Structure Analysis And Characteristic Study Of Dual-parameter Sensing Model Based On High-performance Photonic Crystal Microcavity

The development of silicon-based integrated photonic devices has benefited from advances in silicon photonics and complementary metal oxide semiconductor(CMOS)micro-nano processing technology.And it is of great significance for the applications such as optical interconnection and optical sensing.In view of the ever-increasing requirements for the detection sensitivity,response speed,minimum required sample volume,portability and so on in the field of optical biochemical sensing,the development of 'Lab on chip' has attracted more and more attention.Due to its ultra small footprint,high sensitivity,fitting in integration,label-free detection,and mature CMOS manufacturing process,silicon-based photonic crystal(PhC)microcavity sensor has become the primary choice for on-chip integrated sensing.In order to improve the performance of photonic crystal microcavity sensors such as quality factor(Q)and sensitivity(S),solve the problem of temperature disturbance on silicon-based devices and realize high-efficiency sensing and detection,SOI-based one-dimensional(1D)photonic crystal nanobeam cavities(PCNC),two-dimensional(2D)photonic crystal microcavity and 1D photonic crystal ring(PhCR)resonator were designed,analyzed and fabricated.The effects of refractive index(RI),temperature(T)and the real(n)and imaginary(?)part of refractive index on the resonance modes were studied.And the dual-parameter sensing mechanisms were analyzed.The main work of the thesis can be summarized as follows:(1)Achieving a microcavity with both high Q and high S by using 1D photonic crytsal nanobeam cavity and improving the optical field overlapping integral in the analyte.Firstly,a rectangular holes based air mode 1D PCNC sensor with high quality factor-to-mode volume ratio(Q/V)and small footprint was designed.The optical field of the resonance mode is mainly localized into the air holes in the low refractive index region.Compared with traditional dielectric mode 1D PCNC sensors,the sensitivity is improved.When the length of the nanobeam cavity is about 8 ?m,the Q factor,V,Q/V,S,detection limit(DL)and figure of merit(FOM)are 1.27×05,0.745(?/nSi)3,1.7×105(?/nSi)-3,252.65 nm/RIU,4.7×10-5 RIU and 2.10×104,respectively.Then,in order to further improve the sensitivity,1D PCNC including a slot was designed.Most of the optical field is localized in the slot area,resulting in increasing overlapping integration of optical fields in the analyte,thereby enhancing the interaction between light and matter.This design can achieve ultra-high S?835 nm/RIU,ultra-high Q?5.50×105,and ultra-low DL?3.4×10-6,resulting in FOM higher than 2.92×105.The effective sensing area only occupies about 12 ?m×0.08?m.Finally,to solve the problem of overlapping among the resonant modes for multiplexed sensing induced by limited free space range(FSR),a high-performance band-stop filter based on 1D photonic crystal nanobeam waveguide was designed and integrated with PCNC sensor to realize multi-channel integrated multiplexing sensing.(2)Eliminating the temperature noise of silicon-based sensor by simultaneous sensing of refractive index and temperature based on single 1D photonic crystal nanobeam multi-mode cavity.Firstly,the feasibility of dual-parameter sensing based on the fundamental and first-order modes of the air-mode 1D PCNC was verified by numerical simulation.Then,a design method to confine both dielectric mode and air mode in a single PCNC was proposed and experimentally demonstrated.The measured air mode and dielectric mode of the PCNC have high Q factors of 1.90×104 and 2.56×104 at the resonance wavelengths of 3.728?m and 3.875 ?m,respectively.The simulated refractive index sensitivities of the air and dielectric modes are 186 nm/RIU and 135 nm/RIU,respectively,and the temperature sensitivities are 147 pm/? and 158 pm/?,respectively.In addition,the liquid sensing was performed by integrated with microfluidic channel.It was proved that the air mode and dielectric mode in the single PCNC have different responces to the changes of external environment.(3)Improving the sensing and detection efficiency by multiplexing and simultaneous sensing of the real and imaginary parts of the refractive index.The high performance width-modulated line-defect cavity is formed by decreasing the width of W1 waveguide by shifting a few holes in the first row towards the line defect,confining the guide mode of modulated waveguide.Two cascaded microcavities were designed to achieve a multiplexed structure obtaining two resonant falling peaks for multiplexed sensing.The sensing parameters include n and ?.During the detection,two independent physical quantities,wavelength shift ?? and line width change ??? are obtained.And they change linearly with n and ?respectively.The Q factors for the two cavities are 15725 and 15817,respectively.The real part refractive index sensitivities are 174.1 nm/RIU and 167.6 nm/RIU,respectively.The imaginary sensitivity of the refractive index are 291.8 nm/RIU and 298.7 nm/RIU,respectively.(4)Enhancing the absorption sensitivity by using slow light effect and improving the overlap integral of the optical field in the analyte.The resonant modes near the band edge of 1D PhCR have slow light effect,and can achieve a higher optical field overlap integration in the analyte when operating in a high-order photonic band gap(PBG).Therefore,in MIR wavelength range of 3.64-4.0 ?m,the slow light effect and absorption enhancement factor at the edges of the first-and second-order PBG edges of 1D PhCRs were experimentally demonstrated and compared for the first time.For the dielectric edge mode of the second-order PBG of PhCR,the experimentally measured ng is?11,and the Q factor is?7425.The absorption enhancement factor is?5.Compared with the unfolded 1D photonic crystal waveguide structure,the effective optical path length increases at least three-fold.In addition,the thermo-optic tuning ability of the PhCR device was demonstrated.By comparing the temperature sensitivities,it was proved that second-order PBG bandgap edge mode has a larger optical overlap in the analyte.In summary,this thesis has proposed,designed and demonstrated high performance photonic crystal cavities and the dual-parameter sensing models considering the following four aspects:simultaneously achieving high Q and high S,eliminating temperature disturbance to silicon-based sensing devices,improving the efficiency of sensing and detection,and enhancing MIR absorption sensitivity.The research results provide reference for the design of high-performance silicon-based photonic crystal microcavity sensors,paving the way to realize lab-on-chip sensing.