  Time-delayed optical feedback is known to trigger a wide variety of complex
dynamical behavior in semiconductor lasers. Adding a second optical feedback
loop is naturally expected to further increase the complexity of the system and
its dynamics, but due to interference between the two feedback arms it was also
quickly identified as a way to improve the laser stability. While these two
aspects have already been investigated, the influence of the feedback phases,
i.e. sub-wavelength changes in the mirror positions, on the laser behavior
still remains to be thoroughly studied, despite indications that this parameter
could have a significant impact. Here, we analyze the effect of the feedback
phase on the laser stability in a dual-feedback configuration. We show an
increased sensitivity of the laser system to feedback phase changes when two
feedback loops are present, and clarify the interplay between the frequency
shift induced by the feedback and the interferometric effect between the two
feedback arms.
