Optical Properties And Applied Research Of A Two-dimensional Triangular Lattice Photonic Crystal

Photonic crystal is an artificial crystal structure which is formed by the periodic arrangement of the different dielectric constant materials in space. Using photonic band gap may conveniently manipulate the electromagnetic waves'propagation in it. It is widely applied in optical fiber, optical filter, omnidirectional total reflector, optical switch, and light emitting diode, etc.Two-dimensional triangular lattice is the simplest two-dimensional photonic crystals structure. What have been studied indicates that two-dimensional triangular lattice photonic crystals with air rod can easily make the wide complete band gap and the making preparation can also be done easily, So it is vital to go on with further study on the two-dimensional triangular lattice.This paper made a thorough study on the band structure of the two-dimensional triangular lattice photonic crystals with air rod by using the transfer matrix method, and based on the research, it discussed systematically about the features of defect mode which were made by introducing various defects. In addition, this paper simulated the reflection efficiency of a new two-dimensional photonic crystal hetero structure under the shining of omnidirectional incident light and the changing law of band structure of two-dimensional triangular lattice photonic crystals infiltrated with liquid crystal under external field. The result of research can provide the theoretical basis for the application of two-dimensional photonic crystal in optical narrow pass band filters, solar cell reflector, and optical switch, etc. So, it has important value of reference. The major contents of the thesis are as follows:(1) Made the research about the effect of dielectric refractive index and lattice structural parameters on the band structure of two-dimensional triangular lattice photonic crystals with air rod. The result shows that as the filling ratio increases, photonic band gap moves toward short wavelength and consequently the bandgap width broaden. When the filling ratio increases to 0.4, the bandgap width arrives at its maximum; the photonic band gap become broader with the increase of dielectric refractive index; If the lattice constant increases, the photonic band gap moves towards long-wavelength, at the same time bandgap width increases. In addition, with the increase of the deflection angle of incident light, the reflectivity curve of the photonic crystals will take place a great change, whose correctness is tested by plane wave expansion method.(2) Two different kinds of point defects and a line defect are introduced in the two-dimensional triangular lattice photonic crystals. With the introduction of defects, a high transmittance defect mode appears in photonic band gap in TM mode. The change of the radius of the air rod and dielectric refractive index will take effect in the band structure and the location of the defect mode. As the radius of the defect air rod increase, defect mode will move towards short-wavelength. But the increase of the refractive index will result in the red shift of defect mode. Adjusting the type and parameter of the defect, the defect mode will vary in the wave band of 1050-1150nm. So we can take it as the optical narrow pass band filters in different band and applies to wavelength division multiplexing in optical communication.(3) In this paper, a two-dimensional photonic crystal heterostructure is designed for solar cell reflector. It also compares the reflectivity of visible to near infrared light when the incident angle is different. It turns out that the photonic crystals show an increasing average reflectivity towards 400-750nm visible wavelength as the deflection angle of the incident light increases. In terms of the 750-1200nm near infrared incident light, when the deflection angle is 30°, the reflectivity comes to its lowest, that is 90%. In any other deflection angle, the reflectivity will reach up to 98%, which is a relatively high reflectivity. The heterostructure provides a omnibearing reflective band and expands the application of reflector in visible to near infrared light as well as makes it possible to produce the omnidirectional total reflector that covers the whole visible to near infrared light(4) Take the two-dimensional triangular lattice photonic crystals as a modelboard, we fill the air hole with optical anisotropy liquid crystal—phenylacetylene, and figure out the corresponding relationship of effective refractive index of the liquid crystal when the rotation angle of the liquid crystal varied in 0°～90°. And therefore, we get the photonic band structure of photonic crystals infiltrated with liquid crystal in different polarization mode. We find out that in TM polarization mode, it is possible to cut off or open the 1550nm wavelength light through changing the rotation angle of liquid crystal in external field, which is vitally important in the network technology of optical fiber transmission. Moreover, the research shows that the directional bandgap of photonic crystals infiltrated with liquid crystal will greatly change its directional bandgap.If directional bandgap can be modulated in a large scale, it is useful to produce light switch of excellent functions.