What Is a Fiber-Optic Coupler?

Optical fiber coupler (coupler), also known as splitter, connector, adapter, and optical fiber flange, is an element used to implement optical signal splitting / combining, or to extend an optical fiber link, and belongs to optical passive components. In the field, it can be applied to telecommunication networks, cable television networks, subscriber loop systems, and local area networks.

Fiber coupler

(Fiber Optic Coupler)

Optical device that realizes the distribution or combination of optical signal power among different optical fibers. It is constructed by using the mutual exchange of guided wave energy in different fiber faces close to the core area of the fiber. According to the type of fiber used, it can be divided into multi-mode fiber, single-mode fiber and polarization maintaining fiber coupler.

Optical fiber coupler is a device for detachable (movable) connection between optical fiber and optical fiber. It precisely connects the two end faces of the optical fiber so that the optical energy output by the transmitting fiber can be coupled to the receiving fiber to the maximum extent And make it interfere with the optical link to minimize the impact on the system. For a waveguide fiber coupler, it is generally a component with a Y-branch, and the optical signal input by an optical fiber can be divided equally. When the opening angle of the branch of the coupler increases, the light leaking into the cladding will increase so that the excess loss is increased, so the opening angle is generally within 30 °, so the length of the waveguide fiber coupler cannot be too short.

Single-mode fiber couplers are the most widely used. The 2 × 2 single-mode fiber coupler is typical, and its structure is shown in the figure. It has two inputs and two outputs

The principle and structure of the multimode fiber coupler are basically similar to the above, except that the grinding and polishing device requires strong coupling, so the grinding and polishing plane enters the fiber core. On the basis of the grinding and polishing 2 × 2 fiber coupler, an adjustable coupler can also be manufactured. At a certain wavelength, the coupling ratio changes with the angle formed by the two grinding and polishing fibers, so adjusting the relative directions of the two fibers can change the coupling ratio.

In fiber optic local networks or other occasions, l × N, N × 1 couplers or N × M couplers (also called star couplers) are used, where the first number represents the number of input terminals and the second number represents the number of output terminals. These couplers are made by fusion drawing.

According to the difference of the coupled optical fibers, there are the following classifications:

SC fiber optic coupler: It is applied to SC fiber optic interface. It looks very similar to RJ-45 interface, but the SC interface is flatter. The obvious difference is the contacts inside. If it is 8 thin copper contacts, then It is RJ-45 interface, if it is a copper pillar, it is SC fiber interface.

LC fiber optic coupler: It is a connector used in the LC fiber optic interface to connect SFP modules. It is made of a modular jack (RJ) latching mechanism that is easy to operate. (Commonly used by routers)

FC optical fiber coupler: It is applied to FC optical fiber interface. The external reinforcement method is a metal sleeve, and the fastening method is a screw buckle. Generally used on the ODF side (most used on distribution frames)

ST fiber optic coupler: It is used in ST fiber optic interface, often used in fiber optic distribution frame, the shell is round, and the fastening method is screw. (For 10Base-F connection, the connector is usually ST type. Commonly used in optical fiber distribution frame)