Efficient Fiber Coupling and Low-Cost MID-IR Fiber Combiner for Quantum Cascading Laser

Mid-infrared sources are key enabling technologies for various applications, including remote chemical and bio-sensing, defense communications and countermeasures, and bio-photonic diagnostics and therapeutics. Conventional mid-IR sources encompass optical parametric amplifiers, quantum cascade lasers (QCL), synchrotron, and free electron lasers. Notably, QCLs offer numerous advantages over other mid-IR laser technologies since their introduction in the mid-1990s. In this proposal, Raytum Photonics aims to present a comprehensive solution for Quantum Cascade Laser (QCL) diode laser power combining. The proposed solution encompasses an optics system designed to efficiently couple the laser beam out of the emitter, an Anti-Reflection (AR) coating applied to the fiber surface to mitigate excessive Fresnel loss, and the introduction of a novel and cost-effective combiner to merge outputs from multiple QCL lasers. The resulting output power from the fiber combiner is contingent upon both the QCL laser power and the structure of the fiber combiner. Our innovative fuse-less fiber combiner structure exhibits several key advantages: • Ease of Processing: The entire device is easily processed as it obviates the need for polishing and mid-IR fiber to mid-IR fiber splices. This attribute enhances component robustness and reliability.   • Enhanced Heat Management: Significant improvements in heat management can be achieved. All fibers, when affixed using low-index epoxy, allow for the utilization of either passive or active cooling methods. Even at power levels in the tens of watts, no substantial temperature rise is observed. For Phase I, we anticipate to use the QCL diode with a 3W output. Our primary objectives include demonstrating a fiber coupling efficiency exceeding 90% and validating that the fuse-less combiner structure achieves a coupling efficiency of more than 90% at mid-IR wavelengths. In Phase II, we aim to scale the output power by incorporating more input fibers into the delivery fiber, with the ultimate goal of achieving an overall output power exceeding 50W.