Fiber Optic Wavelength Bands (O, E, S, C, L, U) and Operating Windows
Wavelength decides attenuation, dispersion and which transceiver you can use. This table lists the ITU optical bands and the specific windows used by multimode links, PON systems and test gear, so you can check a number before you order optics or run a test.
| Band / window | Range or wavelength (nm) | Typical use |
|---|---|---|
O-band (original) | 1260 to 1360 | Zero dispersion region of standard singlemode fiber; 1310 nm links, 10GBASE-LR, upstream PON |
E-band (extended) | 1360 to 1460 | Water peak region near 1383 nm; used by CWDM channels on low water peak fiber |
S-band (short) | 1460 to 1530 | CWDM channels, GPON downstream at 1490 nm |
C-band (conventional) | 1530 to 1565 | Lowest-loss region for long haul, DWDM, EDFA amplification |
L-band (long) | 1565 to 1625 | Extended DWDM capacity, CWDM 1570 to 1610 nm channels |
U-band (ultra-long) | 1625 to 1675 | Mainly monitoring and OTDR testing in live fiber |
First window (multimode) | 850 | Short-reach multimode: 1000BASE-SX, 10GBASE-SR, VCSEL optics |
Second window | 1300 or 1310 | Multimode 1300 nm and singlemode 1310 nm links |
Third window | 1550 | Singlemode long reach, lowest attenuation of silica fiber |
SWDM multimode channels | 850, 880, 910, 940 | Shortwave WDM over OM5 wideband multimode fiber |
GPON downstream | 1490 | ITU-T G.984 downstream, OLT to ONT |
GPON upstream | 1310 | ITU-T G.984 upstream, ONT to OLT |
RF video overlay | 1550 | Analog or digital video broadcast on a PON |
XGS-PON downstream | 1577 | 10G symmetric PON, ITU-T G.9807.1 |
XGS-PON upstream | 1270 | 10G symmetric PON upstream |
XG-PON downstream | 1577 | 10G asymmetric PON, ITU-T G.987 |
XG-PON upstream | 1270 | Upstream wavelength of XG-PON |
OTDR multimode test | 850 and 1300 | Standard test pair for multimode links |
OTDR singlemode test | 1310 and 1550 | Standard test pair; comparing both shows macrobends |
OTDR live-fiber monitoring | 1625 or 1650 | Out-of-band test wavelength beside live traffic |
Visual fault locator | Approx 650 | Red light for finding breaks and bends over short distances |
Band edges follow the ITU-T optical band naming. Equipment and standards may use slightly different edges; confirm with the transceiver or standard in use.
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How to read the table
Start with the window you plan to use. Multimode links run at 850 nm (and 1300 nm on legacy gear), while singlemode links run at 1310 or 1550 nm. Telecom systems pick bands by loss and amplifier availability: the C-band has the lowest attenuation and is where erbium amplifiers work. Search any wavelength to see the band and the systems that use it.
Why wavelength matters on the factory floor
Insertion loss, connector loss and cable attenuation all change with wavelength, so a certification report must state the test wavelength. Test at both windows for singlemode because a macrobend shows up as extra loss at 1550 nm versus 1310 nm. Light sources and power meters must be matched to the same wavelength, and calibrated meters hold calibration factors per wavelength.
- Always record the test wavelength with every power reading.
- Use the 850/1300 pair for multimode and 1310/1550 for singlemode.
- Use out-of-band 1625 nm only with filters when traffic is live.
Common mistakes
Do not use a 1310 nm source with a meter set to 1550 nm. Do not connect a PON ONT to a link with unfiltered CWDM traffic. Be careful with SWDM optics: they need OM5 or at least well-specified OM3 and OM4 fiber, and wavelengths other than 850 nm are not covered by all OM3 and OM4 bandwidth ratings.
Frequently Asked Questions
What are the fiber optic wavelength bands?
The ITU names six singlemode bands: O (1260 to 1360 nm), E (1360 to 1460), S (1460 to 1530), C (1530 to 1565), L (1565 to 1625) and U (1625 to 1675). The C-band has the lowest attenuation in silica fiber.
Why do OTDR tests use 1310 and 1550 nm?
These are the two main singlemode windows. Testing at both shows whether a bend or stress point exists, because bend loss rises faster at 1550 nm than at 1310 nm. A single wavelength can miss it.
What wavelengths does GPON use?
GPON sends downstream at 1490 nm and upstream at 1310 nm, with an optional 1550 nm video overlay. XGS-PON moves to 1577 nm down and 1270 nm up so both can share the same fiber.
Which wavelength is used for multimode fiber?
Most multimode links use 850 nm with VCSEL sources, and legacy links use 1300 nm. OM5 fiber also supports short wavelength division multiplexing in the 850 to 940 nm region.
If your optical test results live in spreadsheets, Netray can help move them into your ERP or quality system with wavelength and operator attached to the lot.
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