Polarization beam combiner for optical fiber coupling mode

Polarization beam combining technology, as an effective approach to enhance laser power, faces challenges such as excessive discrete optical components when applied to fiber coupling. We presented a reflective metasurface beam combiner designed to simultaneously manipulate two orthogonally linearly polarized beams (XLP and YLP) with a wavelength of 4.6 μm at ±15° off-axis incidence through subwavelength structural engineering. The metasurface combiner consisted of multiple discrete unit cells measuring 2 μm×2 μm. It had an overall dimension of 120 μm×120 μm and a focal length of 200 μm. Each unit cell features a layered structure comprising a gold substrate, a silica spacer, and a top rectangular silicon pillar. By employing particle swarm optimization to adjust the side lengths of the silicon pillars, we achieved a combining efficiency of 75.2% for both polarized beams. The innovative integration of polarization selection, beam combining, and focusing functions within a single device offers a novel solution for developing compact, high-power mid-infrared light sources.