Study On Multiple Quasi-Phase Matching Techniques In Optical Superlattice

The thesis investigates multiple quasi-phase matching (QPM) techniques in optical superlattice theoretically and experimentally. A novel algorithm for the design of optical superlattice: self-adjusting method is proposed. Aperiodic optical superlattice and Nonperiodic optical superlattice can be designed by self-adjusting method, thus achieving random second-order nonlinear optical process with ideal conversion efficiency. The thesis expands the theory of QPM to the field of left-handed materials (LHM), proposes novel QPM conditions in LHM, and designs unique optical superlattice based on LHM and mixed construction of LHM and right-handed materials (RHM). Finally, multiple QPM processes in coupled fourth harmonic generation (FHG) occurred in periodically poled LiNbO3 (PPLN) with periods of 6.5μm is studied experimentally, and the effects on conversion efficiency by coupled mode, polarized mode, and QPM order are also studied.Based on coupled wave equations of 2nd nonlinear optical processes, the thesis analyses multiple QPM processes involved in coupled THG and coupled FHG, comparing the conversion efficiency under coupled mode and cascading mode, respectively, educing a series of new conclusions. Multiple QPM processes in coupled FHG occurred in PPLN with periods of 6.5μm is studied experimentally, as a supplement to the theory of multiple QPM, of which the conversion efficiency under different coupled modes, polarized mode, and QPM orders is studied.A novel algorithm: self-adjusting method is proposed for the design of opticl superlattice. By analyzing the multiple QPM processes involved, any predesigned nonlinear optical process is equivalent to multiple-second harmonic generation (SHG), and realized by optical superlattice designed by self-adjusting method. In this thesis, AOS and NOS are constructed to achieve multiple-SHG, SHG with broadened bandwidth, multiple coupled third harmonic generation (THG), multiple coupled fourth harmonic generation (FHG), and other nonlinear optical processes. Besides, the effects on conversion efficiency caused by errors of environment temperature, incident angles and domain-length are also discussed. The concept of"ideal sum of conversion efficiency"is proposed for multiple QPM, as the criterion of judging algorithms. In theoretical simulation, any second nonlinear optical processes can be achieved by NOS designed by self-adjusting algorithm, with ideal conversion efficiency. The theory of QPM is extended to LHM for the first time, and the model of phase matching in LHM is built. In order to achieve random second-order nonlinear optical process with high conversion efficiency., QPM structure, which is based on LHM, and interspace phase matching structure, which is based on the mixture of LHM and RHM, are proposed and designed. The combination of LHM and QPM, as well as the development from LHM to the mixture of LHM and RHM, open an avenue of application of LHM.