In this review, we report the results of numerical investigations of the dynamical behavior of an integrated device composed by a semiconductor laser and different cavities that provide optical feedback. Due to the influence of the feedback, under the appropriate conditions the systems display chaotic behavior appropriate for chaos based communications. The optimal conditions for chaos generation are identified. It is found that the longitudinal double cavity feedback requires lower feedback strengths for developing high complexity chaos as compared with a single cavity. The synchronization of two unidirectional coupled (masterslave) systems and the influence of parameters mismatch on the synchronization quality are also studied. Examples of message encoding and decoding within chaos modulation technique for longitudinal double cavity optical feedback are presented and discussed. We find that the resynchronization time for the T-like double cavity optical feedback scheme can be two orders of magnitude shorter as compared with that of the single-cavity feedback case. Very good conditions for message encoding by using the on/off phase shift keying encryption method are identified, and examples of message encoding/decoding are presented.