The sensitivity of a hybrid distributed feedback semiconductor (DFB) laser heterogeneously integrated onto silicon (Si) is extensively characterized in the presence of external optical feedback at different bias and temperature conditions. The unique modal engineering approach of the device allows the light generated in the III-V material to be stored in the low-loss Si region to significantly enhance the quality (Q) factor of the cavity resonator. This design leads to an increased temperature tolerance of the laser without impacting the transmission efficiency even under the most severe feedback conditions. At a temperature of T = 35◦C, the laser continuous to unveil optimal performance and exhibits feedback insensitivity when externally modulated at 10 Gbps transmission over a 10 km fiber coil. The study presented here demonstrates the ability of a high-Q laser to achieve floor-free transmission at different operating conditions with a power penalty degradation no greater than 1.5 dB. The prolonged transition to the coherence collapse regime at a much higher reflection level evidenced by this device when compared to its III-V counterparts in addition to its ability to withstand perturbations associated with temperature variations and unintentional back-reflections delivers a step forward towards isolator-free applications. This work suggest that this type of semiconductor lasers can serve as a promising solution for the development of compact and reliable photonic integrated circuits (PICs).
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 laser3. 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.
The Gunfire Detection System (GDS) is an acoustic passive sensor designed to rapidly detect, locate, and report on hostile fire from small arms upon detection of a blast wave from a bullet exiting the gun barrel and/or the supersonic wave of the bullet. Upon the detection of the muzzle blast and/or the acoustic shock wave caused by the moving bullet the GDS notifies the user and displays the azimuth, elevation and range to the gunfire origin (shooter). This information allows the GDS user to swiftly move, return fire or take other appropriate action. The paper presented examines the militarization process of a Commercial Off The Shelf (COTS) item and provides lessons learned.
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