The core reason of G.657 fiber is preferred over G.652 fiber for ftth drop cable installation is that there are significant differences in the bending resistance and mechanical adaptability of both fibers.
The specific analysis is as follows:
Bend Resistance Comparison
G.657 Fiber’s Bend Resistance Advantages
G.657 fiber (especially the G.657.A2 subtype) is designed for high-bend scenarios, with a minimum bend radius as low as 5mm (G.657.A1 is 10mm). In contrast, G.652 fiber requires a bend radius of at least 30mm to avoid signal attenuation. In home applications, optical cables often need to pass through narrow ducts, corners, or gaps in furniture. The strong bend resistance of G.657 significantly reduces the risk of macrobending losses.
Limitations of G.652 Fiber
G.652 fiber exhibits high dispersion in the 1550nm band and is sensitive to microbending. When the bend radius is less than 30mm, macrobending loss increases dramatically, potentially causing excessive optical signal attenuation at the entrance (measured additional loss can exceed 3dB).
Differences in scene adaptability
| Features | G.657 fiber | G.652 fiber |
| Applicable Scenario | High-density cabling, confined spaces (such as homes and offices) | Long-distance trunk lines, metropolitan area network backbones |
| Bending Radius | Minimum 5mm (Class A2) | Recommended ≥30mm |
| Mechanical Strength | Optimized twist and kink resistance | Normal strength, prone to loss due to twisting |
| Typical Applications | FTTH to the home, data center interiors | Inter-regional communications, core networks |
Note: The FTTH cable usually adopts G.657.A2 (with the best bending performance). If the pigtail from the fiber optic splitter box to the user terminal mistakenly uses G.652, it will become the main cause of weak light.
Actual Failure Case Analysis
Twisting Loss:
Even with G.657 fiber, if the FTTH cable twists during installation (e.g., due to stress after tying a knot), additional loss can still be as high as 3.24dB. Using G.652 fiber will further increase loss.
Cost and Reliability Balance:
Although G.657 is slightly more expensive per meter, it reduces maintenance costs due to bending loss, offering superior overall benefits.
Conclusion
G.657 fiber, due to its excellent bend resistance and mechanical adaptability, is the preferred FTTH cable. However, G.652 fiber, due to its sensitivity to bending loss, is only suitable for backbone networks primarily laid in straight lines.
Forcibly using G.652 fiber in the drop section will result in signal degradation and increased operation and maintenance costs.
Standardized installation procedures are also required to avoid twisting to ensure performance.
