It has been recognized for some time that the spontaneous emission by atoms is not necessarily a fixed and immutable property of the coupling between matter and space, but that it can be controlled by modification of the properties of the radiation field. This is equally true in the solid state, where spontaneous emission plays a fundamental role in limiting the performance of semiconductor lasers, heterojunction bipolar transistors, and solar cells. If a three-dimensionally periodic dielectric structure has an electromagnetic band gap which overlaps the electronic band edge, then spontaneous emission can be rigorously forbidden.
"Photonic crystals (PCs) are artificial materials consisting of periodic modulation in refractive index . This affects to the propagation of electromagnetic wave as same as the crystal structure in semiconductor affects the electron Bloch wave defining allowed and forbidden electron energy bands. "
[Show abstract][Hide abstract] ABSTRACT: The phase shift on reflection from the colloidal photonic crystal film was measured by the Fabry-Pérot resonant cavity along the cross-section of the photonic crystal film without additional optical parts. The wet colloidal photonic crystal film was fabricated by dip-coating an agarose-gel-coated glass substrate into a suspension containing monodisperse polystyrene nanospheres with the diameter about 188 nm. The ordered structure of monodisperse spheres in the wet film on hydrogel contributed the reflection stopband of photonic crystals together with Fabry-Pérot interference fringes of this uniform wet film over the entire visible region. The spectrum of reflectance was observed under the reflected microscope with the optical fiber spectrometer. The analyzed experimental results show the thickness of film about 20 µm and the photonic stopband peak at ~470 nm. The variation of phase shift values between both edges of the peak varies from 0.07π to 0.88π which is in range of 0 to π as reported by other works. Moreover, these extracted optical properties are slightly changed due to the gradual water evaporation of the wet film. This stopband peak of photonic crystal is shifted to a shorter wavelength due to the more packing of nanospheres after drying.
International Conference on Photonics Solutions 2015, Hua Hin, Thailand; 07/2015
"Therefore, they can be considered as an effective medium whose dielectric function has been proved to be a plasmonic form. On the other hand, when P is comparable to the wavelength, the Bragg scattering plays an important role and microwave band gap (MBG) or photonic band gap (PBG) emerges in the structure, as in the broadly studied photonic crystals    . "
[Show abstract][Hide abstract] ABSTRACT: We propose a multiscale spoof–insulator–spoof (SIS) waveguide by introducing periodic geometry modulation in the wavelength scale to a SIS waveguide made of a perfect electric conductor. The MSIS consists of multiple SIS subcells. The dispersion relationship of the fundamental guided mode of the spoof surface plasmon polaritons (SSPPs) is studied analytically within the small gap approximation. It is shown that the multiscale SIS possesses microwave band gap (MBG) due to the Bragg scattering. The ‘gap maps’ in the design parameter space are provided. We demonstrate that the geometry of the subcells can efficiently adjust the effective refraction index of the elementary SIS and therefore further control the width and the position of the MBG. The results are in good agreement with numerical calculations by the finite element method (FEM). For finite-sized MSIS of given geometry in the millimeter scale, FEM calculations show that the first-order symmetric SSPP mode has zero transmission in the MBG within frequency range from 4.29 to 5.1 GHz. A cavity mode is observed inside the gap at 4.58 GHz, which comes from a designer ‘point defect’ in the multiscale SIS waveguide. Furthermore, ultrathin MSIS waveguides are shown to have both symmetric and antisymmetric modes with their own MBGs, respectively. The deep-subwavelength confinement and the great degree of control of the propagation of SSPPs in such structures promise potential applications in miniaturized microwave device.
Journal of Physics D Applied Physics 05/2015; 48(20). DOI:10.1088/0022-3727/48/20/205103 · 2.72 Impact Factor
"The photonic band gap (PBG) is usually a basic property of PC, and the propagation of light within the frequency range of PBG would be forbidden. Since its discovery in 1987 by Yablonovitch  and John , PC with its unique PBG property has attracted much attention as a possible platform for densely integrated photonic circuit and novel photonic functionality –. The unique properties of these artificial crystals derive from their geometrical structures rather than atomic compositions. "
[Show abstract][Hide abstract] ABSTRACT: Slow light in photonic crystal waveguide (PCW) is now being heavily investigated for applications in optical devices. However, slow light with high group index in perfect PCW is usually accompanied by large group velocity dispersion (GVD), which would severely limit the bandwidth of slow light, deform optical pulses, and disturb its practical applications. In this review, various optimization methods that are proposed to overcome these drawbacks are introduced and compared. These methods rely largely on the ability to modify the slow light properties of PCWs with a change in their structural parameters or a change in their effective refractive indexes through external agents. For each optimization method, the corresponding group index, GVD, bandwidth, and normalized delay-bandwidth product are all presented along with the physical parameters, the potential advantages, and the fabrication complexity of PCW that enable them. Finally, the key problems and future development directions of slow light in PCW are discussed.
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