3D-printed micro-nano-scale structures on fiber tip for orbital angular momentum mode conversion at 2 μm wavelength band

<p>Two-photon polymerization (2PP)-based three-dimensional (3D) printing enables the fabrication of device structures with nearly arbitrary geometries at the nanoscale. Leveraging this capability, we demonstrate spiral phase plates (SPPs) with topological charges of l &#61; ±1 on fiber tips. Two types of SPPs, continuous-type and staircase-type, are studied both in simulation and experiment. These microstructures on the fiber tip can effi ciently convert Gaussian light at a wavelength of 2 μ m into an orbital angular momentum (OAM) beam. Experimental results show that the mode conversion efficiency and insertion loss differ between the two types of SPPs. For the OAM &#43;1 mode, the conversion efficiencies of the continuous-SPPs and staircase-SPPs are 93.12% and 90.71%, with insertion losses of 0.69 dB and 1.20 dB, respectively. For the OAM 1 mode, the conversion efficiencies are 93.34% and 90.23%, with insertion losses of 0.793 dB and 1.25 dB, respectively. The proposed OAM mode converter offers advantages such as high integration, high conversion efficiency, and low insertion loss, demonstrating potential for application in the 2 μ m wavelength band.</p>