What are Passive Optical Splitters

Today, GPON (Gigabit Passive Optical Network) and EPON (Ethernet Passive Optical Network) networks are widely deployed, as PON (Passive Optical Network) architecture has lots of advantages compared with AON (Active Optical Network).

PON vs. AON: the difference

Referred to as the First Mile, the concept of PON was first proposed by British Telecommunications in 1987. Since then, PON architecture has been the standard solution to the FTTH (fiber to the home). PON design reduces installation, maintenance, and operating expenses by eliminating active components between the transmitting terminal and the subscriber.

Initially developed by Verizon Fios, PON is designed for a point-to-multipoint network. Purely passive optical components require no electronic power, meaning they’re unpowered. Generally speaking, PON has excellent advantages, such as:

• Cost-effective, as mentioned above.
• High flexibility and reliability, easy to maintain and upgrade
• Significantly increase the total efficiency of the cabling system
• allow for analog broadcasts, simplifying the delivery of analog television.

In contrast with PON, AON components use electric power to switch the appropriate signal only to the relevant customer. As shown in figure 1, a switching device will typically route signals to up to about 500 customers. This switch functionality is impossible for PON due to its passive functionality. PON needs an OLT(optical line terminal) to push out each signal to everyone served by the passive fiber optical splitter. In addition, PON also needs to reach extenders to achieve the distance from the central office that is possible with outside plant-based AON.

What is a passive optical splitter?

To put it simply, a passive optical splitter is a passive component used to split the signal, then redistribute the split signals to each end-user served by it. For instance, an OLT sends downstream signals through a fiber with a splitter that distributes the signals among as many as 32 output fibers, one for each home served. Or, if you want to divide the same signal into many equal portions, one for each subscriber, you could use a simple l-to-n splitter, which divides the signal equally among n outputs.

As shown below, starting at the central office, one single-mode optical fiber strand runs to a passive optical power splitter near a housing complex, an office park, or another campus environment. At this point, a passive splitting device simply divides the optical power into N separate paths to the subscribers. The number of splitting directions can vary from 2 to 64, but normally there are 8, 16, or 32 paths. Individual single-mode fibers then run to each building or serving equipment from the optical splitter. The optical fiber transmission span from the central office to the user can be up to 20 km.

Configurations

There’re different configurations, including 1×2 splitter, 1×6 splitter, 1×12 splitter, 1×16 splitter, 1×32 splitter, 1×64 splitter, and 1×128 splitter.

Insertion Loss of passive optical splitters

Among PON components, the fiber splitter has the largest attenuation. 28 dB loss corresponds to about 20 km with a 32-way split. As shown below figure, typical losses for splitters are:

Splitter Ratio	Ideal Loss / Port (dB)	Excess Loss (dB, max)	Typical Loss (dB)
1:2 fiber splitter	3	1	4
1:4 fiber splitter	6	1	7
1:8 optical splitter	9	2	11
1:16 optical splitter	12	3	15
1:32 optic splitter	15	4	19

In addition, here we provide the Insertion Loss Table Reference of FBT splitter and PLC splitter:

For FBT splitters:

Port Count	2	4	8	16	32	64	128
Min loss (dB)	3.40	6.70	10.00	13.00	16.50	19.67	22.92
Average loss (dB)	3.63	7.22	10.72	13.95	17.30	20.78	24.19
Max loss(dB)	3.90	7.70	11.40	14.50	18.30	21.84	25.40

For PLC splitter:

Port Count	2	4	8	16	32	64	128
Min loss (dB)	3.40	6.40	9.70	12.90	16.20	20.50	22.77
Average loss (dB)	3.78	7.30	10.75	14.30	17.33	21.50	24.65
Max loss(dB)	4.50	8.00	11.60	14.70	18.50	22.00	25.43

Applications

Passive fiber optic splitters are widely used for FTTx/PON applications, remarkably lowering the fiber count required because a fiber splitter can split a single fiber up to 128 parts to support 128 end-users.

FBT splitter vs PLC splitter

These are two main types of passive fiber splitters. The FBT(fused biconical taper) splitter is usually cheaper than the PLC (planar lightwave circuit). Yet, the PLC splitter has better performance, higher reliability, a wider range of operating temperature, and can work at full wavelength.

The production process of the FBT splitter is similar to a fusion splice. Two or more fibers are bound together, stretched on a  fused biconical taper machine to be tapered, and at last, a double cone will be formed. The technique is not difficult, and its material comes from common fiber. The splitting ratio can be modulated, but generally, the FBT splitter has non-uniform spectroscopy. When the splitter ratio is above 1:8, the failure rate is high, and the risk of unreliability increases.

The production process of the PLC splitter is based on planar lightwave circuit technology, using silica glass waveguide circuits aligned with a v-groove fiber array chip, and several ribbon fibers are coupled on both ends of the chip. Its design is compact, and its size is small, so it is ideally suitable for a high-density limited-space environment.

Here is a rough comparison chart of FBT vs. PLC splitter:

	PLC splitter	FBT splitter
Operating Wavelength	1260-1650nm (full wavelength)	850nm, 1310nm, 1550nm
Splitting Ratio	Equal for all branches	Customized, but with high risk when ratio above 1:8.
Performance	Reliable, stable for all branches	Under the 1:8 ratio, its performance is good, yet a larger ratio has a higher failure rate.
Input/Output	One or two inputs with an output maximum of 64 fibers	One or two inputs with an output maximum of 32 fibers
Housing	Bare, Blockless, ABS module, LGX Box, Mini Plug-in Type, 1U Rack Mount	Bare, Blockless, ABS module

Conclusion

A passive optical splitter plays a critical part in FTTH/PON networks because its passive functionality provides lots of advantages. It reduces installation costs and maintenance costs. It also dramatically improves the efficiency of end-users bandwidth utilization.