Answer the following problems.

problem 1) A graded index fibre has core with a parabolic refractive profile which has a diameter of 50 μm. The fibre has a numerical aperture of 0.2. find out the total number of guided modes propagating in the fibre when it is operating at a wavelength of 1 μm.

problem 2) A photodiode has a quantum efficiency of 65 percent when photons of energy 1.5 x 10^-19 J are incident on it.

(a) Compute the wavelength at which the photodiode is operating and

(b) Incident optical power required when the current through the diode is 3μA.

problem 3) Describe the optical receiver with the help of schematic diagram.

problem 4) Describe in detail the block diagram of a receiver showing various types of noise generated giving the expression for each type of noise.

problem 5)(a) Compute the refractive indices of the core and the cladding materials of an optical fibre whose NA = 0.35 and Δ= 0.01.

(b) Describe in detail WDM systems with appropriate diagrams.

problem 6)(a) Compute for both single mode and multimode fibres, the critical radius of curvature at which large bending losses occur in a step index fibre of core refractive index of 1.45 and relative index difference of 3% at an operating wavelength of 1.5 μm and core radius of 5 μm.

(b) Describe in detail the operation of small signal modulation.