Design and Fabrication of Long-Wave Infrared Wide-Angle Metalens Arrays
Objective With the advancement of society and continuous technological development,infrared thermal imaging technology has found widespread applications in various scenarios,such as rapid body temperature screening and fault detection.The application of infrared thermal imaging spans multiple fields,from daily health monitoring to industrial equipment maintenance.In recent years,especially in the medical and industrial sectors,the demand for this technology has seen explosive growth.The primary reason is that infrared thermal imaging can measure temperature quickly and non-invasively,thus providing valuable data for medical diagnosis and equipment maintenance.However,most currently employed infrared cameras rely on traditional lens modules that are based on the principle of curved surface light modulation.This design has certain limitations,resulting in inefficient space utilization and making it difficult to meet the requirements of modern miniaturization and micro-design.As a result,metasurface technology has emerged as a revolutionary solution to tackle these challenges.Metasurfaces are artificial surfaces with sub-wavelength structures that can be designed to flexibly manipulate the amplitude,phase,polarization,and other physical parameters of electromagnetic waves.Compared to traditional refractive and diffractive optical elements,metasurfaces are considered the third generation of novel optical elements,providing new possibilities for the lightweight and integrated design of imaging devices.In infrared imaging systems,the field of view(FOV)is a critical performance metric.A wider FOV allows the imaging system to capture environmental information more comprehensively,which is particularly beneficial for monitoring and diagnostic applications.Traditionally,complex multi-lens combinations are adopted to offset the monochromatic aberrations caused by wide-angle incident light focusing to expand the FOV of infrared lens modules.However,this approach causes bulky and heavy lens modules with poor space utilization,serving as a barrier to integrated and lightweight designs.Therefore,addressing this problem with metasurfaces has become an increasingly popular research hotspot.Methods Traditional infrared imaging devices utilize multi-lens assemblies to correct the monochromatic aberrations caused by wide-angle incident light and then expand the FOV.However,this approach results in bulky lens modules,which are not conducive to the modern goals of integration and miniaturization.To this end,we propose a long-wavelength infrared wide-angle metalens array device designed and fabricated by employing silicon material.Silicon exhibits high transmittance and a low extinction coefficient at a wavelength of 10 μm.Additionally,as a semiconductor material,silicon is compatible with micro-nano fabrication processes.Meanwhile,silicon is chosen as the material for the long-wavelength infrared wide-angle metalens array to simplify the design and fabrication complexity of the device.For the designed long-wavelength infrared wide-angle metalens array device,we select cylindrical structures as the shape of the metasurface unit cells and establish a unit cell structure database.We simulate the unit cell structures and sub-lenses with different design angles.The simulation results show that at a wavelength of 10 µm,the transmittance of the unit cells exceeds 55％at incident angles of 0°,20°,and 30°.Additionally,the ideal phase curves of the sub-lenses with different design angles match well with the phases provided by the unit cell structures.These results indicate that the unit cell structures can meet the phase control requirements of the metalens array(Figs.4 and 5).The metalens array device achieves its functionality by introducing an angle-dependent phase distribution function and carefully designing the phase distribution of each sub-lens within the array.This design allows each sub-lens to form a clear image within a specific angular region,ensuring the clarity and accuracy of the entire wide-angle imaging process.The innovation of this design lies in its ability to precisely stitch together images formed by sub-lenses with different design angles,thereby achieving seamless wide FOV imaging.This design captures a broader scene without compromising image quality and detail.The angle-dependent phase distribution function is the key factor in the entire design process,as it compensates for phase shifts caused by different incident angles,thus maintaining image integrity across the entire wide FOV.Results and Discussions After the device is fabricated,imaging verification experiments are conducted.By employing a blackbody light source,a target,and a filter,we perform imaging experiments at a wavelength of 10 μm.During the experiments,the five sub-lenses successfully produce clear images of different angular regions of the target.The images formed by the sub-lenses,each responsible for a different angle,are then extracted and stitched together according to their respective regions.The final results realize wide FOV imaging with high image quality.The imaging experiments demonstrate that the actual imaging FOV of the metalens array device is consistent with the theoretical design,with a FOV greater than 60°(Fig.8).Conclusions We present the design and fabrication of a long-wavelength infrared wide-angle imaging metalens array based entirely on silicon material.By introducing an angle-dependent phase distribution function,the phase distribution of each sub-lens within the metalens array is carefully designed,thereby leading to a long-wavelength infrared metalens array capable of wide FOV imaging.Experimental validation confirms that the performance of the metalens array device is consistent with the design,achieving an imaging FOV greater than 60°.The application of metasurface technology in infrared imaging highlights its significance in optical component design.With thoughtful design and optimization,metasurface technology is poised to play a crucial role in a broader range of optical applications in the future.As technology continues to advance,the potential applications of metasurface technology in various fields will be further explored to provide new possibilities for enhancing the performance of optical systems.
optical devicesmetalens arraymetasurfacelong-wave infraredwide field of view
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