Influence Of The Butt-coupling Status Between Single-mode Waveguide And Fiber On The Polarization Dependent Loss Of Device

Optoelectronic integration(OEIC)is inevitable trend in the development of optoelectronic devices,monolithic integration can improve the response speed of the device,the optoelectronic conversion efficiency,the power consumption of the device,the crosstalk,the stability of device performance,and the yield of products.But,integration development is based on the waveguide technology,so the mode field of OEIC is small and elliptic,while the mode field of optical fiber is large and circular,causing severe mode field mismatch.Thereby,in optical networks,the fiber-waveguide butt coupling caused insertion losses of integrated components become a big challenge.However,due to the interdependent relationship between the insertion loss(IL)and polarization dependent loss(PDL),the investigation for the PDL is inevitable in the research process of IL,the related study of PDL is indispensable.To date,optical waveguides have been developed to the planar lightwave circuit(PLC)level,the stability in product performance,the design and processing technology maturity,and the lower cost of production have made remarkable achievements,and even some products have been gradually proliferated in industry.Thus,in the research,development and production of a device,the coupling process between fiber and chip is not only an unavoidable step,but the this their coupling state also has a paramount important impact upon the performance and packaging of this product.Currently,all research efforts on PDL are starting with the birefringence property of device functional material,while seldom efforts on the theorem of causing the PDL and the involved key factors are reported.Thereby,based on the principle and its relationship with polarization state of optical beam,this project is aimed to systematically investigate the IL and PDL in the fiber-waveguide butt-coupling(FW-BC)process in the three aspects: the theoretical analysis,the professional software simulation and the experimental test.First,we build the polarization dependent electro-magnetic fields of optical guided-modes based on the beam propagation method(BPM)theory and further analyze the FW-BC process with a matching theory of two field vectors and discover the key physical factors and conditions impacting upon the polarization dependences of the FW-BC coupling efficiency,including the coupling gap size,the angle and roughness of waveguide end.Then,we build the mathematical model for the FW-BC caused IL and PDL,in which the field distributions of both fiber and waveguide guided-modes are obtained by using the BPM software,and further perform the numerical simulations to maintain the polarization dependence of the guided-modes in the FW-BC process.Finally,by processing the end surfaces of fabricated waveguide chip and fiber to have the required roughness and angle,we experimentally measure the IL and PDL in FW-BC process.The simulations show that for the 0° and 8° waveguide ends,when the air gap changes from 2?m to 10?m,the IL increases from 2.0dB to 5.0dB,and the PDL keeps at 0.1-0.2dB;while the experimental measurements show that when the minimum IL value is 2dB,the corresponding gas size is about 2?m,when it increased by 5 times,namely,about 10?m,the IL increases to 3.5dB,while the PDL keeps at 0.1-0.25 dB.The above results show the agreeability between the theoretical values and experimental results.