Components of the optical budget

1. Transmitter power (P_tx): The output power of the optical transmitter.
2. Receiver sensitivity (P_rx): The minimum optical power required by the receiver to function correctly.
3. Fiber loss (L_fiber ): The attenuation of the fiber itself, typically measured in dB/km.
4. Connector loss (L_connector): The loss introduced by connectors in the network.
5. Splice loss (L_splice ): The loss at splice points where fiber segments are joined.
6. Tap loss (L_tap): The loss introduced by fiber TAPs used for monitoring purposes.
7. Safety margin: An additional margin to account for unforeseen losses and aging of the components.

Optical budget calculation

Light Budget = P_tx - P_rx

Total Loss = L_fiber + L_connector + L_splice + L_tap + Safety Margin

The total loss should be less than or equal to the light budget for the system to function correctly.

Network TAP insertion loss

Insertion loss is the total amount of optical signal losses between two specific points in the fiber path. Every device or piece of equipment in the network path adds inherent insertion loss, measured in decibels (dB). For network TAPs, this means the maximum amount of optical loss introduced by the TAP when it is deployed on a fiber connection. In Fiber TAPs, split ratio affects insertion loss on the network and monitor ports, with a stronger signal resulting in lower insertion loss, and a weaker signal resulting in higher insertion loss. Profitap TAPs feature some of the lowest insertion loss on the market.

What influences optical budget in fiber connections

Several factors influence optical budget in fiber optic networks. These factors include:

⦿ Link distance: The length of the fiber optic link affects the amount of optical power loss experienced.
⦿ Fiber type: Different types of fiber optic cables have varying levels of optical power loss.
⦿ Launch power: The power at which the optical signal is initially transmitted.
⦿ Receiver sensitivity: The sensitivity of the receiving device to optical signals.
⦿ Connector loss: Losses at the connection points where fibers are joined or connected to equipment. Quality of connectors, alignment, and fiber cleanliness are critical factors. The presence of dust can significantly increase this type of loss, and the use of appropriate fiber cleaning equipment as well as the placement of dust caps on unused connectors helps to mitigate it.
⦿ Splice loss: Losses at the points where two fiber ends are spliced together. Proper splicing techniques are essential to minimize these losses.

Split ratios for fiber TAPs

Fiber TAPs are used to monitor optical signals in a fiber optic network without disrupting the main signal path. They split a portion of the optical signal for monitoring purposes while allowing the rest of the signal to continue along the primary path. The split ratio of a fiber TAP determines how much of the signal is diverted for monitoring and how much continues along the main path.

Split ratio:

• The split ratio is commonly expressed as percentages, with the first number representing the network output, and the second number representing the monitor output. For example, a 50/50 split ratio means that 50% of the optical signal continues along the main path, and 50% is tapped off for monitoring.
• Split ratios can vary, such as 50/50, 60/40, 70/30, etc., depending on the monitoring requirements and the network design.

Impact on light budget:

• Main path loss: The main path loss increases as the split ratio allocates more signal to the monitor port. For example, a 70/30 split introduces less loss to the main path compared to a 50/50 split.
• TAP path loss: The monitor port will typically have a signal lower than or equal to that of the main path. The sensitivity of the monitoring equipment’s receiver needs to be sufficient to handle the lower power levels of the monitor port, and is not placed too far away from the TAP. 

Example calculation: Assume a fiber TAP with a 70/30 split ratio

• Main path loss: The main path experiences a minimal loss through to the TAP, 70% of the signal is sent through on the main path.
• TAP path signal: The tap port receives 30% of the original signal, significantly lower than the main path. This can be enough for monitoring purposes, considering the monitoring tool is placed close to the TAP.

When designing a network monitoring setup, the chosen split ratio must balance the need for adequate monitoring signal strength with minimal disruption to the main signal. Properly calculating and managing the optical budget ensures that both the primary communication path and the monitoring path operate within acceptable performance levels.

Profitap 1-Link LC Fiber Optic TAP

Regeneration TAPs for signal amplification

Regeneration TAPs ensure optimal light budget inside the monitoring network. The solution for mitigating split ratio loss is using active regeneration TAPs. These devices actively regenerate the signal, meaning they can potentially amplify signals before splitting them. This feature allows for more flexible management of the light signal, including compensating for losses introduced by the TAP itself or the network environment.

Profitap LC Regeneration TAP

Practical Considerations