Freeform optics design maintains energy for 3D imaging systems

The pursuit of enhanced imaging systems continually drives innovation in optical design, with recent efforts focusing on freeform surfaces to overcome limitations inherent in traditional lens and mirror configurations. These complex shapes offer greater flexibility in manipulating light paths, potentially leading to improved image quality and reduced aberrations. Sanjana Verma, Lisa Kusch, and colleagues from Eindhoven University of Technology, alongside Wilbert L. IJzerman from Signify Research and Eindhoven University of Technology, detail a novel approach to designing three-dimensional imaging systems in their article, “Design of a three-dimensional parallel-to-point imaging system based on inverse methods”. Their work presents an inverse method, a mathematical technique working backwards from desired image characteristics to determine the necessary optical component shapes, for creating a system utilising freeform reflectors and demonstrates superior performance compared to a classical Schwarzschild telescope design through ray tracing simulations.

Freeform optics represent a significant development in optical design, allowing for the creation of high-performance imaging systems specifically tailored to particular applications and moving beyond the limitations inherent in traditional, rotationally symmetric, quadratic designs. Researchers currently develop novel methods for designing three-dimensional imaging systems utilising these complex surfaces, establishing a fundamental imaging condition which asserts that energy distribution remains constant between the source and the target. This principle, rooted in the law of conservation of energy, is leveraged to formulate a mathematical model applicable to parallel-to-point imaging systems comprised of two freeform reflectors. A parallel-to-point system focuses light originating from parallel rays onto a single point.

The team specifically applies this methodology to create an inverse freeform imaging system, utilising a Schwarzschild telescope – a classical design renowned for its ability to correct aberrations, or imperfections in an optical system – to define initial parameters. Ray tracing simulations, employing parallel light beams, are conducted to assess the performance of both the newly designed freeform system and the Schwarzschild telescope, providing quantitative evidence of the improvements achieved. Results consistently indicate superior imaging capabilities in the freeform design, evidenced by demonstrably smaller spot sizes, confirming the effectiveness of the inverse approach. Smaller spot sizes directly correlate with enhanced resolution and reduced aberrations, paving the way for the development of advanced optical systems.

The established mathematical framework provides a robust foundation for future developments, allowing for the systematic design of imaging systems with tailored performance characteristics. This approach moves beyond the limitations of traditional rotational symmetry, exploring new possibilities in optical engineering and opening avenues for research and development. Successful implementation and validation through ray tracing confirm the viability of the inverse method for practical applications.

The research team collaborates with industry partners to translate findings into practical products, accelerating the adoption of freeform optics in fields including medical imaging, aerospace, and consumer electronics. They disseminate knowledge through publications in scientific journals and presentations at international conferences, fostering collaboration within the scientific community. The team also invests in training the next generation of optical scientists and engineers through mentorship of students and postdoctoral fellows.

Future work will extend to exploring freeform optics in other imaging modalities, such as microscopy and spectroscopy, and developing more efficient optimisation algorithms to further improve system performance. The long-term vision is to create a new generation of imaging technologies that are more powerful, versatile, and accessible.