Tian Yi, Sun Gang, Yan Hui, Zhang Li, Li Zhuo
Appl Opt. 2014 Oct 10;53(29):6820-9. doi: 10.1364/AO.53.006820.
In order to reduce the complexity of splicing the mirrors of an infrared (IR)/millimeter wave (MMW) beam combiner into a plane, the wavefront division imaging technique (WDIT) was proposed. However, WDIT would lead to the difference of air gap thicknesses among different mirrors, which will further cause the nonuniformity of the MMW field. Simultaneously, there were slots between every two mirrors after the mirror array was spliced and adjusted, which would also affect MMW and IR diffraction. Thus, the aperture field integration method (AFIM) was proposed to compute the MMW near field distribution and the IR far field distribution. The method was validated by comparing the results obtained from the multilevel fast multipole method and experiment. The experimental results showed that the diffraction phenomenon caused by a tilt slot or a hole can approximate that caused by a slot with the width or a hole with the edge diameter along the tilt direction multiplied by cosine of the tilt angle. The variations of both MMW and IR field distributions were caused by three factors: different tilt angles, air gap thicknesses, and slot widths were analyzed by using AFIM in the spatial domain and the time domain. The simulation results showed that the three factors will affect the uniformity of the MMW field. And the uniformity introduced by the air gap thicknesses was the worst. However, the uniformity still satisfied the requirement for phase error when the variation of the air gap thicknesses was less than 1 mm. Although the three factors would cause the loss of energy and an enhancement in the background noise received by an IR focal plane array, the resolution of the IR system would not be affected. Thus, the WDIT was validated through the above analysis.
为了降低将红外（IR）/毫米波（MMW）光束组合器的反射镜拼接成平面的复杂性，提出了波前分割成像技术（WDIT）。然而，WDIT会导致不同反射镜之间气隙厚度的差异，这将进一步导致毫米波场的不均匀性。同时，在反射镜阵列拼接和调整后，每两个反射镜之间存在狭缝，这也会影响毫米波和红外衍射。因此，提出了孔径场积分方法（AFIM）来计算毫米波近场分布和红外远场分布。通过将该方法与多级快速多极子方法得到的结果以及实验结果进行比较，对该方法进行了验证。实验结果表明，倾斜狭缝或孔引起的衍射现象可以近似为由沿倾斜方向宽度的狭缝或边缘直径的孔乘以倾斜角的余弦所引起的衍射现象。利用AFIM在空间域和时间域分析了毫米波和红外场分布的变化是由三个因素引起的：不同的倾斜角、气隙厚度和狭缝宽度。仿真结果表明，这三个因素会影响毫米波场的均匀性。气隙厚度引入的均匀性最差。然而，当气隙厚度变化小于1mm时，均匀性仍满足相位误差要求。虽然这三个因素会导致能量损失和红外焦平面阵列接收到的背景噪声增强，但不会影响红外系统的分辨率。因此，通过上述分析验证了WDIT。
