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Fiber-optic coupling is the practice of either combining or splitting optical signals between three or more fiber-optic cables. Most fiber-optic couplers are relatively small devices, though they can vary considerably in complexity, depending on how many inputs and outputs there are. It is possible for a fiber-optic coupler to split or combine signals by converting the optical signals into electrical ones or by maintaining the signals in their optical form.
The most common type of fiber-optic coupling is done with three cables, one which is an input and two which are outputs. Optical information, which is in the form of pulses of light, enters the coupler through the input cable and is then split between the two output cables. The wave of light can be split directly in half, though fiber-optic coupling can also be used to split the beam in other specific ratios. The specifications of this split are usually given as a part of the description of the fiber-optic coupler.
Besides splitting an optical signal between two fiber-optic cables, a fiber-optic coupler can also be used to combine the signals of two or more fiber-optic cables. In this type of fiber-optic coupling, the signals enter the coupler through several input cables and exit through a single output cable. Though these devices are often made with three connections, they can be designed to handle many more connections at once.
Fiber-optic coupling can be either a passive or an active process. In passive coupling, the optical information is kept in optical form as it is split or combined. An active coupler, on the other hand, converts optical information into an electrical signal and then back into an optical signal before it is sent through the fiber-optic cable on the other side. An active device requires a more sophisticated electronic system, which includes a light source, such as a laser, and a semiconductor with a photosensitive surface.
Aside from the simple one to two combiners and splitters, there are a few other common designs in fiber-optic coupling. One of these is known as the star coupler. In this device, there are an equal number of inputs and outputs, usually ranging from two to 64. Another common design is the tree coupler, which has a number of inputs and a single output or a number of outputs and a single input.