TECH FOCUS FREEFORM OPTICS
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axis systems found, construct freeform systems and correct the optical power of the entire system. Four, for every freeform system constructed, improve the system imaging quality to its highest value by calculating the shape of each optical surface and finding the optimal tilt angle for the image plane. And five, calculate the system imaging quality metric (or other evaluation metrics) and output the systems that meet the given requirements. According to the researchers,
this is the first time such functionality has been realised in the field of optical design. Following the procedures above, they developed a program using MATLAB and deployed it on a high- performance computing cluster system. To demonstrate their method,
the researchers sought after a freeform imaging system working in the visible band (420 to 680nm) with the primary system wavelength being 587.6nm. The object distance was set to infinity, the full field-of-view angle to 4° × 4°, the focal length to 450mm, the entrance pupil diameter to 50mm and the F-number to 9. After 35.3 hours of computation without human interaction, a total of 59 freeform systems were obtained, with the average time to obtain one system being 35.9 minutes. The curve of the number of running jobs versus the running time is shown in figure 1, as well as some of the output results. The number marked alongside each system is the average of the root-mean- square values of the wavefront error of the system with a unit of λ = 587.6nm. The researchers provide
an analysis of the figure 1 results as follows: ‘Systems V9-4, V39-3, and V11-3 have the three typical structures contained among the output
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results. Systems V10-1, V142-2 and V258-1 all have the same structure but have different volumes. Systems V773-4, V911-3 and V912-3 have similar structures but have different image plane positions. Systems V26-6, V27-5 and V452-3 have structures that are rarely seen and the volume of system V452- 3 is relatively small. Systems V989-4 and V1006-3 both contain small tertiary mirrors with short back working lengths. In system V1014-4, the primary mirror and the tertiary mirror are located close together and can be fabricated on the same substrate. In system V144-5, the structure could be folded by placing planar mirrors in the middle of the light path to allow the structure to be more compact. Systems V789-3, V347-1 and V240-1 have smaller volumes and compact structures. V240-1 is possibly the best design among all the output results.’ Out of the five phases of the design method, the majority of the computing time is currently spent conducting phase four, according to the researchers, with the rest of the time typically spent by each phase being as follows: phases one and three generally take seconds of calculation, because phase one calculates the surface curvature radii and surface distances targeting at the focal length, and phase three only involves the calculation of freeform shape of three mirrors. Phase two takes hours of calculation to perform an exhaustive search of possible unobscured systems, depending on the number of computing jobs and searching density. In phase five, it takes minutes of calculation to evaluate the imaging qualities of the systems and output good design results. The rest of the time (the bottleneck of the time consumption) is in phase four.
SYNOPSYS FEATURED PRODUCT
Freeform optics design with Synopsys software
Today’s optical designers are often tasked with finding ways to correct more aberrations and use fewer surfaces, and do so in more compact geometries that must fit within anything from smaller medical instruments to more wearable augmented reality (AR) systems. Setting up compact geometry, with multiple reflecting or refracting surfaces, can be challenging when there are numerous folded surfaces or complex optical path constraints. To help support this type of design work, Synopsys offers unique and powerful freeform design and optimisation tools.
If you are designing freeform optics, read our blog article about the top five tools that will support your design optimisation and analysis in Code V.
https://blogs.synopsys.com/optical-solutions/2021/02/11/top-5- tools-for-designing-freeform-surfaces-in-code-v/
A tool for both research and engineering The method proposed in their work provides, according to the researchers, a new thought for the realisation of fully automatic optical design. It enables people to obtain a variety of high-quality systems with only basic knowledge of optical design. ‘In the field of scientific
research, people can explore the solution space of optical systems and the boundaries of a system’s performance based on the results obtained, or conduct research on the disciplines of optical design,’
the researchers said, when announcing their research. ‘In the field of engineering applications, optical design tools based on the proposed method are expected to change the working mode and core content of optical design. People can focus on system specification, manufacturability and cost.’ EO
Reference [1]
Light: Science & Applications volume 10, Benqi Zhang, Guofan Jin & Jun Zhu, ‘Towards automatic freeform optics design: coarse and fine search of the three-mirror solution space’,
https://doi.org/10.1038/s41377-021- 00510-z
July 2021 Electro Optics 31
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