The maximum digital transmission rates for unipolar return-to-zero data transmissions over an optical fiber 10-km long with specified pulse-spreading constant of 10 ns/km is : 

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  1. 5 Mbps
  2. 10 Mbps
  3. 20 Mbps
  4. 25 Mbps

Answer (Detailed Solution Below)

Option 2 : 10 Mbps
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Concept:

The maximum digital transmission rate over an optical fiber is limited by pulse dispersion, which spreads the signal in time and can cause inter-symbol interference (ISI).

For Return-to-Zero (RZ) data transmission, the bit interval must be at least equal to the total pulse spreading to avoid overlap between bits.

Calculation:

Given:

Fiber length = 10 km, Pulse spreading constant = 10 ns/km

Total pulse spread = \(10~\text{km} \times 10~\text{ns/km} = 100~\text{ns}\)

In unipolar RZ transmission, the maximum bit rate is the reciprocal of the bit period.

\( \text{Bit rate} = \frac{1}{\text{Bit interval}} = \frac{1}{100~\text{ns}} = 10~\text{Mbps} \)

 

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