Adiabatically driven electron dynamics in a resonant photonic band gap: Optical switching of a Bragg periodic semiconductor

Abstract

The adiabatic driving of the resonant electron dynamics in a one-dimensional resonant photonic band gap is proposed as an optical mechanism for nonlinear ultrafast switching. Pulsed excitation inside the photonic gap results in an ultrafast suppression and recovery of the gap. This behavior results from the adiabatic carrier dynamics due to rapid radiative damping inside the band gap.The time scale of the optical response in nano-optical systems near resonance is limited by the response time of the structured material and the duration of the excitation pulse. If all intrinsic relaxation processes in the material are fast compared to the duration of the excitation pulse, the optical pulse adiabatically drives the material variables and determines their temporal response. 1 In this Paper, we theoretically analyze and quantitatively explain this principle for pulse shaping and optical switching in a half-wavelength (i.e., spacing /2) periodic semiconductor structure, recently observed experimentally in Ref. 2. The analysis of the nonlinear reflection experiments 2 in pump-probe geometry, is carried out on the basis of the coupled semiconductor Maxwell-Bloch equations, recently used to explain the transmission of short single pulses through multiple quantum well Bragg structures. 3 In multiple quantum well structures (MQW), with spacing great enough to eliminate direct Coulomb interaction between the quantum wells (QWs), the excitonic resonances inside the different QWs couple radiatively. 4-6 If the QWs are in Bragg periodicity, a super-radiant mode develops leading to a broad resonant photonic band gap 3,7-13 which for a large number of QWs results in the band gap of a onedimensional photonic crystal. 14,15 Long-lived and short-lived polariton modes in such Bragg (and anti-Bragg) structures have been discussed. 16 Also the influence of defects in MQW photonic crystals and their optical properties have been studied. 17 Typical bandwidths are on the order of 10-20 meV, compared to 1-2 meV for the spectral width of a switching pulse. The resonant band gap itself is similar to a passive dielectric band gap of a Bragg reflector caused by multiple reflection at the periodic surfaces and interference effects (analytic solutions are known from atomic systems 18 ). However, in contrast to passive dielectrics, the excitonic resonance which forms the band gap, can be directly influenced by the strength of the light field because of strong optical nonlinearities due to Coulomb many body and other interaction effects, and Pauli blocking. Such nonlinearities may lead to exciton saturation resulting in a breakdown of the band gap. 19 In this Paper, we show that a strong laser pulse propagates-besides reflection-without strong reshaping if its spectrum is completely inside the optical band gap. This pulse suppresses the photonic band gap for the time of its duration, thus allowing for a femtosecond switching mechanism. This behavior is caused by Pauli blocking and Coulomb nonlinearities of the carrier density which adiabatically f...

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