Wideband chaos in hybrid III-V/silicon distributed feedback semiconductor lasers under optical feedback

The dynamics of hybrid III-V/silicon Distributed Feedback (DFB) semiconductor lasers were studied under a combination of long and short feedback conditions. The allure of silicon photonics lies in the potential for production of low-cost, compact circuits that integrate photonics and microelectronics on a single Photonic Integrated Circuit (PIC)(1,2). It has been recently demonstrated that such tight integration of optical components increases the risk of short-cavity reflections within a PIC that can destabilize the laser(3). Using novel III-V/Si DFB lasers, we simulated such reflections by coupling the laser using a cleaved fiber, thus creating a free-space cavity between the laser and the fiber tip. The sensitivity of such devices to this short feedback and its phase was then studied by comparing measurements performed with either a cleaved or a lensed anti-reflection-coated fiber, and revealed the modal and temporal dynamics created by the short-cavity feedback. A long fibered feedback cavity was then created within the experimental setup to study the route to chaos of the devices under long feedback, as well as the impact of the short feedback's phase on this route. Due to a relatively high relaxation oscillation frequency of 15 GHz and the destabilization of the laser by both the short cavity and the long one; very wide chaos can be achieved when combining both types of feedbacks. This study thus reveals the impact parasitic reflections can have on a DFB laser's characteristics in a PIC, as well as how these reflections can affect the dynamics of the laser in a well-known optical feedback scheme.