For normal fiber broadband, the ideal range of light attenuation is -20dBm to -25dBm. For speeds up to 200M, the light attenuation must be less than -25dBm. With light attenuation at -27dBm, speeds are limited to a maximum of 100M, and with light attenuation at -28dBm, speeds are limited to a maximum of 50M.

What is light attenuation?

Light attenuation generally refers to its luminous flux, when charging the surface of the photoconductor drum, with the accumulation of charge on the surface of the photoconductor drum, the potential also continues to rise, and finally reaches the "saturation" potential, which is the highest potential. Surface potential will decline over time, the general work of the potential are lower than this potential, the potential with time to naturally reduce the process, called the "dark decay" process.

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Photoreceptor drum by scanning exposure, the dark area potential is still in the dark decay process; bright area of the photoconductive layer of carrier density increases rapidly, conductivity rises rapidly, the formation of the photoconductive voltage, the charge disappears rapidly, the surface potential of the light conductor is also a rapid decline. Called "light decay".

Fiber attenuation calculation

Some customers in the use of optical fiber, often encounter packet loss phenomenon, equipment detection is normal, and finally found that the fiber attenuation is caused by too large. So how is the fiber attenuation calculation?

1, ODN full attenuation accounting:

According to the worst value method for transmission index accounting, the transmission distance between EPON OLT-ONU should meet the following formula:

Fiber attenuation coefficient * transmission distance + optical splitter insertion loss + the number of active connectors * loss + fiber optic cable line attenuation richness ≤ EPON R/S-S/R points allow the maximum attenuation.

2.EPON R/S-S/R point attenuation range:

OLT PON port transmit optical power 2dB~7dBm, receive optical sensitivity -27dBm;

The ONU transmits optical power of -1dBm~4dBm and receives optical sensitivity of -24dBm;

Considering the 1dB optical channel cost, the maximum allowable attenuation between R/S-S/R of the EPON system is:

Uplink (ONU-OLT, 1310nm): 25dB;

Downstream (OLT-ONU, 1490nm): 25dB;

3. Fiber attenuation factor (including fixed fusion loss):

Uplink (ONU-OLT, 1310nm): 0.4 dB/km

Downstream (OLT-ONU, 1490nm): 0.3 dB/km

4. The typical values of splitter insertion loss (uniform splitting, excluding connector loss) are shown in the table below:

Type Specification Insertion loss (dB)

FBT 1x2 ≤3.6

FBT 1x4 ≤7.3

PLC 1x8 ≤10.7

PLC 1x16 ≤14.0

PLC 1x32 ≤17.4

PLC 1x64 ≤21.6

5、Active connector loss: 0.5dB per live connector connection loss;

6, fiber optic cable line richness:

Transmission distance ≤5km, take 2dB

Transmission distance ≤10km, take 2~3dB

Transmission distance > 10km, take 3dB

7. Considering the above factors, the transmission distance between OLT-ONU can be derived;

Fiber attenuation: 0.36 dB /km at 1310nm wavelength

Splitter insertion attenuation value: 1:64 optical splitter to take 14.0 dB

No. Name Unit Quantity Attenuation value (dB)

1 Fiber optic cable km 1.00 0.36

2 Optical active connector 6 3.0

3 1:64 optical splitter 1 14

4 Fiber optic cable line richness kilometer ≤10km 2

5 Total dB -- 19.36

Note: Fiber optic cable attenuation value is taken as the attenuation of fiber optic cable length in A direction, and the attenuation value in B direction is taken as the reference value.

Additional Learning Hub Resources 

Fiber optic connector general troubleshooting methods introduced 

What are the general types of optical fiber connectors? How to clean better? 

How to Convert Multimode to Single Mode Fiber and Vice Versa for beginers guides