of a Rb Vapor-Cell Magneto-Optical Trap in our lab, Cooling and trapping of Rb atoms in MOT. The main work accomplished are as follows:1. The dependence of n₂ of a three-level A-type atomic system via electromagnetically induced transparency (EIT) is numerically calculated based on a simple theoretical model. The result show: The cross-kerr nonlinear refractive index n₂ is greatly enhanced by the atomic coherence when the condition of near two-photon resonance satisfied.2. Using lock-in amplifier and PID (Proportional, Integral, Derivative) electric circuit, the frequency of diode laser is stabilized on a Fabry-Perot (FP) cavity transmission peak with highly mechanical stability. When the frequency locking system working, the frequency tunable range of the laser is about 4GHz around the D1 transition of Rb. This system was used in the experimental investigation of the interaction between light and atoms, especially, in the case of far off the atomic resonance.3. The design and construction of a ring-cavity, which used to measure cross-kerr nonlinear refractive index n₂ are described in details. The enhanced cross-kerr nonlinear refractive index n₂ of a three-level A-type atomic system via electromagnetically induced transparency (EIT) is experimentally measured.4. A ring cavity lock-in system are designed and constructed for the investigation of optical bistabiliy and all optical switching.5. The dependence of the shift of an optical bistability hysteresis curve on the nonlinear phase shift induced by a controlling light is observed in a four-level atomic system of 87Rb inside an optical ring cavity. The observed effects are reasonably explained with the change of cavity resonant condition resulting from the enhanced cross-phase nonlinearity owing to atomic coherence via a simple physical model.6. We demonstrated that the OB hysteresis curve can shift toward different directions by two suitably tuned optical signals under the condition of keeping the intensity of the coupling light beam constant. For a given intensity of the probe beam, the OB system can be reliably changed from its lower stable state to the upper state under the triggering of an optical signal pulse. The inverted OB upper state does not drop to its initial lower stable state after the triggering signal pulse ends, but moves to the upper branch of the initial OB curve and stays there stably until another optical signal tuning to another atomic transition comes by. These results show the possibility of information storage in the current four-level atomic OB system. The new mechanism of information storage might have important applications in the all-optical information processing.7. A ultrahigh-vacuum chamber and A optical system are designed and constructed for Rb MOT.The characterized works among the above are as follows:(1). we present an experimental observation to the cross-phase shift in a three level coherent hot atomic system inside an optical ring cavity. The cross-phase nonlinear index of refraction as a function of controlling (proble) light frequency detuning was experimentally measured. The cross-phase shift of it induced by controlling light on the probe wave has been observed under a relatively low controlling power of 16.2mW. (2). In an optical bistability system consisting of an optical cavity and four-level atoms positive and negative phase shifts of an intracavity optical mode can be observed under the action of contral signal pulses tuned close to certain energy levels of the atoms. The bistability hysteresis curve can thus be shifted and switching between the "low" and "high" transmission states obtained in a controlled manner. Based on the above effects we have realized all-optical storage and optical switching controlled with low...