Study On Mode Converters Based On Photonic Integrated Chip

With the development of information age,people’s demand for high quality and high speed of data processing promotes the research of integrated optics and free space optics using light as information carrier.In the design of integrated optical devices,the silicon-on-insulator(SOI)platform is widely used due to its excellent compatibility with complementary metal oxide semiconductor(CMOS)processes.However,the high refractive index contrast between SOI platform materials makes the photonic devices designed based on it have strong polarization sensitivity,the proposal of polarization splitter and rotator(PSR)effectively solves this problem.In addition,integrated optics mainly uses photonic route encoding,polarization encoding and other ways to process information,while free space optics mainly uses photonic frequency,phase,spin angular momentum and orbital angular momentum.Therefore,the two information processing methods are different,and the mode of photonic needs to be converted in order to transmit information.In this paper,two mode converters based on the SOI platform are proposed,the main contents are as follows:1: A conical polarization splitter and rotator(CPSR)based on the SOI platform is proposed,which adopts a conical design in the coupling region of CPSR.According to the mode coupling theory between waveguides,the input TM mode and the TE mode are separated,and the TM mode is converted into TE mode,achieving the separation and conversion of waveguide polarization modes.By numerical simulation,the polarization splitter and rotator effect of the CPSR is analyzed,and the mode transmission,polarization extinction ratio and operating bandwidth are calculated,and then the manufacturing tolerance of CPSR is analyzed.The designed CPSR realizes the separation and rotation of waveguide polarization mode on chip,which provides a feasible way to solve the polarization sensitivity of photonic integrated devices.2: Based on the designed conical polarization splitter and rotator,and combined with the transitional adiabatic conical waveguide and waveguide surface holographic grating,an integrated optical waveguide polarization mode to free space orbital angular momentum mode converter(POAMC)is proposed,which realizes the optical waveguide TM/TE mode to OAM optical conversion,and the transition between TM mode and TE mode superposition state and OAM superposition state.By numerical simulation,the conversion efficiency,extinction ratio,fidelity of the generated OAM beam,and operating bandwidth of the POAMC are calculated and analyzed.POAMC has good mode transformation performance and provides a feasible mode transformation method for information transmission from integrated optics to free space optics.