Definition-Fiber Optic Coupler?

A fiber coupler is a common optical device that connects one or more fiber ends to allow light waves to travel in multiple paths. The device can combine two or more inputs into one output port, or divide one input into two or more outputs. Compared with input connectors or connectors, fiber couplers can further attenuate signals because input signals can be distributed between output ports.

The classification of fiber couplers is mainly based on the number of input and output ports. There are different types, such as X coupler, combiner, splitter, star and tree. Can be roughly divided into active or passive devices. Active fiber couplers require an external power source, while passive fiber couplers require no power source for operation. Fiber optic couplers are used to split the input signal into two or more outputs, in which case they are called splitters. On the other hand, some types of couplers can be used to combine two or more inputs into one output, in which case they are called combiners. The tree coupler performs the functions of a combiner and a splitter simultaneously in one device.

Among them, the splitter can be further divided into a Y coupler and a T coupler, the former has an equal power distribution, and the latter has the characteristics of uneven power distribution. A star coupler helps distribute power from the input to the output. Tree couplers can be either multiple-input single-output or multiple-output single-input. When considering fiber couplers, the important parameters are splitting ratio, insertion loss, cable type, coupler type, signal wavelength, number of inputs, number of outputs, and polarization-dependent loss. The three main types of manufacturing technology used in fiber couplers are fused fiber, mode hybrid rods, and planar waveguides.

Double cone cone coupler (or fusion coupler)

Fused couplers are one of the most common technologies. If the cladding portion of two or more fibers is removed and the fibers are placed next to each other closely over a certain length, some light will be coupled from one fiber to the other. The coupling ratio can be freely controlled by the thickness of the remaining cladding and the length of the area near the fiber. This type of coupler can be made by taking a set of fibers with bare cladding, applying tension, and heating the splice. The coupling fraction is controlled by the amount of tension and heating time.

Mode Hybrid

The second technique uses a mode hybrid rod as the coupling mechanism. The mode mixing rod is a glass rod with a diameter of a few millimeters, and its length allows the light from all input positions to be fully expanded to evenly illuminate the end of the rod. All output fibers are uniformly excited.

In addition to this transmission configuration, the rod can be cut in half, a specular reflective surface can be applied, and the output fiber can be moved to the input side of the device to form a reflection system.

Planar waveguide coupler

The planar waveguide may be a strip deposited on top of a planar substrate. The air and the substrate are combined together to function as a cladding in the optical fiber. The simplest waveguides are straight, but can form more complex patterns, such as branches or merges, making them the planar waveguide equivalents of fused fiber couplers. There are many benefits to using fiber couplers. They have very low excessive losses, high stability, dual operating windows, high reliability and low polarization-dependent losses. They also have advantages such as high directivity and low insertion loss. Many applications utilize fiber optic couplers such as community antenna networks, optical communication systems, and fiber-to-the-home technology.