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).

How these fibres are produced and why their tolerances are what they are — preforms, drawing, coating, proof test: How fibre is made; the documents behind every designation, from ITU-T G.65x to IEC categories and national standards: Standards map.