Silicon Photonic Devices For Switching And Modulation

With the popularization of cloud computing,the Internet of Things,media videos,5G,and various intelligent terminals,the demand for data is increasing.The requirements for a communication system in terms of communication capacity,speed,and power consumption are becoming higher and higher.Traditional communication technology is gradually failing to meet the needs of massive data transmission.Benefiting from its thermal stability,large bandwidth,low energy consumption,and compatibility with CMOS process,silicon photonics shows many advantages such as large bandwidth,high speed,low cost,energy efficiency,etc which is promising to become the next generation of communication technology.Recently,various silicon integrated devices with excellent performance have been demonstrated.However,there is still a huge challenge of the large-scale integration of silicon photonics.The main reasons can be included in the following two parts:(1)How to break through the limitations of silicon materials to realize active devices on silicon substrates.(2)How to realize high-consistency silicon optical passive devices and large-scale integration.To solve the challenges mentioned above,this thesis focuses on Mach-Zehnder interferometer(MZI).The main research areas are silicon EO polymer hybrid modulation,low random phase error 2×2 switches,and calibration-free switch arrays.First of all,considering the bottleneck of a high-speed EO modulator,this thesis explores a new heterogeneous integration system combining OEO polymer(high EO coefficient)with a silicon photonic platform,which can make a breakthrough in footprint and bandwidth.In this thesis,an MZI modulator with large bandwidth is designed by combining SWG with OEO polymer.Traveling-wave electrodes can achieve beyond 50-GHz modulation bandwidth with only?1.5 dB optical insertion loss.In order to achieve a smaller footprint and lower power consumption of devices,this paper studies the MZI modulator based on plasmonic waveguides,whose footprint is only 10 ?m and that is expected to achieve modulation speed in THz level.To overcome the large absorption of the metal,a novel silicon-plasmonic hybrid waveguide is proposed,where the loss is reduced by two times.Larger fabrication tolerance can be observed compared with traditional plasmonic waveguides.What's more,a sodium plasmonic waveguide is introduced to further reduce optical loss,which is 3-7 times lower than the traditional plasmonic waveguide based on gold.In terms of experiments,the MZI EO modulators based on SWG and Au plasmonic waveguides are explored in this thesis.The EO modulation effect is preliminarily observed,which paves the way for high-performance electro-optic modulators.Secondly,the MZI optical switch has been studied.Optical switches and switch arrays are the key devices in multi-path multiplexing and reconfigurable systems.However,the traditional switch shows a large random phase error and accurate calibration of each switch state is required,causing extra optical loss,additional power consumption,and requiring complex control feedback systems.Therefore,the concept of a calibration-free 2X2 switch is proposed by reducing the influence from the interaction between the optical field and the nonuniform sidewalls of the MZS arm waveguide.Firstly,a widened phase shifter and shorten phase shifter are introduced to reduce the accumulated random phase shift.Then,an Euler curve waveguide with tapered curvature and width is proposed,which significantly reduces the random phase error.This thesis demonstrates a 2×2 MZI optical switch cell based on Euler curve waveguide with nearly zero random phase error,whose phase-shifter waveguide footprint is 2 ?m×30 ?m,and the Euler curve waveguide is 9×9 ?m2.Compared with the traditional design,the mean and standard deviation of the random phase error of the new-type MZS are reduced to 1/375 and 1/11.Finally,to further reduce the crosstalk of the switch,an optimized MMI coupler by PSO is designed to control the high-order mode excitation components.Devices with ultra-low loss(<0.1 dB)and low crosstalk(<-25 dB)in a wavelength range of 1520?1590 nm are realized.The ??/?w is only 0.0083 ?/nm.Finally,the calibration-free switch arrays were experimentally realized for the first time,including 4×4,8×8,and 16×16.Based on the TES-bend uncalibrated 4×4 MZI optical switch array,the additional loss under the initial uncalibrated state is?3 dB,the crosstalk is-20 dB,and the 30 Gbps eye diagram is obtained.This thesis optimized TES-bend with further reduced the inter-mode crosstalk,and expanded the switch ports to 8×8 and 16×16.To facilitate the test,the chip is electrically packaged,and the devices of 8×8 and 16×16 switch arrays are tested.The additional loss and crosstalk of the 8X8 MZI switch array without calibration are 3 dB and-18 dB,respectively;The additional loss and crosstalk of the 16×16 MZI switch array without calibration are?4 dB and-15 dB,respectively.In order to realize a larger-scale non-calibrated optical switch array,the design tolerance of the switch cell needs to be determined.This thesis established a signal transmission model for the NxN MZI optical switch array for the first time,and analyzed the signal degradation of coherent or incoherent optical multi-port input and output ports.The scale of the optical switch array is simulated by the Monte Carlo method.The relationship between crosstalk and random phase error provides a guide for the design of optical switch units and the analysis of switch arrays.