:: The need for fiber optic couplers

We use electronic couplers all the time – like a telephone coupler that allows you to connect a phone and a fax machine to the same phone line. Or a CATV coupler that allows you to connect multiple televisions to a single Comcast cable. You can basically buy these couplers from Home Depot or other electronic retailers.

Optical couplers have the same functionality as electronic couplers: they split the signal at various points (devices). Fiber optic couplers are required for capture (signal quality monitoring) or more complex telecommunications systems that require more than simple point-to-point connections, such as ring architectures, bus architectures, and star architectures.

:: Passive couplers and active couplers

Fiber optic couplers can be active or passive devices. The difference between active and passive couplers is that a passive coupler redistributes the optical signal without optical-to-electrical conversion. Active couplers are electronic devices that divide or combine the signal electrically and use fiber optic sources and detectors for input and output.

:: The difference between electronic couplers and fiber optic couplers

Electronic couplers are easy to make because electrical current flows whenever there is physical contact between the conductors. But the optical signal is in a completely different domain. You need to align the tiny fiber optic cores precisely (9um for singlemode and 50um or 62.5um for multimode fibers) so there won’t be a lot of power loss when you split the signal.

:: Understanding the types of fiber optic couplers

Fiber optic coupler types are often defined by their input and output port numbers. They are designed to meet different applications.

1. T-couplers

T-couplers are also called Y-couplers, which is based on their appearance. T-couplers are three-port devices with one input and two output. An important application is tapping (energy monitoring): the input energy is divided into 5% and 95% respectively in the two outputs. The 5% port is connected to system monitoring hardware to monitor line quality. Another important application is dividing the input into two equal outputs.

2. Tree couplers

Tree couplers generally take one input and divide it into multiple (more than two) outputs. Tree couplers can also be used backwards (bi-directional) like a combine harvester. Multiple output signals (now function as the input actually) are combined into a single input (now as the output actually).

3. Star couplers

Star couplers are different from tree couplers in that they have multiple inputs and multiple outputs. The fibers radiate from the central point like a star. They often have the same number of inputs and outputs (although this is not always the case).

4.Selective wavelength couplers

Wavelength selective couplers are actually WDM (Wavelength Division Multiplexer). They divide the signal not based on its power, but based on its wavelengths. The input signal has various wavelength channels (such as 1510nm, 1520nm, 1530nm, 1540nm, and 1550nm, etc.). The wavelength selective coupler then routes each wavelength to a different output port.

:: Fiber optic coupler manufacturing technologies

There are mainly three types of manufacturing technologies for fiber optic couplers: micro-optical, fused fiber, and planar waveguide.

Micro-optics The technologies use individual optical elements such as prisms, mirrors, lenses, etc. to build an optical path that works as a coupler. This is an expensive approach and not as popular as the other two types.

Fusible Fiber Couplers use the most basic material: optical fibers. Several fiber cores are fused to allow light to pass between them.

Plane waveguides they are more like semiconductors. A flat wafer is used to make waveguide couplers. They are most often used for high-port number couplers, such as 12, 24, and 36 output ports.