OTDR Wavelength : Complete Information

OTDR Wavelength : OTDR Wavelength 850 nm, 1300 nm, 1310 nm, 1550 nm and 1625 nm detail information will be provided by this article. The behavior of an optical system is directly related to the wavelength transmission. Not only optical fiber will exhibit various loss characteristics at different wavelengths, but the value of splice losses will also vary wavelength.

In general, the fiber should be tested with the same wavelength as that used for transmission. This means 850 nm and/or 1300 nm for multi-mode systems, and 1310 nm and/or 1550 nm and 1625 nm for single-mode systems.

OTDR wavelength Optical fiber testing

Why need 1310 nm, 1490 nm 1550 nm, and 1625 mm testing

Parameters of OTDR wavelength

If the test is to be done at only one wavelength, the following Parameters need to be considered:

Dynamic range, 1550 nm OTDR wavelength used for the longer distances, 1550 nm wavelength is used to measure the distance over approx 40 KM optical fibers. But 1310 nm wavelength used for the short distances. For ease we can say that 1310 nm wavelength used for the measurement of less than 40 KM distances.Used to measure distance due to the lower attenuation in the fiber. For details mentioned below-

➤If you measure the optical fiber at the range of 1310 nm wavelength, you will get 0.35 dB / Km loss. It means approximately 01 dB of signal is lost every 3 Km.

➤If you measure the optical fiber at the range of 1550 nm wavelength, you will get 0.2 dB / Km loss. It means approximately 01 dB of signal is lost every 5 Km.

We all know that single mode optical fiber has larger mode field diameter at 1550 nm than 1310 nm wavelength but larger mode of fields are less sensitive to lateral offset during splicing. But more sensitive to bending loss during installation or in the cabling process.

I will show diagrammatically below that  1550 nm is more sensitive to bends in optical fiber than1310 nm wavelength. This can also be termed as macrobending.

Splice and connector losses generally measure at 1310 nm,losses will be more in compare at 1550 nm These results come from a Corning study of over 250 splices where the 1310 nm values were shown to be typically higher by 0.02dB over the 1550nm values for dispersion-shifted fiber.

Bending radius 

Sensitivity to bending radius

OTDR Wavelengths 1310 nm, 1490 nm, 1550 nm and 1625 nm.

Whenever we talk about optical fiber measurement, the first thing that comes to our mind is at which wavelength optical fiber to be measured. Why we all think like this? We can measure optical fiber by setting any wavelength range in the OTDR but it does not.

We select certain wavelengths like-1310 nm, 1490 nm, 1550 nm and 1625 nm. We will discuss in this article why we select this particular wavelength.

Typically we use an OTDR that supports 1310 and 1550 nm to confirm splitting losses, fiber attenuation rates, discrete reflectors and fiber lengths. On the range of OTDR wavelength 1310 nm and 1550 nm  , we get information on the exact splice loss and connector loss.

OTDR users generally used the two-wavelengths provide the best balance of functionality and value. OTDR testing at 1310 nm and 1550 nm is normally sufficient to certify point-to-point or FTTx PON fibers and allows the detection of macro bends. Very easy for the detection of macro bends at the OTDR wavelength 1310 nm and 1550 nm.

The biggest thing is that fiber specifications such as bend and loss (in dB / km) are currently required by international standards for various fiber types at only 1550 nm. 1310, 1550, and 1625 nm is required for DWDM testing (which usually also goes up to the 1600 nm range), however, a three-lambda OTDR that performs tests at . In the DWDM for the C-band measurement which range is 1530-1565 nm,the best window is 1550 nm.

The wavelength 1625 nm or 1490 nm also used respectively for DWDM or FTTx network. Infect testing at 1625 nm allows testing of the L band(1565 – 1625 nm). 1490 nm testing is required by some network operators to certify FTTx PONs. Some special type of OTDR certify dark fibers at 1310/1550 nm, fault locate live FTTx PON fibers at 1625 nm, and measure FTTx power levels at 1490 and 1550 nm, all from a single test port.

For the optical fiber measurement OTDRs are one of the best tools to detect and locate the bends of a fiber link (the three traces at 1310, 1550 and 1625 nm. The bending effect in optical fiber is not something new problem. When 1550 nm wavelength was first introduced and added to the 1310 nm transmission wavelength, the bending effect had to be analyzed. Many optical fiber reports with, for example, 1550 nm splice losses compared with 1310 nm splice losses, in order to detect possible bending effects are still to be seen. Now with the 1625 nm wavelength, a similar picture emerges.

During the measurement environmental temperature generates more problems at 1625 nm than for lower wavelengths. This temperature induced cable loss (TICL) can be detected at 1625 nm more than at any other wavelength. This will generate more losses in the optical fiber cable. However, this effect is usually very low compared to other parameters.

It becomes clear that if the L band (and U band of course) is used, then loss test in transmission becomes necessary upper wavelength band range. This is the reason that new testing equipment is starting now 1625 nm test. We must do this for the right result.

In last I would like to mention the DWDM transmission window bands details.Might make you easier to understand.

DWDM transmission window

Starting with C band area (1530- 1565 nm), the wavelength band is limited mainly by equipment manufacturer of pure optical amplifiers And the operators now want to expand this band to other areas. you can see below the list of possible bands to be used:

1260 – 1360 nm - O Band

1360 – 1460 nm - E Band

1460 – 1530 nm - S Band

1530 – 1565 nm - C Band

1565 – 1625 nm - L Band

1625 – 1675 nm - U Band

Last Word

Why do we use different wavelength for optical fiber measurements. I have tried to give you complete information about it. When and why we use wavelength 1310 nm, 1490 nm 1550 nm, and 1625 mm for the measurement of optical fiber is also mentioned. It is also mentioned what information we get if we measure the optical fiber at different wavelengths 1310 nm, 1490 nm 1550 nm, and 1625 mm. If you are satisfied with the information given by me then please like and share my page.Stay with me for similar information.