Research On Key Technologies For Mode Division Multiplexed Photonic Integrated Interconnection

Recent years,since the increasingly high growth of global Internet data traffic,the optical fiber communication system and data center infrastructure are keep evolving to-wards larger capacity and higher density.The transmission capacity of a single fiber re-lying on wavelength division multiplexing technology has been approaching its capacity limit.While,mode division multiplexing（MDM）or space division multiplexing tech-nology can effectively break this bottleneck and continue to increase the capacity by two orders of magnitude.The integrated optical transceiver module is the core component of the data center optical communication network,and MDM can effectively improve its transmission rate and fiber port density.However,at present,most of the researches on MDM photonic integrated interconnection are confined in the on-chip interconnects.The multimode optical coupling interface,which is necessary for the optical intercon-nects between integrated chip and fiber,still has many issues in the footprint,loss and reliability.Besides,for the on-chip active controlling of multimode signals,such as mul-timode optical switches and routings,it still lacks of solutions with high efficiency and scalability,which restricts the practical application of MDM technology in integrated optical interconnect systems.This thesis mainly studies the key devices and systems for MDM photonic integrated interconnection,focusing on two devices,the integrated multimode optical coupling in-terface and integrated multimode optical switch,aiming to provide a solution for MDM photonic integrated interconnections with large capacity,low power consumption and high density.The innovations and main achievements of this thesis are listed as follows:1)In order to solve the issues of multi-mode optical coupling interface in terms of footprint,loss and reliability,Multimode edge coupling and vertical coupling schemes are studied on the CMOS-compatible silicon-on-insulator（SOI）platform.The proposed multimode edge optical interface is based on multimode interferometer and triple inverse tapers.The simulation and experimental results show the optical edge coupling with broadband and high efficiency between the TE₀,TE₁modes in silicon integrated waveg-uides and the LP₀₁,LP₁₁modes in two-mode fiber.The proposed multimode edge cou-pler acts as optical interface at transmitter side,and verified by a 2×100-Gbps data trans-mission.The results provide a silicon integrated solution for multimode edge coupling within a small size.The proposed vertical optical interface is based on an inversely-designed apodised 2D grating coupler.It supports broadband and efficient multimode excitation including six degenerate modes in LP₀₁and LP₁₁mode groups,with the max-imum coupling efficiency of-3.3 dB and-3.9 dB,and 1-dB bandwidth of 24.4nm.In order to keep the efficient coupling away from the fluctuations of polarization states and orientations in few-mode fiber,the on-chip linear processing system is implemented based on Mach-Zehnder interferometers network.Therefore,the polarization-and orientation-insensitive two-mode optical interface is proposed,which promotes the stability and ro-bustness of multimode optical interface.2)In order to solve the limitations of conventional’demux-mux’multimode opti-cal switches in system footprint,scalability,efficiency and power consumption,a novel architecture of multimode optical switch is proposed based on an inversely designed com-pact multimode optical splitter.The 4-mode optical switch is designed composed of the4-mode optical splitter and 4 phase shifters,with<1.5 d B insertion loss and>10 d B mode extinction ratio.Experimental results show the ability of reconfigurable optical switch-ing among TE₀,TE₁,TE₂and TE₃four modes.On the basis of the proposed multimode optical switch,and combined with micro-ring switch array or mode（de）multiplexers,the multimode optical routing and add-drop multiplexer systems are realised.The scalability of multiplexed modes and channels is discussed as well.Despite sacrificing some of the switching states,the proposed novel architecture for multimode optical switch has sim-ple structure,small footprint,low power consumption and high scalability,improving the efficiency of on-chip multimode signal processing.3)For the study of MDM photonic integrated interconnection,MDM photonic in-tegrated circuit is firstly designed and fabricated based on Chalcogenide platform.Low-loss optical waveguide and passive devices including optical coupling interfaces,power splitters and mode multiplexers are fabricated.On-chip MDM optical interconnects are achieved at 2-micron waveband with total capacity of 3×80 Gbps.Afterwards,facing the integrated optical transceiver module for data center,an MDM-based 400G silicon transceiver scheme is proposed.The proposal of integrated optical module,photonic integrated circuits and module packaging are designed and discussed,in which the self-proposed polarization-and orientation-insensitive multimode grating coupler is imple-mented as multimode optical interface.The mask layout of photonic integrated circuit is drew as well.The proposed MDM scheme further improves the transmission capacity of single fiber and also enhance the panel density of integrated optical transceiver,paving the way for the practical implementation of MDM technology in optical transceivers.