Optical responses of active multi-quantum well photonic band gap structures are mostly determined by the excitonic effects (superradiant excitons) and the contrast between the background refractive indices of the wells and barriers (nonresonant effects). Recently we studied coherent control of such photonic band gaps via infrared dressing of the superradiant excitons. This was done considering an infrared laser field near resonantly coupled such excitons with the excitons associated with the second conduction subbands of the quantum wells. This led to the formation of photonic electromagnetically induced transparency and disentanglement of the excitonic contributions from those associated with the nonresonant effects via destruction of the superradiant modes. Here we study how such a disentanglement process dramatically changes transmissions of the Bragg multiquantum well structures. In particular, we show that when the infrared laser intensity is high, the non-resonant effects form an incomplete passive band gap around the Bragg wavelength. Such a band gap, which is immune against the infrared laser, is flanked by two non-photonic gaps (absorption peaks). These peaks are associated with the large absorption of two dressed exciton states, i.e., Aulter-Townes doublet. Any variation in the intensity of the infrared laser changes the wavelengths of these peaks, making them closer or farther to the passive photonic band gap.
In an active photonic band gap structure, a control laser can manipulate the probe signal coherently if the
probe field satisfies the Bragg condition and is resonant or near resonant with the electronic or excitonic
transitions of the constituting material structure. Using coherent effects in the conduction intersubband
transitions of an n-doped quantum well, recently, we showed that one could convert a fully transparent
waveguide into an active photonic band gap. Such an active photonic band gap was different from those based
on superradiant excitons in two main issues: (i) the probe field was near resonant with the conduction
intersubband transitions of the quantum well, and (ii) one needed a control field to generate the coherent
effects and, thereafter, the band gap. Here we use such coherent processes, which include electromagnetically
induced transparency and coherent enhancement of refractive index, to study a one-dimensional functional
photonic band gap structure. In the absence of a control laser field such a structure acts as a conventional
photonic band gap created by an off-resonant (background) refractive index perturbation. In other words, the
probe field does not feel any resonance in this structure and the photonic band gap is passive. In the presence
of the control field, the structure is activated and transformed into a resonant structure. Under this condition, the probe field becomes near resonant with the intersubband transitions while still satisfies the Bragg condition. We study how the coherent effects in such transitions can lead to destruction and enhancement of the photonic band gap in a waveguide structure.
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