Samenvatting
Semiconductor ring lasers (SRLs) are laser devices consisting of a circular optical cavity. Because of this symmetry, they allow two directional modes: a clockwise and a counterclockwise propagating mode. These modes operate at the same optical wavelength and use the same carrier reservoir for optical gain. The directional modes are coupled by backscattering effects in a linear way. Gain saturation effects produce a nonlinear coupling. SRLs are suitable for monolithic integration in photonic integrated circuits.Because of the nonlinear coupling, SRLs can exhibit a bistable operating regime where either one of the two directional modes has the highest intensity. Therefore, SRLs can be used in optical memory elements. Switches between the coexisting states in the bistable regime might be induced by injection of an external pulse or might happen randomly due the presence of spontaneous emission noise in the system. It has been demonstrated experimentally that coupled SRLs can be used as optical memories. However, the underlying dynamics of coupled SRLs is largely unknown. In this work, we study point-coupled SRLs where a coupling is realized by placing the rings in each other's proximity so that evanescent tails of light in one ring couple into the other.
A model consisting of a set of rate equations is derived for a single SRL and expanded to coupled SRLs. Using techniques from the theory of nonlinear dynamics, the dynamical behavior of coupled SRLs is studied in this work. We find that coupled SRLs can operate in a bidirectional regime where all directional modes have an equal intensity. Analytical expressions for the steady state optical intensity, carrier density and phase differences between the directional modes are derived in this regime. A stability analysis is condicted, showing a possible destabilization of the bidirectional regime which has not been observed in a solitary SRL.
By using continuation of solutions to the coupled SRL system, we study other operating regimes besides the bidirectional regime. The influence of the ring coupling on the stability of the different operating regimes in coupled SRLs is studied. Again, a possible destabilization of the regimes is observed and investigated.
In order to investigate resonances in coupled SRLs and the dynamical behavior once the bidirectional regime is destabilized, we use numerical techniques based on the integration of the rate equation model. We find that the coupled SRLs can exhibit periodic, quasi-periodic and chaotic behavior.
The approach followed in this thesis provides an overview of the stable operating regimes in coupled SRLs as a function of the system's parameters.
| Datum prijs | 2009 |
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| Originele taal | English |
| Begeleider | Jan Danckaert (Promotor), Stefano Beri (Jury), Lendert Gelens (Jury) & Guy Van Der Sande (Jury) |