What Is Fused Fiber Optic Coupler? How it works?

What’s Fused Fiber Optic Coupler？

Fused fiber optic coupler is a kind of optical light distribution devices, technically based on Fused Biconical Taper (FBT) technology, so it is also called FBT fiber coupler.
As an important passive optical component in fiber optic communication system, the main functions of a fused fiber optic coupler is light branching and splitting in fiber access networks, wavelength multiplexing / de-multiplexing, filtering, polarization selective splitting and wavelength independent splitting.
Fused fiber optic splitters are available in single-mode and multi-mode fibers compliant with a variety of connector types pre-terminated, and widely accepted and used in passive optical networks where the split configuration is smaller (1×2, 2×2, 1×4 etc).
Fused splitters support wavelengths of 850nm / 1310nm / 1490nm / 1550nm. For single mode fused fiber coupler, we have single window 1310nm or 1550nm, dual window 1310/1550nm or triple window 1310nm / 1490nm / 1550nm for option.

1x2 fused fiber optic coupler, FBT splitter, fusion fiber coupler

fiber fusion of FBT fiber optic splitter

Fused Biconical Taper (FBT) Process

A fused fiber optic coupler is a structure formed by two independent optical fibers. These parallel optical fibers are twisted, stretched and fused together so that the coupling substantially takes place through interaction between the cladding modes. During the operation, the power output values form the output ports are monitored, and the process can be stopped at any desired coupling ratio. This process is known as the Fused Biconical Taper (FBT) process. The fused biconical taper is the most widely used method in make of optical fiber coupler, with many advantages of low excess loss, precise coupling ratio, good consistency and stability.

How Does Fused Fiber Optic Coupler Work?

In the FBT process the cores of two identical parallel fibers are so close to one another that the evanescent wave can “leak” from one fiber core into the other core which allows an exchange of energy. The FBT couplers work as a result of energy transfer between the optical fiber cores and the energy transfer is dependent on the core separation (d) and the interaction length (L). It is easy to see that if the coupling length is long enough, a complete transfer of energy can take place from one core into the other. If the length is longer still, the process will continue, shifting the energy back into the original core.