Research On The Key On-chip Reconfigurable Mode-division Multiplexing Devices And System

To satisfy the rapidly increasing demands on high-speed data transfer for cloud computing and data-intensive applications,optical interconnects have attracted wide attentions as a promising candidate for the next-generation solution alleviating the communication bottleneck and unfavorable power scaling.Silicon-on insulator(SOI)platform is attractive for optical interconnects owing to high refraction index contrast,high transparency in telecom wavelength band and compatibility with well-established complementary metal oxide semiconductor(CMOS)processes.On the other hand,various advanced multiplexing techniques such as wavelength-division-multiplexing(WDM),polarization-division multiplexing(PDM)and Mode-division multiplexing(MDM)have been utilized to improve the communication capacity.Alternatively,on-chip MDM technique is emerging since multiple spatial modes can be simultaneously applied to further increase the throughput of a single-wavelength link of optical interconnects.As all mode channels share same wavelength emitted from a laser diode,it is an efficient way to decrease cost and power consumption for the hardware.Resembling the WDM system,a multi-functional MDM system integrating various multimode elements is also highly desired.The research object of this paper is on-chip reconfigurable multimode devices and MDM system.The purpose is to effectively improve the throughput of optical interconnect.The devices used to construct MDM system are mainly divided into three categories: mode multiplexers,transmission multi-mode devices and reconfigurable multimode devices,which realize the functions of mode multiplexing,transmission and selective routing respectively.The performance of these three types of devices has also become a key challenge to limit the development of monolithic integrated MDM systems.We have done representative work in three aspects.Moverover,on the basis of these high-performance multi-mode devices,we have constructed a large-scale monolithic integrated MDM system.The main contents of this paper are as follows:Mode multiplexers play the most important role in an on-chip MDM system.The purpose of mode multiplexers is to excite and combine the complete set of eigenmodes of a multimode bus waveguide independently for multimode system.A high-performance mode multiplexer requires low crosstalk,broad bandwidth,low insertion loss and large fabrication tolerance.To address small fabricaton-tolerance,narrow bandwidth,small mode scalability,we propose a novel two-mode multiplexer consisting of adiabatic couplers and Y-junction,a mode multiplexer which can process dual-path mode-division multiplexing signals and avoid mode conflict,a polarization multiplexer based on adiabatic couplers.The passive devices performing connecting and transmission functionalities are essential for chip-scale layout.High-performance filters,waveguide bends and intersections are the indispensable parts to form a complete on-chip circuit.We experimentally demonstrate,a tuable mode filter.On the other hand,the design of multimode waveguide bend and crossing with compact footprint is a big challenge.We proposed a 90° sharply bent multimode waveguide and a compact and low-loss multimode waveguide crossing.We achieve record-low losses for the multimode waveguide crossing and bend with compact footprint.The reconfigurable photonic integrated device is one of building blocks of optical networks that promises high-speed data transmission,low latency and power consumption.Here,we propose and demonstrate an on-chip 1?×?1 multimode switch and a 1?×?2 multimode switch without de-multiplexing.To extend the freedom degree of reconfigurable routing,we propose a 2?×?2 multimode switch which can realize reconfigurable inter-mode plus interpath routing for fully flexible on-chip optical networks.The multimode switch can be easily upgradable to a larger scale.It is further extended to two types of 4?×?4 switch fabrics with cross-bar and ring-bus architectures,as demonstrations of high-level integration.To make the MDM technology more practical,we experimentally demonstrate for a fully integrated large-scale silicon multimode multiplexed network.By introducing the external optical carriers,it can realize on-chip data transmission and reconfigurable routing function,through parallel optical signal modulation by micro-ring modulator,mode multiplexing/demultiplexing by adiabatic couplers,add-drop data transmission,multimode signal reconfigurable switching and parallel optical signal detection by Ge Photodetectors.