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>