Typical values and limits: a cheat sheet

The numbers that come up in every design review, acceptance test and fault call, collected on one page with the material that explains each of them. Values are typical for modern components unless a standard is named; the data sheet of the actual fibre, cable, connector or module always wins.

Attenuation of fibre

Fibre	850 nm	1310 nm	1383 nm	1550 nm	1625 nm
G.652.D single-mode, bare fibre typical	—	0.33–0.35 dB/km	≤ 0.35 (low water peak)	0.19–0.20 dB/km	0.20–0.23 dB/km
G.652.D cabled, data-sheet maximum	—	0.36–0.40 dB/km	—	0.22–0.25 dB/km	0.25 dB/km
G.652.A/B (older), water peak	—	0.35–0.40 dB/km	1–2 dB/km	0.22–0.25 dB/km	—
G.654.E	—	—	—	0.15–0.17 dB/km	—
OM3 / OM4 / OM5 multimode	2.5–3.0 dB/km (3.0 max)	0.6–1.0 dB/km (1.5 max)	—	—	—
OM1 62.5 µm	3.0–3.5 dB/km	1.0 dB/km	—	—	—

Rayleigh scaling: loss at 1550 ≈ 0.51 × loss at 1310 (Attenuation & windows).

Loss allowances for components

Component	Typical	Design value	Standard maximum
Connector pair, single-mode LC/SC UPC or APC	0.1–0.3 dB	0.3–0.5 dB	0.75 dB (TIA-568.3-D); IEC 61753 grade B ≤ 0.12 mean / 0.25, grade C ≤ 0.25 / 0.5
Connector pair, multimode	0.1–0.3 dB	0.5 dB	0.75 dB
MPO/MTP pair, 12–24 fibres	0.2–0.35 dB	0.5 dB	0.75 dB (low-loss 0.35 dB)
Fusion splice, single-mode	0.02–0.05 dB	0.1 dB	0.3 dB (TIA); project limit usually 0.1–0.15 dB
Fusion splice, multimode	0.05–0.1 dB	0.1 dB	0.3 dB
Mechanical splice	0.1–0.3 dB	0.3 dB	0.5 dB
Splitter 1:2 / 1:4 / 1:8	3.5 / 7.0 / 10.5 dB	+0.5 dB excess	3.7 / 7.4 / 10.8 dB
Splitter 1:16 / 1:32 / 1:64	13.5 / 17.0 / 20.5 dB	+0.5–1 dB	14.0 / 17.5 / 21.0 dB
CWDM mux or demux, 4–8 channels	1.0–2.0 dB	2.5 dB	per data sheet
DWDM AWG mux or demux, 40 channels	3–5 dB	5.5 dB	per data sheet
OADM, 1 channel add/drop	1–2 dB	2 dB	—
Fixed attenuator	1–25 dB nominal	±0.5 dB	—
Field-installable connector	0.2–0.5 dB	0.5 dB	0.75 dB
Pigtail splice + adapter, per panel	0.35 dB	0.5 dB	0.85 dB

(Passive plant, Splicing & termination)

Reflectance and return loss

Item	Value
Open flat endface, glass–air	−14.4 dB (−14.7 dB often quoted)
UPC pair, clean	−50 … −60 dB (spec ≤ −50)
APC pair	−60 … −70 dB (spec ≤ −60)
Mechanical splice	−40 … −60 dB
Fusion splice	< −70 dB
Dirty connector	−25 … −40 dB
Required ORL: 10G Ethernet / DWDM / PON / analogue CATV	≥ 12 / ≥ 24 / ≥ 32 / ≥ 45 dB
Maximum discrete reflectance: 10G–100G NRZ / 400G PAM4 / PON	≤ −26 / ≤ −35 / ≤ −35 dB

(Reflections & return loss)

Fibre geometry and optical parameters

Parameter	G.652.D	G.657.A2	OM3/OM4
Core / cladding diameter	8.2–9 / 125 ± 0.7 µm	8.6 / 125 µm	50 ± 2.5 / 125 ± 1 µm
Coating diameter	245 ± 10 µm (200 µm option)	245 or 200 µm	245 µm
Mode field diameter at 1310 / 1550 nm	9.2 ± 0.4 / 10.4 ± 0.5 µm	8.6 ± 0.4 / 9.8 µm	—
Numerical aperture	0.12–0.14	0.13	0.200 ± 0.015
Cabled cutoff wavelength	≤ 1 260 nm	≤ 1 260 nm	—
Core–cladding concentricity	≤ 0.6 µm	≤ 0.5 µm	≤ 1.5 µm
Cladding non-circularity	≤ 1 %	≤ 1 %	≤ 1 %
Group index at 1310 / 1550 nm	1.4675 / 1.4680 (data-sheet value)	similar	1.482 / 1.477 at 850 / 1300 nm
Effective area at 1550 nm	≈ 80 µm²	≈ 70 µm²	—
Proof test	0.69 GPa (1 %)	0.69 GPa	0.69 GPa

(Fibre types, How fibre is made)

Dispersion and bandwidth

Parameter	Value
Chromatic dispersion G.652 at 1310 / 1550 / 1625 nm	≈ 0 / 16–18 / 20–22 ps/(nm·km)
Zero-dispersion wavelength, slope (G.652)	1 300–1 324 nm; ≤ 0.092 ps/(nm²·km)
Chromatic dispersion G.655 / G.653 / G.654 at 1550 nm	2–6 / ≈ 0 / 18–22 ps/(nm·km)
PMD link design value: modern G.652.D / 1990s fibre / 1980s fibre	≤ 0.1–0.2 / 0.5 / 1–2 ps/√km
Dispersion limit: 10G NRZ / 40G NRZ / 100G coherent / 400ZR	≈ 1 000–1 600 / 60–100 / ± 50 000 / ± 2 400 ps/nm
PMD limit (mean DGD): 10G / 40G NRZ / coherent	10 / 2.5 / 25+ ps
Modal bandwidth OM1 / OM2 / OM3 / OM4 / OM5 (850 nm, EMB)	200 / 500 / 2 000 / 4 700 / 4 700 MHz·km
10GBASE-SR reach on OM1 / OM2 / OM3 / OM4	33 / 82 / 300 / 400 m
100GBASE-SR4 on OM3 / OM4	70 / 100 m

(Dispersion & bandwidth, Reach tables)

Mechanical limits

Item	Value
Bare fibre bend radius, long-term: G.652 / G.657.A1 / A2 / B3	30 / 10 / 7.5 / 5 mm
Patch cord bend radius	≥ 30 mm standard, 15 mm with G.657
Cable bend radius	20 × outer diameter under tension, 10 × installed
Fibre strain: proof / installation / long-term	1 % / ≤ 0.6 % / ≤ 0.2 %
Cable tensile: outdoor loose tube installation / long-term	1 500–2 700 N / 600–1 000 N
Cable crush	1 000–3 000 N per 100 mm
Duct fill for blowing	cable diameter 55–80 % of duct bore
Slack per closure	10–30 m each side
Connector matings	500–1 000
Cable temperature: installation / operation / storage	−10 … +50 / −40 … +70 / −40 … +70 °C

(Cable construction, Installation, Reliability & ageing)

Wavelengths and grids

Item	Value
Bands: O / E / S / C / L / U	1 260–1 360 / 1 360–1 460 / 1 460–1 530 / 1 530–1 565 / 1 565–1 625 / 1 625–1 675 nm
Multimode windows	850 nm (VCSEL), 1 300 nm; SWDM 850–953 nm on OM5
CWDM grid (G.694.2)	18 channels 1 271–1 611 nm, 20 nm spacing; 8-channel sets 1 471–1 611 or 1 271–1 411
DWDM grid (G.694.1)	193.1 THz anchor; 100 GHz ≈ 0.8 nm, 50 GHz ≈ 0.4 nm; C-band 40–48 (100 GHz) or 80–96 (50 GHz) channels
PON: GPON down / up; XGS-PON down / up; video overlay	1 490 / 1 310; 1 577 / 1 270; 1 550 nm
OTDR test wavelengths; live-fibre monitoring	1 310, 1 550, 1 625; 1 625 or 1 650 nm
BiDi pairs	1 310/1 490, 1 310/1 550, 1 270/1 330, 1 490/1 550 nm

(Wavelength bands)

Speed, latency, OTDR

Item	Value
Speed of light in fibre	≈ 204 000 km/s (c / 1.468)
Latency	4.9 µs per km one way; 1 ms ≈ 204 km one way, 102 km round trip
OTDR distance error per 0.0015 of index	0.1 %
Backscatter coefficient G.652, 1 ns pulse, 1310 / 1550 nm	≈ −79 / −81 … −82 dB
Rayleigh ORL floor of a long fibre, 1310 / 1550 nm	≈ 29–31 / 31–33 dB
OTDR dead zones at 10 ns / 100 ns / 1 µs	event 1–1.5 / 10 / 100 m; attenuation 3–5 / 15–25 / 150–250 m
Usable OTDR range	(dynamic range − 6 dB − event losses) / attenuation
Excess fibre length in loose-tube cable	0.1–0.5 %

(Reading an OTDR trace)

Link budgets of common interfaces

Interface	Channel insertion loss / budget	Distance
1000BASE-LX	4.5–7.5 dB (typical modules)	10 km
10GBASE-LR	6.2 dB	10 km
10GBASE-ER	10.9 dB (engineered 40 km: ~15 dB)	30–40 km
10GBASE-ZR (non-IEEE)	23–24 dB	80 km
100GBASE-LR4 / ER4	6.3 dB / 18 dB (30 km)	10 / 40 km
100GBASE-SR4 (OM4)	1.9 dB	100 m
400GBASE-DR4 / FR4 / LR4	3.0 / 4.0 / 6.3 dB	500 m / 2 km / 10 km
GPON B+ / C+; XGS-PON N1 / N2 / E1 / E2	13–28 / 17–32; 14–29 / 16–31 / 18–33 / 20–35 dB	20 km
400ZR unamplified	≤ 11 dB	≈ 40 km
Design margin	3 dB (2 dB minimum on short links)	—

(Link budget, Ethernet PMD reference, ODN classes)

Power and safety

Item	Value
Typical transceiver Tx power: SR / LR / ER / ZR	−7 … −1 / −8 … +0.5 / −4.7 … +4 / 0 … +4 dBm
Receiver overload (typical)	+0.5 … +3 dBm (SR/LR), −7 dBm for some ER/ZR APD receivers
EDFA output; Raman pump	+17 … +23 dBm; +27 … +30 dBm
Laser Class 1 limit at 1550 nm (approx.)	≈ 10 mW (+10 dBm)
Hazard level 3B / 4 threshold	500 mW (+27 dBm)
Fibre fuse threshold	≈ 1–1.5 W in single-mode fibre
DDM accuracy	±3 dB specified, ±1–2 dB typical; ±0.1 dB relative

(Safety & handling, Accuracy & limits)

Conversions

dBm	mW	dBm	mW
+10	10	−10	0.1
+3	2.0	−13	0.05
0	1.0	−20	0.01
−3	0.5	−30	0.001
−7	0.2	−40	0.0001

3 dB halves or doubles the power; 10 dB is a factor of 10; 1 dB is 26 % (Units & conversions, Formulas & calculations).

In CodingBox

Most of these limits are checked against a real module on the bench: Tx power against the class and the receiver's overload, wavelength against the plan, connector code and rated lengths against the cable. CodingBox shows the module's own values next to the numbers in this table (Check transceiver, DDM in the app).