| As a new subject,photonics technology with high information capacity and efficiency,fast response speed,great storage capacity,strong interconnection and parallelism has achieved rapid development.And it has been widely used in optical sensing,information transmission,high speed information processing,information storage and display,etc.The relationships of mutual supplement,interaction and promotion between photonic technology and electronic technology have been formed,which makes the share of photonic technology in the commodity market increase rapidly year by year.Photonic biochemical sensing has become one of the important photonic research fields.Rapid advancements of photonic technology have significantly enhanced the photonic biochemical sensor performance,especially in the areas of interaction between the light and analyte,device miniaturization and multiplexing,and fluidic design and integration.The photonic sensing devices should have higher sensitivity,lower detection limit,less sample consumption,faster detection time,and lower detection cost.The microring resonator?MRR?based on silicon on insulator?SOI?has high quality factor and super compact structure,especially combined with slot waveguide,which can realize high sensitivity and low limit of detection?LoD?.With the increasing sensitivity,the slot MRR?SMRR?is only suitable for detecting the liquid with the medium and low concentration viarations and gas due to the limitation of free range region?FSR?,while the liquids with high concentration viarations are out of the detection range.The main research contents and innovations of this thesis about increasing the detection range and enhancing the sensitivity and so on are summarized as follows.1.Main research contents:?1?The transmission mode of optical waveguide is studied.Based on Maxwell's equations,the transverse Helmholtz equations are derived,and they are applied to the three-layer plate waveguide to obtain the field distribution forms of the transverse electric mode?TE?and transverse magnetic mode?TM?.Combining with the boundary conditions,the characteristic equations of TE mode and TM mode are derived.The field distributions and characteristic equations of rectangular and slot waveguides are derived.And effective index method?EIM?is adopted to calculate the transmission modes of rectangular weak waveguide.Finite-difference method?FDM?and finite element method?FEM?verify the results of fundamental mode and two high-order modes based on EIM,and three methods are in good agreement,which shows EIM is very suitable for the mode analysis of weak waveguides.The effective index solving of EIM on SOI waveguides causes big errors due to ignoring the optical fields of four corners.Therefore,FDM and FEM are utilized to calculate the transmission modes of SOI rectangular and slot waveguides,optical field distributions and effective refractive index values,which provides a theoretical basis for subsequent design of suitable waveguide sizes.?2?MRR theory and its sensing mechanism are studied.The output spectra,phase shifts,ring cavity enhancement factors and resonant equations of all-pass and add-drop MRRs are derived.The meaning and expressions of the MRR's important characteristic parameters,which include extinction ratio?ER?,free spectrum region?FSR?,full width at a half maximum?FWHM?,quality factor?Q-factor?and fineness?F?,are summarized,and FWHM is also 3 dB bandwidth or spectral line width.The sensing mechanism of MRR is described,and the performance indicators such as sensitivity,LoD,dynamic range and noise are introduced,and the sensitivity as an emphasis is studied.?3?A compact inner-wall grating SMRR?IG-SMRR?biochemical liquid sensor is proposed.The device combines the advantages of the small size of MRR and the wider operating range of grating,which solve the problems of the limitation of MRR by FSR and the large size of the grating.The grating plays a role in the suppression on side mode,enabling the sensor at 1450 nm1650 nm only one main resonant point,which greatly broaden the operation range of the device.The device optimization process is described,and the size tolerance analysis of grating is carried out.Sodium chloride solution and D-glucose solution are regarded as the analyte,the sensor performance of the device is calculated and analyzed.The concentration sensitivities of the two solutions are up to 996.91 pm/%and 968.05 pm/%,respectively,and the corresponding refractive index?RI?sensitivity are 559.5 nm/RIU and 558.3 nm/RIU,and the LoD is as low as 2.2×10-5 RIU.The designed sensor is really appropriate for the fields of high sensitivity and large detection range.?4?A three-slot hybrid plasma waveguide MRR?TSHP-MRR?biochemical gas sensor is proposed.The conventional silicon slot microring on the SOI platform forms the TSHP-MRR due to the presence of metal inner and outer the ring resonator,and the inner and outer slots are regards as the plasma slots.The optical field distributions at1550 nm in the TSHP are described,and the plasma slot widths are optimized in terms of the important parameters of MRR.The calculation results show that the smaller plasma slots result in the higher sensitivity,but which causes the larger loss of plasma waves and the less extinction ratio?ER?and the difficulty for the gas molecules to enter the slots.Therefore,this chapter takes into account the sensitivity and the plasma slots comprehensively.MRR can operate at the critical coupling state by scanning the coupling distance between the bus waveguide and the ring waveguide.The sensor performance is analyzed with biochemical gas as the analyte.The calculations show that the sensitivity is up to 841 nm/RIU,and LoD is 1.5×10-55 RIU.As the refractive index of the gas varies in a small range,the FSR of the MRR completely satisfies the gas concentration variation.Compared with the IG-SMRR,this device without considering the influence of side mode has higher sensitivity.This TSHP MRR is also suitable for the liquids with the medium and low concentration variations,and the proper small plasma slot widths can obtain the biochemical sensor with higher high sensitivities without persuing high ER.In addition,this TSHP MRR is applied for optical modulator,electrodes do not need to be fabricated due to the metals inner and outer the ring resonator.2.Main innovations:?1?The biochemical liquid sensor with high sensitivity and ultra-wide detection range is obtained by combining MRR with grating.?2?The biochemical gas sensor with ultra-high sensitivity is obtained by combining Si slot waveguide and surface plamon slot waveguide.?3?Both of the two optical biochemical sensors proposed in the thesis are compact in structure and only need a small amount of samples,enabling integration into the biochemical sensing arrays. |
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