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FBT Splitters vs PLC Splitters: What’s The Differences

Fiber splitters provide great flexibility and an easy future upgrade option to end-users among passive optic components. Currently, FBT (fused biconical taper) splitter and PLC (planar lightwave circuit) are the two main types of fiber optical splitters. Though they’re commonly deployed, some people may still not know their differences. We’ll focus on the comparison between FBT splitters and PLC splitters.

What is an FBT splitter?

The FBT splitter, also called FBT 3-dB coupler or fused-fiber coupler, is a passive fiber optical splitter designed to split an optical signal into several output ports.

When discussing couplers and splitters, it is customary to refer to them regarding the number of input and output ports on the device. For example, a device with two inputs and two outputs would be called a “2 × 2 coupler.” An N × M coupler has N inputs and M outputs.

The FBT splitter is fabricated using the fused biconical taper technique. First appeared around 1990, this technique  can be used to fabricate passive components, such as filters, attenuators, and couplers. The original motivation for tapering fibers was to access the optical field and facilitate the coupling of light from one fiber to another.

Figure 1: The fabrication process of FBT splitter
Figure 1: The fabrication process of the FBT splitter

Operational principles

The FBT splitter is fabricated by twisting, melting, and pulling two single-mode fibers, so they get fused. When the taper is gradual, the field can be accessed at its center to provide a means of coupling power from one fiber to another. Ideally, two adjacent fibers are heated and stretched, forming an input taper, a coupling region, and an output taper. Consequently, as the optical signal enters the coupling region, an increasingly larger portion of the input field now propagates outside the core of the fiber. This portion of the field thus penetrates through the thinned cladding regions and gets coupled into the adjacent fiber.

Moreover, if two or more tapered fibers are fused, then coupling of light from one fiber to another can be achieved. The tapering and fusing processes can make wavelength-enhanced couplers, which can be used as wavelength-division multiplexers or nearly wavelength-independent couplers or splitters.

The idea is to fuse many fibers and elongate the fused portion to form a biconically tapered structure. In the tapered portion, signals from each fiber mix are shared almost equally among its output ports.

In specifying the performance of an optical coupler, one usually indicates the percentage division of optical power between the output ports using the splitting ratio or coupling ratio.

By adjusting the coupler parameters to divide power evenly, with half of the input power going to each output, one creates a 3-dB coupler. A coupler could also be made in which almost all the optical power at 1500 nm goes to one port, and virtually all the energy around 1300 nm goes to the other port.

Figure 2: Schematic of a fused biconical taper coupler
Figure 2: Schematic of a fused biconical taper coupler


During fabrication, the input and output powers from different ports can be monitored in real-time until the desired coupling ratio is reached.

Fused couplers survive harsh environments without significant degradation in performance, operating from -40 to +85 C temperature.

What is a PLC splitter?

A PLC splitter is a micro-optical component based on planar lightwave circuit technology. The PLC splitter consists of one optical chip with several optical ribbon fibers on both ends of the chip. It is fabricated with silica-on-silicon technology by making two arrays of SiO2 waveguides, separated by a central slab region. Like the techniques used in fabricating semiconductors, PLC technology could enable high splitting ratios, uniform spectroscopy, equal parts of signals, and excellent performance.

PLC splitter is available in various splitting ratios, such as 1:4, 1:8, 1:16, 1:32, 1:64, etc. Besides, there’re subcategories of PLC splitters, including Bare PLC splitter, Blockless PLC splitter, ABS splitter, LGX box splitter, Fanout PLC splitter, Mini plug-in type PLC splitter, etc. PLC splitters are ideal for GPON ODNs because they need large, concentrated splits.

ABS Box PLC Splitter
Figure 3: ABS Box PLC Splitter

Comparison between FBT splitter and PLC splitter

Here is the detailed comparison chart of FBT vs. PLC splitter.

FBT SplitterPLC Splitter
Fabrication MethodSimilar 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 coupled with several optical arrays depending on the output ratio. Rather complicated.
Operating Wavelength830, 1310, 1490, 1550nm1260-1650nm (full wavelength)
PerformanceUp to 1:8 – reliable. The reliability will be reduced for a larger split ratio, and installation space will be restricted.Good for all splits. High level of reliability and stability.
Input/OutputOne or two inputs with an output maximum of 32 fibers.One or two inputs with an output maximum of 64 fibers.
Splitting ratiosCustomizedEqual
Operating temperature-40 to 85 ℃-40 to 85 ℃
dimensionmulti-demultiplexer (e.g., 1 × 16,1 × 32) volume is relatively large.Compact and more petite, meaning small occupation space
HousingBare, Blockless, ABS module, LGX Box, Mini Plug-in Type, 1U Rack MountBare, Blockless, ABS module
detailed comparison chart of FBT vs. PLC splitter.


Generally speaking, FBT is more cost-effective than PLC splitter, especially when the splitting ratio is not above 1:8; within this ratio, FBT splitters have equivalent performance to PLC splitters, while the former is inexpensive, and the latter is relatively expensive.

However, from the perspective of optimal performance and future upgrade options, we recommend the PLC splitter, particularly when the splitting ratio is large.


Keiser, Gerd. Fiber Optic Communications. Singapore: Springer Singapore, 2021.

Tekippe, V. J. “Passive Fiber-Optic Components Made by the Fused Biconical Taper Process.” Fiber and Integrated Optics 9, no. 2 (1990): 97–123. https://doi.org/10.1080/01468039008202898.

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