Optical Power Bidget Calculation

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Question	How do I calculate the Optical Power Budget?
Question Type	Application
Updated	Feb 27,2008
Hits	797
Products	SFP-1G Series, EDS-510A Series, EDS-726 Series, EDS-518A Series, EDS-516A Series, EDS-505A/508A Series, EDS-405A/408A Series, EDS-316 Series, EDS-309 Series, EDS-P308 Series, EDS-305-M12 Series, EDS-305/308 Series, EDS-205/208 Series, ED6008, EDS-405, EDS-50/505, OS5008, EDS-728 Series, PT-7

Solution

Optical power budget is term used to describe total amount of light energy amplitude available over a certain link path. The budget can be determined by subtracting the Receiver Sensitivity from the Optical Output Power. The optical budget serves as a useful estimation to determine if sufficient optical output power remains on the receiver side of an optical link. The optical power budget also refers to the allocation of available optical power (transmitted into a given fiber by a given source) among various loss-producing mechanisms.

The loss is caused by various factors. Typical losses are caused by fiber attenuation (per km), slice attenuation (per slice), and connector attenuation (per connector pair).

[Suggestions]

1. Power Budget = (Output / Launch Power) - (Receiver Sensitivity)
2. Worse case Optical Power Budget = (Min TX power) - (Max RX sensitivity) - (LED aging factor) - (insertion loss)

We'll use the following values to illustrate:
Min Tx Power = -9.5 dBm
Max Rx Sensitivity = -20 dBm
Estimated LED aging = 1 dB
Estimated Insertion loss = 1 dB

3. Therefore:
Optical Power Budget = (-9.5 dBm) - (-20 dBm)
Maximum Allowable Loss = 10.5 dB

4. Worst case OPB = Power Budget - Total Optical Power Loss =>
10.5 dB - 1dB (for LED aging) - 1dB (for insertion loss) - 1 dB (for per connector pair) - 2dB (safety factor) = 5 dB

5. Worst case distance = {Worst case OPB, in dB} / [Cable Loss, in dB/Km]

The Optical Power Budget is based on a theoretical calculation, and is for reference only. We still strongly recommend that you perform on-site testing to verify the result. On the data sheet, the supported fiber transmission distances are stated on each switch, with fiber port orSFP fiber modules. The customer can select the desired model without performing the power budget calculation.