They provide incredibly powerful communication signals with high bandwidths and great reliability. The value greater than zero indicates that the link has sufficient power for transmission.As we all know, fiber optic lines are complicated, powerful, and delicate. Take the 10km SMF case as an example, the power budget is 13dB and the link loss is known as 6.8dB, thus the safety budget is 13dB - 6.8dB = 6.2dB. The formula is P M = P B - LL.įigure 2: Power budget, link loss, and power margin It represents the amount of power available after subtracting link loss from the power budget. Suppose the average transmitter output power is -15dBm, the receiver sensitivity is -28dBm, the power budget will be -15dB - (-28dB) = 13dB.Īfter calculating the link loss and power budget, you can calculate the power margin, which is also referred to as safety margin. The calculating formula is P B = P T - P R. The power budget (P B) is calculated as the result of the difference between the sensitivity of the receiver (P R) and the output of the transmitter into the fiber (P T). ![]() The link will operate normally only when the link loss is within the loss budget. It is used for comparison with the calculated total loss to ensure the cable plant is installed properly. How does this link loss value matter for the whole transmission? Here we have to mention another closely related term - power budget. Note that the estimates are just assumed, the easiest and most accurate way is to use OTDR trace of an actual link. The total loss for this link is 5dB + 1.5dB + 0.3dB = 6.8dB. ![]() Use the TIA/EIA maximum loss as 0.3 per splice and the total splice loss is 0.3dB × 1=0.3dB.Ĭalculate the other component loss if there are any other components such as attenuators.Īdd the cable loss, connector loss, and splice loss and get the total link loss. In practical calculation, the actual connector loss can refer to the value in the fiber optic cable specifications provided by suppliers.Ĭalculate the total splice loss. Use the TIA/EIA maximum loss per pair as 0.75 and the total connector loss is 0.75dB × 2 =1.5dB. According to the standard chart above, the light attenuation of 1310nm SM outside optical fiber cable is 0.5dB/km, therefore the total cable attenuation is 0.5dB/km × 10km = 5dB.Ĭalculate the total connector loss. The cable has 2 ST connector pairs and 1 splice.įigure 1: Calculate link loss over 10km SMFĬalculate the fiber cable attenuation loss. There is a single mode fiber optic cable installed between two buildings, with a distance of 10km and the optical wavelength of 1310nm. Let’s take a practical case as an example to demonstrate the calculation steps. ![]() It must be noted that the total loss calculated in this way is just an estimation that assumes the possible values of component losses so the actual loss could be higher or lower depending on various factors. Splice Loss (dB) = Number of Splices × Splice Loss Allowance (dB)Īs these formulas show, the total loss is the maximum sum of the worst variables within a fiber segment. The Total Link Loss = Cable Attenuation + Connector Loss + Splice LossĬable Attenuation (dB) = Maximum Cable Attenuation Coefficient (dB/km) × Length (km)Ĭonnector Loss (dB) = Number of Connector Pairs × Connector Loss Allowance (dB) First, you should be aware of the fiber loss formula: ![]() It is often the case to calculate the maximum signal loss across a given fiber link during optical cable installation. To detect whether the link runs properly, the following calculation should be performed. How to Calculate Losses in Optical Fiber?
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