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High-purity amplification of circularly polarized orbital angular momentum modes in an active spun ring-core tapered fiber

Iuliia Zalesskaia, Hassan Asgharzadeh B., Zahra Eslami, Hossein Fathi, Evgenii Gribanov, Andrey Grishchenko, Florian Lindner, Katrin Wondraczek, Evgeny Savelyev, Marco Ornigotti, Valery Filippov, Regina Gumenyuk

Abstract

Structured light, optical fields engineered in their spatial, polarization, or phase degrees of freedom, has become a key resource across advanced communication, sensing, imaging, and quantum technologies. Optical fibers nowadays play an essential role in this landscape, providing stable and scalable platforms for guiding, and amplifying complex modes such as vector and orbital angular momentum (OAM) beams. In this work, we demonstrate an active spun ring-shaped tapered fiber as a gain medium for efficient amplification of OAM modes preserving their modal purity and polarization topology. OAM beams with topological charges l = 1 and l = 2 carrying 60 ps pulses at 15 MHz repetition rate at 1030 nm wavelength are amplified over 1.2 W average power with modal purity over 95%. The spatially resolved measurement of the OAM beam polarization topology revealed small distortion due to the coupling in to neighbour modes. These results demonstrate the high potential of active spun ring-shaped tapered fibers for power scaling of complex beams, preserving their phase and polarization structure simultaneously.

High-purity amplification of circularly polarized orbital angular momentum modes in an active spun ring-core tapered fiber

Abstract

Structured light, optical fields engineered in their spatial, polarization, or phase degrees of freedom, has become a key resource across advanced communication, sensing, imaging, and quantum technologies. Optical fibers nowadays play an essential role in this landscape, providing stable and scalable platforms for guiding, and amplifying complex modes such as vector and orbital angular momentum (OAM) beams. In this work, we demonstrate an active spun ring-shaped tapered fiber as a gain medium for efficient amplification of OAM modes preserving their modal purity and polarization topology. OAM beams with topological charges l = 1 and l = 2 carrying 60 ps pulses at 15 MHz repetition rate at 1030 nm wavelength are amplified over 1.2 W average power with modal purity over 95%. The spatially resolved measurement of the OAM beam polarization topology revealed small distortion due to the coupling in to neighbour modes. These results demonstrate the high potential of active spun ring-shaped tapered fibers for power scaling of complex beams, preserving their phase and polarization structure simultaneously.

Paper Structure

This paper contains 15 sections, 5 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Theory
  3. Materials and methods
  4. Double-clad tapered fiber with a ring-shape active core
  5. Experimental setup
  6. Modal analysis
  7. Polarization Topology
  8. Results
  9. Phase, modal and spectrum characterization of the amplified OAM beams
  10. Theoretical modeling results
  11. Conclusion
  12. backmatter
  13. Funding
  14. Acknowledgment
  15. Disclosures

Figures (5)

  • Figure 1: Theoretically calculated longitudinal cladding-diameter profile of the sT-RCF.
  • Figure 2: The longitudinal cladding-diameter profile of the sT-RCF. Top left inset: fiber facet at the wide side. Bottom right inset: refractive-index and Yb2O3 concentration profile of the initial core material.
  • Figure 3: Schematic of the sT-RCF amplifier experimental setup and beam diagnostic modules. Top left (M1): polarimetry setup. Top right (M2): digital off-axis holography setup and phase reconstruction. Bottom left: $\ell=1$ (OAM1) and $\ell=2$ (OAM2) beams generated by vortex plates and their intensity modes at the focal point of a cylindrical lens.
  • Figure 4: Experimental phase, modal and spectral characterization of the amplified OAM beams at the sT-RCF output. Measured intensity and phase distributions, cylindrical-lens (astigmatic) patterns, mode decomposition, polarization maps and optical spectrum for OAM1 and OAM2 at two output power levels (446 mW and 1315 mW for OAM1; 490 mW and 1250 mW for OAM2).
  • Figure 5: Simulation data obtained for the amplified OAM beam at the sT-RCF output. The output power, intensity and phase distributions, mode decomposition, and polarization maps corresponding to OAM1 and OAM2 are presented in rows 2–5, respectively. For each OAM value, low (left column) and high (right column) output power data are presented, mirroring the structure of Fig. \ref{['fig:resultExp']}. The values for the simulation parameters are the same as those listed in Table \ref{['tab:parameteres']}.