Optomechanical Infrared Detector Based On Micro-metalens

With the development of industry and society,the demand for infrared detection is increasing rapidly in security,medical and other civil fields.The development of high-performance uncooled infrared detectors has become one of the most important directions of infrared detection.Long wave infrared spectrum(8～14 μm)is not only the window of atmospheric transmission,but also the spectral peak of the thermal radiation of room temperature objects like human and buildings.The optomechanical uncooled long-wave infrared detector has significant advantages in manufacture process and thermal isolation.Nevertheless,the fill factor of optomechanical detector is usually only about 40%,which greatly limits the utilization efficiency of incident light energy.As a binary optical element,the metalens has drawn great attention due to its versatility in light wave manipulation and compatibility with general MEMS techniques.With integration of metalenses,the effective fill factor of the infrared detectors is expected to be greatly improved.However,small aperture of the detector-integrated metalenses and deep-subwavelength periodic for unit cell bring new challenges to structure design due to diffraction and wave guide coupling effects.This dissertation focuses on the optical wave characteristics of solid-immersed micro-metalens at subwavelength and diffraction scale,and a novel optomechanical infrared detector enhanced by metalens is designed,fabricated and evaluated.Firstly,theoretical analysis methods were developed for the design of micrometalens array integrated with infared detectors.Based on the phase control mechanism of the propagation phase,the coupling among the adjacent subwavelength waveguides and its effect on the phase modulation were demonstrated by optical waveguide analysis and FDTD simulation.Scalar diffraction analysis illustrated that the small aperture of the micro-metalens leads to 30%relative defocus due to the combination of amplitude attenuation factor and vibration in-phase factor.Secondly,the photomechanical infrared detectors enhanced by metalens were designed.The three-stage nested thermomechanical structure and the series-parallel hybrid thermal isolation structure were proposed.With the enhanced infrared absorption efficiency and better thermal isolation,the thermal conversion coefficient of the infrared detector is increased by 50%compared with traditional design.And the three-stage structure further doubles the thermomechanical sensitivity.Therefore,the overall performance of the detector is significantly improved.Thirdly,the fabrication process of optomechanical infrared detector with integrated micro-metalens was developed.The process involves five coatinglithography-etching steps.And the key manufacturing challenges and solutions were discussed.Finally,the performance of the metalens-integrated infrared detector was experimentally evaluated.The focusing effect of the infrared metalens is demonstrated visually with an infrared camera.The thermomechanical sensitivity of the cantilever is tested to be 0.2 μm/K.The fabrication uncertainties were analyzed in details and their effects on the device sensitivities were discussed quantitatively.By comparing the infrared responses of the detectors with and without integrated metalenses,it was demonstrated that an 85.7%improvement can be achieved with the focusing of the incident energy by metalenses under small incident angle conditions.Furthermore,aiming to matching the design of the detector micro-optical system and the imaging main optical system,a micro-metalens edge ray method based on the generalized refraction law is proposed,which provides a design baseline for the geometric optical design of the concentrating micro-metalens.In this paper,the design challenges of detector-integrated long wave infrared metalens are investigated regarding subwavelength wave propagation,diffraction and geometrical optics.The design,fabrication and testing of the metalense integrated optomechanical detector were discussed in details.It is demonstrated that the metalens can significantly improve the performance of the detector.The optomechanical infrared detectors with integrated micro-metalens have great potential to be applied in high performance uncooled infrared detection techniques.