EE 230
Optical Fiber Communications
Homework 4
1. SMF-28 fiber has a dispersion of 17 ps/nm-km at 1550 nm. Type A dispersioncompensating fiber has D= -98 ps/nm-km; Type B has D= -134 ps/nm-km. (a)
What is β2 for each type of fiber? (b) How much of each type of DCF would be
needed to compensate the dispersion from an 80-km link of SMF-28?
2. SMF-28 has a dispersion slope of 0.057 ps/nm2-km, while that of Type A DCF is
0.1 and that of Type B is -0.2 ps/nm2-km. (a) What is β3 for each type of fiber?
(b) Which type of DCF will do a better job, using the lengths determined above,
for a wavelength 7 channels away, on each side, from 1550 nm at a spacing of
100 GHz in a WDM system?
3. If the nonlinear index n2 of SMF-28 fiber is 3.18x10-20 m2/W, what should the
core radius be changed to in order to use this fiber in a soliton system with 25 ps
pulses at 1550 nm with a power of 3 dBm? The NA of this fiber is 0.13. Is this a
practical approach?
4. The C and L spectral bands cover a wavelength range from 1.43 to 1.61 µm. How
many channels can be transmitted through WDM when the channel spacing is 25
GHz? What is the effective bit rate-distance product when WDM signals
covering the two bands are transmitted over 2000 km at 10 Gb/s?
5. A 2x2 fiber coupler has 2.6 dB insertion loss for output 1 and 4.8 dB for output 2.
(a) Determine the output powers for fibers 1 and 2 if the input power is 2 mW.
(b) Determine the excess loss of the coupler. (c) Determine the splitting ratio.
6. A 2x2 waveguide coupler has =0.4 mm-1, α=0.06 mm-1. Neglecting excess loss,
how long should the coupling region be to make it a 3 dB coupler? If the length is
doubled, what fraction of the input power emerges from the second channel?
7. Using 2x2 Mach-Zehnder interferometers, design an 8x1 multiplexer for a
channel spacing of 25 GHz. Let the shortest wavelength be 1550 nm. Assuming
that the effective index of refraction is 1.45, specify L for each MZ.