Research On Compact Passive Coherent Imaging Technology With High Resolution

Compact Passive Coherent Imaging Technology with High Resolution?CPCIT?is a new imaging technology based on interference principles and photonic integrated circuits.CPCIT replaces traditional film,CCD or CMOS detection methods with a compact array of interference arrays based on photonic integrated circuits.It can overcome the limitations of volume,weight and power consumption to achieve a higher image resolution or reduce the volume,weight and power consumption of the detector to 1/10¹/100 of the original under the same image resolution conditions.Given that the cost of space is expensive and that the traditional imaging system is approaching the limit,research on CPCIT can provide a new choice for high resolution,small volume,low weight and low power consumption in future designs.As a new generation of imaging technology,it not only has important scientific value in the mechanism of military space imaging but also can be applied in many fields,such as space exploration and reconnaissance,and has important practical value.CPCIT has attracted many researchers'attention worldwide,but it is still in its initial stage and faces many challenges in theory and engineering application.The challenges that need to be solved are summarized as follows:?1?the arrangement of the lenslet array of the system determines the quantity and quality of the spatial frequency sampling.At present,insufficient research on the layout design of the lenslet array leads to insufficient spatial frequency coverage.?2?Photonic integrated circuits are the key parts of the whole system;however,the size and optical path design of the current photonic integrated circuits cannot meet the requirements of the imaging system.The complex and large number of optical paths produced by imaging applications pose great challenges to the design of large-scale photonic integrated circuits.?3?CPCIT directly obtains complex measurements of the amplitude and phase information of the incomplete spatial frequency of the target;thus,image reconstruction is an ill-posed inverse problem.How to reconstruct images accurately according to the characteristics of the system is a major challenge.In this paper,CPCIT is introduced as a whole,and the key issues are studied:from the introduction of basic principles and models to the analysis and discussion of the main problems.The main contributions of this research are summarized as follows:1.Based on the basic imaging principle,the global optical process of CPCIT is established.The imaging process and the performance parameters,such as the coupling efficiency,the field of view and the resolution of the system,are reasearched.In addition,the advantages and disadvantages of CPCIT are analysed and a simulation analysis model is established.2.To analyse the influence of different arrangement modes of the lenslet array on spatial frequency sampling,the arrangement modes of the lenslet array,which includes multiple interference arms and a single interference arm,are compared and discussed.A lenslet arrangement?CS-CPCIT?based on a photonic integrated circuit with a compressed sensing design and its upgraded version?CS-CPCIT+?are proposed,which can increase the number of different baselines composed of 2N lenslets from N to 2N-1 and,respectively.In CS-CPCIT+,a nested array of lenslets is proposed,which can increase the longest baseline by N/2 times.In the simulation with the wavelength range 1223nm¹568nm,when SPIDER uses 24lenslets to form 12 baselines with the longest baseline is 20.88 mm and the angular resolution is 0.74 mrad,CS-CPCIT+can form 144 baselines,the longest baseline is103.68 mm,and the angular resolution is 0.12 mrad.3.Based on the idea of time-division sampling,rotation system design schemes with super-large apertures are proposed.Through uniaxial rotation,static aperture+rotating truss and multi-rotating truss,these schemes can use a small number of apertures to obtain equivalent super-large apertures and relatively complete spatial frequency coverage.In the static+rotating apertures design,a 20 m equivalent aperture with an angular resolution of 25 nrad can be achieved using a rotating uniaxial and 7 static apertures with radius of 0.25 m in the wavelength range500⁹00nm.With the rotating truss rotates 45 times,the reconstructed image has a PSNR of 26.45 dB.4.Aiming at the problem that the photonic integrated circuit needs to arrange complex and huge numbers of optical paths,an optimized layout design and upgrade scheme of photonic integrated circuits based on compressed sensing are proposed,which reduce the N sets of transmission,interference and measurement equipment needed for 2N lenslets to only one set.While simplifying the design of the photonic integrated circuit,the number of spatial frequency samples is increased by 2 times and N times,respectively.In the simulation with the wavelength 700nm,when SPIDER uses 72 lenslets to form 36 baselines with the longest baseline is 0.36 m and the angular resolution is 1.9(6(9,CS-CPCIT+can form 1296 baselines,the longest baseline is 6.48 m,and the angular resolution is 0.11(6(9.5.Aiming at the ill-posed inverse problem of image reconstruction in the system,this paper combines the theory of astronomical synthetic aperture image reconstruction and proposes a theoretical framework of image reconstruction.This paper then gives the realization and simulation verification of various image reconstruction algorithms under this theoretical framework.For the USAF image,the image reconstruction is performed using the norms with the equality constraint.Compared with PSNR=16.58 dB of the direct IFFT,the PSNR=21.69 dB for TV norm,which is increased by 31%;the PSNR=19.17 dB for ₁ norm,the improvement is 16%;PSNR=17.53 dB of the ₀ norm,the improvement is 6%.It is verified that the improvement effect of ₀ norm,₁ norm and TV norm on reconstructed image is:TV norm>₁ norm>₀ norm.When the number of interference arms is 37 and the number of samples on a single interference arm is increased from 6 to 144,the PSNR using IFFT is increased from 9.93 dB to 16.81 dB.When the number of samples on a single interference arm is 72,the number of interference arms is increased from 7 to111,the PSNR using IFFT increased from 11.33 dB to 28.16 dB.By studying the influence of the number of interferometer arms and the number of sampling on a single interferometer arm on the image quality,it is verified that increasing the number of samples by increasing the number of interference arms is better than increasing the number of samples on a single interference arm.6.A systematic verification test of optical coherence detection was carried out.In the experiment,optical fiber devices are used to replace the optical devices and optical fibers are used to connect to form a baseline.By sampling the spatial frequency information corresponds to the baseline,the feasibility of the passive coherence theory is verified.The experimental results and influencing factors are analysed and discussed.Based on the above research contents,researchers expound on the overall structure and solutions to the key problems of CPCIT,providing theoretical and technical support for the practical research.These areas also provide new ideas for the development of new large-aperture and high-resolution imaging technology.