How does the FBT System achieve optical signal coupling between fibers?

The FBT (Fiber Fused Biconic Taper) System achieves optical signal coupling between fibers through a specific manufacturing process and optical principles. Here's a detailed explanation:

Manufacturing Process

1. Fiber Preparation:

   • Several optical fibers are selected and their protective coatings are removed at the ends that will be fused.
   • The bare fibers are then cleaned to ensure that there are no contaminants that could interfere with the fusion process.

2. Fiber Alignment:

   • The bare fibers are precisely aligned with each other, usually using a specialized alignment fixture.
   • The alignment must be very precise to ensure that the light signal is efficiently coupled between the fibers.

3. Fusion Splicing:

   • The aligned fibers are placed in a fusion splicer, which uses an electric arc or laser to heat the fibers until they melt and fuse together.
   • As the fibers melt, they are gently pulled apart to form a biconic taper region. This region has a gradually changing diameter, which helps to minimize reflections and scattering of light.

4. Cooling and Solidification:

   • After the fibers have been fused, they are allowed to cool and solidify. This forms a permanent, low-loss connection between the fibers.

Optical Principles

1. Evanescent Wave Coupling:

   • In the biconic taper region, the light signals traveling in the fibers interact through an evanescent wave. This is a type of electromagnetic wave that extends slightly beyond the physical boundary of the fiber.
   • As the fibers are closely spaced and have a gradually changing diameter, the evanescent waves from adjacent fibers overlap and interact. This results in coupling of the light signals between the fibers.

2. Mode Matching:

   • For efficient coupling, the modes of light propagating in the fibers must be matched. This means that the light signals should have similar spatial distributions and polarization states in the fibers.
   • In the FBT system, the biconic taper design helps to match the modes of the light signals, thereby maximizing the coupling efficiency.

3. Loss Minimization:

   • The design and manufacturing process of the FBT system are optimized to minimize optical losses. This includes ensuring precise alignment, minimizing reflections and scattering, and using high-quality materials.

In summary, the FBT System achieves optical signal coupling between fibers through a combination of precise manufacturing processes and optical principles. The fusion splicing process creates a low-loss, high-strength connection between the fibers, while the biconic taper design helps to match the modes of the light signals and minimize losses.