This tool provides two engineering-style approximations for bend-induced loss. Use constants taken from your fiber datasheet, lab test, or vendor note.
- Empirical exponential: Loss/turn = A · e^(−B·R)
- Critical radius: Loss/turn = 0 when R ≥ Rc, else K · (1/R − 1/Rc)^p
Total loss is computed as Loss_total = (Loss/turn) · N. Coil length is L = 2πRN, enabling dB/m and dB/km reporting.
- Select a model that matches your available parameters.
- Enter the bend radius and number of turns in the coil.
- Provide wavelength for record-keeping and comparisons.
- Fill model constants from measurement or documentation.
- Press Calculate and review results shown above the form.
- Use the export buttons to keep your calculations archived.
| Model | R | N | λ | Constants | Loss/turn | Total loss | Coil length |
|---|---|---|---|---|---|---|---|
| Empirical exponential | 30 mm | 10 | 1550 nm | A=1 dB/turn, B=120 1/m | ≈ 0.027 dB/turn | ≈ 0.27 dB | ≈ 1.885 m |
| Critical radius | 20 mm | 10 | 1550 nm | Rc=30 mm, K=0.02, p=2 | ≈ 0.011 dB/turn | ≈ 0.11 dB | ≈ 1.257 m |
1) Purpose of a bending loss estimate
Bending loss is the extra attenuation introduced when an optical fiber is forced to follow a curved path. In tight coils, guided light can leak into the cladding and radiate outward, reducing received power. This calculator converts your coil geometry and model coefficients into loss per turn, total loss, and normalized loss values.
2) Where bending loss appears in real links
Macrobending is common in patch panels, splice trays, cabinets, and compact routing paths. Even when a link budget looks safe on paper, repeated small bends can accumulate measurable loss. Practical checks include cabinet door closures, pigtail storage loops, and strain-relief points near connectors.
3) Inputs and what they represent
The key geometric inputs are bending radius R and number of turns N. Radius controls field confinement, while turns scale the total loss linearly in both models. Wavelength is included to document conditions, because bend sensitivity generally increases at longer wavelengths for many fibers.
4) Choosing a calculation model
Use the empirical exponential model when you have fitted coefficients from measurements or a datasheet curve. The critical-radius model is useful for quick “safe radius” checks and for exploring how loss rises once you go below a threshold. Always calibrate A, B, K, and p to match your fiber type and installation method.
5) Reading the outputs
Loss/turn helps compare different coil radii directly. Total loss is what matters for your link budget and margin. dB/km and dB/m normalize results using coil length L = 2πRN, which is helpful when comparing to attenuation specifications or to lab measurements taken over known lengths.
6) Typical engineering checks
For patch and cabinet work, radii are often in the “tens of millimeters” range, while turns can vary from one to several loops. If computed total loss approaches your available margin, increase bend radius first, then reduce turns, and finally re-route to avoid stacked coils. Confirm results with a power meter if the design is critical.
7) Limits and practical cautions
These models are simplified and do not explicitly represent microbending, ovalization, temperature effects, or packaging stresses. Loss can change with coating, buffer type, and how tightly the fiber is constrained against a surface. Treat the calculator as a planning tool, then validate with representative samples or vendor curves.
8) Documenting results for audits
Use the CSV export to capture the numeric summary for spreadsheets and test reports. The PDF export provides a fast, readable record of the chosen model, inputs, and calculated loss metrics. Keeping consistent documentation improves troubleshooting and supports repeatable installations across teams and sites.
1) What is the difference between macrobending and microbending?
Macrobending comes from large-radius curves like coils. Microbending comes from small, irregular deformation caused by pressure points or rough routing. Both add attenuation, but their causes and mitigation steps differ.
2) Why does the calculator report both total loss and dB/km?
Total loss impacts link margin directly. dB/km and dB/m normalize the result by coil length, making it easier to compare different layouts or match measurements taken over known fiber lengths.
3) Which model should I select?
Select the empirical model if you have fitted coefficients from a curve or lab data. Use the critical-radius model to explore “safe radius” behavior when you know an approximate threshold and scaling response.
4) How do turns affect loss?
In both models, total loss scales roughly with the number of turns because each loop adds a similar incremental attenuation. Reducing turns is a quick way to recover margin when space is limited.
5) Does wavelength matter for bending loss?
Yes. Many fibers become more bend-sensitive at longer wavelengths because the mode field extends further into the cladding. Use wavelength mainly to document conditions and keep comparisons consistent.
6) Can I use this for connector or splice loss?
No. Connector and splice losses come from alignment, end-face quality, and Fresnel reflections. This calculator targets bend-induced attenuation from coil geometry and should be combined with other budget terms separately.
7) How do I validate the output against measurements?
Build a representative coil, measure insertion loss with a stable source and power meter, and compare to the calculated total loss. Then adjust model constants to match, keeping radius and turns identical.