Study On Optical Diodes Based On Slow Light Waveguide

Controlling the flow of light is fundamental for on-chip optical signal processing.The non-reciprocal transmission of optical diode,which permitting the transmission of light with a low loss in one direction while blocking it in the opposite direction,is of great importance in the fields of building all-optical network and improving optical information processing technology.A ideal optical diode should not only ensure the function of unidirectional conduction,but also improve its transmission contrast as much as possible（which is defined as the transmission intensity ratio of forward and backward incident signal under the same conditions）,and increase the operating bandwidth and unidirectional transmittance,so as to continuously improve its application performance.On the other hand,in order to improve the efficiency of information processing in all-optical network,sometimes we hope that the conducting direction of optical diode can realize a controllable inversion.However,the reported methods are still very few,and most of them can flip the conducting direction only when the signal’s wavelength is changed,and often needs to readjust the incident power,which is not effective to practical application.In this paper,we investigate the optical nonreciprocal transport properties by designing a side-coupled WG-Resonator system that introduces Kerr nonlinearity.Our new all-optical diode has achieved a large transmission contrast(C_max=167)and high unidirectional transmittance（up to 70%）.What’s more,a effective method is proposed to realize the controlled reversal of the light conducting direction for the same signal light.In the first chapter,we briefly introduce the basic structure,important characteristics and practical applications of photonic crystals,describe the implementation mechanism and research status of optical nonreciprocal transmission,and finally summarize the slow light effect and its related development in photonic crystal waveguides.The second chapter introduces two common theoretical methods to study the band structure and optical transmission characteristics of photonic crystals:plane wave expansion（PWE）method and finite difference time domain（FDTD）method.The third chapter focuses on the design and implementation of the structural model of optical diode:the slow light slot waveguide-nanocavity side coupling structure based on photonic crystal.In the linear case,we study the influence of the width of the slot waveguide on the slow light of the waveguide and the transmission spectrum of the system,so as to optimize the structure.At the same time,the bistable phenomenon of photonic crystal in direct-coupling and side-coupling mode is briefly analyzed,which is prepared for the later study of the characteristics of optical diode in the case of nonlinearity.In Chapter 4,combined with theoretical analysis and simulation experiments,we study the non-reciprocal transmission characteristics of a cavity-waveguide asymmetric coupling structure under Kerr nonlinear effect,and discuss how to realize the controllable reversal of the conduction direction for the optical diode.