Non-Hermitian Mode Cleaning in Periodically Modulated Multimode Fibers

Area of Science:

• Optics and Photonics
• Wave Propagation in Optical Fibers

Background:

• Graded-index multimode fibers (GRIN-MMF) typically support multiple transverse modes, leading to signal degradation.
• Controlling mode coupling is crucial for achieving high-quality optical transmission.

Purpose of the Study:

• To investigate the effect of simultaneous modulation of propagation constant and gain/loss on mode coupling in GRIN-MMF.
• To demonstrate a method for controlling higher-order transverse mode excitation and achieving mode cleaning.

Main Methods:

• Semi-analytical prediction using a Gaussian beam approximation.
• Numerical verification by solving the wave propagation equation with a non-Hermitian modulated potential.

Main Results:

• Simultaneous modulation induces unidirectional coupling among fiber modes.
• The modulation parameters determine whether higher-order mode excitation is enhanced or reduced.
• Effective mode cleaning, leading to single-mode output, is predicted under specific modulation conditions.

Conclusions:

• The proposed modulation technique offers a novel approach to control mode behavior in multimode fibers.
• This method has the potential for applications requiring high-quality, spatially coherent optical output.