May 01, 2019

For complex optical systems design, Physical Optics Propagation is the answer

For complex optical systems design, Physical Optics Propagation is the answer

Ray tracing is a powerful and flexible tool for designing and optimizing optical systems; however, in some cases, the fundamental wave nature of light can be a critical issue. While rays can be a good way to predict where light will go on a coarse scale, the effects of diffraction will cause light to propagate in ways that can’t be predicted. One common example of this is laser beams traversing a complex optical system. Shooting a laser beam at a faraway target or simulating light through a pinhole or other diffraction effects that are far away from focus require physical optics propagation. The Physical Optics Propagation (POP) tool in OpticStudio gives users the capability to use diffraction calculations to propagate a wavefront through an optical system surface by surface. The coherent nature of light is fully accounted for by this capability.

Following are some additional examples and design applications of the Physical Optics Propagation tool in OpticStudio.

Anamorphic beams
If you’re building optics that propagate a beam through an anamorphic prism, Physical Optics Propagation can correctly demonstrate the change in the beam’s radius. Simple ray tracing incorrectly estimates the change in radial waist size, but physical optics propagation allows for greater accuracy when propagating astigmatic or anamorphic beams. You can visualize additional analysis detail with built-in displays, such as cross-sectional plots.

Fiber coupling
Fiber optics are everywhere these days, but the efficient injection of light into a fiber requires attention to many physical optics phenomena. When you need to make computations for coupling light from free space into fiber, the physical optics propagation function of OpticStudio is a great choice. The built-in modes directly report coupling efficiency, allowing rapid feedback on the design. Whether the application is cable TV, medical imaging, or anything in between, it’s important to be able to see all the possibilities based on variables such as the size of the receiving fiber and the waist size of the pilot beam. 

Gibbs phenomenon
Geometric ray tracing does not allow for modeling of even very fundamental effects like the Gibbs phenomenon, but physical optics propagation does. It propagates arrays of complex amplitude in which the phase of the beam can be displayed as well. This is especially important for cases where near-field diffraction is significant. To propagate the beam from one surface to another, OpticStudio uses either a Fresnel diffraction propagation algorithm or an angular spectrum propagation algorithm. OpticStudio automatically chooses the algorithm that yields the highest numerical accuracy. The diffraction propagation algorithms yield correct results for any propagation distance and for any arbitrary beam, and can account for any surface aperture, including user-defined apertures.

Spatial filters
Sometimes spatial filters are necessary to clean up a beam. But because most spatial filters have sharp edges, you’ll get significant diffraction. Ray tracing won’t account for that diffraction, but Physical Optics Propagation will. It can show you beam cleanup with an accurate depiction of the reduction in beam power.
If you’re designing a system that involves coherent light sources, you’ll need design software that accounts for that coherence. In these cases, interference effects don’t average out the way they do for incoherent light. Whether your application includes fiber coupling (single or multimode), computing shifts in best waist focus position due to aberrations, computing beam flux, or irradiance on optical surfaces, there are a multitude of use cases in which the wave nature of light makes a crucial difference and geometric ray tracing simply won’t cut it. Physical Optics Propagation in OpticStudio is a powerful tool that’s far superior to geometric ray tracing for applications such as beam propagation or fiber coupling that involve coherence and diffraction.


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