All-fiber spatial rotation manipulation for radially asymmetric modes

Area of Science:

• Optical Engineering
• Photonics
• Fiber Optics

Background:

• Controlling the spatial orientation of light modes is crucial for advanced optical communication and sensing systems.
• Existing methods often suffer from polarization or spatial mode coupling, limiting precise control.
• Radially asymmetric modes require specialized techniques for effective manipulation.

Purpose of the Study:

• To propose and experimentally demonstrate a novel method for spatial rotation manipulation of radially asymmetric modes.
• To investigate the use of polarization-maintaining few-mode fibers (PM-FMFs) for controlled spatial mode rotation.
• To compare the performance of different PM-FMF designs for this application.

Main Methods:

• Theoretical modeling of spatial rotation in PM-FMFs, focusing on suppressing polarization and spatial mode coupling.
• Fabrication of two types of PM-FMFs: elliptical core and panda type.
• Experimental characterization of the spatial orientation rotator, including performance metrics like insertion loss and temperature sensitivity.

Main Results:

• A clear linear relationship was established between the twist angle of PM-FMFs and the spatial rotation of radially asymmetric modes.
• Both elliptical core and panda type PM-FMFs successfully enabled spatial rotation of the LP₁₁ mode within a ±360° range.
• Comprehensive performance data including insertion loss, temperature sensitivity, polarization maintenance, and mode scalability were obtained and compared.

Conclusions:

• The proposed method effectively controls spatial rotation of radially asymmetric modes using PM-FMFs.
• The suppression of unwanted couplings is key to achieving predictable and manageable spatial rotation.
• PM-FMFs offer a viable platform for developing spatial orientation rotators with tunable characteristics.