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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Functional photonic band gap structures based on electromagnetically induced transparency in the conduction intersubband transitions of quantum wells

Wei Li, Seyed M. Sadeghi, Xun Li, Wei‐Ping Huang

Published Sep 13, 2007• 1 citation
Publisher

Abstract

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.

DOI
10.1117/12.733323

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IEEE Journal of Selected Topics in Quantum Electronics•Nov 1, 2006•5 citations
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.
We use electromagnetically induced transparency combined with coherent enhancement of refractive index in the conduction intersubband transitions of a n-doped quantum well structure to study one-dimensional functional (active) photonic band gap structures. In the absence of a control laser field, such structures act as conventional photonic band gaps created by off-resonant (background) refractive index perturbations. In the presence of the control field, they are transformed into resonant structures with transitions around the Bragg wavelength. We show that this process can be used to (i) destroy the band gap, making the structure fully transparent around the Bragg wavelength, or (ii) coherently tune the band gap while enhancing its width by nearly a factor of 2. Using these phenomena we then study coherent localization of electromagnetic modes in photonic band gap structures without having any structural defects. Such a localization process here happens via partial illumination of such structures by the control field, generating electromagnetically induced optical defects. We show that the phase associated with such defects can be adjusted by the control field, allowing us to generate tunable electromagnetically induced transmission resonances (or photonic electromagnetically induced transparency) within the band gap.
We propose coherently generated photonic heterostructures using a functional photonic superstructure. In the absence of a laser field (control field), such a structure exhibits a conventional passive (off-resonant) photonic band gap. When a region(s) of such a structure is illuminated by the control field, coherent enhancement of refractive index increases the refractive index perturbations of that region, while electromagnetically induced transparency keeps it lossless. This forms a photonic heterostructure consisting of a passive (unilluminated region) and an active (illuminated region) photonic band gap structures. Using such a superstructure, we study a coherently generated photonic quantum well structure wherein two active photonic band gaps sandwich a passive region. We show that, since the active photonic band gaps are roughly twice wider than the passive band gap, they form two photonic barriers around the transparency band located at the longer wavelength side of the passive photonic band gap. This leads to formation of resonant transparency states or photonic subbands, similar to the conduction or valence subbands in electronic quantum well structures. We show that the energies and linewidths of such photonic subbands can be coherently controlled by just adjusting the control field beam.
We propose one-dimensional bright and dark optical lattices where Bragg scattering occurs, respectively, via periodic generation of gain without inversion and electromagnetically induced absorption in the absence of any refractive index perturbation. The absorption and gain processes are caused by quantum interference in the conduction intersubband transitions of a corrugated nnn-doped quantum well structure interacting with an intense infrared laser. The quantum well structure is embedded between two optical confinement layers, forming a periodic structure with a Bragg wavelength similar to that of the intersubband transition between the second and third conduction subbands of the quantum well. We show that in the absence of the intense infrared laser this transition is transparent, and the periodic structure forms a passive one-dimensional photonic gap generated by the background refractive index contrast of the corrugated region. In the presence of this laser, the intersubband transition is influenced by the quantum coherence effects, causing dramatic changes in the photonic band gap. We show that when one adjusts the intensity and wavelength of such a laser properly these effects can (i) destroy the one-dimensional photonic band gap, and (ii) form periodic regions of gain without inversion or electromagnetically induced loss, while the index perturbation is completely canceled out. Such bright and dark optical lattices can scatter a light at Bragg wavelength when its frequency is the same or close to that of the intersubband transition.
The phenomenon of electromagnetically induced transparency has been studied when a four-level atom is located in a photonic band gap material. Quantum interference is introduced by driving the two upper levels of the atom with a strong pump laser field. The top level and one of the ground levels are coupled by a weak probe laser field and absorption takes place between these two states. The susceptibility due to the absorption for this transition has been calculated by using the master equation method in linear response theory. Numerical simulations are performed for the real and imaginary parts of the susceptibility for a photonic band gap material whose gap-midgap ratio is 21%. It is found that when resonance frequencies lie within the band, the medium becomes transparent under the action of the strong pump laser field. More interesting results are found when one of the resonance frequencies lies at the band edge and within the band gap. When the resonance frequency lies at the band edge, the medium becomes nontransparent even under a strong pump laser field. On the other hand, when the resonance frequency lies within the band gap, the medium becomes transparent even under a weak pump laser field. In summary, we found that the medium can be transformed from the transparent state to the nontransparent state just by changing the location of the resonance frequency. We call these two effects anomalous electromagnetically induced transparency.
We utilize electromagnetically induced absorption (EIA) in a one-dimensional functional (active) photonic band gap structure to propose a coherently generated purely loss-coupled distributed feedback (DFB) laser. Such a laser happens when interaction of the photonic band structure with a control laser field totally removes its refractive index perturbation and replaces it with periodic regions of EIA, forming an optical dark lattice. Such a lattice does not have any stop band, but scatters light coherently at the Bragg wavelength. We also show that before the optical dark lattice happens, the photonic band gap structure can act as a coherently generated partly loss-coupled DFB laser with dominant lasing mode at the longer wavelength side of the stop band. We expect such a distinct feature makes this laser quite stable.
In this paper, quantum interference effects and atomically flat monolayer thickness fluctuations (growth islands) have been used in quantum well (QW) structures to propose a method to spatially modulate their refractive indexes and absorption/gain. The interference effects are caused by an infrared (IR) laser field, near resonantly driving the conduction intersubband transitions of an n-doped QW. The growth islands, on the other hand, laterally modulate these effects along the QW plane. It is shown that, when such a QW structure is properly designed, one can utilize these features to generate submicrometer regions (isles) of electromagnetically induced transparency (EIT) in the plane of the QW. This process occurs as the refractive indexes of these regions are coherently enhanced. The same laser field, in other regions of this plane, generates a large amount of gain or absorption with smaller refractive indexes. It is also shown that by varying the intensity and wavelength of the IR laser, one can dynamically switch over the EIT process from the lateral regions associated with a specific type of growth islands to other regions associated with either different types of islands or the nominal region of the QW. In the absence of this laser, such submicrometer-scale photonic structures do not exist, and the QW is transparent with a laterally uniform refractive index. These results can introduce a new trend for the generation of active photonic lattices, planar integrated optical circuits, and active photonic nanostructures