基于离轴自由曲面的激光通信光学天线设计

为了提高空间激光通信系统的工作范围,简化光学系统的结构,提出了基于离轴自由曲面的大视场两镜无焦光学天线的设计形式。该光学天线采用无焦结构,无需再使用准直透镜元件,可以极大地简化系统结构,克服了传统聚焦光学天线体积过大、大功率光源情况下焦点处功率密度过高等问题。首先,基于三级像差理论,推导了两镜无焦系统的消像差公式,并对求解结果进行了分析总结。然后,根据求解结果和实际需求设计了一款无焦光学天线,该系统的有效通光口径为100 mm,放大倍率为5倍,波段为500~1100 nm,全视场角为0.6°,主镜为凹抛物面的一部分,次镜采用XY多项式表征的自由曲面,并用MATLAB对次镜自由曲面面形进行了仿真。结果表明,光学系统全视场的波像差优于λ/14(λ=500 nm),斯托列尔比大于0.8,系统能量集中度较高,像质接近衍射极限,光学视场相对于传统二次曲面系统增加了26.7%。因此,该种天线结构在激光通信领域具有较强的实用性和很好的发展前景。

Design of optical antenna for laser communication based on an off-axis freeform surface

We propose a design for a large-field two-mirror afocal optical antenna based on an off-axis free-form surface to improve the working range of space laser communication systems and simplify the structure of optical systems.The optical antenna adopts an afocal structure without using collimating lens elements,which can greatly simplify the system structure,overcome the problems of traditional focusing optical antennae such as them being too large in volume or having a power density that is too high at the focus when using high power light source.First,based on third-order aberration theory,the aberration-free formula of this class of two-mirror afocal optical antenna is derived,and relative results are analyzed.Then,an afocal optical antenna is designed according to the analyzed results and practical requirements.The effective aperture of the system is 100 mm,the magnification is 5,the range of the wavelength is 500~1100 nm,the full field of view is 0.6°,the primary mirror is part of the concave paraboloid and the secondary mirror is a freeform surface characterized by XY polynomials.MATLAB software is used to simulate the freeform surface of the secondary mirror.The design results show that the total field of view wavefront error of the optical system is better thanλ/14(λ=500 nm),the Strehl ratio is greater than 0.8,the system has a higher energy concentration,and the image quality is close to the diffraction limit.The field of view of the freeform surface optical system increased by 26.7%compared with that using traditional conic surface system.Therefore,this antenna structure is highly applicable and shows strong prospects for development in the field of laser communica-tion.