Coupling Characteristics Of Photonic Crystal Waveguide And Its Application

As the artificial materials with a periodic dielectric structure,photonic crystal has caused worldwide attention,due to the characteristics of the photonic band gap(PBG). Photonic crystal waveguide can be constructed by introducing a line defect to a perfect photonic crystal.A low loss even zero loss of energy transport can be realized in photonic crystal waveguide with sharp bends.A variety of opto-electronic devices based on photonic crystal waveguides have been rapidly developed,due to the small size,easy for large-scale optical integration and other advantages.The directional coupler based on photonic crystal waveguides is an important component in the field of optical communication and the directional coupler can also be used to construct many other opto-electronic devices.The main research works are as following:1.We investigated the relation between the band gap for TM polarization and the radius of the dielectric rods of 2-D photonic crystal with a triangular lattice and the relation between the band gap for TE polarization and the radius of the air holes of 2-D photonic crystal with a triangular lattice.The transmission spectra of TM mode in the bend waveguide with triangular lattice of dielectric rods and TE mode in the bend waveguide and TM mode in the straight waveguide with triangular lattice of air holes have been calculated.It provides a basis for the design of devices based on photonic crystal waveguides directional coupler in this thesis.2.We analyzed the coupling feature of two and three parallel photonic crystal waveguides.On the basis of the analysis,we investigated the coupling feature of two and three parallel photonic crystal waveguides with a structural fine-tuning.The results show that a structural fine-tuning will change the result of the guide modes interference due to the redistribution of the optical field.3.On the basis of self-image theory,we investigate the coupling feature of multiple photonic crystal waveguides(five and seven photonic crystal waveguides) when the optical field symmetrically entering the system.The article presents a new way of obtaining uniform splitting of the power of the optical power by directional coupling between the photonic crystal waveguides.By simply tuning the effective refractive index of two dielectric rods in the coupler symmetrically,then inducing the redistribution of the power of the optical field,uniform or free splitting can be achieved.Compared with the results having been reported,this way is simpler, feasible,more efficient and has extensive practical value in future photonic integrated circuits.4.A new way of obtaining free splitting of the input power entering 1×2 beam splitter composed of photonic crystal waveguides directional coupler are proposed. By tuning the refractive index of one row dielectric rods,free splitting of the input power and high transmittance of the whole beam splitter can be realized in a certain range.5.Directional coupler can be constructed by putting two photonic crystal waveguides with triangular lattice of air holes together,between which there are three rows of air holes.The propagation of TE(electric field parallel to the axis of the air holes) and TM(magnetic field parallel to the axis of the air holes)polarizing light entering this system was analyzed numerically.The results show that the coupling length of TE light reduces whereas the coupling length of TM light does not change when the radius of one row of the dielectric air holes between the two waveguide of the coupler are modified.On the basis of this structure,ultracompact polarizing beam splitter was designed and the length of the device is only 10.0688μm.Compared with the previous results of 24.2μm,this device is smaller,more efficient.So the device has an important potential practical value in future photonic integrated circuits.