High-efficiency coupling method for high-power adjustable ring-mode laser optical switch based on freeform surface

With the increasing demand for integrated multi-station processing in intelligent manufacturing, high-power laser optical switches, critical components enabling multi-station laser energy multiplexing, have emerged as pivotal elements for achieving efficient system-level coordination. However, current adjustable ring-mode laser optical switches confront two challenges. First, dimensional and numerical aperture mismatches between input and output annular fibers necessitate independent magnification adjustments for central and annular beams. Conventional rotationally symmetric aspheric lenses have a limited ability to meet this requirement, resulting in mismatched magnification and diminished coupling efficiency in the optical switch. Second, thermal effects during high-power laser transmission induce lens deformation and focal spot drift, which may critically undermine the stability of the optical switch. Aiming at these issues, this paper introduces a differential magnification coupling scheme utilizing a freeform surface. By tailoring the freeform surface geometry, an independent and efficient coupling of the central and annular beams was achieved. In addition, a water-circulating convective cooling technique was introduced to effectively mitigate the thermally induced focal drift and stabilize the coupling performance. For the first time, we present a differential amplification coupling scheme based on freeform lenses for application in the optical switch. By optimizing the freeform surface profile, synchronous and efficient coupling between the central and annular beams was achieved. Meanwhile, a water-circulation cooling technique was introduced to effectively suppress thermally induced focal shifts affecting coupling performance, and a comprehensive tolerance analysis was conducted to guide the design of precision adjustment mechanisms. A high-performance optical switch was subsequently developed, achieving coupling efficiencies of 98.2% for the central beam and 90.4% for the annular beam, and maintaining stable output for one hour at a total power of 4 kW with fluctuations below 1%. This work provides a novel and efficient system-level solution for achieving stable and efficient coupling of high-power tunable ring-mode lasers.