Research On Fano Enhanced Tunneling Measurement And Fano Enhanced Nonlinearity In Quantum Wells

Quantum well structures show great potential in the field of the optoelectronic devices recently,due to its controllable quantum confinement effect and mature fabrication technique.On one hand,the tunneling effect between two adjacent wells provides the rich and adjustable energy structure,because it can be adjusted by the bias voltage.On the other hand,its inherent characteristics,e.g.large electric dipole moments and long coherence time,provide the basis for the study of the nonlinear optics.Based on the tunneling induced Fano interference in the quantum well structure,this thesis studies the nonlinear optical properties and its application in the tunneling measurement.The main results include:(1)The modified optical properties of the quantum well structure are studied based on the Fano interference.Due to the thin barrier,tunneling effect can appear between the discrete state and the continuum,and then the interference between the different transition paths leads to the Fano effect.Using the semi-classical theory of the light-atom interaction,the optical Bloch equation can be obtained.Combined with the knowledge of the nonlinear optics,the response of the linear absorption and nonlinear absorption spectrum to the tunneling strength can be obtained.From the simulation results,the asymmetry index shows a linear dependence on the tunneling strength.In addition,the detection sensitivity based on the nonlinear absorption spectrum is about 10 times larger than that of the linear absorption spectrum.(2)The enhanced fifth-order nonlinearity is studied based on the Fano interference.Using the probability amplitude method of the light-atom interaction,the linear,self-Kerr,and fifth-order susceptibilities can be obtained with the knowledge of the nonlinear optics.Due to the Fano interference,the nonlinear gain can well balance the linear absorption,which causes a transparency window.Also,the fifth-order nonlinearity can be enhanced with the increase of the Fano interference index.Under the appropriate conditions,the fifth-order nonlinearity can be enhanced by 10 times approximately from the simulation results.In summary,the tunneling effect induces the Fano interference and then the optical properties of the quantum well structure can be modified,which provides an optical approach for detecting the tunneling effect.In addition,the enhanced fifth-order nonlinearity may have certain guiding significance for the research on the nonlinear optics at a low light level in quantum wells.