Stray Light Analysis

1. Introduction

  With the advancement of modern optical technology and the continuous expansion of application fields, the simulation and design of imaging optical systems has become increasingly complex. In analyzing and optimizing image quality, designers now often need to address not only inherent aberrations but also the suppression of unwanted light at the image plane, which we refer to as stray light.

  In imaging systems, stray light can be categorized by origin into three types:

1. Light originating from sources outside the field of view.
2. Light reaching the image plane through unintended internal optical paths.
3. Self-radiated light from internal elements due to thermal emission (mainly in infrared optical systems).

  It can also be classified by its manifestation:

• Ghosting: Secondary imaging caused by unintended reflections or higher-order diffraction from gratings.
• Glare: Produced by out-of-field rays, thermal radiation, and internal scattering.

  Stray light analysis has long been a focus in optical design research globally. The authoritative reference in this field is Stray Light: Analysis and Control by Eric C. Fest [1]. There is also a translated edition, Stray Light Suppression Design and Analysis by Professor Qinghua Yu [2], which thoroughly analyzes the fundamental theories of stray light generation and suppression and offers summarized strategies:

• Move it: Shift objects out of critical or illuminated surfaces.
• Block it: Prevent objects from being critical or illuminated surfaces.
• Coat/Paint it: Apply coating or paint to surfaces to reduce scattering and reflection.
• Clean it: Minimize particulate contaminants on surfaces to reduce scattering.

  Recent advancements in non-imaging optical design call for an expanded definition of stray light. Broadly, in imaging systems, all light reaching the image plane unexpectedly can be considered stray light, while in non-imaging systems, any unintended images or light distributions qualify. Simulating stray light requires a solid understanding of each setting's purpose within the software and correctly filtering the traced data to yield realistic results. From a software development standpoint, effective stray light analysis necessitates accurately defining complex materials, surface properties, geometric modeling, and light source characteristics. More importantly, data categorization, statistical analysis, and dynamic visualization tailored to specific application needs enable designers to improve analysis efficiency and address potential issues proactively.

  This guide provides examples of stray light analysis for various optical systems using the Rayzen optical simulation software, covering component setup, physical model parameterization, computational simulation, and result analysis. The aim is to equip software users with hands-on knowledge of the software's usage, enabling designers to understand stray light requirements across different fields and offer an advanced, user-friendly tool that contributes to the progress of optical design.

  This guide employs Rayzen optical system simulation software for stray light analysis across various optical systems. Rayzen leverages low-discrepancy sequence Monte Carlo methods, non-sequential forward ray tracing, and fast intersection algorithms. By analyzing surface morphology, optical properties, and internal material characteristics, Rayzen assesses how light propagates, refracts, reflects, and scatters within complex optical systems. It is well-suited for imaging system stray light analysis, illumination distribution in lighting systems, and light and guidance in concentrator and waveguide systems. Future developments aim to establish Rayzen as an essential tool across imaging and non-imaging optical design, optoelectronic components, photonic system integration, display panels, and thin-film optics.

  This guide introduces the method of conducting stray light analysis on optical systems using Rayzen software. Currently, Rayzen provides complete ray tracing results with optical path categorization and statistics. Once specific filtering by elements, surfaces, optical attributes, regions, and angular ranges is supported, and interactive visualization is enhanced, more special topic on stray light analysis will be further introduced, in which we believe it will provide simulation designers with detailed operational guidelines and result analysis.