We experimentally and numerically report on polarization switching (PS) mechanism which involves a two-mode limit
cycle dynamics in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection from a master
laser (ML). The VCSEL (slave laser, SL) emits a horizontal linearly polarized (LP) fundamental mode, without optical
injection. The VCSEL is injected by a vertically polarized light from ML. Dynamical characteristics of the VCSEL are
investigated as a function of optical injection parameters, i.e., injection strength and frequency detuning between master
and slave lasers. We experimentally resolve an injection parameter region for which, as the injection strength is
increased for fixed detunings, a limit cycle dynamics in both non-injected and injected modes is abruptly excited. For
larger injection strengths, the VCSEL switches from the two-mode to a single-mode limit cycle dynamics which
involves only the injected mode. Using continuation methods, we numerically identify two torus bifurcation
mechanisms, namely TR1 and TR2, which support such a switching scenario. We show that both TR1 and TR2 originate
from a particular Hopf bifurcation which plays a key role in the polarization dynamics of the injected VCSEL.
Furthermore, our results reveal that the newly observed switching dynamics are generic features of VCSEL two-mode
systems.
We use an asymptotic method to simplify the rate equations for a semiconductor laser subject to filtered optical feedback. The simplified equations provide insights on the physical mechanisms involved in two different oscillatory instabilities, namely: relaxation oscillation undamping, and the onset of optical frequency oscillations. We proceed to an analytical stability analysis of the external cavity modes and determine simple scaling laws for their stability boundaries in parameter space. We also point out a couple of remarkable properties of the frequency oscillation regime; in particular, we draw analogies with a related dynamical response predicted for semiconductor lasers subject to both conventional feedback and optical injection.
We study analytically the bifurcations of phase-locked emission modes of a semiconductor laser subject to both optical feedback and CW optical injection. The theory is valid for a large external cavity and for weak injection and feedback rates. Full calculation details are given in a dedicated appendix.
Recent experiments using lasers subject to strong external injection [Simpson, Opt. Commun. 170, 93 (1999)] have demonstrated that adding a small reference current modulation to the dc-bias current can easily lock the oscillation frequency of the laser to the reference frequency. Tunable, locked outputs from 9.5 to 13.1 GHz have been obtained. We explain why synchronization is readily achieved at high injection rates. We describe the locking phenomenon in detail and derive useful analytical expressions for the frequencies and locking range in terms of the laser parameters.
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