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160 Fiber Optic Communications

Power transmission P 0 P 0 P out 11 0 1 0 1

–5V /4 –V π /4 0 V /4 5V /4 Message voltage t
π
π
π
1
1
0
1
0
1
t
Figure 4.20 Power transmission function of the MZM. V = V ∕2.
bias
Polar RZ signal
1 0 1 1 1
t
Power 1 0 1 1 1
RZ-ASK signal

Field MZM t
Laser
t
(a)
Polar NRZ signal
1 0 1 1 1 Power 1 0 1 1 1
Power 1 0 1 1 1
t
t
t RZ pulse
carver
Field
Laser MZM
t
(b)

Figure 4.21 Generation of RZ-ASK. (a) Using RZ signal in electrical domain. (b) Using RZ pulse carver in optical
domain.

4.7.2 Phase-Shift Keying

The optical field envelope of the MZM output can be written as (Eq. (4.55))
[ ]
m(t) V bias
A = A cos − . (4.82)
out 0
V 2V