Adiabatic Light Transport In Three-Waveguide Coupled Systems

The propagation of light in coupled optical waveguides is a hot research topic in the field of atomic and molecular optics,which has attracted many scientists' interest in recent years.This research has many potential applications in physical,chemical and biological systems,such as energy transfer between waveguides,mode conversion,polarization rotation,quantum information communication and so on.And it was shown that the spatial dynamics of coupled waveguides is analogous to the temporal dynamics of quantum optical systems driven by external electromagnetic fields.Owing to the strong similarity between quantum mechanics and wave optics,many protocols based on quantum optical techniques were proposed to manipulate the propagation of light in waveguides.In this thesis,based on the introduction of the development history,applications,design objectives of optical waveguide couplers and the similarities between optical systems and quantum systems,we study adiabatic optical transport in three-waveguide coupled systems.Our work mainly includes two parts.Without considering the nonlinearity associated with the waveguide structure,we design light transfer and split waveguide couplers in Vitanov-style and Gaussian-style models.We also design light split waveguide couplers with arbitrary proportion.We have employed recently developed dressed state technique in the adiabatic regime to the couplers.The approach was proposed to speed up adiabatic quantum state transfer that do not require additional couplings.Compared with the STIRAP-based waveguide couplers,the advantages of the new design are as follows.First,it can reduce the device length of the couplers significantly,keeping the power transfer efficiency near 100 %.Second,the couplers are more robust against parameter variations.In the experiment,we can fabrication the relative distance between the coupled waveguides along the propagation axis z by using a dry-etching technique or photo-bleaching technique,resulting that the coupling constants can fit the design.The present scheme is potential to realize more complex integrated optical devices.For nonlinear three-waveguide couplers,we design waveguide couplers via Resonance-locked inverse engineering.This approach can significantly speed up adiabatic state transfer.We design light transfer and light split waveguide couplers.The new couplers can achieve stable light transfer and light split under large nonlinearity.By changing the refractive index in the transverse plane of waveguides via ion exchange technology,we can set propagation constants vary along z to compensate the nonlinearity caused by increasing the power of the input beam.The couplers can achieve light transfer or light split with highfidelity and good robustness.We think Resonance-locked inverse engineering can be applied to more complex nonlinear waveguide couplers.