Problem #$2$: An optical fiber with a core diameter $8$ microns and cladding diameter $125$

microns. The refractive index of core is $1\mathrm{.}449$ and the refractive index of cladding is $1\mathrm{.}445.$

The operational wavelength is $1\mathrm{.}55$ micron. Please calculate

$($a$)$ Acceptance angle

$($b$)$ Numerical aperture of the fiber

$($c$)$ Is this single mode or multimode? Why?

Problem #$3$: An optical fiber with a core diameter $50$ microns and cladding diameter $125$

microns. The refractive index of core is $1\mathrm{.}449$ and the refractive index of cladding is $1\mathrm{.}445.$

The operational wavelength is $1\mathrm{.}55$ micron. Please estimate the number of modes in this

optical fiber.

Problem #$4$: An optical fiber has an input power $10$ mW$.$ The absorption coefficient of the

fiber is $0\mathrm{.}25$ dB$/$km$.$ Please calculate the output power after traveling $50$ km$.$

Problem #$5$: Please describe the working principle of voice link fiber optic system.