Optical design is an art of science and engineering of modelling an optical setup to meet a required performance, footprint, cost and other constrains. In a nutshell to make light do something useful at the set budget. This requires a thorough understanding of underlying science of optics, in order to know what is physically achievable and application of engineering principles to end up with a sound design. It always needs to be considered what is practical in terms of available technology, manufacturing ability, desire to utilize off the shelf components and their availability, cost etc.
We work in multiple areas of optical design and use different techniques (fundamental calculations, sequential and non-sequential ray tracing) to achieve the set goals. We typically use ZEMAX Optics Studio- a powerful software package that allows ray tracing in both sequential (rays are limited to propagating from one object to the next) and non-sequential mode (rays to propagate through optical components in any order and allows rays to be split, scattered, and reflected back to an object etc.). It combines complex physics and interactive visuals so one can analyze, simulate, and optimize optics, lighting and illumination systems, and laser systems, all within tolerance specifications.
The key strands that CAPPA has substantial expertise and has undertaken projects are detailed below:
Lens in its simplest form is just a piece of material, usually glass or plastic, with at least one curved face. The goal of designing a lens is achieving specific performance goals and characteristics. These goals are quantified using specific metrics such as focal length, numerical aperture, thickness. Lenses could be obviously combined in order to satisfy more demanding constrains and requirements- for instance a camera lens usually contains 3+ individual lenses. This type of designs is usually done using sequential ray tracing.
Imaging systems span from simple lenses to more complex assemblies such as compound objectives, telescopes or scanning systems. These could represent fixed (prime lenses) or variable magnification/viewing angle (zoom lenses). One Very important factor is image quality- aberrations, stray light, ghost reflections degrade image quality. These all could be minimalized through design- use of elements application of optical coatings and surface finish. Another key factor is “numerical aperture” (NA, F-number or “speed” of the system)- in case of detection systems it should match, if attainable the detection system’s numerical aperture. The design process requires not only knowledge of how the light will behave going from the object/ source to the image but also the mechanical constrains. Lenses (single and compound) could also be used for harnessing light (without care for image quality) for light detection purposes. This type of design is usually done using sequential ray tracing.
Imaging and detection system design
Imaging systems span from simple lenses to more complex assemblies such as objectives, telescopes or scanning systems. The design process requires not only knowledge of how the light will behave going from the object/source to the image but also the mechanical constrains and is typically done using sequential ray tracing.
CAPPA uses a very powerful tool known as Zemax. NASA and industry leaders’ have used Zemax software physics core to analyse and validate complete product designs. Zemax helps companies to get a qualified design more quickly by streamlining the workflow and communications between optical and mechanical engineers.
The use of lasers spans a vast range of applications, from consumer products to high end laser guidance systems, fluorescence imaging, ranging and sensing to laser materials processing. Laser optics may include lenses, afocal assemblies such as beam expanders, scanning systems, laser sources and laser cavities itself and we could model laser beam propagation through such optical systems. In laser optics designs, the sources are typically coherent laser beams that often display complex behavior. The beam properties such as modal structure, M2, numerical aperture, coherence, divergence angle, directionality etc. could all be defined and accounted for in numerical models. Obviously, a good foundation in the design process is experimental characterization of the laser source.
Optical fiber systems and laser diode coupling
Fiber optics is a common ingredient of optical system. We can comprehensively model the coupling of single or multi-mode fibers or combination of both. These could be achieved using very accurate fiber coupling calculation tools or physical optics propagation toolbox in sequential mode. In case of multimode fibers, we can use geometrical rays’ models. It is possible to cater for various geometries, materials, cleaving and face geometry (taper etc.). Sometimes fibers are used as detection channels or illumination guides- this could also be numerically simulated in non-sequential mode.
In practice fiber coupling systems are realized using arrangement of lenses:
- Single lens (spherical, aspherical, ball lenses etc.)
- Lens arrangements (usually dual) with for example a collimating (from the source side) and focusing (onto the receiver side) lenses (these again could be spherical, aspherical, ball lenses etc.)
- Fiber to fiber physical contact coupling (butt coupling)
The exact design scenario depends upon the expected design outcomes (required efficiency, footprint, system cost etc.) and system parameters (source and receiver type, NA etc.).
Physical phenomena modelling (photoluminescence, scattering, stray light)
When light impinges upon material it can be either reflected, scattered (often undesirable stray light), absorbed and also subsequently emitted as the result of as photoluminescence (the phenomenon where photons are absorbed in a medium and part of the absorbed energy is reemitted back as photons at slightly longer wavelength). All these phenomena could be very comprehensively numerically modeled- this is usually done using non-sequential ray tracing.
Modelling of reflections and scattering (how light “bounces” of the surface) is of critical importance in designing imaging, light detection and lighting systems. It allows developing understanding of how surface interacts with light (in either desired or undesired way). These along with photoluminescence simulation capability allows for example for modelling, on fundamental level, of complex light sources (such LEDs) and photo-physiological processes such as tissue scattering and fluorescence.
Illumination (incandescent, LED) systems modelling
CAPPA often uses Zemax Optics Studio, which is a powerful software package that allows ray tracing in both sequential and non – sequential mode for the design and analysis of both imaging and illumination systems. It can model the effect of optical elements such as simple lenses, aspheric lenses and diffractive optical elements and can produce standard analysis diagrams.
Producing illumination patterns to conform with the design requirements from real light sources (incandescent, LED etc.) is critical in optical systems development. This type of lighting and illumination design is often challenging as since illumination sources tend to be non-uniform and often represent complex assemblies and is usually done in non-sequential mode. We can model and numerically characterize complex sources and their interactions with assembly materials surfaces, textures etc.