Study On Mid-wave Infrared Filter Based On MEMS-FP Microstructure Array

The spectral imaging involving both the spectral information and the image information of targets,is an important method for performing target detection and recognition.The typical spectral structures or devices used in traditional imaging spectrometers mainly include prisms,gratings,spectral interference and spectral acousto-optic modulation device,etc.,which still demonstrate the defects of the relatively complex structure and driving control.Combining the Micro-Electro-Mechanical System(MEMS)with Fabry-Perot(FP)interference microcavity and further integrating the MEMS-FP interference filtering and arrayed photosensing,the constructed imaging spectrometers can be miniaturized and light weighted and the imaging detection and recognition efficiency can also be continuously improved.In this dissertation,a mid-wave infrared(3-5?m)filter based on the MEMS-FP microcavity beam interference is designed and fabricated,and the infrared spectral characteristics of the principle sample are tested.The FP-Fano microcavity interference phenomenon is discovered and analyzed.The major works are presented as follows.First of all,based on the working principle of the FP interference filtering and the MEMS operation,the supporting microbridge of the mid-wave infrared MEMS-FP array is studied.Three types of microbridges including the square reflector straight arm,the round reflector folded arm and the square reflector folded arm,are designed.The displacement and stress distribution of the microcavity bridge deck according to the electrostatic driving are calculated by COMSOL.Three types of microbridge surface characters are compared and analyzed based on the aspects such as the optical tuning range,the microbridge deck flatness,and the reflector filling-factor.To the current reflectors with a relatively low filling-factor of the existing MEMS-FP structure,a square reflector folded arm microbridge deck is selected for experiment.Then based on the theory of the DBR films,an optical structure of the mid-wave infrared FP filter is designed and optimized.Both DBRs of the FP microcavity are designed and optimized by TFCalc,and the reflectance of the DBR and the transmittance of the FP microcavity are calculated.The infrared transmission characteristics of FP microcavity,which are influenced by the factors such as the number of the film layer,the incident angle and the micro-cavity depth,are analyzed.A three-layered film architecture of the Ge/Si O₂/Ge as a reflector in the wavelength range of 3-5?m are determined.To the problem of the spectral transmission efficiency being affected by the uneven reflector of the FP microcavity with a high reflector filling-factor,the influence of the flatness and surface roughness of the DBR on the FP filtering performance is simulated by COMSOL.The spatial interference phenomenon owing to typical Fano spectral interference caused by the unevenness of the reflector is discovered and studied.Researches of using sharpened Fano-FP spectral filtering for performing hyperspectral imaging detection by configuring the shaped reflectors with uneven or even patterned surface morphology and then conducting coupled interference filtering based on the Fano-FP and MEMS-FP,are carried out.Finally,based on the common surface micromachining technology,a 4×4 filter array is fabricated and tested.The measurement results show that the developed MEMS-FP array with a high reflector filling-factor can be used to achieve the filtering in the mid-wave infrared wavelength range with a typical peak transmittance of?30%and a FWHM of?220nm.What's more,the disturbing Fano-FP microcavity interference can be effectively avoided by optimizing fabrication process.The study lays a foundation for further implementation Fano-FP interference filtering with a hyperspectral resolution through reasonable configuration of the structure and fabrication parameters,as well as realizing spectral interference filtering by coupling the Fano-FP and MEMS-FP.