Function And Characteristics Of Micro-structured Optical Devices

The micro-structured optical devices will bring about broad applications in optical communication systems, optical sensing techniques and integrated optical circuits in the future. Therefore the investigation in the micro-structured optical devices is significant in both theory and engineering application. Photonic crystals (PCs) have attracted a great deal of attention because of their remarkable features compared with some common materials in recent years since it was reported firstly by E. Yablonovitch and S. John in 1987. The photonic crystal is a periodic electromagnetic medium in the optical wavelength scale. Similar to semiconductor, it is possible for a photonic crystal to exhibit one or more photonic band gaps (PBG). The electromagnetic waves with frequencies within the PBG are prohibited to propagate in the photonic crystal, regardless of the polarization and the propagating directions of the electromagnetic waves. The light propagation can be controlled by introducing a defect into a photonic crystal. This will lead to many interesting physical phenomena and important applications, such as optical switching, optical filter, optical coupler, photonic crystal laser and so on. Thus photonic crystals will be the best choice for fabricating micro-structured optical devices consequentially.The new idea of all optical fibers integrated system originates from the long-period research on optical fiber techniques. Many optical devices will be integrated in single optical fiber, which means that this optical fiber is a multifunctional micro-system. It is significant to accelerate development of optical fiber integrated technology by embedding photonic crystal devices in an optical fiber.The function and characteristics of micro-structured optical devices are investigated in the thesis. PC devices have been proposed and integrated into the optical fiber. Our work demonstrates the feasibility of integrating PC devices into the optical fiber. The details are presented as follows: (1) Firstly, the progress of PCs and their application prospects are summarized. Beginning with Maxwell equations, the eigenvalue equation in micro-structured optical devices is deduced. The theoretical calculation methods, such as plane wave expansion (PWE), finite difference time domain method (FDTD), finite element method (FEM), beam propagation method (BPM), are elaborated in detail in the thesis.(2) The photonic band structures in 2D photonic crystals with different lattices are studied by use of plane wave expansion method. The effects of geometry parameters on photonic band gap are analyzed. We lay a strong emphasis on studying the effects of magnetic permeability on photonic band gap structures in 2D photonic crystals with hexagonal-arrayed scatters. It is found that the photonic band gaps tend to exist in the magnetic photonic crystals, and the magnetic permeability affects on the photonic band gaps strongly.(3) Two new configurations of photonic crystal heterostructures(PCH) with complete PBG are proposed and the interface guide modes are analyzed. The influences of longitudinal sideslipping and transverse displacement of lattices on the guide modes are discussed. The achieved results show that the guide modes can exist in the heterostructures without any shift of lattices, and guide modes are highly sensitive to transverse shift, however, the sideslipping affects guide modes slightly.(4) The effects of coupling interaction length, waveguide-channel space and scatterers' shape variations between the two coupling channels on the coupling properties of the photonic crystal polarization coupler with the square lattice are analyzed. The important conclusion is drawn that the coupling length can be reduced greatly by most of scatterers' shaping variations between the two coupling channels. A polarizing beam splitter and a non-polarizing beam splitter based on a photonic crystal directional coupler are demonstrated. The PC M-Z interferometer also is investigated and the PC devices formed directly within a optical fiber are proposed. (5) The parameters of photonic crystal fiber, including model field distribution, effective refractive index of fundamental mode and normalized frequency etc, are calculated. The characteristics of transition-layer of photonic crystal fibers used in liquid sensors are analyzed. The multi-core photonic crystal fiber couplers are designed and coupling properties between the cores are investigated.Finally, a simple coupling approach between a one-core and a multi-core single mode fiber is proposed and demonstrated. By way of splicing and tapering at the fusion point, an effective coupling technique is implemented. The coupling processing is simulated by BPM. The theoretical prediction is confirmed by the experimental results.