Abstract
Variable-polarization optical feedback (VPOF) induced
unpredictability enhancement in a vertical-cavity surface-emitting
laser (VCSEL) is investigated numerically based on the spin-flip
model. The chaotic unpredictability is evaluated quantitatively via
an information-theory-based quantifier, the permutation entropy
(PE). The role of polarizer angle on the chaotic unpredictability is
focused on. The influences of feedback strengths, feedback delays,
and injection currents are also considered. A critical polarizer
angle, at which the PE reaches its maximum, is existed for
relatively high feedback strength and injection current. The
representations on Poincaré sphere are further given to provide
physical insight into the unpredictability enhancement. Besides,
larger feedback strength leads to lower critical polarizer angle,
while larger injection current contributes to higher critical
polarizer angle. These results show that, by selecting critical
polarizer angles, the unpredictability of chaotic signals of VCSELs
with VPOF can be enhanced significantly, which is extremely useful
for VCSELs-based chaotic communication systems.
© 2011 IEEE
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