High coupling efficiency wedge-shaped cylindrical lensed fiber for the 2  µm band

It has always been difficult to achieve high-efficiency optical coupling from edge-emitting semiconductor laser diodes (LDs) to fibers, especially for the mid-infrared wavelength range due to the larger divergence angle. To improve the coupling efficiency, we systematically put up a theoretical model based on the hyperbolic-shaped fiber and used a genetic algorithm to optimize the wedge angle and tip radius of the wedge-shaped cylindrical lensed fiber, calculating the maximal coupling efficiency. The effect of working distance between the LD and fiber on coupling efficiency is also studied. The coupling efficiency can reach over 97% when the mode-field radius of the fiber equals the initial spot size of the laser in the slow-axis direction, providing a solution for efficient mid-infrared fiber coupling.