Power margin of a fiber-optic system

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SUMMARY

The discussion focuses on calculating the power margin of a fiber-optic system using specific parameters: transmitter power of -10dBm, connector loss of 1.5dB, attenuation of 3dB/km, total length of 2km, and a receiver threshold of -30dBm. The power budget is calculated as PB = Pt - Pr, resulting in 20dB. The power margin is derived from PM = PB - Total losses, leading to a calculated value of 12.5dB after correcting the subtraction error. The confusion arises from an incorrect reference answer of 9.5dB, which was clarified by participants in the discussion.

PREREQUISITES
  • Understanding of fiber-optic terminology, including transmitter power and receiver threshold.
  • Familiarity with decibel (dB) calculations and conversions.
  • Knowledge of power budget calculations in optical systems.
  • Ability to apply attenuation formulas in fiber-optic contexts.
NEXT STEPS
  • Review fiber-optic power budget calculations in detail.
  • Study the impact of connector loss on overall system performance.
  • Learn about different types of fiber-optic attenuation and their effects.
  • Explore common errors in dB calculations and how to avoid them.
USEFUL FOR

Students studying fiber optics, optical engineers, and professionals involved in designing or troubleshooting fiber-optic communication systems.

MattH150197
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Homework Statement


Im going over some revision for fibre optics and I've come across an example question to calculate the power margin of the system with the following info is given:
transmitter power = -10dBm
Connector loss = 1.5dB
Attenuation = 3dB/Km
Total length= 2KM
Receiver threshold = -30dBm

Homework Equations


Power budget = Pt - Pr
Power Margin = PB - Total losses

The Attempt at a Solution


PB = -10 - - 30 = 20
PM = 20 - ((3*2) + 1.5)) = 13.5dB
However it says the answer is 9.5dB, i didnt write the formulas wrong did i when i was making notes or can you see where I've gone wrong anywhere?
 
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If you have written the problem correctly and completely, then I agree with your result and suspect that the "answer" is wrong.
 
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MattH150197 said:
PM = 20 - ((3*2) + 1.5)) = 13.5dB
Should be 12.5 dB. Unfortunately still not 9.5dB.
 
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Oops right, I didn’t subtract that properly in my head!
 
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I'd like to know how the given answer was obtained if you ever find out.
 
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  1. Oops! Sorry yeah I meant 12.5, I really have no idea where 9.5dB has come from and it was really frustrating why I was getting different. So thanks for clearing it up guys!
 

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