Synchronization of Unpredictability-Enhanced Chaos in VCSELs With Variable-Polarization Optical Feedback

The generation and synchronization of unpredictability-enhanced chaos in vertical-cavity surface-emitting lasers (VCSELs) are investigated numerically. The master VCSEL is subject to variable-polarization optical feedback. Two injection schemes, the polarization-preserved optical injection (PPOI) and variable-polarization optical injection (VPOI) are considered for the slave VCSELs. The influences of unpredictability degree on the synchronization quality and the synchronization properties of unpredictability-enhanced chaos are focused on. For the PPOI scheme, the synchronization quality is hardly affected by the unpredictability degree; high-quality synchronization can be achieved between unpredictability-enhanced chaos due to injection locking. However, for the VPOI scheme, the unpredictability degree affects the synchronization quality significantly. High degree of unpredictability leads to low synchronization quality. Only the low-unpredictability chaos can be well synchronized, while the unpredictability-enhanced chaos cannot be synchronized even with large injection strength. The achievement of unpredictability-enhanced chaos synchronization by the PPOI scheme is extremely useful for the security-enhanced VCSELs-based chaos communication systems.