:: 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 lets you connect multiple TVs to a single Comcast cable. You can basically buy these couplers at Home Depot or other e-retailers.
Optical couplers have the same functionality as electronic couplers: they split the signal at several points (devices). Fiber optic couplers are needed 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 electrically split or combine the signal 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 fabricate 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 there isn’t a lot of power loss 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. One important application is tapping (power control): the input power is divided into 5% and 95%, respectively, on 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 generally 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 working as the actual input) are combined into a single input (now working as the actual output).
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. Wavelength Selective 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 multiple wavelength channels (such as 1510nm, 1520nm, 1530nm, 1540nm, and 1550nm, etc.). The wavelength selective coupler then routes each wavelength to a different output port.
:: Manufacturing technologies of fiber optic couplers
There are mainly three types of manufacturing technologies for the 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 transmit them.
Planar waveguides they are more like semiconductors. A flat wafer is used to make waveguide couplers. They are most often used for couplers with a large number of ports, such as 12, 24, and 36 output ports.