As we all know, if an optical fiber is designed with the right material and properly bent, light can be transmitted along the fiber with very little attenuation.
Figure 1 shows the interaction of radiation F with a conical structure. The cone is a hollow mass with an internal reflector layer or a homogeneous mass of transparent material. Due to the non-ideal incident angle of radiation F (as shown in figure 1), radiation F will be easily reflected back or transferred out of the cone.
In the case of the above cone is a system of multiple optical fibers (figure 2). Optical fibers are arranged as a multi-branch tree: Start by an optical fiber at the bottom, then it is gradually branched at the upper rows and the top row will have the most fibers. Optical fibers have one narrow end below and the other larger end above. The optical fibers are separated by a vacuum layer so that total internal reflection can occur optimally. It can be noticed that radiation F will be easily transmitted along the fiber inside the cone.
We find that with the same incident angle and interaction position, radiation F in the two figures will have two different directions. It can be seen that a system of multiple optical fibers will have a much larger acceptance angle.
The key is to find the right material for the fiber and bend the fibers properly (without bending too strongly) so that radiation F is not refracted out of the fiber during transmission.
Extending from radiation F, can we use the above multiple optical fibers system to optimize solar energy harvesting (similar to Winston cones or Fresnel lenses but with higher efficiency)?
Dear Viet Nguyen ,
nice idea.
You should have a look at the planes perpendicular to the fibers. I assume you think on circular fibers . So the net area when picking up the light in the case of fibers is much smaller than the real area which is exposed to light. So you will pick up only about 2/3 of the light. At the planes where you will transfer the light from one fiber system to the next you will have additional areal losses.
Have you taken all these losses into account?
From that point of view, I think, any lense (e.g. a Fresnel lense) will have a better efficiency than your system.
Please check the areal coupling losses.
Good luck
By the way: In your drawing you have presented one of the very few rays which successfully end up at your output port. There are a lot of rays which will not end up there, even for perpendicular incidence at your entrance port.
Dear Viet Nguyen ,
additional remarks:
a) Any bending or tapering (as in your case) will cause severe transmission losses compared to a straight cylindrical fiber rod.
b) Furthermore, according to your sketch, you will have 8 exit/entrance surfaces at the fiber ends, which also will cause a few % of transmission losses each, if not using an antireflection coating or index matching fluid/grease.
Any lense only has two of such surfaces.
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