环形孔径折叠成像系统的光-数联合无热化设计(封面文章·特邀)

Athermalization design for annular aperture folding imaging system based on light-digital combination(cover paper·invited)

环形孔径折叠成像系统通过光路折叠可以实现光学系统的小型化。然而环形孔径折叠成像系统由于仅使用一块基底材料,且没有补偿镜,无法通过光学被动无热化实现宽温度范围的高质量成像。为了减小温度对成像质量影响的同时简化光学系统结构,引入波前编码的方法来设计光-数联合的环形孔径折叠成像系统。文中研究了光-数联合的环形孔径折叠成像系统设计原理,推导了遮拦比与相位掩膜板参数的关系,以实现离焦一致性。在图像解码部分,文中研究了不同权重下的点扩散函数(PSF)的图像复原效果,通过模拟退火算法构建了合成PSF模型。根据理论分析设计了光-数联合的环形孔径折叠成像系统,焦距为70 mm,系统总长为25 mm,F数为1,全视场8°。在−40~60℃范围内,高温和低温下的峰值信噪比(PSNR)比其他方法分别提高了4.7090 dB和5.0442 dB,实现了单一滤波器的图像复原。文中研究在简化红外成像光学系统的同时,采用光-数联合的方法克服了环形孔径折叠成像系统的温度限制,为宽温度范围红外系统小型化提供了新的思路。

Objective With the advancement and development of science and technology,the demand for miniaturized optical systems is becoming increasingly significant.The total length of the optical system can be reduced by folding the optical path in the annular aperture folding imaging system.However,the annular aperture folding imaging system only uses a piece of base material,so the annular aperture folding imaging system cannot achieve high-quality imaging in a wide temperature range.In order to reduce the impact of temperature on the imaging quality and simplify the optical system structure,the wavefront encoding method is introduced to design a lightdigital combined annular aperture folding imaging system.Methods The design principle of the annular aperture folding imaging system based on light-digital is studied.The relationship between the obscuration ratio and the phase mask parameters is studied to achieve defocus consistency(Fig.5).In the image decoding part,the image restoration effect is analyzed.The synthetic PSF model is studied through simulated annealing algorithm(Fig.2).High-quality imaging in a wide temperature range is achieved through a light-digital combination method.Results and Discussions A long-wave infrared annular aperture folding imaging system is designed(Fig.3).The focal length is 70 mm,the system aperture is 98 mm,the full field of view is 8°,and the total length is 25 mm.The synthesized PSF is constructed by simulated annealing algorithm.When over a wide temperature range,the high-quality image restoration is achieved through a single filter.Although the PSNR of the restored image dropped by 3.5723 dB at the design temperature,the PSNR of the restored image at−40℃also increased from 19.4173 dB to 24.4615 dB,which increased by 5.0442 dB.The PSNR of the restored image at 60℃also increased from 19.7519 dB to 24.4609 dB,which increased by 4.7090 dB.This method outperforms traditional PSF image restoration at the design temperature.Image artifacts and blur are significantly reduced by this method.Conclusions Athermalization of infrared annular aperture folding imaging system is achieved.The light-digital combination method is introduced into the annular aperture folding imaging system.The annular cubic phase mask is introduced into the annular aperture folding imaging system,and the restored image is achieved through image restoration.The relationship between central obscuration and phase mask parameters is studied.The conclusion that increasing central obscuration will reduce PSF consistency is studied.The synthesized PSF is constructed by simulated annealing algorithm.When over a wide temperature range,high-quality image restoration is achieved through a single filter.In order to verify the effectiveness of this theoretical model,an annular aperture folding imaging system based on light-digital combination is designed.The total length is 25 mm,the focal length is 70 mm,the system aperture is 98 mm,and the full field of view is 8°.High-quality image restoration is achieved by synthesizing PSF when the temperature is between−40℃and 60℃.Although the PSNR of the restored image dropped by 3.5723 dB at the design temperature,the PSNR of the restored image at−40℃also increased from 19.4173 dB to 24.4615 dB,which increased by 5.0442 dB.The PSNR of the restored image at 60℃also increased from 19.7519 dB to 24.4609 dB,which increased by 4.7090 dB.Compared with PSF image restoration at design temperature,this method significantly reduces image artifacts.The study not only simplifies the infrared imaging optical system,but also uses a light-digital combination method to overcome the temperature limitations of the annular aperture folding imaging system.A new idea is provided for the miniaturization of infrared systems across a wide temperature range.