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With the increasing application of GPON, XGPON, and XGSPON, we sometimes encounter customers who are confused about whether to use tapered fiber splitters or PLC splitters for XGPON and XGSPON networks, and which one is better?
This is a very good question, as it involves the selection of key equipment in PON network upgrades. The simple and direct answer is: Theoretically possible, but not recommended, especially for new or large-scale XGS-PON deployments. The situation is slightly better for XG-PON.
Below, Yingda will explain the specific reasons in detail, hoping to assist you in product selection and actual deployment.
Technical Principles: Fused Biconical Taper (FBT) Splitter vs. Planar Lightwave Circuit (PLC) Splitter
Fused Biconical Taper (FBT) Fiber Splitter
FBT fiber splitter is made by fusing and stretching two or more optical fibers. It is a device strongly dependent on wavelength; its splitting ratio changes with the transmission wavelength. Common test wavelengths are 1310nm, 1490nm, and 1550nm. Because it achieves splitting through fiber fusion, it is low-cost, but has poor splitting uniformity and weak temperature stability, making it suitable for low splitting ratio applications
Planar Lightwave Circuit (PLC) Splitter
An optical waveguide splitter device manufactured on a semiconductor wafer using photolithography and etching processes. It has weakly wavelength-dependent characteristics within the design wavelength range (e.g., 1260nm~1650nm), meaning the splitting ratio is very stable at different wavelengths. Due to the use of photolithography technology, it offers uniform splitting and multiple channels (up to 64 channels or more), making it suitable for high splitting ratios and complex environments.
Compatibility Analysis of XG-PON and XGS-PON
Wavelength Planning for XG-PON and XGS-PON:
- Downstream: 1577 nm (Same for XG-PON and XGS-PON)
- Upstream: 1270 nm (Same for XG-PON and XGS-PON)
- Coexistence: XGS-PON is designed to coexist with GPON and XG-PON on the same ODN network through WDM technology.
Key Issues:
The “wavelength dependence” of the fused biconical taper splitter is its fatal weakness. Its performance is not flat across the wide spectral range of 1260nm to 1650nm. And FBT splitters have average input power at 1550nm and 1310nm wavelengths, but require filters to isolate the XG-PON/XGS-PON wavelengths.
For XG-PON (1270nm upstream / 1577nm downstream):
The 1270nm upstream wavelength is close to the design center of traditional splitters (e.g., 1310nm), so this usually doesn’t pose a problem.
The 1577nm downstream wavelength is very close to the edge where the performance of tapered fiber splitters begins to degrade (performance usually starts to drift above 1550nm). This may lead to:
- Increased and unstable insertion loss: The loss at 1577nm may be several dB higher than the nominal value (tested at 1310/1490nm) across different batches or branches.
- Poor splitting uniformity: The optical power difference between output ports may exceed standard requirements, resulting in weak signals for some users.
For XGS-PON (1270nm upstream / 1577nm downstream):
In addition to the problems faced by XG-PON at 1577nm mentioned above, XGS-PON has stricter power budget requirements for the upstream link (because the upstream rate is as high as 10Gbps). Any additional loss or non-uniformity introduced by the splitter may lead to insufficient upstream signal sensitivity, increased bit error rate, or even failure to register.
Conclusions and Recommendations
| Scenario | Recommended Splitter Type | Reason |
| Building a new XG-PON/XGS-PON network | Planar waveguide optical splitter | Ensuring stable performance, low loss, and good uniformity across the entire working wavelength range (1260~1650nm), fully meeting standard requirements, makes it the preferred choice for operators. |
| Smooth upgrade from GPON to XG-PON | Existing tapered fiber splitters can be carefully evaluated. | If the existing ODN uses high-quality fused biconical taper splitters and has sufficient power budget, it might support XG-PON. However, rigorous field testing is necessary (testing loss and uniformity at 1577nm and 1270nm wavelengths). The risk is high. |
| Upgrading from GPON to XGS-PON, or building a new XGS-PON network | Planar waveguide splitters are strongly recommended. | XGS-PON is more sensitive to upstream optical power, and the wavelength characteristics of fused biconical taper splitters are likely to become a bottleneck in network performance, leading to unstable user services. |
| Networks requiring coexistence with GPON | Planar waveguide optical splitters must be used. | To ensure balanced power at each user end after splitting for both GPON (1490nm downstream) and XG(S)-PON (1577nm downstream) wavelengths, planar splitters must be used. |
Conclusion
From the perspective of technical standards, network performance stability, and future evolution, planar waveguide optical splitters are the inevitable choice for XG-PON and XGS-PON. Tapered fiber splitters (FBT fiber splitters), due to their inherent wavelength dependence, cannot guarantee performance in the 1577nm band, and will introduce unpredictable risks to the network when building new or upgrading to higher-speed PON networks (especially XGS-PON).
In actual procurement and deployment by operators, almost all next-generation PON networks utilize planar waveguide splitters (PLC Splitter). If your existing network uses tapered fiber splitters and you are considering an upgrade, the safest approach is to conduct wavelength characteristic testing or directly replace them with planar waveguide splitters.
FAQ
- What is the working wavelength of FBT fiber splitter?
FBT splitter working wavelength is1310nm, 1490nm, 1550nm for single mode coupler, if mulitmode coupler should use 850nm wavelength. But it can not use in 1577nm or 1270nm, which need isolator if needed.
2. What is the working wavelength of PLC splitter?
PLC splitters operate over a broad, wavelength-insensitive range, typically from 1260 nm to 1650 nm, supporting common PON wavelengths like 1310nm, 1490nm, and 1550nm for high compatibility in FTTx and data networks, unlike FBT splitters which are specific to certain wavelengths. And it is the best splitter for GPON, XGPON and XGS-PON network.
3. Can FBT couplers evenly split optical signals?
Yes, FBT (Fused Biconical Taper) couplers can evenly split optical signals, but they can also achieve unequal splitting. By controlling the coupling length and angle during the fiber fusion and tapering process, devices with various splitting ratios can be manufactured, ranging from uniform splitting 50/50 to unbalanced splitting (such as 1/99, 10/90, 30/70).
4. If unequal power splitting is required, should I choose a PLC splitter or an FBT splitter?
Unequal power splitting means that the output optical power at different ports is not equal, and both types of splitters can achieve this function.
For access networks like FTTH, where temperature variations are not significant and the splitting ratio is less than 1:4, a fused biconical tapered (FBT) splitter should be chosen for cost reasons. This is because FBT splitters offer high variability and flexibility, allowing for customized unequal splitting ratios (e.g., 10/90, 30/70).
However, if the splitter is to be used in GPON, XGPON, or XGSPON systems, or if the system will be upgraded in the future, it is recommended to use a PLC splitter. Although PLC splitters are commonly used for equal power splitting ratios such as 1:4, 1:8, 1:16, 1:32, and 1:64, unequal splitting ratios like 1:3, 1:5, 1:9, and 1:17 are also becoming widely used.
