Single-mode fiber attenuation and chromatic dispersion require separate, wavelength-specific inputs. Attenuation determines the distributed optical power loss in dB/km; chromatic dispersion determines how group delay changes with wavelength, in ps/(nm·km). Neither coefficient alone establishes a usable transmission distance.
For G.652.D cable, ITU-T G.652 (08/2024) specifies a maximum attenuation coefficient of 0.30 dB/km across 1530–1565 nm. At 1550 nm, its chromatic dispersion coefficient limits are 13.3–18.6 ps/(nm·km). These are specification limits, not typical measured values for every cable.
The tables below separate normative, representative, and vendor-specific data. Match the fiber category, wavelength, document edition, and cable or link boundary before selecting a calculation input.
G.652 Attenuation Reference Table
The following values come from Tables 1 and 2 of ITU-T G.652 (08/2024), Characteristics of a single-mode optical fibre and cable. “Normative maximum” identifies a limit in the recommendation’s main specification tables; it does not establish that a particular delivered or installed cable meets that limit.
| Fiber category | Wavelength or region | Attenuation coefficient, α | Value classification | Specification basis | ITU-T edition |
|---|---|---|---|---|---|
| G.652.B | 1310 nm | ≤0.40 dB/km | Normative maximum | Table 1; cabled factory lengths | G.652 (08/2024) |
| G.652.B | 1550 nm | ≤0.35 dB/km | Normative maximum | Table 1; cabled factory lengths | G.652 (08/2024) |
| G.652.B | 1625 nm | ≤0.40 dB/km | Normative maximum | Table 1; cabled factory lengths | G.652 (08/2024) |
| G.652.D | 1310–1625 nm | ≤0.40 dB/km | Normative maximum | Table 2; general spectral limit, with the tighter limit below applying across 1530–1565 nm | G.652 (08/2024) |
| G.652.D | 1530–1565 nm | ≤0.30 dB/km | Normative maximum | Table 2; cabled factory lengths | G.652 (08/2024) |
| G.652.D | 1383 ±3 nm, after hydrogen aging | ≤0.40 dB/km | Normative maximum | Table 2; hydrogen-aging type test on sampled fibers | G.652 (08/2024) |
Source: G.652 (08/2024), clause 7.1 and Tables 1–2.
These cable attenuation limits exclude connector, splice, splitter, and other component losses. The table notes also state that the attenuation coefficients should not be applied to short cables such as jumpers, indoor cables, and drop cables. Use the applicable assembly or cable specification for those products.
Do not extend the 1310 nm value unchanged to shorter wavelengths. For G.652.D, Table 2, Note 2 describes extending the wavelength region down to 1260 nm by adding 0.07 dB/km of induced Rayleigh scattering loss to the attenuation value at 1310 nm. That qualification is not a wavelength-independent allowance.
G.652 Chromatic Dispersion and Slope Reference
Chromatic dispersion is not a single fixed property attached to the label “single-mode.” Its value and sign depend on wavelength and fiber characteristics.
The zero-dispersion wavelength, (\lambda_0), is where the chromatic dispersion coefficient crosses zero. A fiber whose zero-dispersion wavelength lies near 1310 nm does not necessarily have zero dispersion at exactly 1310 nm.
| Fiber category | Wavelength or fitting region | Chromatic dispersion specification | Dispersion slope specification | Value classification and basis | ITU-T edition |
|---|---|---|---|---|---|
| G.652.B | 1310 nm region | (\lambda_0) between 1300 and 1324 nm; (D(\lambda)) bounded using the parameters in clause 6.10 | Zero-dispersion slope (S_0 \leq 0.092) ps/(nm²·km) | Normative parameters; Table 1 and Equation 6-1 | G.652 (08/2024) |
| G.652.D | 1260–1460 nm | (\lambda_0) between 1300 and 1324 nm; wavelength-dependent dispersion envelope | (0.073 \leq S_0 \leq 0.092) ps/(nm²·km) | Normative parameters for the three-term Sellmeier fitting region; Table 2 and clause 6.10 | G.652 (08/2024) |
| G.652.D | 1550 nm | (13.3 \leq D \leq 18.6) ps/(nm·km) | Use the specified long-wavelength dispersion envelope, not (S_0) | Normative limits within the 1460–1625 nm linear-fitting region; Table 2 | G.652 (08/2024) |
| G.652.D | 1625 nm | (17.2 \leq D \leq 23.7) ps/(nm·km) | Use the specified long-wavelength dispersion envelope, not (S_0) | Normative limits within the 1460–1625 nm linear-fitting region; Table 2 | G.652 (08/2024) |
Source: G.652 (08/2024), clause 6.10 and Tables 1–2.
The distinction between (S_0) and slope at an operating wavelength matters. (S_0) describes the dispersion slope at the zero-dispersion wavelength; it is not a constant slope that can be applied unchanged from 1310 to 1625 nm.
For G.652.D, the recommendation uses different fitting regions: 1260–1460 nm and 1460–1625 nm. It specifically warns that extrapolating a dispersion description fitted around 1310 nm into the 1550 nm region may not provide sufficient accuracy. For an intermediate operating wavelength, use the applicable clause 6.10 envelope, a supplier’s wavelength-dependent specification, or suitable measurement data—not an assumed zero at 1310 nm.
Representative Link Values Are a Different Data Set
Appendix I of G.652 provides representative values for concatenated optical fiber links. The appendix is informative rather than an integral part of the recommendation. Its link values must not be relabeled as cable acceptance limits.
| Fiber or link category | Wavelength or region | Attenuation coefficient | Chromatic dispersion coefficient | Dispersion slope | Classification and design basis | ITU-T edition |
|---|---|---|---|---|---|---|
| Concatenated G.652 optical fiber links | 1260–1360 nm | 0.50 dB/km | Not tabulated for this region | Not tabulated for this region | Representative link value; Table I.1 | G.652 (08/2024) |
| Concatenated G.652 optical fiber links | 1530–1565 nm; dispersion parameters referenced to 1550 nm | 0.275 dB/km | (D_{1550}=17) ps/(nm·km) | (S_{1550}=0.056) ps/(nm²·km) | Representative link values; Table I.1 | G.652 (08/2024) |
| Concatenated G.652 optical fiber links | 1565–1625 nm | 0.35 dB/km | Not separately tabulated for this region | Not separately tabulated for this region | Representative link value; Table I.1 | G.652 (08/2024) |
Source: G.652 (08/2024), Appendix I, clauses I.2–I.4 and Table I.1.
There is an important qualification beside the appendix’s dispersion calculation: ITU-T states that, following revision of the normative G.652.D dispersion specification, Equation I-2 is no longer representative for that fiber type. The listed 17 ps/(nm·km) and 0.056 ps/(nm²·km) values therefore should not be combined into a universal G.652.D wavelength model.
The attenuation values also have a different boundary from the factory-cable limits. Before using an effective link coefficient, determine which losses its source includes. Do not assume it represents only distributed fiber loss and then add potentially overlapping allowances.
Vendor-Specific Example: Corning SMF-28 Ultra
A product specification may provide tighter limits than the general fiber category. The following values are from Corning SMF-28 Ultra Optical Fiber, PI1424, issued July 2025. Corning identifies the product as G.652.D-compliant, but these numbers remain product-specific specifications rather than limits for all G.652.D fibers.
| Product and category | Wavelength | Maximum attenuation | Maximum chromatic dispersion coefficient | Slope or zero-dispersion information | Specification basis |
|---|---|---|---|---|---|
| SMF-28 Ultra; supplier identifies G.652.D compliance | 1310 nm | 0.32 dB/km | Not separately listed at 1310 nm | (\lambda_0=1304–1324) nm; (S_0 \leq 0.092) ps/(nm²·km) | Vendor-specific maximums; PI1424, July 2025 |
| Same product | 1383 nm | 0.32 dB/km, after hydrogen aging | Not listed at this wavelength | Same product-level zero-dispersion specification | Vendor-specific maximums; PI1424, July 2025 |
| Same product | 1490 nm | 0.21 dB/km | Not listed at this wavelength | Same product-level zero-dispersion specification | Vendor-specific maximums; PI1424, July 2025 |
| Same product | 1550 nm | 0.18 dB/km | 18 ps/(nm·km) | (S_0) is not a specified 1550 nm slope | Vendor-specific maximums; PI1424, July 2025 |
| Same product | 1625 nm | 0.20 dB/km | 23.7 ps/(nm·km) | No separate operating-wavelength slope listed | Vendor-specific maximums; PI1424, July 2025 |
Source: Corning PI1424, Optical Specifications. The product sheet does not identify an edition date for its G.652.D compliance statement.
These are optical fiber product specifications, not a complete installed-cable loss guarantee. Confirm the purchased cable specification, applicable test conditions, and installation acceptance requirements before using them as project limits.
The same product sheet permits attenuation to exceed its 1550 nm reference-wavelength value by up to 0.02 dB/km across 1525–1575 nm. Thus, the 0.18 dB/km limit at exactly 1550 nm should not be copied unchanged to every channel in that range.
Calculating Fiber Attenuation and Total Link Loss
For a uniform cable section at a specified wavelength:
where:
- (A_{\text{fiber}}) is distributed fiber attenuation, in dB.
- (\alpha) is the selected attenuation coefficient, in dB/km.
- (L) is the actual optical fiber length, in km.
For sections with different coefficients:
Use optical path length, including installed slack and other traversed fiber, rather than map distance alone. Cable remaining unused on a reel is not part of the optical path.
To build a link loss allowance from cable-only coefficients:
=
\sum_i \alpha_i L_i
+
\sum_j A_{\text{splice},j}
+
\sum_k A_{\text{connection},k}
+
\sum_m A_{\text{component},m}
+
M
Here, splice, connection, and component terms are in dB, and (M) is a separately identified design allowance in dB. Connection losses should use a consistent boundary, such as one loss value per mated connector pair. Appendix I.1 of G.652 similarly separates cable attenuation, splices, line connectors, and allowances for future changes; it notes that equipment connector losses are not included in its equation.
Example: A 40 km G.652.D Link at 1550 nm
Assume the following planning inputs:
| Input | Selected value | Basis |
|---|---|---|
| Actual fiber length | 40 km | Example assumption |
| Cable attenuation coefficient | 0.30 dB/km | G.652.D maximum across 1530–1565 nm, Table 2 |
| Fusion splices | 8 at 0.10 dB each | Example allowance, not an ITU-T splice limit |
| Mated connector pairs | 2 at 0.50 dB each | Example allowance, not an ITU-T connector limit |
| Other passive component losses | 0 dB | Example assumes none |
| Design allowance | 3.0 dB | Example assumption |
The distributed fiber loss is:
The total design loss allowance is:
=
12.0+(8\times0.10)+(2\times0.50)+3.0
=
16.8\ \text{dB}
The 16.8 dB result is a planning allowance, not a measured insertion loss. Only the cable attenuation coefficient is taken from G.652; the splice, connection, and design allowances are explicit example assumptions.
For comparison, multiplying the Corning product’s 1550 nm maximum of 0.18 dB/km by 40 km gives 7.2 dB of fiber attenuation. Substituting that figure into a cable design requires confirmation that the purchased cable supports the selected coefficient; the fiber product sheet alone does not establish the installed link’s loss.
Neither result establishes receiver compatibility. That comparison also requires the transmitter’s applicable minimum output, receiver sensitivity for the operating mode, and the relevant interface reference points. Receiver overload must be checked separately using maximum launch power and minimum path loss.
Calculating Accumulated Chromatic Dispersion
For a uniform fiber section at a fixed wavelength:
where:
- (CD) is accumulated chromatic dispersion, in ps/nm.
- (D) is the chromatic dispersion coefficient, in ps/(nm·km).
- (L) is the actual fiber length, in km.
For a link containing different fiber sections:
Preserve the sign of each coefficient. G.652 Appendix I.2 explicitly describes summing factory-length contributions with linear dependence on length and due regard for their signs. If a link includes a dispersion-compensating component, include its specified signed dispersion separately rather than treating it as fiber length.
Example: Dispersion Range for 40 km at 1550 nm
Using the G.652.D coefficient limits of 13.3–18.6 ps/(nm·km):
A 40 km link composed of fiber sections meeting those coefficient limits therefore has a fiber-only planning range of 532–744 ps/nm at 1550 nm, before any separate dispersion contribution from other components. This is an endpoint calculation, not a probability interval or a prediction of the most likely installed value.
If 17 ps/(nm·km) is selected as an illustrative coefficient:
That single-input estimate does not replace the 532–744 ps/nm range when the actual coefficient is unknown.
Compare accumulated dispersion with the equipment’s specified chromatic dispersion tolerance for the exact wavelength, line rate, modulation format, and operating mode. A result in ps/nm is not itself a pass/fail statement, and an acceptable power budget does not establish an acceptable dispersion budget.
Converting Dispersion to a First-Order Delay Spread
For a sufficiently narrow wavelength interval over which (D) is approximately constant:
where (\Delta t) is differential group delay across that interval, in ps, and (\Delta\lambda) is its width, in nm.
With the illustrative (CD=680) ps/nm and an assumed spectral width of 0.10 nm:
When used as a pulse-broadening estimate, the spectral-width convention must be defined consistently. This first-order calculation does not model transmitter chirp, pulse shape, receiver processing, or dispersion compensation, so it cannot establish a supported bit rate by itself.
Selecting a Coefficient for a Project
Choose the input according to the decision being made:
| Decision | Appropriate input basis | Required qualification |
|---|---|---|
| Establish a cable procurement limit | Applicable category and contract edition, plus purchased cable specification | Keep normative limits separate from product-specific commitments |
| Estimate distributed cable loss | Wavelength-specific cable attenuation coefficient and actual fiber length | Add separately identified connection, splice, and component losses |
| Assess an existing installed path | Suitable path measurements and documented reference points | Do not treat total measured insertion loss as a cable-only coefficient |
| Estimate accumulated dispersion | Wavelength-specific section coefficients or measured path dispersion | Preserve signs and include separate compensating components |
| Compare a path with optical equipment | Path loss and dispersion results plus exact interface specifications | Check each impairment against its own equipment limit |
G.652 distinguishes fiber attributes, cable attributes, and concatenated-link attributes because these boundaries serve different purposes. Its measurement references are G.650.1 for linear deterministic attributes and G.650.2 for statistical and nonlinear-related attributes.
For an existing contract, retain the specified edition unless the project formally adopts another. Do not transfer these G.652 tables to another single-mode fiber family solely because it is also described as “single-mode.” Record the fiber category, operating wavelength, source document and edition, value classification, and whether the input represents a fiber, cable, or complete link.