基于波前编码的大焦深弹载双色红外探测系统

Double bands missile-borne infrared detection system of extended focus depth based on wavefront coding

波前编码技术通过在光学系统光瞳位置加入特殊的相位掩模板,对目标信号光波进行编码调制,并在图像处理端对该编码信号进行解码而恢复原图像,由于被编码调制后的波前对离焦等像差的不敏感度扩大了十数倍,能显著扩大光学系统焦深。因此,波前编码技术能在编码与解码之间解决恶劣力热条件或多色制导体制对弹载红外探测系统带来的离焦和对准误差。文中基于波前编码扩大焦深基本原理,对一长长双色红外光学系统进行了10倍焦深扩大的波前编码像差钝化设计。集成样机后,进行了波前编码成像实验。以小孔点靶编码像作为PSF解码10倍离焦位置处的十字靶和四条靶图像,十字靶和四条靶解码图像清晰可辨,证明波前编码技术对于系统像差或离焦像差的抑制是有效的。最后,对波前编码成像效果进行了分析:解码图像的水波纹是由于空间采样PSF不足导致的,可提取不同视场位置PSF,使用空间变化解码算法实现条纹消除;由于解码图像会在放大信号的同时放大噪声,因此,解码算法需要进一步研究噪声抑制算法,以期满足弹载高能量、高信噪比应用的要求。

In the technology of wavefront coding, a special phase mask is put at the position of optical system stop. Then the goal signal wavefront will be coded. At the image processing part, the coded signal will be decoded to the original image. Because the insensitivity of the coded wavefront to the defocus and other aberrations is ten times more, the focus depth will be extended ten times more. So the wavefront coding can solve the defocus and alignment error caused by terrible mechanics and heat environment using coding and decoding. Based on the extended focus depth principle of wavefront coding, an aberration inactivation long/long double bands infrared optical system was designed. The focus depth was extended to be 10 times more. Imaging test was carried out with the wavefront coding prototype. The coding image of the spot-bar was used as the PSF to decode the image at the 10 times defocus position of cross-bar and four-bar. After decoding, the image of cross-bar and four-bar was with high resolution. At the last, the imaging results of wavefront coding were analyzed. The ripple of decoding picture was caused by not enough spatial sampling. After sampling PSF of different field, the ripple could be eliminated by using decoding algorithm of spatial transformation. The signal and noise would be extended at same time while the image was decoding. So the noise suppression algorithm used in decoding should be further researched to satisfy the missile-borne demand of more energy and higher signal to noise ratio.