Research On The Tunable Multimode Interference Devices Based On Thermal Poling Ring Core Fiber

The fused silica material has central inversion symmetry structure,so it does not possess second-order nonlinear optical effects.The thermal poling can break this structure and induce considerable second-order nonlinear optical effect in it.The ring core optical fiber can be regarded as crimped and integrated the planar waveguide in the optical fiber,so the ring core optical fiber has multi-mode interference effect in itself,that is: at the output port,the output light field can obtain one or more images of the input light field.In this paper,we combine those two characteristics and propose a ring core fiber based on thermal poling.This fiber can realize electro-optic tunable function and can be used to power splitters,wave separators,allfiber optical switches and sensors.In this paper,a hollow ring core fiber is proposed,and on this basis,multimode interference effect and thermal poling in the ring core optical fiber are analyzed.Combining those two characteristics,a power splitter and a wave separator based on the thermally poling are proposed.The main content is as follows:Firstly we introduce the research background and significance of this subject,specifically introduce the existing multimode interference technology,and summarize the development process of two important multimode interference technologies,then introduce the thermal poling technology of optical fiber and the second-order nonlinear effect induced by thermal poling.Secondly,we study the multimode interference effect and the principle of thermal poling,and explain the multimode interference process.Then,we study the principle of secondorder nonlinear effect induced by thermal poling in fiber,and introduce the establishment process of two-dimensional charge dynamics model.Then we introduce two numerical analysis methods and software used in this paper in detail.Finally,the theoretical model is establish,and the simulation calculation of the ring core optical fiber is carried out.The multimode interference characteristics and the electro-optic tunable function induced by thermal poling are studied.Based on those methods,a 1×4 power splitter and a 1×2 wave separator are proposed.Among them,in the 1×4 power splitter,the nonuniformity of power distribution is 0.014 d B,the ratio of power in every out ports are about 1 : 1 : 1 : 1,and the insertion loss is 0.88 d B,this kind of power splitter has low loss and high uniformity of power splitting.The 1×2 wave separator separates the input light with the wavelength of 1.24 μm/1.55 μm,and the crosstalk interference of the two wavelengths is-22.1 d B and-23.5 d B respectively,which has the advantages of low port crosstalk interference and high separation.The power splitter and wave separator based on thermally poling ring core optical fiber,which is designed in this paper have the advantages of small size,strong anti-interference,and can induce linear electro-optic tunable function in the fiber by thermal poling.This kind of fiber has potential application scenarios in the fields of optical communication and fiber sensors in the future.