Study On Silicon Based Photonic Crystal Cavity Properties And The Applications In Side And Direct Coupled Sensor Arrays

In recent years,all-optical sensors have been widely researched in the area of chemical safety,biological research and environmental monitoring.Miniaturization and integration of all-optical sensors have become important trends in future integrated optical devices.Among those photonic structures,photonic crystal(PhC)sensors obtain high performances in sensitivity,resolution,Anti-interference,response speed,miniaturization,integration,et.al.Meanwhile,PhC can realize high quality factor,low mode volume and small footprint at the same time,which make PhC one of the most important foundations in future optical integrated circuits and devices.Silicon-based PhC cavity sensors obtain the advantages of high refractive index and ease of on-chip integration,which provide the abilities for realizing high-sensitivity,strong photon con finement and high compactness sensor design.The next generation of sensing platforms should have excellent ability of multiple target detection.Therefore,the PhC sensor arrays design becomes one of the most popular research areas these years.However,in recent researches of sensor arrays,sensing performance is limited because of the need for multiple sensing,such as limited sensitivity of each sensing segment and narrow free space range of the resonance caused by the feature of PhC cavities.In order to solve those problems,one dimensional(1D)PhC nanobeam cavities,two dimensional(2D)slabs PhC cavities,1D PhC band-stop filters,Y shape power splitters and couplers based on SOI are used as study subjects.By using plane wave expansion methods,the photonic band calculation of PhC structures are simulated.By using 2D and 3D finite-difference time-domain method,optical field distribution and transmission spectrum of PhC cavities,PhC filters,Y shape power splitters and power couplers are simulated.Eventually,high-performance PhC cavities and PhC sensor arrays are realized.The main results of this dissertation are as follows:(1)The research of the design and the sensing performance of 2D slab photonic crystal cavities.By adding low refractive index(RI)region in a traditional PhC Ln(n=7)cavity,the symmetric-shaft-shape photonic crystal cavity is designed.By enhancing the percentage of the electric field localized in the low RI region,the cavity obtained high sensitivity,high Q factor and broad free spectral range(FSR)in small cavity size.The cavity is side-coupled with a PhC W1 waveguide in the simulation for sensing.The sensitivity is 398 nm/RIU,which is 6 times higher than a traditional Ln cavity.In order to get even higher sensitivity,slot structure is used in the PhC cavity design,in which the slot obtains the capacity to concentrate optical power in the slot when the width of the slot is much smaller than the characteristic decay length inside the slot.A 2D three-slot PhC cavity sensor with a small print of 12×2.3 ?m2,quality factor(Q)of 1.4×106 and mode volume(Vm)of 0.015(?/nair)3.is designed and simulated.The Q/Vm value is as high as 8.95×107,and the bulk RI sensitivity reaches the high value of over 900 nm/RIU.Compared with the symmetric-shaft-shape PhC cavity,the sensing performance is greatly enhanced.Meanwhile,a low sidelobe 1D photonic crystal nanobeam bandgap filter is designed to connect with the slot cavity,in order to suppress the higher-order modes while remaining the fundamental mode.The FSR of the cavity is enhanced.Compared with other 2D PhC cavities,the footprint of the connected structure is small,which is only 25×2.3 ?m2.The 2D PhC cavity designs in my dissertation are good candidates for designing high-performance integrated sensor arrays.(2)The research of the design and the sensing performance of 1D photonic crystal nanobeam cavities.In order to reduce the difficulty in realizing multiple sensing,a 1D PhC nanobeam cavity connected with a 1D PhC bandgap filter is designed,which realizes the transmission with only fundamental mode in the wavelength range from 1500 nm to 1700 nm.The sensitivity of the structure is as high as over 400 nm/RIU,with a small footprint of 26×0.65?m2.In order to enhance the ability of light confinement and single-molecule sensing,high subwavelength confinement of photon is needed.Therefore,in this dissertation,bowtie-nonbowtie 1D PhC nanobeam cavities are designed and simulated and a mix and match method for the cavity design is proposed.The bowtie-antislot 1D PhC nanobeam cavity can significantly enhance the photon localization,which realizes ultra-small mode volume(10-4(?/nair)3)and enhances the fabrication tolerance.The simulated Q factor can reach 104,and the measured Q factor of the cavity reaches 103.Compared with antislot 1D PhC nanobeam cavities,our design obtained a similar Q factor while the mode volume is two times of magnitude smaller and suitable for single molecule sensing.The 1D PhC cavity designs in this dissertation are promising in designing single molecule sensing and high-performance integrated sensor arrays.(3)Research of the PhC cavity sensor in sensor array design with cascade and parallel connection.In order to realizing parallel multiple sensing,the integration of 1×8 splitter and 8×1 coupler on the silicon-on-insulator(SOI)substrate based on silicon wire waveguides with low loss in the bandwidth of 400 nm,from 1400 nm to 1800 nm is designed.The total excess loss of the splitter and coupler integration is 0.36 dB,and the optical power uniformity is less than 0.32 dB at the wavelength of 1550 nm.By connecting 1×8 power splitter,eight 1D PhC slot nanobeam cavities connected by additional 1D PhC tapered nanobeam bandgap filters,and an 8×1 power combiner in series,the 1×8 highly sensitive ultra-compact on-chip integrated sensor array is designed on substrate.Eight sensing segments interrogated simultaneously by one input and one output port is realized,with the ultra-compact footprint of 64×16 ?m2(26×16 ?m2 in sensing region),and the bulk RI sensitivities of the eight 1DPC-SNCs are all over 400 nm/RIU.Therefore,this design is a promising platform for realizing large-scale photonic integrated circuits with high integration density,especially for ultra-compact multiple on-chip sensing.Setting in cascade alongside a PhC W1 waveguide,four symmetric-shaft-shape PhC cavities generate four dips in the transmission spectrum in the wavelength between 1515 nm and 1600 nm.Each cavity of the PhC sensor arrays is designed with different width of slots.By using 2D-FDTD method,the simulation result obtained indicates the performance of the sensor arrays.The sensitivities of the four sensor units are 178,252,328 and 398 nm/RIU,respectively.Those properties show that the proposed symmetric-shaft-shape photonic crystal sensors array is a promising platform for application in multiplexed sensing and integrated optical devices.In conclusion,high-performance silicon based PhC cavities suitable for multiple sensing are designed focusing on the need for integrated optics development.Then those cavities are used to design cascaded and parallel sensor arrays and analyzed their sensing performances.The research in this dissertation provides promising candidates for future nano-optical integrated sensing.