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Intermodal beat lengths in birefringent two-mode fibers.

D Ostling, B Langli, H E Engan

|November 3, 2009

Summary

We measured beat lengths in elliptical-core and high-birefringence (Hi-Bi) fibers using an acousto-optic method. Elliptical-core fibers lack the predicted beat length minimum, impacting two-mode device applications.

Area of Science:

Optical Physics
Materials Science
Fiber Optics

Background:

Understanding mode propagation in optical fibers is crucial for developing advanced photonic devices.
Polarization-maintaining fibers and high-birefringence (Hi-Bi) fibers offer unique properties for specialized applications.
The behavior of different fiber core geometries in supporting multiple modes requires detailed investigation.

Purpose of the Study:

To measure and analyze the beat lengths between the LP(01) and LP(11) modes in elliptical-core and bow-tie Hi-Bi fibers.
To investigate the influence of fiber type and wavelength on mode beat lengths.
To compare experimental findings with theoretical predictions for circular-core fibers and discuss implications for two-mode devices.

Main Methods:

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Utilized an acousto-optic method for precise measurement of mode beat lengths.

Conducted measurements across a wide range of optical wavelengths.

Employed elliptical-core polarization-maintaining fibers and bow-tie Hi-Bi fibers.

Main Results:

Observed significant polarization splitting in the beat lengths of the Hi-Bi fiber across all measured wavelengths.
Found that the elliptical-core fiber does not exhibit the theoretically predicted minimum beat length in the two-mode region.
Demonstrated distinct beat length characteristics for different fiber types.

Conclusions:

The absence of a beat length minimum in elliptical-core fibers deviates from circular-core fiber theory.
The polarization splitting in Hi-Bi fibers significantly affects mode beat length measurements.
Findings provide insights into the selection and application of different fiber types in two-mode optical devices.