To calculate the pulse spreading caused by material dispersion, we need to consider the following formula:

$\text{Pulse Spreading} = \frac{D \cdot \Delta \lambda \cdot L}{c}$

Where:

• $D$ is the material dispersion coefficient, typically in $\text{ps}/\text{nm·km}$.
• $\Delta \lambda$ is the spectral width of the light source (in nm).
• $L$ is the length of the fiber (in km).
• $c$ is the speed of light in the fiber (approximately $3 \times 10^8$ m/s).

1. Pulse Spreading for the Laser Diode:

For a laser diode with a 3.5 nm spectral width, the dispersion coefficient $D$ depends on the wavelength of operation. Without the fiber length and dispersion coefficient, we can calculate the spreading relative to given conditions but not an absolute value.

2. Material-Dispersion-Induced Pulse Spreading for the LED:

For the LED with an 85 nm spectral width at 1650 nm:

• The dispersion coefficient $D$ at 1650 nm can be approximately $15 \, \text{ps}/\text{nm·km}$.

Using this, the formula becomes:

$\text{Pulse Spreading} = \frac{15 \, \text{ps}/\text{nm·km} \times 85 \, \text{nm} \times L \, \text{km}}{c}$

This simplifies to:

$\text{Pulse Spreading} = \frac{1275 \, \text{ps/km} \times L}{c}$

Given that the actual length $L$ and speed of light are constants, the formula can be directly applied with the length of the fiber if known.

Would you like a more detailed calculation based on specific fiber length or have any questions about this concept?

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Related Questions:

1. How does material dispersion vary with wavelength in optical fibers?
2. What are the key differences between LED and laser diode sources in fiber optics?
3. How does pulse spreading affect the performance of optical communication systems?
4. Can material dispersion be mitigated in fiber optic systems?
5. How does the spectral width of a source influence signal integrity in long-haul fiber optics?

Tip:

Understanding how dispersion affects pulse spreading is crucial in designing high-speed optical communication systems. The wider the spectral width of your light source, the more significant the pulse spreading.