Research of a sphere–cone window with good aberration characteristic

Optical windows with external surfaces that shaped to satisfy operational environment needs are known as special windows. A novel special window, sphere–cone (SC) window, is presented. The equations used to decide geometrical parameters of this window are deduced. A SC MgF2 window with a fineness ratio (F) of 1.33 is designed as an example. The field-of-regard (FOR) angle is ±80°. From the window system simulation results by the calculated fluid dynamics (CFD) and optical design software, we find that the SCP shape compared to conventional window forms not only introduces relatively less drag in the airflow, but also makes the minimal effect to imaging. After a correcting lens is adopted in the SC window optical system, the lowest modulation transfer function (MTF) value at 17 Lp/mm reaches 0.610 and the root-mean-square (RMS) spot size is approximately 1.57–2.12 times than the diffraction limit. The design results show that the SC window optical systems can achieve high image quality across very wide FOR by the simplest static correction.