What is a fiber optic coupler?

A fiber optic coupler is definitely an optical device that combines or splits signals travelling on optical fibers. A port is an input or output point for light; a fiber optic coupler is a multiplying device.

A fiber optic coupler is passive and bidirectional. Because the coupler is not a perfect device, excess losses can happen.

These losses within fibers are internal to the coupler and occur from scattering, absorption, reflections, misalignments, and poor isolation. Excess loss does not include losses from connectors attaching fibers to the ports. Further, since most couplers contain an optical fiber each and every port, additional loss can occur because of diameter and NA mismatches between the coupler port and the attached fiber.

Couplers and Fiber optic networks

A coupler (for example, FBT coupler) is really a device which will divide light from one fiber into several fibers or, conversely, will couple light from numerous fibers directly into one.

Important application areas for couplers are in networks, especially neighborhood networks (LANs), and in wavelength-division multiplexing (WDM).

Networks are composed of a transmission medium that connects several nodes or stations. Each node is a point at which electronic equipment is connected to the network. The network includes a complex arrangement of software and hardware that ensures compatibility not only of signals but also of knowledge.

Most notable inside a network is its logical topology. The logical topology defines the physical and logical arrangement. The most common logical topologies are point-to-point, star, ring, or bus structure.

Fiber Optic Network Topologies

Point-to-point logical topologies are commonplace in the current customer premises installations. Two nodes requiring direct communication are directly linked by the fibers, ordinarily a fiber pair (one to transmit, someone to receive). Common point-to-point applications include: computer channel extensions, terminal multiplexing, and video transmission.

An extension from the point-to-point may be the lucid star. This is a assortment of point-to-points, with a universal node that is in control of the communications system. Common applications include: switches, such as a PBX, and mainframe computers.

The ring structure has each node connected serially using the one on each side of it. Messages flow from node to node in one direction only around the ring. Examples of ring topologies are: FDDI and IBM's token ring.

To improve ring survivability in case of a node failure, a counter-rotating ring can be used. This is when two rings are transmitting in opposite directions. It takes two fiber pairs per node rather than the one pair utilized in a simple ring. FDDI utilizes a counter-ring topology.

The logical bus structure is supported by emerging standards, specifically IEEE 802.3. All nodes share a common line. Transmission occurs in both directions around the shared line instead of in one direction as on a ring. When one node transmits, the rest of the nodes get the fiber optic transmission at approximately the same time frame. The most popular systems requiring a bus topology are Ethernet, and MAP, or Manufacturing Automation Protocol.