针对传统光学元件在红外波段色差校正方面存在系统结构复杂、光能损失严重、质量大等问题,以红外波段4.8 μm和10.6 μm存在的色差为例,将槽栅型表面微结构用于红外波段的色差校正;根据广义斯涅尔定律及时域有限差分(FDTD)理论计算微结构表面的相位分布,采用FDTD Solution软件仿真双方柱槽栅型微结构;设计两个槽栅型微结构宽度L₁=400 nm、L₂=950 nm,槽栅高度K=500 nm;采用离心式涂胶法、电子束光刻、离子刻蚀等一系列工艺技术,制备双方柱槽栅型微结构样品,分析胶膜厚度、曝光图像质量、刻蚀槽型的影响因素。结果表明:改变L₁和L₂的大小可实现在4.8 μm和10.6 μm这两种波长下分别达到0~1.5π和0~2π范围的相位调制;L₁=408 nm,L₂=944 nm,K=495.32 nm,表面粗糙度为16.32 nm,相关参数在误差允许范围之内;4.8 μm和10.6 μm这两个红外波段的峰值透过率分别为71%和64%;利用平行光位置色差测试原理测得两个红外波位置色差减小到30%,从而验证了槽栅型微结构器件对红外色差的校正作用。

For traditional optical components, there are some issues in chromatic aberration correction of infrared bands, such as complexity of system structure, great loss of light energy, large mass and so on. Taking the chromatic aberration of 4.8 μm and 10.6 μm infrared wavebands as an example, we study the chromatic aberration correction in the infrared band with the grooved grating surface microstructure. According to the generalized Snell law and the theory of finite difference time domain (FDTD), the surface phase distributions of the microstructures are calculated. The double square cylinders grooved grating microstructure is simulated with FDTD Solution software. The widths of the grooved grating microstructure are designed to be L1=400 nm and L2=950 nm, and the height of the grooved grating is K=500 nm. Double square cylinders grooved grating microstructure samples are prepared by a series of other process technologies of centrifugal coating method, electron beam lithography, and ion etching. The influencing factors of photoresist thickness, exposure image quality, and etching groove type are analyzed. The results show that the phase modulation for ranges of 0 to 1.5π and 0 to 2π can be achieved under the condition of two kinds of wavelengths of 4.8 μm and 10.6 μm by changing L1 and L2. L1=408 nm, L2=944 nm, K=495.32 nm, and surface roughness is 16.32 nm, which are within the allowable range of error. The peak transmittances of two infrared bands of 4.8 μm and 10.6 μm are 71% and 64%, respectively. Using the principle of parallel light measuring longitudinal chromatic aberration, we test the longitudinal chromatic aberration of the two infrared waves reduce by 30%, which proves the effect of the grooved grating microstructure device on the chromatic aberration correction.