Research On Basic Theory And Application Of Reconfigurable Light Field Dimension Resource Manipulation

The physical dimensions of light include amplitude,phase,time,wavelength/frequency,polarization,and transverse space structure.Applying these physical dimensions to optical communications through modulation or multiplexing can effectively improve the communication capacity of the system.To enable efficient utilization,it is necessary to perform effective manipulation of physical dimensions of light.Manipulation techniques for wavelength/frequency and spatial dimensions are critical to the continued growth in capacity demand in future.However,traditional optical elements utilized to manipulate wavelength/frequency dimension suffer from a single function,limited tuning range,and non-reconfigurable spectrum,which are not conducive to flexible management in optical networks.For the manipulation of the spatial dimension,traditional optical elements have shortcomes such as large volume,low accuracy,which are disadvantageous for achieving compact and high precision spatial light manipulation.Silicon photonic devices have advantages in a compact structure and flexible operation when compared with traditional optical elements.Therefore,in order to solve the key problems existing in the manipulation of the light physical dimensions,theoretical and experimental studies are carried out,focusing on the manipulation of wavelength/frequency dimension based on integrated devices,manipulation of spatial dimension by traditional and integrated devices,and application of spatial multiplexing in optical communications.The major contents of this dissertation are summarized as follows.1)Theoretical and experimental studies on wavelength/frequency dimension manipulation based on integrated devices.（1）The spectral response of cascaded microring is theoretically studied.（2）A reconfigurable and tunable chip-scale comb filter and（de）interleaver on a silicon platform is proposed and demonstrated.By appropriately adjusting the micro-heaters in tunable Mach-Zehnder interferometer（MZI）couplers and cavity,switchable operation between comb filter and（de）interleaver and extinction ratio and wavelength tunable operations of comb filter and（de）interleaver are achievable by thermo-optic tuning.2)Theoretical and experimental studies on spatial dimension manipulation based on traditional and integrated devices.（1）A metasurface-assisted orbital angular momentum（OAM）carrying Bessel-Gaussian laser is proposed and simulated.Replacing axcoin with metasurface-based reflector,it meets the requirement of compact Bessel-Gaussian beam laser.By appropriately selecting the size of the output mirror and inserting a mode-selection element in the laser cavity,different orders of OAM-carrying Bessel-Gaussian lasing modes are achievable.（2）An OAM reconfigurable and wavelength tunable twisted light laser with achievable high-order OAM modes on a hybrid free-space and fiber platform is proposed and experimentally demonstrated.By appropriately switching the phase pattern loaded onto spatial light modulators and adjusting the bandpass filter,twisted light laser with reconfigurable OAM and tunable wavelength is implemented in the whole C band.（3）A compact and ultra-broadband OAM generator/synthesizer formed by fork grating on top of a silicon waveguide is fabricated.The OAM₊₁ mode,OAM₊₂ mode,and synthesization of OAM₊₁ and OAM_-1 modes are generated.By changing the relative phase shift between the synthesized OAM₊₁ and OAM_-1 modes,a reconfigurable chip-scale OAM synthesizer is also demonstrated.（4）An ultra-compact chip-scale broadband polarization diversity OAM generator is designed（holographic method）and fabricated.Utilizing the holographic grating,it couples the in-plane waveguide modes to the out-plane free-space OAM modes(x-/y-polarized OAM₊₁/OAM_-1).（5）Two kinds of OAM emitters are designed using the inverse design method.One is a broadband polarization diversity OAM generator.The generated OAM modes have much higher purity than generated by the holographic grating.The other is multi-OAM states emitter.The generated OAM modes include OAM₊₁,OAM_-1,OAM₊₂,OAM_-2.3)Theoretical studies on the capacity limit of space-division multiplexing（SDM）communications.The basic types of SDM and the parameters of the line-of-sight（LOS）communication system are introduced.Based on the LOS system,the spectral efficiency（SE）and effective degrees of freedom（EDOF）of three types of multiplexing/demultiplexing methods are analyzed.Moreover,taking the demultiplexing complexity into account,the results indicate that OAM（with a perfect OAM demultiplexer）is better than the other two methods.