An understanding of the wavefront is an important in the Laser optics, fiber optics system etc in the biomedical application. This concept has been used to explain and detect conditions in refractive surgery, cataract surgery, and ocular surface abnormalities. And In many cases, it is technically preferable to maintain wavefront with a smooth and simple shape. Wavefront quality is also associated with the degree of spatial coherence. How to predict and analyze it, this article will help you a bit.
In this example, we will demonstrate how to sample and analyze wavefront from a fiber coupling system.
Let’s also look at the waverfront in the system. The system below has an NA of 0.2 from a fiber and a focal distance of roughly 40 mm. The lenses have an F/# of about 2.4. An NA of 0.2 corresponds to a waist radius of about 1.56 microns.
let’s inspect the sampling of the wavefront. In general, wavefront phase profiles change more quickly and are more challenging to sample than the beam intensity profiles.
Please note:
A lens generally imparts a quadratic wavefront phase across an incident beam. In Zemax, the Wavefront phase is plotted from -pi to pi only. If the lens imparts a wavefront phase change of more than pi, a plot of the phase will show “phase wrapping.” For example, a phase of 3pi/2 will be displayed as pi/2. The phase wrapping is just a plotting convention, and does not indicate actual discontinuities in the wave front phase introduced to the beam by the lens!
I’ve also adjusted the sampling before and after the lenses.
Let’s look at the front of the lens, surface 4. The intensity profile looks fine.
Let’s look at the wavefront.
You can see that without wave front phase wrapping, the wavefront introduced by the lens would have a smooth shape and that it is well sampled. The first few rings in the phase are sampled correctly. Moving toward the edge of the aperture, the slope of the phase is steeper, and the rings are not sampled well. This causes aliasing: the phase is changing quickly, but the function is sampled more slowly, resulting in strange geometric patterns that don’t represent the true wavefront in the lens.
A cross-section of the phase at the front of the lens also shows the undersampled regions clearl
For many fast systems, though, the ray-based Fiber Coupling algorithm is appropriate and POP is not needed. For the majority of fiber coupling systems, the diffraction effects from the edges of the lenses aren’t significant. Every surface in a system must be checked to insure that sampling of the wave front phase profile is adequate. Fast lenses may require very high sampling and very long computation times.
The design file used in this particle is attached, please download it here: How to analyze the wavefront in a fiber coupling system
Reference Source:
- https://www.zemax.com/
- Zemax Optical Design Program User’s Guide, Zemax Development Corporation
- https://en.wikipedia.org/wiki/Main_Page
