Classified by Manufacturing Technologies
Technologies used for constructing optical couplers can be complex and difficult to understand. Three major manufacturing techniques are micro-optics, fused-fiber, and planar waveguide.
Micro-optics couplers use individual optical elements such as prisms, lens, mirrors, etc. to construct an optical route. These elements divide the input optical signal into two or more separated light beams.
Fused-fiber couplers used the most basic material–optical fiber. Two or more fiber cores are twisted, fused and tapered together in a length.
Planar waveguides are more like a semiconductor. A planar wafer is used to make a waveguide coupler, and the reflections occur only in y-directions. Planar waveguides are more often used to make high port count couplers, such as 1 x 12 PLC splitter, 1 x 24 PLC splitter.
Classified by Shape
If we see optical couplers by shape, there is Y coupler, T coupler, X coupler, star coupler and tree coupler, which split the optical signal based on the power.
A Y coupler resembles the letter Y. Y coupler also called optical tap coupler. The input signal is split into two output fibers. Sometimes, to meet users’ specific applications, the power distribution ratio also can be controlled precisely.
Unlike the Y coupler, a T coupler has an uneven power distribution. The power of one output signal is greater than the other output signal. Popular splitting ratios include 10:90 percent and 20:80 percent. This optical coupler is often used in small networks with less port counts.
X Coupler (2×2)
X couplers carry out the function of a splitter and a combiner in one package. The X coupler combines and divides the optical power from the two input fibers between the two output fibers. Another name for the X coupler is 2 x 2 coupler.
A star coupler generally has several input and output port combinations, in which the optical power is distributed from more than two input ports among several output ports. The number of input and output ports may or may not be equal in star couplers such as 2×4, 4×4, 8×16, etc. However, in all possible input and output port combinations, the distribution of power among the output ports remains equal.
A tree coupler is also a multiport coupler. It splits optical power from one input fiber to more than two output fibers. A tree coupler may also be used reversely to combine the optical signal from more than two input fibers to one output fiber.