Causes of dispersion in single mode fibers

Question

Answer the following questions.

Question 1) What do you mean by graded index fibers? How do they considerably reduce intermodal dispersion? What is the optimum refractive index profile parameter for minimum dispersion (or maximum BL product)?

Question 2) Usually, for single longitudinal mode Laser operation, control of longitudinal modes is essential. How do we achieve it in different laser structures?

Question 3) Write a brief note on LED structures and their characteristics.

Question 4) An APD with a multiplication factor of 20 operates at a wavelength of 1.5 μm. Compute the quantum efficiency and photocurrent from the device if its responsivity at this wavelength is 0.6 A/W and 10¹⁰ photons of wavelength 1.5μm are incident upon it per second.

Question 5) Describe the design of MSM photodetectors.

Question 6) What are the causes of dispersion in single mode fibers? Describe each of them in detail.

Question 7) Make the power budget and calculate the maximum transmission distance for a 1.3 μm light wave system operating at 100 Mb/s and using an LED for launching 0.1 mW of average power into the fiber. Suppose 1 dBlkm fiber loss, 0.2 dB splice every 2 km, 1 dB connector loss at the each end of fiber link, and 100 nW receiver sensitivity, Allow 6 dB system margin.

Question 8) What are the optical components required to implement WDM technology for optical communication systems? Explain the operational principle of each of them briefly.