Fibre types: G.65x single-mode, multi-mode grades, specialty fibres

"Single-mode fibre" is a family, not one product: the ITU-T G.652 to G.657 recommendations describe fibres that differ in dispersion, cutoff, bend tolerance, loss and effective area, and a plant may contain three of them spliced together. Multi-mode has its own ladder of grades, and beyond both lie specialty fibres — dispersion-compensating, erbium-doped, polarization-maintaining, hollow-core — that appear inside systems rather than in ducts. This page is the catalogue: what each type is, its key parameters, where it is used, what happens when types meet at a splice, and how to identify what is already in the ground.

Single-mode fibre by ITU-T recommendation

Type	Name	MFD at 1310 / 1550 nm	Zero-dispersion λ₀	D at 1550 nm	Attenuation 1310 / 1550	Bend radius (min)	Use
G.652.A/B	standard SMF (legacy)	8.6–9.5 / ~10.4 µm	1300–1324 nm	≈ 17 ps/(nm·km)	≤ 0.5 / ≤ 0.4 (B: 0.35 / 0.22); water peak at 1383	30 mm	pre-2000 plant; avoid E-band
G.652.C/D	low-water-peak SMF — the default	8.6–9.2 / ~10.4 µm	1300–1324 nm	≈ 17	≤ 0.4 / ≤ 0.3 (typ. 0.33 / 0.19); 1383 ≤ 0.4	30 mm	everything from access to 400ZR; full CWDM band usable
G.653	dispersion-shifted (DSF)	~8 µm	≈ 1550 nm	≈ 0	0.35 / 0.22	30 mm	1990s single-channel 1550 long haul; unsuitable for DWDM (four-wave mixing)
G.654.A–E	cut-off shifted, low loss, pure-silica core	~10.5–12.5 µm	≈ 1300	≈ 17–22	— / 0.15–0.19	30 mm	submarine (A–D); G.654.E terrestrial 400G+ long haul (large effective area, low nonlinearity)
G.655	non-zero dispersion-shifted (NZ-DSF: LEAF, TrueWave)	~8.4–9.6 µm	outside C-band	+2 … +10 (or negative)	0.35 / 0.22	30 mm	10G DWDM long haul of the 2000s; small D suppresses FWM while limiting dispersion
G.656	wideband NZ-DSF	~8 µm	< 1460	+2 … +14 over 1460–1625	0.35 / 0.22	30 mm	S+C+L band DWDM
G.657.A1 / A2	bend-insensitive, G.652.D-compatible	8.6–9.2 µm	as G.652.D	≈ 17	as G.652.D	10 / 7.5 mm	FTTH drops, indoor, dense panels; splices to G.652 with ≤ 0.05 dB
G.657.B2 / B3	bend-insensitive, not necessarily G.652-compatible	6.3–9.5 µm	—	—	as G.652.D	7.5 / 5 mm	in-building, terminal boxes; MFD mismatch to G.652 possible (0.1–0.3 dB)

Key parameter definitions: How light propagates, Dispersion & bandwidth.

Multi-mode fibre grades

Grade (ISO/IEC 11801)	IEC 60793-2-10	TIA	Core	EMB 850 nm	OFL bandwidth 850 / 1300	Attenuation 850 / 1300
OM1	A1b	492AAAA	62.5 µm	— (200 MHz·km OFL)	200 / 500	3.5 / 1.5
OM2	A1a.1	492AAAB	50 µm	— (500 OFL)	500 / 500	3.5 / 1.5
OM3	A1a.2	492AAAC	50 µm	2 000	1 500 / 500	3.0 / 1.5
OM4	A1a.3	492AAAD	50 µm	4 700	3 500 / 500	3.0 / 1.5
OM5	A1a.4	492AAAE	50 µm	4 700 (850), 2 470 (953)	3 500 / 500	3.0 / 1.5

OM3/OM4/OM5 are "laser-optimised": their index profile is measured by differential mode delay (DMD) to guarantee bandwidth with VCSELs. OM1/OM2 were specified for LEDs (overfilled launch, OFL). Reaches: Reach tables.

Specialty fibres

Fibre	What is special	Where you meet it
Dispersion-compensating (DCF)	D ≈ −80 … −150 ps/(nm·km), small core, higher loss (0.5 dB/km)	DCM spools in 10G DWDM amplifier sites (Dispersion)
Erbium-doped (EDF)	Er³⁺ ions in the core; gain 1530–1565 nm when pumped at 980/1480 nm	inside EDFAs (Amplification)
Polarization-maintaining (PM)	stress rods (PANDA, bow-tie) keep polarization axes	coherent transceiver internals, sensors, pump combiners
Photosensitive	Ge/B doping for UV-written Bragg gratings	FBG filters, DCMs, sensors
Large-effective-area	A_eff 110–150 µm² vs 80	G.654.E for long haul: lower non-linearity (Non-linear effects)
Hollow-core (HCF)	light in air: ~30 % lower latency (≈ 3.3 vs 4.9 µs/km), very low non-linearity, loss now < 0.2 dB/km	trading links, emerging long-haul; special splicing
Multicore (MCF)	2–7 cores in one 125 µm cladding (space-division multiplexing)	new submarine systems; needs fan-in/fan-out devices
Few-mode	2–6 guided modes as separate channels	research; mode-division multiplexing
Plastic optical fibre (POF)	1 mm PMMA core, 650 nm visible, 100+ dB/km	home networks, automotive (MOST), industrial short links
Hard-clad silica (HCS) 200 µm	large core, robust	industrial, medical, sensing
Radiation-hardened, high-temperature	pure silica core, special coatings	nuclear, downhole, aerospace

When types meet: splices and connectors between fibres

Joint	Extra loss	Notes
G.652.D ↔ G.652.D	0	reference
G.652.D ↔ G.657.A1/A2	≤ 0.05 dB	designed to be compatible
G.652.D ↔ G.657.B3	0.1–0.3 dB	MFD mismatch; use splicer's dissimilar-fibre program
G.652 ↔ G.655	0.1–0.3 dB	MFD 9.2 vs 8.4–9.6 µm; OTDR shows a "gainer" one way
G.652 ↔ G.653	0.2–0.5 dB	plus the DSF's DWDM problem downstream
G.652 ↔ G.654.E	0.1–0.3 dB	larger MFD; bridge fibre sometimes used
OM3 ↔ OM4	≈ 0	same geometry; link bandwidth = weaker grade
OM1 (62.5) ↔ OM2–OM5 (50)	2–4 dB in the 62.5→50 direction	avoid entirely
SMF ↔ MMF	modal noise / > 10 dB	never in a permanent link (Physical mismatches)

Splicing technique for dissimilar fibres: Splicing and termination.

Choosing a fibre type

Application	Recommended	Why
Data-centre intra-building ≤ 100–150 m	OM4 (OM5 if SWDM planned) or OS2 for future proofing	VCSEL optics cheap; SMF removes the reach ceiling
Campus, metro, access, PON	G.652.D (OS2)	universal, cheapest, every optic works
Indoor drops, terminal boxes, dense panels	G.657.A2	bend tolerance without compatibility issues
New long-haul / 400G+ DWDM	G.654.E	loss and non-linearity headroom
Existing DWDM on legacy G.655	keep, but check dispersion map for 100G+	coherent DSP handles residual dispersion
Legacy G.653 plant	single-channel or coherent only	FWM ruins DWDM at 1550
Ultra-low latency	hollow-core where affordable	1.5 µs/km saved

Identifying installed fibre

Clue	How
Cable jacket print	manufacturer, type ("G.652.D", "SM 9/125", "OM3 50/125"), year, metre marks
Jacket colour (indoor)	yellow SMF; orange OM1/OM2; aqua OM3/OM4; lime OM5 (Labels & colour codes)
Documentation	as-built drawings, splice diagrams, test reports (Maintenance & restoration)
OTDR	backscatter coefficient differs by type; "gainers" mark transitions; 1383 nm attenuation reveals pre-LWP fibre
Dispersion / PMD test	chromatic dispersion analyser tells G.652 from G.653/G.655; PMD test for old plant
Installation era	pre-1995: expect water peak, higher PMD, possibly G.653 on long-haul routes

In CodingBox

Modules are specified against fibre types through the compliance codes and length fields: a "10 km SMF" module assumes G.652-class dispersion and loss, an SR4 module its OM3/OM4 metres. CodingBox shows these fields so the module matches the fibre actually in the ground (Check transceiver, Memory map).