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What is a good dB level for fiber?
Knowledge Base + 2023.12.08

The acceptable dBm for fiber optics is typically between -10 dBm and -25 dBm. However, it is important to note that the optimal dBm level can vary based on the specific fiber optic system and network requirements.

As a comparison, here are some typical reflectances:

  • Fiber end with flat cleave: -14 dB

  • Good multimode PC connection: -35 dB or lower

  • Good singlemode PC connection: -50 dB or lower

  • Good angle-polish connection: -60 dB or lower

  • Good fusion splice: -60 dB or lower

There is a limit to the range of values that can be measured for optical reflectance. The maximum optical reflectance is limited by where the signal saturates at the top of the trace. The minimum optical reflectance is limited by where the signal is too small relative to the noise to be detected. Likewise, ORL is limited when any part of the signal saturates or the entire trace is not captured (such as when there is insufficient dynamic range).

The limits listed are typical. The range for measuring optical reflectance depends on a number of factors wavelength, pulse width, backscatter coefficient, attenuation, and dynamic range.

The limits listed in the table are based on using the default FOTP-8 values for backscatter coefficient. Using different values should not affect the maximum limits much if the backscatter coefficient value is accurate for the fiber being tested and the backscatter level is at least 2 dB below the saturation level (top of the trace).

For the minimum limit of the reflectance, the backscatter coefficient has a direct impact, as can be seen by comparing 62.5 mm to 50 mm fiber. However, as the backscatter level nears the noise floor (bottom of the trace), increased noise limits the detection of small reflections.

The term near-end implies negligible fiber attenuation, which is expected for reflections near the OTDR port (say, within 100 meters) with good connections and low insertion loss and little fiber attenuation. At longer distances, higher reflectances can be measured. As an extreme example, for single-mode fibers using the widest pulse width (1000 ns), a reflection that has its backscatter level near the noise floor could be measured as high as about -20 dB. However, when the backscatter level is within 5 dB above the noise floor, smaller reflections become hidden in the noise. Reflections at the noise floor level have a minimum limit as much as 7 dB higher than listed in the table. 

How to Choose an Ethernet SFP Module?

Choose SFP Copper or Fiber Module?

SFP module comes in various types on the basis of different classification standards. It works with copper Ethernet cables or fiber optical cables.

On the fiber optics side, there are single mode SFP module and multimode SFP module, which allows users to select the appropriate transceiver according to the required optical range for the network. Operation wavelength ranges from 850nm to 1550nm. Commonly, 850nm SFP can reach up to 550 meters with multimode fiber optics, and the 1550nm SFP supports up to a maximum of 160km via single mode fiber cables. On the other hand, copper SFP modules primarily are 1000BASE-T SFP and 1000BASE-TX SFP modules, which are excellent used in gigabit Ethernet networking within 100 meters.

Choose SFP or Advanced SFP+?

SFP and SFP+ are applied at different transmission speeds. SFP module supports 1Gb data rate, and the SFP type includes 1000base-T/TX, 1000base-SX, 1000base-LX/LX10, 1000base-BX10, 1000base-LX/LH, 1000base-EX, 1000base-ZX and so on.

SFP+ is used in 10-gigabit Ethernet applications but shares the same form factor with SFP. In the SFP+ family, there are primarily SFP+ SR, SFP+ LR, and SFP+ ZR modules for 10 Gigabit ethernet networking.

Choose an MSA Compatible SFP or Not?

Compatibility is often the most important parameter users care about when buying an MSA SFP module. MSA (multi-source agreement) is an agreement supported by a number of manufacturers who came together to collaborate and standardize the fit-form and try to provide a reliable mean of mixing and matching SFP brands successfully. Third-party companies also have developed their own tools to program SFP modules to be compatible with the OEM. So, the MSA compatibility Gigabit SFP module can be used successfully in most networks.

SFP vs. SFP+

Here is a table of comparison between SFP and SFP+




Stands for

Small Form-factor Pluggable

Small Form-factor Pluggable plus (standard form)

Data rate







Dual fiber

Single Fiber/WDM



Dual fiber

Single Fiber/WDM