Research On The Silicon-Based Reconfigurable Device And Its Applications In Optical Communication

Silicon-based photonic integrated chips(Si PICs)have been developed rapidly,as they are favored by the academic and business communities with the advantages of low loss,compact size,and microelectronic process compatibility.With the help of the abundant optical manipulating mechanisms,Si PICs are capable of manipulating multiple dimensions of the optical field,including phase,polarization,spatial distribution,wavelength,and time,by constructing the reconfigurable optical devices whose transfer function and working state are reconfigurable.Such reconfigurable devices can greatly enrich the application scenarios of the on-chip optical systems and improve their flexibility and stability.Thus,the reconfigurable devices are of great significance for promoting the development of the Si PICs.The dissertation focuses on the research on the silicon-based reconfigurable device and its applications in optical communications.Starting from the optical manipulating mechanisms,the reconfigurable devices and systems based on the Mach-Zehnder interferometer(MZI)are adopted to manipulate different dimensions of the optical field.The reconfigurable optical transmitter which can generate different modulating formats,the inter-chip optical interconnecting systems which can support multiple modes,and the optical receiving system which can stabilize the polarization state of incoming light are realized.Thus,the function of the optical transmitter is expanded,the communication capacity of the inter-chip interconnection is enlarged,and the stability of the optical receiving systems is enhanced.The major research content of the dissertation can be summarized as follows:(1)The theoretical basis of the silicon-based reconfigurable devices is deeply studied.Starting from the optical manipulating mechanisms,the principle of the thermal phase shifters,which are widely used in reconfigurable devices,is analyzed by modeling and simulating.On this basis,the MZI is modeled,and its transfer function is derived.The optical manipulating principle of the reconfigurable devices is explained from the perspective of its transfer functions,paving the way for the further design of the reconfigurable devices and systems.(2)As the on-chip optical transmitting systems can only transmit limited modulation format,a reconfigurable optical transmitter which can transmit multiple formats is proposed.By making using the reconfigurability of the MZI,the optical signals including on-off keying signal,binary phase-shift keying signal,four-level pulse amplitude modulating signal,quadrature phase-shift keying signal,polarization division multiplexing on-off keying signal,and polarization division multiplexing binary phase-shift keying signal,can be generated.These multiple types of modulation formats can be applied to different transmitting scenarios.As a proof-of-concept demonstration,we fabricate the device on a commercial wafer and demonstrate 10 GBaud on-off keying signal,four-level pulse amplitude modulating signal,and polarization diversity multiplexing on-off keying signal.(3)In order to alleviate the mode mismatch and mode crosstalk in the mode division multiplexing inter-chip optical interconnection,a multimode two-dimensional grating coupler,and a mode crosstalk descrambler are proposed.By manipulating the phase and amplitude of the optical signal,the multimode two-dimensional grating coupler is capable of coupling six different modes with the few-mode fiber.It is of great importance in transmitting and receiving the modes in the mode division multiplexing systems.By constructing an inverse matrix of the mode-crosstalk matrix of the few-mode fiber,the mode crosstalk descrambler can descramble the mode crosstalk in the mode division multiplexing systems.By making using the above two devices,a 100 m four-mode inter-chip optical interconnection system is experimentally demonstrated.The loss of each channel is about-25 d B and the mode crosstalk is below-15 d B.(4)In order to alleviate the polarization sensitivity of the on-chip optical receiving systems,a polarimeter-assisted polarization stabilizer is proposed.The stabilizer adopts an MZI-based reconfigurable device to manipulate the state of the polarization(SOP)of the incoming light.Two different polarization stabilizing algorithms,namely feed-forward stabilizing algorithm and feedback stabilizing algorithm,are adopted to control the stabilizer.The feed-forward stabilizing algorithm which makes use of the polarimeter can stabilize the SOP in one-time manipulating.The feedback stabilizing algorithm which makes use of the feedback photodetector can optimize the stabilizing accuracy.The proposed stabilizer is fabricated and experimentally characterized.With help of the feed-forward stabilizing algorithm,the stabilizer consumes only 30 μs to stabilize SOP.With the help of the feedback stabilizing algorithm,the stabilizing accuracy of the stabilizer achieves 99%.