TAILIEUCHUNG - Optoelectronics Devices and Applications Part 16

Tham khảo tài liệu 'optoelectronics devices and applications part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Nanophotonics for 21st Century 589 introduced defects in the crystal. The later is similar to electronic dopants give rise to localized electromagnetic states in linear waveguides and point-like cavities. The crystal can thus form a kind of perfect optical insulator that can confine light without loss around sharp bends in lower-index media and within wavelength-scale cavities among other novel possibilities for control of electromagnetic phenomena Joannaopoulos et al. 2008 . The periodicity of the photonic crystals can be in one two and three dimensions that allow interesting properties such as bending light at 90 around corners as shown in figure 12. Fig. 12. Bending of light at 90 around corners in the photonic crystals. One-dimensional periodic system continued to be studied extensively and appeared in applications from reflective coating to distributed feedback diode lasers. In the former case the reflection band corresponds to the photonic band gap and for the later a crystallographic concept is inserted in the photonic band gap to define the laser wavelength. Yablonovitch and co-workers Yablonovitch 1987 produced the first photonic crystal by mechanically drilling holes a millimeter in diameter into a block of material with a refractive index of . The material which became known as Yablonovite prevented microwaves from propagating in any direction and exhibited a 3-dimensional photonic band gap. Other structures that have band gaps at microwave and radio frequencies are currently being used to make antennae that direct radiation away from the heads of mobile-phone users Sajeev 1987 Lodahl 2004 Kim 2008 Sonnichsen 2005 . Later on photonic crystals of semiconducting colloidal particles were fabricated for realizing photonic band gaps in the visible region of the electromagnetic spectrum. They are also fabricated by the spontaneous self-organization of mono-disperse colloidal spheres such as silica or polystyrene to form a three-dimensional crystal having .

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