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Photonic crystals is a new class developing very rapidly in recent years, it has been attracted much attention and deep study. Due to its "photonic band gap" and "photon localization" feature , photonic crystals have broad application prospects. But it is still a valuable subject that how to make full use of the special band structure, band gap and transmission characteristics in practice. Based on the wide application potential, the author mainly relate the research to the photonic crystal filter resonator and one-dimensional photonic crystals with negative refractive index , making a systematic analysis of the main factors influencing on the photonic crystals filter and the method of improving the filter efficiency, finally the writer designs an efficient multi-channel photonic crystals filter.
Firstly, the author introduces us the all-optical half adder based on cross structures in two-dimensional photonic crystals. As is known, full adders are the basic parts of CPU and they are built with the half adder. it is critical to investigate all-optical half adders (AOHA) for the realization of all-optical CPU. In this paper, we analysis “AND gate” and “XOR gate” of two-dimensional photonic crystals, then establish the models of the basic all-optical half adder based on the defect cavity and cross waveguide. After making research on the shape of the photonic crystal unit, the crystal structure and permittivity dielectric cylinder , we found that the greater the dielectric constant of dielectric, the greater the band gap crystals; the greater media column larger duty cycle,the greater the band gap crystals. Then we study the relationship between the radius of the resonance cavity defects and coupled wavelength, the simulation results show that when radius of the defects media rod is shorter than that of the crystal, the wavelength increases with the defective media rod radius increases; when the radius of defect media rod is longer than that of the crystal, the wavelength becomes shorter and the coupled efficiency is relatively low. Therefore, radius of defects media rod should be chosen smaller than that of the photonic crystal. After calculating defect waveguide, we analyze the reflective properties of the waveguide, and the results show that the dielectric constant is set to multiple times of the crystal dielectric constant, the reflective index gets the maximum; then we analyze the way to improve the waveguide and resonator coupling efficiency. Through the analysis, it is found that changing the radius of waveguide edge rod has a great impact on the coupled efficiency. It is also proved that changing the radius of medium rod between waveguide and its corresponding resonance cavity and width of waveguide influence a lot on the efficiency of the resonator and waveguide. Through the FDTD method, numerical simulations demonstrated successfully that the structure presented does function as an all-optical half adder. The ON to OFF logic-level contrast ratio for this half adder could reach at least 16dB, and when omitting the material-wave response time of Kerr effect, the optimal operating speed is found to be as high as 0.91Tbits/s. This structure is useful in designing all-optical signal processing circuits and optical computer systems.
Then we made research on the THz waveguide of photonic crystals and THz doubled reflective waveguide. In theory, deep study on relevant waveguide devices has been carried out. During the experiments, researches and designs on photonic crystal THz waveguide combined cavity are made. For guiding photonic crystals resonator’s design and application, firstly we create a physical model of one-dimensional photonic crystals resonant cavity, and analyze the relations and influences of the various parameters in the resonator. After a systematic study on photonic crystals cavity , relations between the various parameters, and the structure and nature of THz signal detection of the combined cavity with high sensitivity, through testing and calculations, we conclude that the relationship between defect layer thickness, resonance wavelength, the quality factor show that for every level, with the defect layer thickness increases, the quality factor increases and then decreases, and there is a maximum value, the changing trend depends on the periodic structure of the band; We have investigated a combined coupled cavity, composed of a PDC and a WGR. The field intensity in the PDC in the combined cavity under simultaneous resonance is much higher than that in a simple separate PDC. The quality factor is also promoted through the cavity combination and mutual coupling. To meet the requirement of simultaneous resonance, a dielectric slab for phase shifting is necessary to add in the WGR. If adding a dielectric pole in the PDC in double resonance, the maximum quality factor of the new structure is promoted by 34.7%, and the maximum localized field intensity in the point defect cavity is promoted by 314% over that in the earlier structure.
For the better understanding of photonic crystal polarizer, first we make use of the features that different polarization modes in photonic crystals have different band gap, thus we can have a study on polarization characteristic of the single one-dimensional photonic crystals, and design a polarizer made by one-dimensional photonic crystals. We mainly use the transfer matrix method to test characteristics of two polarization modes TE and TM in the one-dimensional photonic crystals. Then we discuss the characteristics of two kinds modes which vary with dielectric ratio; In conclusion, we have proposed and demonstrated a polarizer with integrated functions of both NBP frequency domain filtering and NTA space-domain filtering, by combining two one-dimensional with PCs anisotropic materials. Without introducing anisotropic materials into the PCs, one can not obtain a polarizer for normal (0°) incident waves.
Lastly, we study the characteristics of the one-dimensional photonic crystals composed by the special materials. We discuss the structure of the doubled defect one-dimensional photonic crystals. And the calculation show that if we change the refractive index of the defect, the interaction effect of defect modes will change, thus making the impurity band of the photonic gap band change. If taking the appropriate value of the refractive index, we can get several sharp peaks and wide pass band in the band gap.In this part, the author make a systematic analysis about the special materials of photonic crystals and its structure parameters’ impact on filtering properties; Based on the zero-n gap of the photonic QWs, the photonic QW is very weak dependent on the incident angle and polarization, and also insensitive to thickness disorder of the barrier PCs. These features are benefit to improve the performance of the multiple channeled filter. In summary, we propose the construction of new optical filters with Gaussian-distributed refractive index. This kind of filter can smooth the sharp resonant peaks in the transmission spectrum and enlarge the extension of the pass-bands. For different incident angles, the central frequency of the pass-band can be significantly changed but the pass-band width for the TE mode remains unchanged. However, for the TM mode, while increasing the incident angle, not only the central frequency of the pass-bands is shifted but also their extensions are evidently enlarged. We also observe that in the PCs with the Gaussian-distributed thickness of the optical barriers, they have quite similar characteristics to those of the PCs with the Gaussian modulation of the refractive index of the optical barriers. The main findings in this work may provide useful information for the design of the favorable PC filters.
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