Simulation And Femtosecond Laser Fabrication Of Air-clad MMI Optical Splitter Based On SU8 Photoresist

With the rapid development of communication technology,people's requirements for high-speed data transmission are constantly increasing.The high delay,large loss,and low bandwidth of traditional inter-board interconnection technology can no longer meet the needs of modern communication technology.The optical interconnection between chips has become one of the most promising research directions in the communication industry.Passive optical splitters are an important part of optical interconnection technology.In the development of short-distance communication systems,high efficiency and low loss of light sources are realized.The transmission is particularly important.Due to the limitation of size and the cumbersome photolithography preparation process of traditional polymer optical splitter,further research is needed in the application of highly integrated optical interconnection.Based on the above problems,this paper uses integrated optical BPM(beam propagation method)waveguide software to design an air-clad MMI optical splitter based on SU8 photoresist,and uses femtosecond laser processing technology to prepare it.Research and improvement have been made on materials and preparation techniques.The specific research work is as follows:(1)Based on the theory of beam propagation method(BPM),an air clad MMI type1×16 optical splitter based on SU8 photoresist is proposed.The structure of the splitter is mixed with symmetry and asymmetry.Compared with the traditional optical power splitter,the size of the splitter is greatly reduced due to the improvement of the structure.The cladding layer is air,the substrate is silica glass,the core layer is SU8 photoresist,and the end face is a rectangular structure of 10×10 ?m.The structural parameters of the1×2 multimode interference coupler were obtained by simulation optimization.The curved waveguide and branching Angle connected with the multimode interference coupler were optimized.The structural dimension of the complete 1×16 optical power splitter was obtained,and its length was less than 22,000 ?m.By studying the effect of ultrafast femtosecond laser parameters on the etching of polymer SU8 photoresist,a complete femtosecond laser processing technology of polymer SU8 photoresist was obtained.When the laser power is P=90m W and the scanning speed is v=15mm/s,the femtosecond laser can etch the polymer optical waveguide with the cross section of10x10?m rectangle.The complete polymer air clad 1×16 optical power splitter is prepared by using the femtosecond laser setting the above process parameters.(2)The tolerance of the designed multi-mode interference coupler was analyzed by simulation software,and the tolerance of the width of the multi-mode interference coupling region was ±1.5?m.The input waveguide position error should be controlled within the range of ±1?m.The error range of the output waveguide position should be less than 1.5?m to ensure the device performance to the greatest extent.The test results show that the femtosecond laser machining error is within the above allowable range.The optical fiber coupling test platform was set up to study the spectral performance of the prepared 1×16 power divider.Through optical testing and recording the calculation results,the insertion loss of the device was less than 23 d B and the uniformity was1.48 d B.(3)An improved optical interconnected on-chip structure was proposed based on SU8 photoresist material for the vertical(90° turn)coupling of optical fiber in the backplane of optical waveguide interconnection.The influence of spatial position deviation on the coupling efficiency of optical fiber to a 45° micro mirror was calculated by using the finite-difference time-domain(FDTD)method,and the optimal coupling position was determined.With the maximum normalized output power of0.861,the maximum coupling efficiency of 86.1% can be obtained,and the main reason of coupling loss of 45° micro mirror is simply analyzed.A femtosecond laser was used to etch a 45° micro mirror at the end of a polymer optical waveguide to achieve small size and high efficiency communication.The mirror Angle was measured at 45.64°.