Functional photonic superstructures: Coherent formation of active-passive photonic band gap heterostructures and photonic subbands

Abstract

We propose coherently generated photonic heterostructures using a functional photonic superstructure. In the absence of a laser field ͑control field͒, such a structure exhibits a conventional passive ͑off-resonant͒ photonic band gap. When a region͑s͒ 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 region͒ and an active ͑illuminated region͒ 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.The analogy between photons in spatially periodic dielectric structures and electrons in crystalline semiconductors has led to significant research for fundamental and device applications. These applications include nanodevices, quantum computing, light sources, quantum buffers, etc. 1,2 Significant attempts have been devoted to confine photons in one-, two-, or three-dimensional photonic band gap ͑PBG͒ systems, similar to confinement of electrons in quantum wells, wires, or dots. Construction of a photonic quantum dot via patterning a planar optical microcavity structure has already been reported. 3 Here, by decreasing the lateral size of the structure, the optical modes shift to higher energies. These modes are analogous to sharp discrete states of an electronic quantum dot. 4,5 By bringing two or more photonic quantum dots together, as shown in Ref. 6, one can also form a "photonic molecule." The spectroscopy of such a structure has shown that the energy splitting of the confined photonic modes increases with the decreasing the length of the channel joining the two dots, in close analogy to the emergence of electronic bonding and antibonding modes in diatomic molecules. Photonic quantum wells ͑QWs͒ have also been studied by sandwiching a medium between photonic barriers formed by several layers of semiconductors. The presence of quantized confined states in such structures, similar to those in semiconductor quantum wells, has been investigated. 7,8 In the above cases, the photonic potentials responsible for confining photons were generated by spatial variation of semiconductor materials, either by etching or forming a heterostructure of semiconductor materials with different refractive indices. In this paper, we propo...

Photonic valence/conduction subbands in optically generated photonic quantum wells: Tunable optical-delay line application

“…This changes the light scattering along the waveguide, setting up a photonic barrier or heterostructure. 8 As shown in Fig. 2 the increase of index perturbation here happens via coherent reduction of lower refractive index regions ͑SQW regions͒.…”

“…1͒, that allow photonic barriers and confinement happen via coherent processes caused by a laser beam ͑control field͒. 8 These structures are in fact functional semiconductor waveguides that in the absence of the control field act as passive photonic band gap structures characterized by their background refractive index corrugations. When the control field illuminates one or several parts of such waveguides, those parts are transformed into active photonic band gap structures with much higher refractive index contrast.…”

“…In one limit this can lead to formation of photonic QW structures with valencelike band. 8 In this case the photonic well is formed similar to a type I semiconductor QW with zero conduction band offset. As discussed in this paper, the other limit includes generation of photonic QW structures with conductionlike bands.…”

Triple photonic band-gap structure dynamically induced in the presence of spontaneously generated coherence

“…Recently, to achieve the efficient control and flexible manipulation of light propagation, laser-induced atomic coherence has been extended from the spatially homogeneous pattern into the spatially periodic pattern so that stationary light pulses (SLPs) [5][6][7][8][9][10][11] and dynamic photonic band gaps (D-PBGs) [12][13][14][15][16][17] are theoretically foreseen and experimentally observed. The essence of such an extension relies on the application of at least one standing-wave (SW) driving field on a cold or thermal atomic sample with suitable energy levels.…”

“…So far all investigations on D-PBGs have been restricted to the controlled generation and potential application of one or two band gaps around an atomic resonance [12][13][14][15][16][17]. In this paper we will demonstrate a feasible scheme for the simultaneous generation of three or even more band gaps with the purpose of further improving light-processing capabilities in actual situations.…”