Which loss measurement wavelengths do I need?
Fiber optic loss testing is usually performed at expected current and future operating wavelengths, since optical loss can vary widely across the range of potential operating wavelengths.
|Fiber Type||Most common
operating λ nm
operating λ nm
tests λ nm
|Other λ nm||Out of band
loss tests λ nm
|Plastic 1 mm||650||650||LED|
|PCS 200u||650||850||650 / 850||LED|
|Glass multimode 50/125, 62.5/125||850||1300||850 / 1300||LED||1270 - 1610 CWDM|
|Glass single mode 9.5/125, Traditional||1310||1550||1310 / 1550||Laser||>1580|
|Glass single mode 9.5/125, DWDM||C band
1525 - 1565
1570 - 1610
|1550 / 1610||Laser||S band
≈ 1420 - 1530
|Glass single mode 9.5/125, CWDM||1310, 1490, 1550||1270 - 1610||1310, 1490, 1550||Laser||1383||1625|
It has been standard practice for many years to perform single mode fiber tests at 1550 nm (in addition to 1310 nm), to help find identify cabling stress points. Typically, a kinked cable may pass at 1310 nm, but fail at 1550 nm or beyond.
Laser sources are unsuitable for work on multimode fiber, since very unstable power meter readings are obtained. For optimum multimode accuracy, a mandrel wrap and a LED source with standards compliant characteristics are required.
C band systems may only be loss tested at 1550 nm. C & L band systems are typically loss tested at 1550 / 1625 nm. The S band is currently somewhat ill-defined, and may run into the fiber water absorption peak, so loss measurement will need to be at the shortest relevant wavelength, and 1550 nm.
Attenuation in CWDM systems is usually measured at only a few wavelengths, and varies quite substantially depending on the application and fiber type. The water absorption peak at 1383 nm may require evaluating, and a selected "1383 nm" laser is needed for this task. Most current systems avoid the water peak wavelength area due to this potential loss problem. Loss checking of passive CWDM channel filters requires specific CWDM compliant light sources.
"Out of band" single mode
Has been traditionally specified as "1625" nm. This has traditionally used Fabry-Perot lasers with poor spectral accuracy. New DFB lasers have much better properties for this application, since their actual operating wavelength is more tightly controlled (see table below). For true WDM compliance, the out of band wavelength must be <1620 mn.
There is also an emerging class of "1650" nm OTDRs, however their usually poor wavelength accuracy and high cost makes them less useful.
|Laser Type||Center λ Tolerance
@ 25 °C
Range @ 25 °C
|Typ Center λ
/ °C coefficient
Range 0 - 50 °C
|Typ λ Width
|Total λ Range
0 - 50 °C, FWHM
|1310 nm||Fabry-Perot||± 30 nm||1280 - 1340||± 0.4||1270 - 1350||3||1268.5 - 1351.5||Ge or InGaAs|
|1550 nm||Fabry-Perot||± 30 nm||1520 - 1580||± 0.4||1510 - 1590||3||1508.5 - 1591.5||Ge or InGaAs|
|CWDM||DFB||± 3 nm||1270 - 1610 nm||± 0.1||±5.5 nm||0.1||InGaAs|
|1610 nm||DFB||± 3 nm||1607 - 1613||± 0.1||1604.5 - 1615.5||0.1||1604.5 - 1615.5||InGaAs|
|1625 nm||DFB||± 5 nm||1620 - 1630||± 0.1||1617.5 - 1632.5||0.1||1617.5 - 1632.5||InGaAs|
|1625 nm||Fabry-Perot||± 30 nm||1595 - 1655||± 0.4||1585 - 1665||3||1583.5 - 1667.5||InGaAs|
|1650 nm||Fabry-Perot||± 30 nm||1620 - 1680||± 0.4||1610 - 1690||3||1608.5 - 1691.5||InGaAs|
This illustrative graph shows how typical single mode fiber attenuation varies with wavelength. It may not be exactly accurate
Modern fibers may have a negligible water absorption peak at 1.38 µ
Wavelength uncertainly of tests above 1600 nm can have a major impact on loss measurement
This application note assists in the following application areas...
Single mode fiber
Fiber Optic Test equipment for high bandwidth or long distance telecommunications testing.
Fiber optic test equipment for in-building LAN, ethernet, campus, industrial & education applications.
CWDM / DWDM systems
FO Testers for DWDM, CWDM & SWDM4 systems. Solutions for wavelength selective optical loss testing with WDM calibrations and features, and a broadband variable optical attenuator.
MPO (MTP™) and ribbon fiber
Unparalleled flexibility and test accuracy for high bandwidth data center, enterprise, 5G and WAN applications. Test single mode and multimode networks.
PON / FTTx systems
Simple, cost effective PON / GPON / XGPON testers for last mile passive optical networks (e.g. for fiber to the home FTTH / FTTX equipment). Kingfisher's GPON test equipment is proven to help a smooth installation roll-out and ongoing FTTH fiber support.
Plastic optical fiber (POF, PCS, HCS, PMMI)
Test 1 mm plastic optical fiber, hard-clad or polymer-clad silica fiber (POF, PCS & HCS). Bare plastic fiber and many connector types supported.
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