Research Of Key Technology Of Photonic Crystal Optical Switch

Devices based on photonic crystal follows photonic band gap guiding mechanisms. They are ideal choices for future integrated optical circuit components, with many advantages which traditional devices don't have, and also very small sizes. Therefore, they have attracted a lot of attention of researchers and have been studied intensively and extensively during the past decade. This thesis studied some key technologies of photonic crystal coupling switches, a new kind of optical device based on photonic crystal, proposed three different designs of photonic crystal coupling structures, performed simulation for these structures using Plane Wave Expansion (PWE) method and Finite-Difference Time-Domain (FDTD) method, and analyzed the structures and performance of these coupling switches, thus building a good foundation for further research on photonic crystal coupling switches.In the chapter of introduction, the main theoretic foundations and research background of this thesis are reviewed. First the basic concepts of photonic crystal are introduced. Then the theoretic foundations and the mathematic models for carrying out research and calculation of photonic crystal, including PWE and FDTD, are introduced. Based on these, the coupling features of photonic crystal waveguides are studied, which are the theoretic bases for the designs of photonic crystal coupling structures later on. Last, the concept of slow light is introduced, and research updates are presented.Based on the theories mentioned above, the second chapter proposed a novel design of coupling structure with low crosstalk and very short coupling length, which resolves the trade off between high crosstalk and short coupling length in traditional photonic crystal coupling structures. This structure employs a hetero structure, combining a front waveguide with low crosstalk but long coupling length, a coupling waveguide with high crosstalk but very short coupling length and an end waveguide with low crosstalk but long coupling length. The structure can achieve quite short total coupling length and very low crosstalk at the same time. Simulation is performed using PWE and FDTD on the novel structure. After simulation, a lower crosstalk is obtained, and a very short total coupling length is also achieved. Based on the novel 2×2 directional coupler design, a structure of 4×4 photonic crystal coupler is proposed, in order to realize signal transfer between multiple transmission paths. Excellent transmission performance is obtained by numerical experiment verification.The third chapter studies dynamic control on signals transmitted in photonic crystal coupling structures. Now there is an electric-control method: inject liquid crystal into photonic crystal material and then change the coupling structure by changing the electric field applied, thus realizing dynamic switch function. However, this method can not meet the high-speed requirements for signals in optical communication systems, and it demands many extra assistant devices. A more potential method is to use control light to change the transmission direction of signal lights. According to recent research results, light with very slow group velocity, that is, slow light, is an idea control light to be used in photonic crystal directional coupling switches. This kind of control light can increase the phase shift induced by small changes in refraction index, thus changing the refraction characteristics of photonic crystal material. A novel design of 2×2 directional coupling switch is proposed on the basis of some related research results. This structure can use control light with slow group velocity to achieve dynamic control on signal transmission states. Simulation results using FDTD verifies that dynamic control on signal lights can be realized simply by using control lights.The last chapter discusses further on dynamic photonic crystal coupling switch structures. Since resonator photonic crystal coupling devices are very potential to realize dynamic switch, a novel resonator coupling switch design is proposed. With control light applied to change the parameters of the resonators, which are the key components of the device, the optical characteristics of the device can be easily changed, thus dynamic control on signal lights can be achieved. By simulation using FDTD, dynamic switch of signal lights can be realized successfully, verifying the possibility to use such structures as dynamic switches.This thesis focuses on various novel coupling switch devices based on photonic crystal, which is a new type of material. The structures proposed in this thesis have different innovations and achieved excellent performance in different aspects, which has built a good foundation for future researches. These research results are very meaningful to the research and development of densely integrated photonic devices.