Nowadays, PON (Passive Optic Network) architecture is indispensable in the First Mile from the customers’ point of view. In this topology, fiber optic splitter plays a critical role. Today we’d like to talk about the basic knowledge of fiber optic splitter.
What is PON?
PON was first proposed by British Telecommunications in 1987, aiming to reduce installation and operating costs by eliminating active components between the transmitting terminal and the subscriber.
Often referred to as the last mile from the point of view of ISP (Internet service provider), PON architecture implements a point-to-multipoint topology by using passive fiber optic splitters to ensure some end-users can share one a single fiber, significantly reducing the cost.
PON consists of OLTs (optical line terminals) located at the central office of the ISP, a host of ONUs (optical network units) or ONTs (optical network terminals) located at end-users premises, and the fibers and splitters between them, called ODN (optical distribution network). ONT is an ITU-T (the Telecommunication Standardization Sector of the International Telecommunication Union ) term describing a single-tenant ONU.
As you can see, PON significantly reduces the number of fibers and central office equipment needed if using point-to-point architectures.
What is a fiber optic splitter?
As the key link of FTTH (fiber to the home) PON system, fiber optic splitter servers as part of ODN, dividing the power in an optical signal into a number of different branches. More or less, a fiber optic splitter acts like a medium and a housekeeper simultaneously. As a medium, it redistributes the transmission from the central office to all the ONUs served by it. As a housekeeper, it splits the power into as many parts as the number of ONUs, up to 128, depending on manufacturers. The splitting ratio is either customized or evenly divided.
There’re different configurations of splitting ratio, including 4, 8, 16, 32, 64, and even 128. Although large split radios are required by GPON (Gigabit PON) and EPON (Ethernet PON), for instance, 128 for GPON, up to 32,768 for EPON, usually, most PONs are installed with a split radio of 1:32 or smaller. Also, two small splitters can be arranged in series, so each output of a 1 X 4 splitter could be followed by a 1 X 8 splitter, yielding 32 possible outputs. 28 dB corresponds to about 20 km with a 32-way split.
Normally fiber splitters use box packages or stainless tube packages.
Fiber optic splitter vs. coupler vs. combiner: what’s the difference?
You may wonder why sometimes people call ODN equipment a fiber optic splitter, sometimes call it a fiber coupler or combiner?
The answer is it depends.
When a component is used to divide optical signals, it functions as a splitter, and vice versa. When used to combine optical signals, it functions as a combiner. Furthermore, a given component may simultaneously combine and divide optical signals, as in two-way transmission over a single fiber.  Therefore, wavelength insensitive couplers are also power splitters and combiners.
The working principle of the fiber optic splitter lies in the reallocation technique of optical signal; that is, when two fibers are close enough, the light traveling along one fiber can spread into another fiber.
Passive And Active Splitters
We can classify fiber optic splitters into two basic kinds, i.e., active and passive splitters. In this context, “passive” means unpowered, and passive devices are optical components that require no electronic control for their operation. Thus, a passive splitter avoids the conversion of signals between optical and electronic formats. Conversely, an active splitter uses electrical power to split or combine the signal electrically.
Single-mode fiber splitter often works at 1310 and 1550nm wavelength, whereas multimode splitter usually works at 850 and 1310nm wavelength; the longer the wavelength, the better the performance; however, the higher the cost.
There’re also single and dual window fiber splitters, using one operating wavelength or two.
FBT splitter vs PLC splitter
FBT refers to Fused Biconical Taper, and PLC stands for Planar Lightwave Circuit; these are two manufacturing technologies. FBT is an older technology, and PLC is a more recent one. As shown below, the main differences between FBT splitter and PLC splitter lie in fabrication method, performance, design, and cost.
|FBT Splitter||PLC Splitter|
|Fabrication Method||Similar to fusion splice. Two or more fibers are bound and put on a fused-taper fiber device, with one fiber being singled out as the input. Rather easy.||One optical chip with both ends is coupled with several optical arrays depending on the output ratio. Rather complicated.|
|Operating Wavelength||830, 1310, 1550nm||1260-1650nm (full wavelength)|
|Performance||Up to 1:8 – reliable. For larger splits, reliability will be reduced, and installation space will be restricted.||Good for all splits. High level of reliability and stability.|
|Input/Output||One or two inputs with an output maximum of 32 fibers.||One or two inputs with an output maximum of 64 fibers.|
|Operating temperature||-5 to 75℃. Insertion loss varies with temperature variation is greater (TDL)||-40 to 85 ℃.|
|dimension||multi-demultiplexer (e.g., 1 × 16,1 × 32) volume is relatively large.||Compact and smaller, meaning small occupation space|
Which splitter to choose?
FBT splitter and PLC splitter are the most popular type. Which one can best suit your requirements?
In a word, FBT splitter is cost-effective in smaller ratios, such as when the ratio is below 1:8 because FBT splitter is easy to produce using regular fibers; on the contrary, PLC splitter has a high technique threshold and complicated production process.
Correspondingly, when large ODN equipment is needed, such as in GPON, the required ratio is above 1:8, then the PLC splitter is the best option.
Besides, the PLC splitter is preferred from a future upgrade perspective due to its excellent performance and smaller size.
Hecht, Jeff. Understanding Fiber Optics. Auburndale, MA: Laser Light Press, 2015.
Singal, Tarsem Lal. Optical fiber communications: principles and applications. Delhi: Cambridge University Press. 2016.
Keiser, Gerd. Fiber Optic Communications. Singapore: Springer Singapore, 2021.
 “Passive Optical Network,” Wikipedia (Wikimedia Foundation, January 10, 2022), https://en.wikipedia.org/wiki/Passive_optical_network.