| Artificial compound eyes are advanced optical visual systems with distinct features of a large field of view(FOV),infinite depth of field,and dynamic imaging capability,revealing their significant potential for cutting-edge applications including robotic vision,unmanned aerial vehicles(UAV)detection,and medical diagnosis.So far,artificial compound eye systems have made achievements and progress after over 20 years of development.However,currently available artificial compound eyes that consist of numerous large lenses are generally macroscopic multi-camera systems.More importantly,macroscopic compound eyes cannot meet the requirement for practical applications in micro-robotics,insect robot vision,and minimally invasive surgery,restricted by their relatively large size.The miniaturization and integration of artificial compound eyes is not only the developing direction in the future but also an urgent demand for our national cutting-edge micro-optical devices.However,when the size of the artificial compound eye is down to millimeters or even micrometers,the design,preparation,and integration of the compound eye systems become extremely sophisticated.Challenges including fabrication of high-quality three-dimensional(3D)compound eye lens,opto-electric integration at micron-nano-scale,and multi-view image processing are addressed.Artificial compound eyes are micro-lenses that are closely packed on a curved surface,serving as a swarm of ommatidia.Their complex and delicate 3D structures render them challenging to fabricate using general technologies.For starters,all of the ommatidia are closely packed on a curved surface to realize a complete utilization of space light information and a large FOV detection.Second,the surface profile and smoothness of each ommatidium that govern the imaging quality should be considered.To achieve high-quality imaging,a strategy with controllable progress and nanometer accuracy is highly required.Compared with other methods for fabricating artificial compound eyes,femtosecond laser direct-writing(Fs LDW)has emerged to be a great solution to these demands with its unique feature of high fabrication precision and mask-free process.Therefore,this dissertation proposed miniature artificial compound eye systems based on the femtosecond laser nanofabrication strategy.Solutions are addressed aiming at the problems of opto-electric integration,micro-scale 3D image reconstruction,and large FOV imaging.The main contents are as follows:(1)Introduction: First,the structure and unique features of natural compound eyes are introduced;Then,state-of-the-art manufacturing technologies for artificial compound eyes are summarized.Femtosecond laser direct writing is pointed out as the most ideal approach for fabricating ACEs due to its high fabrication precision and programmable direct writing process.Next,different artificial compound eye systems are reviewed and the development trend for small size systems with curved compound eye lenses is indicated.At last,the application scenarios of artificial compound eyes are summarized,including a large field of view imaging and three-dimensional information detection.(2)Opto-electric integrated camera with 3D compound eye lens and image sensor:To solve the incompatibility between photosensitive detectors that are based on planar technology and curved focusing plane leads by the hemispherical surface arrangement of micro-lenses,compound eye lenses with multifocal ommatidia are proposed.Each micro-lenses are designed with certain different focus lengths,leading to a plane focus surface instead of a curved focus surface.Thus,an opto-electric integration system with a 3D compound eye lens and a planar image sensor is achieved.The size and field of view(FOV)of compound eye lenses are highly flexible as needed.In this chapter,the compound eyes are about hundreds of micrometers in diameter,and contain 7 to 19 single micro-lenses,each of them being about tens of micrometers in diameter.A 3-layered compound eye with a field of view(FOV)of 40° is present.The results prove that the curved focus plane is adjusted to a flat plane both in theoretically and experimentally.Finally,an integrated camera with a designed compound eye lens and the commercial image sensor is fabricated successfully,and the resulting camera shows a clear observation of target objects.(3)On-chip miniature opto-electric compound eye camera: Compound eyes,as multi-aperture systems,are capable of obtaining 3D information from different views.Targeting the 3D detection of small size objects at close distances,this chapter proposed a neural network reconstruction algorithm to explore the 3D detecting ability of the miniature compound eye camera.The 3D position of the observed target(target size:tens to hundreds of micrometers;detection distance: hundreds of micrometers to several milometers)is successfully reconstructed with an average error of 0.44%.Aiming at the real application of the space detection of close range and small size objects,an onchip compound eye camera is prepared to combine artificial compound eye camera with microfluidic chip technology,which further enriches the application of bionic compound eye in the fields of biological monitoring,chemical principle,and so on.(4)Large FOV imaging of compound eye camera: Even though the as-prepared compound eye camera has a large FOV due to the curvature surface of the 3D compound eye lens,the detection range is restricted by the placement of the compound eye camera in 3D space.To obtain a dynamic regulation of the observed direction of the compound eye camera,an integrated system with a miniature compound eye camera and a soft actuator is proposed.The actuator provides a mechanical rotation movement for the artificial compound eye camera thus changing the detect angle.An electrothermal actuator(driving voltage: 0 – 60 V)is prepared to carry the miniature compound eye camera and the resultant integrated system achieves a detection angle of360°.(5)Summary and outlook: This chapter summarizes the work of this dissertation and points out two optimization directions in the fabrication of artificial compound eyes and the 3D reconstruction algorithm. |
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