
189Optical Direct and External Modulation
Optical input
Optical output (signal)
Splitting
Bias T circuit
LN modulator
Driver
Electrical signal
DC bias
input circuit
Bias control
circuit
Photo diode (PD)
Feedback operation
FIGURE 5.35
Arrangement
of bias control by feedback signals from optoelectronic detector fed by tapped optical waves at
the output of the MZIM.
n
Z or C-axis
Z
X
Z-cut Y-prop
(a)
n
o
n
e
Z
Y
Z-cut X-prop
n
o
(b)
n
e
Z
X
Y
X-or Y-cut Z-prop
n
o
(c)
FIGURE 5.36
Refractive
index contours of LiNbO
3
uniaxial crystal with Z or C denoting as the principal axis: (a) lightwaves
propagation in the Z-axis polarize along Y-cut LiNbO
3
, (b) propagation direction Z-axis and X-c