Study And Design On Photonic Integrated Devices Based On Two-dimensional Sampled Gratings And Novel Micro/nano Structures

With the coming of 5G era and the rapid development of the cloud storage and cloud computing,the scale of information interchanging,data processing and communicating are rapidly growing,which requires the improvement of the transmission rate in the optical communication network.In the early stage of the optical communication network,the photonic devices that realize different functions in the network are discrete and independent,which results in the increasing volume,high cost,low efficiency and cannot satisfy the requirement for higher transmission rate.This challenge can be well addressed by Photonic integrated circuits(PICs),which can integrate different photonic devices with different functions on one single chip.For PICs,the transmission rate of the optical transceivers has become 100 Gb/s in 2017 and will increase to 400 Gb/s in 2020.However,there are still some challenges in PICs that need to be well addressed.For example,the source for PICs still need to be further optimized with stable single longitudinal mode operation for large-scale high-density integration.Besides,to further increase the transmission rate,the development of the Wavelength division multiplexing(WDM)technology,Mode division multiplexing(MDM)technology and other advanced multiplexing technology is important for increasing channels for the next-generation optical network.Based on Two-dimensional sampled gratings,we optimized the performances of the Distributed feedback(DFB)lasers by improving the Single-longitudinal-mode(SLM)property so that the DFB lasers can be applied in large-scale high-density integration in PICs.Besides,we investigated on mode conversion properties of the two-dimensional waveguide gratings and designed multi-wavelength mode converter.Also,a broadband,compact and efficient mode converter based on polygonal deeply-etched slot is proposed.By numerical simulation of the two-dimensional sampled gratings and novel micro/nano structures,it is beneficial for the future research.The main content of the paper are:(1)We proposed a new technique to improve the fabrication error tolerance of the photonic devices based on waveguide gratings,which can also enhance the precise control of light responses.Based on Reconstruction-equivalent-chirp(REC)technique,we theoretically analyzed the phase matching in the two-dimensional sampled grating with uniform basic grating and demonstrated that the desired responses can be achieved in the Fourier sub-gratings of the two-dimensional sampled gratings.Due to the nano-scale variations in the grating structure is hard to fabricate,which will limit the further development and application of these photonic devices.This challenge can be well addressed by two-dimensional sampled gratings which can realize desired light responses by designing the micro-scale sampling pattern.Therefore,the study on the two-dimensional sampled grating is beneficial for large-scale high-density integration in the PICs.We also briefly introduced the numerical analysis and optimization method for photonic devices,such as Finite-difference time-domain(FDTD)and Eigenmoe expansion method(EME).(2)We proposed two types of two-dimensional sampled gratings to improve the SLM property of the DFB laser based on REC technique.In the study of two-dimensional gratings,we found that the anti-symmetric and tilted grating can suppress Bragg reflection.Based on this novel optical property,we designed anti-symmetric sampled grating ang tilted sampled grating.By properly designing the sampling pattern,the-1st sub-grating or+1st sub-grating are equivalent as the uniform grating with ? phase shift,which can be utilized as the working channel to filter the light of specific wavelength in the resonator of the DFB laser.Meanwhile,the 0th subgrating is totally suppressed to avoid the amplification and emission of the 0th light.Therefore,the multiple subgratings interactions in DFB laser based on REC technology can be well settled and the SLM property of the DFB laser is highly improved.We experimentally demonstrated the antisymmetric sampled grating in the silicon-on-insulator(SOI)waveguide.In summary,based on two-dimensional sampled gratings,the DFB laser shows good SLM property and is suitable for designing the DFB laser array and tunable DFB laser array.(3)By using two-dimensional samped gratings,we also designed multi-wavelength filter in the Si3N4 waveguide based on mode conversion.Through theoretical analysis,it can be found that the fabrication error tolerance of the target grating can be improved to more than ten times in the two-dimensional sampled gratings,which greatly enhance the precise control of the light responses.We also demonstrated the high-power a-DFB laser and fiber sensing based on tilted sampled grating.Based on tilted sampled grating,we proposed the two-wavelength mode converter and three-wavelength mode converter and analyze the influence that the change of angle and the period of the sampling pattern on mode conversion efficiency and resonant wavelength.(4)Based on polygonal slot structure,we theoretically proposed different kinds of mode converter with broad bandwidth,high conversion efficiency and low crosstalk.We demonstrated mode converter from TE0 to TEi,TE0 to TE2,TEi to TE3 based on tilted slot,bi-tilted slot and tri-tilted slot.As examples,mode converters from the fundamental transverse electric mode(TE0)to the first-order transverse electric mode(TE1)and to the second-order transverse electric mode(TE2)have both been demonstrated with a short device length(<24.0?m),a high mode conversion efficiency(>97.6%),and a low modal crosstalk(<-20.0 dB)over a broad wavelength range from 1500 to 1600nm(?100nm).