EE 164
Problem Set 9
Spring 2005
Problem 1:
A four-port directional coupler has a 4:1 splitting ratio and an excess loss equal to
2 dB.
The coupler’s directionality is 40 dB.
a)
What fraction of the input power goes to each of the ports?
b)
Compute the throughput loss and the tap loss.
c)
Compute the loss (in decibels) due to radiation, scattering, and absorption in the
coupler.
Problem 2:
A laser diode illuminates a 2.5 km length of fiber. The total link loss over the 2.5
km is 4 dB. Power is reflected back toward the laser by the end of the fiber, which
is cleaved so as to have a smooth, polished surface. The fiber end radiates into air.
Compute the level of the reflected light power when it returns to the LD- that is
how many decibels down from the emitted signal is the reflected signal?

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Problem 3:
An ideal tapered and fused single-mode coupler is used as a two-wavelength