Bending-insensitive doughnut beam generation using a polarization-maintaining fiber mode-selective coupler.

Area of Science:

• Optics and Photonics
• Fiber Optics
• Mode Conversion

Background:

• High-stability doughnut beams are high-order modes crucial for optical tweezers, fiber communication, and metrology.
• Existing methods for generating these beams can be sensitive to environmental disturbances like bending.

Purpose of the Study:

• To experimentally demonstrate bending-insensitive doughnut beam generation.
• To investigate all-fiber mode schemes for generating orbital angular momentum (OAM) and doughnut beams.

Main Methods:

• Utilized a polarization-maintaining mode-selective coupler (PM-MSC) for efficient LP01-LP11 mode conversion (>95%) at 532 nm.
• Separated LP11a/b modes using different fiber coupler configurations.
• Investigated two all-fiber schemes: OAM generation via 45° fusion splicing and bending-insensitive doughnut beams via incoherent superposition.

Main Results:

• Achieved high mode conversion efficiency (>95%) with a polarization extinction ratio (PER) of >17 dB.
• Demonstrated stable doughnut intensity profiles maintained under various bending radii.
• Successfully generated bending-insensitive doughnut beams using the proposed PM-MSCs.

Conclusions:

• The developed PM-MSC enables efficient and stable generation of bending-insensitive doughnut beams.
• These beams offer robust solutions for free-space communications, quantum entanglement distribution, and adaptive microscopy, especially in polarization-sensitive applications.