EL6583 Second Take Home Midterm Exam, Dec. 1, 2015

EL6583 Second Take Home Midterm Exam, Dec. 1, 2015
1.

Give a flow chart description on how to transmit a voice message through a digital fiber optic
communication channel from a person to another person.
(30%)

2.

A grad-index fiber with n10 = 1.48 and n2 = 1.45 is used for a 100 km link of digital telephone
lines. If the laser diode (LD) emits at 1.32 µm and has a spectral width of 2 nm. The zero
dispersion wavelength is 1.3 µm. The waveguide dispersion can be neglected. Determine the
maximum voice channels this fiber can handle without multiplexing.
(35%)

3.

Twenty-five SI glass fibers (n1 = 1.48, n2 = 1.46) are spliced together. Each fiber is 2 km long
and has a loss rate 1-dB/km. Each splice adds 1 dB of loss. The system transmits return-to-zero
(RZ) digital pulses at the rate of 100 Mbps; the probabilities of transmitting “1” and “0” bits are
the same. The LD radiates at 1.3 µm, at 10 dBm average output power, and uniformly in a 60o
half cone. The photodetector has a responsivity ρ = 0.8 A/W and is connected to a 1 kΩ load
resistor.
1) What is the output voltage from each “1” bit?
2) repeat the calculation for NRZ pulses.
(35%)