Plan compensation sections to control chromatic dispersion precisely. Compare fiber and module parameters quickly today. Optimize link performance with clear, exportable results for engineers.
Total accumulated dispersion in an optical link is approximated by:
D_{total} = D_f L_f + D_c L_c
To reach a target residual dispersion D_{target} (often zero):
L_c = (D_{target} - D_f L_f) / D_c
If you enter GVD beta2 instead of D, the conversion is:
D = -(2\pi c / \lambda^2)\,\beta2 (with consistent units)
| Wavelength (nm) | Fiber length (km) | Fiber D (ps/nm/km) | Compensator D (ps/nm/km) | Target residual (ps/nm) | Computed Lc (km) | Residual after (ps/nm) |
|---|---|---|---|---|---|---|
| 1550 | 80 | 16.7 | -80 | 0 | 16.700 | ~0 |
| 1550 | 120 | 17.0 | -85 | +50 | 19.412 | 50 |
This overview explains how to interpret the calculator outputs when planning dispersion control in fiber links. It highlights common parameter ranges, sign conventions, and practical checks so you can translate a link budget into an implementable compensator length with confidence.
The compensation length is the amount of dispersive medium required to offset the link’s accumulated chromatic dispersion. In practice, it may be dispersion compensating fiber, a chirped grating module, or another element specified by an equivalent dispersion value.
For many engineering estimates, accumulated dispersion scales linearly with distance: D_link ≈ D_f × L_f. Standard single-mode fiber near 1550 nm is often around 16 to 18 ps/nm/km, so an 80 km span can accumulate roughly 1300 ps/nm. This first-order model works well for budgeting and sizing.
Compensators typically have a larger |D| than transmission fiber. Values like -60 to -100 ps/nm/km reduce the required section length. If the computed length is negative, the compensator sign does not oppose the link dispersion for your target.
Many systems do not require exactly zero residual dispersion. A small designed residual can improve tolerance to nonlinear effects or wavelength drift. Enable the target option to design intentional pre-compensation or a controlled residual at the receiver.
If you enter a spectral width Δλ, the tool estimates residual temporal spreading as |D_residual| × Δλ. It is a quick sensitivity check: broader spectra or larger residuals increase spreading. Use it for comparisons rather than detailed waveform or system simulations.
Some data sheets provide group-velocity dispersion as β2 rather than D. Since D depends on wavelength, the calculator converts β2 to D using your wavelength input. This avoids common unit-mixing mistakes during dispersion budgeting.
Verify that dispersion values are referenced to the same wavelength and sign convention. Confirm whether compensator data is per kilometer or per device. For fixed modules, convert to an equivalent per-length value or treat it as a lumped dispersion element.
This linear model is ideal for first-pass sizing. Wideband systems may require dispersion slope and higher-order terms. If margins are tight, include channel-dependent dispersion and nonlinear effects, then refine the length using detailed simulations or measurements.
1) What is a good target residual dispersion?
Many designs target near zero at the receiver, but some prefer a small residual to manage nonlinearities. Use your system requirements, modulation format, and channel plan to choose an appropriate ps/nm value.
2) Why did I get a negative compensation length?
A negative value usually means the compensator dispersion sign does not counter the fiber dispersion sign for your chosen target. Select a compensator with opposite sign or adjust the target residual dispersion.
3) Should I enter fiber D or beta2?
Enter whichever parameter your data sheet provides. If you use beta2, also enter wavelength so the calculator can convert to D consistently for the link budget.
4) What units does the calculator assume for D?
Dispersion parameter D is treated as ps/nm/km. Fiber and compensator lengths are handled in km internally, even if you input meters for the fiber length field.
5) Is the broadening estimate a full pulse model?
No. It is a first-order estimate based on residual dispersion and optical spectral width. It helps compare scenarios quickly but does not include filtering, chirp, or nonlinear propagation effects.
6) Can I model a grating module instead of a fiber spool?
Yes, if you convert the module’s dispersion to an equivalent D value per length, or treat the module as a lumped dispersion and map it to an effective length using its specified dispersion.
7) How accurate is the computed length?
It is accurate for first-order dispersion budgeting when D values are correct and referenced consistently. Real deployments should validate with measured link dispersion, dispersion slope, and system penalties.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.