How do fiber optic couplers work and how are they made?

:: 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 tuner that allows you to connect multiple televisions to a single Comcast cable. You can basically buy these couplers at Home Depot or other electronic retailers.

Optical couplers have the same functionality as electronic couplers: they split the signal at several points (devices). Fiber optic couplers are required to intercept (monitor signal quality) 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 split 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 manufacture because electrical current flows as long as 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 (9 um for singlemode and 50 um or 62.5 um for multimode fibers), so that there is not a large loss of energy when you split the signal.

:: Understand 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 based on their appearance. T couplers are three port devices with one input and two output ports. An important application is tapping (power control): the input power is split 5% and 95%, respectively, to the two outputs. The 5% port is connected to system monitoring hardware to monitor line quality. Another important application is to split the input into two equal outputs.

2. Tree couplers

Tree couplers typically take one input and split it into multiple (more than two) outputs. Tree couplers can also be used backwards (bidirectional) as a combiner. Multiple output signals (now function as the actual input) are combined into a single input (now function as the actual output).

3. Star couplers

Star couplers are different from tree couplers because 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. wavelength selective couplers

Wavelength selective couplers are actually WDM (wavelength division multiplexer). They divide the signal not according to its power but according to 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 coupler: micro-optics, 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. Multiple fiber cores are fused together, allowing light to pass through them.

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