Optical fibers are very useful to combine several light sources into one bundle. For instance, different wavelengths can be exposed on a biological sample stained with several fluorescence dyes. Several discrete light sources, such as Prizmatix fiber-coupled Black LEDs and Ultra-High-Power Black LEDs, can be directed towards the specific sample by optical fibers which are bundled together to excite the sample. Other applications include unifying several small fibers into a single large one, or the opposite - splitting one large fiber into several thinner branches. In this case the packing factor - the ratio between the areas of the small fibers and the area of the large fibers - becomes important. The greater the packing factor the lower the coupling losses.

In the list below are the optimal ratio between the small and large fibers, and the corresponding packing factor.

'd' denotes the diameter of the small fibers

'n' denotes the number of small fibers

'D' denotes the diameter of the large fiber.

Packing factor is calculated as n*(d/D)^2

• n=2, D/d=2.0, Packing factor= 0.5
• n=3, D/d=2.15, Packing factor=0.65
• n=4, D/d=2.41, Packing factor=0.69
• n=5, D/d=2.8, Packing factor=0.64
• n=6, D/d=3.0, Packing factor=0.66
• n=7, D/d=3.0, Packing factor=0.78