Performance Research Of Photonic Crystal Micro-cavity

Photonic crystal is put forward in 1987 as a new concept and new material. One notable feature of this material is that the photon movement can be controlled. Because of its unique characteristics, high-performance optical devices which have new theories or can not be produced previously can now be produced using PCs. Photonic crystal micro-cavity receives the widespread attention as an important application of photonic crystal. It used to make photonic crystal lasers without threshold value or low threshold value, much theory research and experiment was made abroad, and this work of our country have fall behind, it is necessary to enhance the theory research of photonic crystal micro-cavity. The research of photonic crystal by numerical simulation in this paper as following:1,Research the tuning characteristics and quality factor of one-dimension photonic crystal micro-cavity with symmetrical structure and unsymmetrical structure with transfer matrix method . Results show that with the increase of thickness of defect layer ,the center wavelength of defect mode will increase. Tuning characteristics of micro-cavity relate to the refractive index of medium which surround the defect layer. The more difference of refractive index between defect layer and medium surround the defect layer, the bigger slope of the line about the relation between center wavelength of defect mode and optical thickness of defect layer, and the line become nonlinear from linear. Compare with symmetrical structure,unsymmetrical structure can achieve linear tuning with wide wavelength range but smaller variation of the thickness of defect layer, so it make for smaller device. Quality factor will increase first and then reduce with increase the thickness of the defect layer and it has maximum when the center wavelength of defect mode isλ0.The array of medium with high or low refractive index affects the quality factor of micro-cavity. To the symmetrical structure, quality factor is bigger when the medium surround the defect layer with high refractive index. To the unsymmetrical structure, quality factor is bigger when the first layer with high refractive index.2,Analyze the band gap of two dimensional photonic crystal using the plane wave method. To the dielectric rod, the middle frequencies of the band gap will reduce with the increase of the radius and refractive index of the dielectric rod. Dielectric cylinder in square lattice only has TM band gap. Dielectric cylinder in triangular lattice has bigger TM band gap than dielectric cylinder in square lattice, and the radio of band gap increase. This illuminates that lattice array affects the band gap. Square dielectric rod has big TM band gap no matter in square lattice or in triangular lattice, and the radio of band gap is bigger than 35%. More important is that complete band gaps exist in the two structures. So the shape of the dielectric rod affects the band gap and square rod structure is an important structure with complete band gap. Complete band gap exists in the compound dielectric cylinder structure. Two big complete band gaps exist in honeycomb structure and the radio of band gap of one of them is about 9.92%. Through the above contrast, changing the unite cell not only make for TE band gap, and make complete band gap be possible. Changing the unite cell to reduce the symmetry of the structure is a feasible method to quest for complete band gap.To the air rod structure, the middle frequencies of the band gap will increase with the increase of the width of the square air rods. When increase the material refractive index, the middle frequencies of the band gap will reduce. Air cylinder structure in triangular lattice has big TE band gap and complete band gap, it is an important structure for designing. The radio of TE band gap is about 48.1%, and the radio of complete band gap is 16.14%. Square air rod structure also exists complete band gap, although the complete band gap is small, it is a choice for us to design the two dimensional photonic crystal with complete band gap. To the square air rods, we should choose the high refractive index material to enhance the band gap radio of the complete band gap.Lattice array and shape of the rods and the structure of unite cell are affect the band gap, so we should consider completely when design the structure, and choose the high refractive index material to enhance the band gap radio of the band gap.3,Research the center wavelength of defect mode and the quality factor of two dimensional photonic crystal micro-cavity with FDTD method. The defect mode exists in high frequency area of band gap when increase the effective dielectric constant of photonic crystal whatever single dielectric rod defect photonic crystal micro-cavity in square lattice or single air rod defect photonic crystal micro-cavity in triangular lattice, and the center wavelength of defect mode will increase when increase the effective dielectric constant. Contrarily, defect mode exists in low frequency area of band gap when reduce the effective dielectric constant of photonic crystal and the center wavelength of defect mode will reduce when decrease the effective dielectric constant. To the single dielectric rod defect photonic crystal micro-cavity in square lattice, radius and dielectric constant of center defect will affect quality factor of the micro-cavity, quality factor has the prime value. So when design the micro-cavity, we should consider completely, and choose appropriate parameter. To the single air rod defect photonic crystal micro-cavity in triangular lattice, other resonant modes will exist when increase the radius of defect. Quality factor will increase when enhance the dielectric constant of defect, and quality factor is bigger when the micro-cavity with no center single air rod. Quality factor increases with increasing the background dielectric constant. When design the micro-cavity, we should choose the high dielectric constant material.To the triangular lattice photonic crystal micro-cavity with no center single air rod, center wavelength of defect mode will increase by reducing the radius of two air rods adjacent to the defect horizontally or enhancing dielectric constant of them or moving them away; or by reducing the radius of four air rods adjacent to defect up and down; or by reducing the radius of six air rods adjacent to defect or moving them away or reducing the radius of six air rods base on the point of outside edge. Quality factor increase differently with the methods we used above. And the same point of these methods is that the effective dielectric constant of the area of defect is enhanced, so we can increase the effective dielectric constant of the area around defect by using different methods to enhance the quality factor. The results also show that, increase the area around defect (for example, increase the number of defects) will enhance the quality factor but new resonant modes may exist.4,Research the center wavelength of defect mode and quality factor of photonic crystal slab micro-cavity with FDTD method. When design the photonic crystal slab micro-cavity, we choose the radius of air hole 0.3a and the prime thickness of slab with air holes in triangular lattice is 0.6a. Change the lattice constant in a direction or increases the area adjacent to the defect may enhance the quality factor. For example, we can increase the radius of two air holes adjacent to defect horizontally, or increase the distance of two air holes adjacent to defect move away, or increase the number of defects, or reduce the radius of six air holes adjacent defect. But too many defects or too big the area of defect will make other resonant modes.